Patent Application
20230157584
The present invention relates to a body motion determining (determination) system for determining whether or not there is a body motion in a (human) subject on a bed on the basis of a detection value of a load detector.
For the sites of medical treatment and caregiving service, it is proposed to determine a state of a subject on the basis of such a load of the subject on a bed as detected by load detectors. In particular, for example, it is proposed to determine whether or not the subject has a body motion on the basis of the detected load.
Patent Literature 1 discloses a body motion level determining apparatus provided to determine a body motion level of a user on a bed in a step-up manner on the basis of detection values fed from load sensors arranged under the legs of the bed. Patent Literature 2 discloses a sleep determining apparatus and a turnover detecting apparatus which are capable of determining that there is a body motion in a person on a bed on the basis of detection results of load sensors arranged under the legs of the bed.
An object of the present invention is to provide a body motion determining system capable of determining whether or not a subject on a bed has a body motion with higher precision on the basis of detection values of load detectors.
According to a first aspect of the present invention, there is provided a body motion determining system configured to determine whether or not a subject on a bed has a body motion, the system including:
a plurality of load detectors each configured to detect a load of the subject on the bed;
a respiratory waveform obtaining unit configured to obtain a respiratory waveform of the subject based on a temporal variation of the load of the subject detected by each of the plurality of load detectors; and
a body motion determining unit configured to determine whether or not the subject has the body motion, based on a comparison between a first threshold value and a standard deviation of the temporal variation of the load of the subject detected by at least one of the plurality of load detectors,
wherein the body motion determining unit is configured to compensate the standard deviation to be used in the comparison by an amplitude of the respiratory waveform.
In the body motion determining system according to the first aspect, the body motion determining unit may be configured to compensate the standard deviation to be used in the comparison by a latest amplitude of the respiratory waveform, the latest amplitude being obtained based on a latest peak of the respiratory waveform which is the latest at a point of time of determining whether or not the subject has a body motion, and a peak directly preceding the latest peak.
In the body motion determining system according to the first aspect, the body motion determining unit may be configured to compensate the standard deviation to be used in the comparison by an average value of the latest amplitude of the respiratory waveform and at least one amplitude of the respiratory waveform in a period directly preceding a point of time of obtaining the latest amplitude.
In the body motion determining system according to the first aspect, the body motion determining unit may be configured to continue, after a determination that the subject has the body motion, to compensate the standard deviation using the latest amplitude at a point of time of the determination that the subject has the body motion.
In the body motion determining system according to the first aspect, the compensating may be performed by dividing the standard deviation by the amplitude of the respiratory waveform.
In the body motion determining system according to the first aspect, the plurality of load detectors may include a first load detector, a second load detector, a third load detector, and a fourth load detector; and the body motion determining unit may be configured to determine whether or not the subject has the body motion based on a comparison between the first threshold value and a simple average of σ1/AAVn, σ2/AAVn, σ3/AAVn, and σ4/AAVn, provided that σ1 is a first standard deviation of the temporal variation of the load of the subject detected by the first detector, σ2 is a second standard deviation of the temporal variation of the load of the subject detected by the second detector, σ3 is a third standard deviation of the temporal variation of the load of the subject detected by the third detector, σ4 is a fourth standard deviation of the temporal variation of the load of the subject detected by the fourth detector, and AAVn is the average value.
In the body motion determining system according to the first aspect, the body motion determining unit may be configured to determine a period during which the standard deviation is equal to or lower than a predetermined value as a resting period in which the subject merely performs a respiration, and compensate the standard deviation to be used in the comparison by the amplitude of the respiratory waveform in the resting period.
The body motion determining system according to the first aspect may further include: a non-negative-valued average calculating unit configured to calculate a non-negative-valued average of a detection value of at least one of the load detectors; and
a threshold value setting unit configured to set a second threshold value to be used to determine whether or not the subject has a body motion, based on the non-negative-valued average calculated in the resting period in which the subject merely performs the respiration,
wherein the body motion determining unit may be configured to perform a determination to determine whether or not the subject has the body motion based on a comparison between the second threshold value and the standard deviation, and then, after determining that the subject has no body motion by the determination based on the comparison between the second threshold value and the standard deviation, perform a determination to determine whether or not the subject has the body motion based on the comparison between the first threshold value and the standard deviation; and
the body motion determining unit may be configured to compensate the standard deviation to be used in the comparison with the first threshold value by the amplitude of the respiratory waveform obtained in a period which is determined, by the determination based on the comparison between the second threshold value and the standard deviation, as a period in which the subject has no body motion.
According to a second aspect of the present invention, there is provided a bed system including:
a bed; and
the body motion determining system according to the first aspect.
The body motion determining system of the present invention can determine whether or not the subject on the bed has a body motion with higher precision on the basis of the detection values of the load detectors.
Explanations will be made on a body motion determining system 100 according to an embodiment of the present invention (
As shown in
The load detecting unit 1 includes four load detectors 11, 12, 13, and 14. Each of the load detectors 11, 12, 13, and 14 is a load detector for detecting a load by using, for example, a beam-type load cell. Such a load detector is disclosed, for example, in Japanese Patent No. 4829020 and Japanese Patent No. 4002905. Each of the load detectors 11, 12, 13, and 14 is connected to the A/D converting unit 2 by way of wiring or wirelessly.
As shown in
The A/D converting unit 2 includes an A/D convertor to convert analog signals fed from the load detecting unit 1 to digital signals, and is connected respectively to the load detecting unit 1 and the control unit 3 by way of wiring or wirelessly.
The control unit 3 is a dedicated or general-purpose computer inside which a standard deviation calculating unit 31, a respiratory waveform drawing unit 32 (respiratory waveform calculating unit; respiratory waveform obtaining unit), and a body motion determining unit 33 are constructed.
The storage unit 4 is a storage device for storing data used in the body motion determining system 100 and, for example, a hard disk (magnetic disk) can be used for that purpose.
The display unit 5 is monitor such as a liquid crystal monitor or the like for displaying information outputted from the control unit 3 to users of the body motion determining system 100.
The notifying unit 6 includes a device, such as a speaker, for example, to auditorily perform a predetermined notification on the basis of the information fed from the control unit 3.
The input unit 7 is an interface for performing predetermined inputs for the control unit 3, which may be a keyboard and a mouse.
An explanation will be made on an operation of determining whether or not there is a body motion of the subject on the bed by using the body motion determining system 100 of such kind.
As depicted in the flow chart of
[The Load Detecting Step]
In the load detecting step S11, the load detectors 11, 12, 13, and 14 are used to detect the load of the subject S on the bed BD. The load of the subject S on the bed BD is applied dispersively to the load detectors 11 to 14 arranged respectively under the legs BL1 to BL4 of the bed BD at the four corners. The load of the subject S is detected dispersively by the four load detectors.
Each of the load detectors 11 to 14 detects the load (or variation of load), and outputs the detected load as an analog signal to the A/D converting unit 2. The A/D converting unit 2 converts the analog signal into a digital signal through at a sampling period (or cycle) of 5 milliseconds, for example, and then outputs the digital signal (to be referred to below as “load signal”) to the control unit 3. Hereinafter, the term “load signals s1, s2, s3, and s4” will be used to refer respectively to the load signals obtained in the A/D converting unit 2 by converting the analog signals outputted from the load detectors 11, 12, 13, and 14 into the digital format.
[The Standard Deviation Calculating Step]
In the standard deviation calculating step S12, the standard deviation calculating unit 31 calculates standard deviations σ1, σ2, σ3, and σ4 (moving standard deviations) of a sampling value included in a predetermined sampling period (or time period) (5 seconds for example) for each of load signals s1, s2, s3, and s4. The calculation may be performed at any time (or continuously).
The standard deviation denotes the magnitude of variation(dispersion) of the sampling value. Thus, as depicted in
Therefore, during a period when there is a body motion arising in the subject S, the standard deviations σ1 to σ4 have larger values in comparison to a period when there is no body motion arising in the subject S.
In the present specification and in the present invention, the term “body motion” refers to any motion of the subject's head, torso (trunk, body-trunk), and/or four limbs. The body motion does not include motions of internal organs, blood vessels and the like along with the respirations, heartbeats, and the like. As an example, the body motion can be classified into a large body motion along with the motion of the subject S in the torso (trunk, body-trunk), and a small body motion along with the motion of the subject only in the four limbs, the head, and/or the like. One example of the large body motion is turn-over, sit-up or get-up, or the like, whereas one example of the small body motion is, a motion of the hands, the feet, the head or the like during sleep. When heartbeats, respirations and body motions arise in the subject, the load signals s1 to s4 fed from the load detectors 11 to 14 vary accordingly. The magnitude of variation increases in the order of the variation due to the heartbeats of the subject S, the variation due to the respirations of the subject S, the variation due to the small body motion of the subject S, and the variation due to the large body motion of the subject S.
Note that in the determination of a body motion of the subject described in the present specification and in the present invention, the magnitude of variation in the load signals s1 to s4 due to the heartbeats of the subject S is so small as neglectable. Therefore, in the present specification and in the present invention, the term “the subject only (merely) respires (or the subject merely performs a respiration)”, the load values and the load signals “vary due only to the respiration(s)”, and the like are used to mean that the subject has no body motion, and the load values and the load signals show no variation due to the body motion, but not to mean that the subject does not have heartbeats, the load values and the load signals do not include the variation due to the heartbeats, etc.
[The Respiratory Waveform Drawing Step]
In the respiratory waveform drawing step S13, the respiratory waveform drawing unit 32 (respiratory waveform calculating unit; respiratory waveform obtaining unit) draws a respiratory waveform of the subject S on the basis of the load signals s1 to s4.
The respiration of human is performed by moving the chest and the diaphragm to expand and shrink the lungs. In this context, when the air is inhaled (or an inspiration is performed), i.e., when the lungs are expanded, the diaphragm is lowered downwardly, and the internal organs are also moved downwardly. On the other hand, when the air is expired (or an expiration is performed), i.e., when the lungs are shrunk, the diaphragm is raised upwardly, and the internal organs are also moved upwardly. As disclosed in the specification of Japanese Patent No. 6105703 granted to the present applicant, the center of gravity G (of the subject) moves slightly along with the movement of the internal organs, the moving direction thereof being approximately along the subject's backbone extending direction (body axis direction).
In the present specification and in the present invention, the term “respiratory waveform” refers to a waveform showing an aspect of the oscillation of the subject's center of gravity oscillating in the subject's body axis direction due to the subject's respirations, by plotting the aspect on the temporal axis. One period of the respiratory waveform corresponds to one respiration of the subject (one inspiration and expiration). The amplitude of the respiratory waveform is affected by the subject's (physical) frame (build, physique) and/or respiratory depth. In particular, for example, if the subject has a large frame or the subject performs a deep respiration, then the amplitude becomes large, whereas if the subject has a small frame or the subject performs a shallow respiration, then the amplitude becomes small.
The respiratory waveform drawing unit 32 draws, in particular, the respiratory waveform in the following manner.
First, the respiratory waveform drawing unit 32 calculates the position of the center of gravity G of the subject S at each sampling time on the basis of the load signals s1 to s4 fed from the load detecting unit 1. As depicted in
Next, the respiratory waveform drawing unit 32 draws a respiratory waveform BW (
Note that it is not necessary for the respiratory waveform drawing unit 32 to actually draw the respiratory waveform but it is possible to only obtain data indicating the respiratory waveform.
[The Body Motion Determining Step]
In the body motion determining step S14, the body motion determining unit 33 uses the standard deviations σ1 to σ4 calculated in the standard deviation calculating step S12 and the amplitude of the respiratory waveform BW drawn in the respiratory waveform drawing step S13, to determine whether or not there is a body motion arising in the subject S.
The determination is performed in the following manner in particular for example.
First, the body motion determining unit 33 detects the peaks for the respiratory waveform BW drawn in the respiratory waveform drawing step S13, and calculates the difference between the minimum value over the period between the latest peak μn and the previous peakpn-1, and the latest peak μn, as the latest amplitude An of the respiratory waveform BW (
Note that in order to confirm that the respiratory waveform BW, which is involved in calculating the amplitudes An, An-1, An-2, . . . and the amplitude AAVn, is the respiratory waveform obtained from a resting period (during which the subject only respires without body motion arising), (i.e., in order to confirm that there is no error included due to the movement of the center of gravity because of some body motion), a comparison may be made between a threshold value σ0 and either a simple average σAV of the standard deviations σ1 to σ4 or any one of the standard deviations σ1 to σ4. The threshold value σ0 is set at such a small value as able to reliably determine that there is no body motion arising in the subject S as long as the simple average σAV or any one of the standard deviations σ1 to σ4 is smaller than the small value (conversely, even if the simple average σAV or any one of the standard deviations σ1 to σ4 is not smaller than the small value, it is still possible that there is no body motion arising in the subject S).
Next, the body motion determining unit 33 finds normalized standard deviations σs1 to σs4 by the following (Formula 1).
σsm=σm/AAVn (m=1,2,3,4) [Formula 1]
Then, the body motion determining unit 33 finds a simple average σsAV of the calculated normalized standard deviations σs1 to σs4 and, based on a comparison between the simple average σsAV and a predetermined threshold value σsTH, determines whether or not there is a body motion arising in the subject S. In particular, for example, if the simple average σsAV is larger than or equal to the threshold value σsTH, then it is determined that there is a body motion arising in the subject S, whereas if the simple average σsAV is smaller than the threshold value σsTH, then it is determined that there is no body motion arising in the subject S.
During a period when it is determined that there is no body motion arising in the subject S, the body motion determining unit 33 calculates the latest amplitude An for each one period of the respiratory waveform BW on the basis of the respiratory waveform BW obtained by the respiratory waveform drawing unit 32. Then, using the average amplitude AAVn calculated anew by using the value of the calculated latest amplitude An, and the values of the standard deviations σ1 to σ4 calculated at each sampling time (as an example, every 5 milliseconds), the body motion determining unit 33 calculates, successively, the normalized standard deviations σs1 to σs4 by the Formula 1, and calculates the simple average σsAv.
Determining whether or not there is a body motion arising in the subject S is performed by the successive comparisons between the predetermined threshold value σsTH and the simple average σsAV calculated successively in the above manner.
After it is determined as a result of the determination that there is a body motion arising in the subject S, the body motion determining unit 33 ceases to update the average amplitude AAVn and continues to calculate the simple average σsAV using the average amplitude AAV having been calculated by this point. Then, based on a comparison between the calculated simple average σsAV and the threshold value σsTH, the body motion determining unit 33 continues to determine whether or not there is a body motion arising in the subject S. This is because during a period when there is a body motion arising in the subject S, the amplitude and period of the respiratory waveform BW vary greatly due to the influence of the body motion, and thereby it is difficult to calculate a new amplitude An and the average amplitude AAVn without error.
Next, if it is determined again that there is no body motion arising in the subject S, then based on the respiratory waveform BW obtained by the respiratory waveform drawing unit 32, the body motion determining unit 33 calculates the value of the latest amplitude An and, using the same, calculates the average amplitude AAVn anew. Then, the body motion determining unit 33 calculates the simple average σsAV using the latest average amplitude AAV and, based on a comparison between the calculated simple average σsAV and the predetermined threshold value σsTH, the body motion determining unit 33 continues to determine whether or not there is a body motion arising in the subject S.
Referring to
As depicted in
Next, if another peak μ2 of the respiratory waveform BW and the latest amplitude A2 are obtained at the time t2, then for the period after the time t2, the body motion determining unit 33 uses the average amplitude AAV2 calculated by using the amplitude A2, to successively calculate the normalized standard deviations σs1 to σs4 and the simple average σsAV (to be referred to here as σsAV (AAV2)); and determines whether or not there is a body motion arising in the subject S, based on the comparison between the simple average σsAV (AAV2) and the threshold value σsTH.
At the time t21, if there is a body motion arising in the subject S, then the body motion determining unit 33 determines that there is a body motion arising in the subject S on the basis of the simple average σsAV (AAV2) being equal to or larger than the threshold value σsTH. Then, after that, for the period when the simple average σsAv (AAV2) is equal to or larger than the threshold value σsTH, the body motion determining unit 33 continues to determine the body motion using the simple average σsAV (AAV2).
At the time t22, if the body motion of the subject S has come to an end, then the body motion determining unit 33 determines that there is no body motion arising in the subject S on the basis of the simple average σsAV (AAV2) being smaller than the threshold value σsTH. After that, the body motion determining unit 33 continues to determine the body motion using the simple average σsAV (AAV2) until the latest amplitude An of the respiratory waveform BW is obtained and the latest average amplitude AAVn is calculated again.
The body motion determining unit 33 uses the amplitude An (average amplitude AAVn) of the respiratory waveform to normalize the values of the standard deviations σ1 to σ4. The reason therefor is as follows.
As described above, generally speaking, the values of the standard deviations σ1 to σ4 become larger during a period when there is a body motion arising in the subject S. Therefore, it is conceivable to determine whether or not there is a body motion arising in the subject S by way of comparison between the values of the standard deviations σ1 to σ4 and a predetermined threshold value.
However, according to the discovery and knowledge of the present inventors, for a subject who has a large frame (build, physique), the values of the standard deviations σ1 to σ4 may still be comparatively large even during a period of only performing respirations without the body motion because the movement of his/her internal organs due to the respirations is also large. Further, even for a subject who does not have a large frame, the values of the standard deviations σ1 to σ4 may still become large if, for example, the subject performs a deep respiration. Hence, if the body motion determination is performed by comparing the values of the standard deviations σ1 to σ4 to a predetermined threshold value, in those cases, even though there is no body motion arising in the subject, a mistaken determination may be made to give the incorrect result that there is a body motion arising in the subject.
On the other hand, if the respiratory waveform is focused on, then as described earlier on, the amplitude of the respiratory waveform is affected by the subject's frame and/or respiratory depth; therefore, if the subject has a large frame or the subject performs a deep respiration, then the amplitude becomes large, whereas if the subject has a small frame or the subject performs a shallow respiration, then the amplitude becomes small.
That is, by dividing the values of the standard deviations σ1 to σ4 by the average amplitude AAVn of the respiratory waveform BW to perform the normalization, it is possible to reduce (compensate; correct) the influence on the values of the standard deviations σ1 to σ4, exerted by the subject's frame and/or respiratory depth. Then, by using the normalized standard deviations σs1 to σs4 obtained through such normalization to determine the body motion, it is possible to raise the precision of determining the body motion.
[The Display Step]
In the display step S15, the control unit 3 causes the display unit 5 to display the determination result of the body motion determining step S14. Further, in the display step S15, the notifying unit 6 may be used to perform a notification in addition to or instead of the display using the display unit 5. In this case, for example, when the subject S has a body motion, a notification sound may be emitted to notify the nurses, caregivers and/or others who are the users of the body motion determining system 100 that a body motion is arising.
The effects of the body motion determining system according to this embodiment are summarized as follows.
The body motion determining system 100 of this embodiment determines the body motion by using the simple average σsAV of the normalized standard deviations σs1 to σs4 which are compensated (corrected) by normalizing the values of the standard deviations σ1 to σ4 by the average amplitude AAVn of the respiratory waveform BW. Therefore, there are reduced influences exerted by the change in the respiratory depth and/or the physical description of the subject S, on the values of the standard deviations σ1 to σ4 and, consequently, on the body motion determination. Hence, the determination is made with high precision.
The body motion determining system 100 of this embodiment normalizes the values of the standard deviations σ1 to σ4 by using the average amplitude AAVn, of the respiratory waveform BW, calculated on the basis of the respirations performed by the subject S during the period right before the point of time of determining the body motion of the subject S. In this manner, because the values of the standard deviations σ1 to σ4 are normalized with high precision, having reflected the actual respiratory condition of the subject S, the body motion determination is also made with high precision. Further, because the normalization is performed by the average amplitude AAVn, even if any abnormal value arises in the amplitude An of the respiratory waveform BW for some reason, the influence exerted by the abnormal value on the determination can still be reduced.
The body motion determining system 100 according to this embodiment uses the load detectors 11 to 14 arranged under the legs BL1 to BL4 of the bed BD to determine whether or not the subject S has a body motion. Therefore, it is not necessary to attach any measuring device to the body of the subject S so that the subject S will not feel discomfort and a sense of incongruity.
It is also possible to adopt the following modified embodiments with respect to the body motion determining system 100 according to the above embodiment.
In the body motion determining system 100 of the above embodiment, the standard deviations σ1 to σ4 are normalized by dividing the standard deviations σ1 to σ4 by the average amplitude AAVn to reduce (compensate; correct) the influence on the values of the standard deviations σ1 to σ4, exerted by the frame and/or respiratory depth of the subject S. However, the compensating (correcting) method by utilizing the amplitude of the respiratory waveform BW is not limited to that. In particular, for example, the standard deviations σ1 to σ4 may be normalized by way of dividing the same by the latest amplitude An of the respiratory waveform BW.
Note that, it is also possible to compensate the threshold value by using the amplitude of the respiratory waveform BW and compare the standard deviations σ1 to σ4 to the compensated threshold value, instead of compensating the standard deviations σ1 to σ4 by using the amplitude of the respiratory waveform BW and then comparing the compensated values to the threshold value. In particular, for example, in the above embodiment, instead of dividing the standard deviations σ1 to σ4 by the average amplitude AAVn, it is possible to perform a desired compensation (correction) by multiplying the predetermined threshold value by the average amplitude AAVn. In this manner, the two methods mentioned above are practically equivalent and thus it is possible to appropriately select either the standard deviations or the threshold value used in the comparison for the compensation (correction) by the amplitude of the respiratory waveform. In the present specification and in the present invention, the expression “compensating the standard deviations by the amplitude of the respiratory waveform” is termed to include compensating the threshold value by the amplitude of the respiratory waveform.
In the body motion determining system 100 of the above embodiment, the body motion determination is performed by the comparison between the simple average σsAV of the normalized standard deviations σs1 to σs4 and the threshold value σsTH. However, it is also possible to determine the body motion by a comparison between at least one of the normalized standard deviations σs1 to σs4 and the threshold value, a comparison between simple average values of at least two or more of the normalized standard deviations σs1 to σs4 and the threshold value, a comparison between the total value of at least two or more of the normalized standard deviations σs1 to σs4 and the threshold value, or the like.
Further, in the body motion determining system 100 of the above embodiment, it is also possible to use a variance which is the squared standard deviation instead of the standard deviation. If the variance is normalized by the amplitude of the respiratory waveform, then the variance may be divided by the squared amplitude of the respiratory waveform. Therefore, in the present specification and in the present invention, the standard deviation is termed to include the variance.
The body motion determining unit 33 may provide the threshold value used for the body motion determination with hysteresis. In particular, for example, with a first threshold value and a second threshold value larger than the first threshold value set in advance, under the condition that the subject S is determined as with no body motion arising therein, as far as the simple average σsAV is yet smaller than the second threshold value, the subject S is not determined as with a body motion arising therein. On the other hand, under the condition that the subject S is determined as with a body motion arising therein, even if the simple average σsAV is smaller than the second threshold value, the subject S is not determined as with no body motion arising therein, but is determined as with no body motion arising therein at the point of the simple average σsAV becoming smaller than the first threshold value.
Explanations will be made on a body motion determining system according to a referential embodiment of the present invention, and on a biological state monitoring system 200 including the body motion determining system (
In the following explanation, with the center of the rectangular bed BD (
As shown in
Note that inside the biological state monitoring system 200 having the above configuration, the part excluding the respiratory rate calculating unit 35 of the control unit 3 corresponds to the body motion determining system of this referential embodiment.
An explanation will be made on an operation of monitoring the biological state (presence or absence of a body motion and the respiratory rate) of the subject on the bed by using the biological state monitoring system 200 of such kind.
Monitoring the biological state of the subject by using the biological state monitoring system 200 includes: as depicted in the flow chart of
[The Load Detecting Step]
The contents of the load detecting step S21 are the same as the contents of the load detecting step S11 performed in the body motion determining system 100 of the above embodiment.
[The Body Motion Determining Step]
In the body motion determining step S22, the body motion determining unit 34 uses at least one of the load signals s1 to s4, to determine whether or not there is a body motion in subject S.
As depicted in
The body motion determining step S22 includes, as depicted in
In the body motion determining step S22, the body motion determining unit 34 first carries out the DC component eliminating step S221 using the DC component eliminating unit 341 to eliminate the DC component from each of the load signals s1 to s4. The DC components are eliminated, in particular for example, by finding a moving average over a predetermined period (15 seconds for example) for each of the load signals s1 to s4, and then eliminating the found moving average from the sampling value of each of the load signals s1 to s4.
Hereinbelow, the signals obtained after the DC components are eliminated from the load signals s1 to s4 will be referred to respectively as load signals sc1 to sc4.
The following steps, that is, the resting period determining step S222, the threshold value setting step S223 and the determining step S224, will be carried out using the load signals sc1 to sc4 obtained in the DC component eliminating step S221.
On the premise of carrying out the resting period determining step S222, the threshold value setting step S223 and the determining step S224, the body motion determining unit 34 constantly or continuously calculates a standard deviation σ with the standard deviation calculating unit 342, and constantly or continuously calculates a non-negative-valued average μ with the non-negative-valued average calculating unit 343.
The standard deviation calculating unit 342 constantly or continuously calculates standard deviations σ1 to σ4 of the sampling values included in a predetermined sampling period (time period) (5 seconds for example) for each of the load signals sc1 to sc4 obtained in the DC component eliminating step S221.
The standard deviations σ1 to σ4 calculated in the standard deviation calculating unit 342 are used to determine a resting period (a period in which the subject only respires without body motion) in the resting period determining step S222, and to determine whether or not the subject S has a body motion in the determining step S224 (to be described in detail later on).
The non-negative-valued average calculating unit 343 constantly or continuously calculates non-negative-valued averages μ1 to μ4 of sampling values W11 to W14 included respectively in the predetermined sampling period (time period) (5 seconds for example) for the respective load signals sc1 to sc4 obtained in the DC component eliminating step S221.
An explanation will be made about a method for calculating the non-negative-valued average with an exemplary case of calculating the non-negative-valued average μ1 over the sampling period of 5 seconds for the load signal sc1 outputted in the resting period.
As depicted in
Next, the non-negative-valued average calculating unit 343 calculates an average value of the respective sampling values W11 having been non-negative-valued to acquire (obtain) the non-negative-valued average μ1. The non-negative-valued averages μ2 to μ4 are calculated in the same manner for the load signals sc2 to sc4.
The non-negative-valued averages μ1 to μ4 obtained in the resting period increase in value if the amplitude of load variation due to the respirations of the subject S increases, but decrease in value if the amplitude of load variation due to the respirations of the subject S decreases.
The non-negative-valued averages μ1 to μ4 calculated by the non-negative-valued average calculating unit 343 are used for setting a threshold value σth in the threshold value setting step S223 (to be described in detail later on).
Returning to the flow chart of
Just as described above, the standard deviations σ1 to σ4 become small during the period when the load signals sc1 to sc4 vary little but become large during the period when the load signals sc1 to sc4 vary greatly. Therefore, any of the standard deviations σ1 to σ4 becomes small during a resting period (the period P1 of
Note that as will be described later on, in the resting period, because there is difference among individuals in how small the variation due to the respirations will become in the load signals, depending on a specific subject, it is still possible to maintain the standard deviations σ1 to σ4 at larger values than the threshold value σ0 even during the resting period when the subject only respires without body motion. In such a case, for example, with the standard deviations σ1 to σ4 being kept at certain values being a little larger than the threshold value σ0 through a predetermined period (5 to 10 seconds, for example), it is possible to determine that the subject is in the resting period. Because respirations generally give a certain rhythm, if the standard deviations σ1 to σ4 have certain small values to some degree over a predetermined period, then even with those values being a little larger than the threshold value σ0, there is still a high possibility of that period falling into the resting period.
If the resting period determining step S222 determines that the subject S is in the resting period, then the body motion determining unit 34 causes the threshold value setting unit 345 to perform the threshold value setting step S223.
In the threshold value setting step S223, the threshold value setting unit 345 estimates the magnitude of a respiratory amplitude of the subject S and, based on the estimated magnitude of the respiratory amplitude, sets the threshold value σth to be used in the determining step S224.
The respiratory amplitude of the subject S refers to the amplitude of oscillation of the center of gravity G of the subject S due to the respirations of the subject S. That is, the respiratory amplitude is equal to the amplitude An of the respiratory waveform BW calculated in the body motion determining system 100 of the above embodiment.
The threshold value setting unit 345 selects any one of the non-negative-valued averages μ1 to μ4 calculated by the non-negative-valued average calculating unit 343 in the resting period determined in the resting period determining step S222 and, according to the magnitude of the selected value, estimates the magnitude of the respiratory amplitude of the subject S. It can be said that if the non-negative-valued averages μ1 to μ4 in the resting period are large (or small), then the amplitudes of the oscillations of the load signals s1 to s4 and sc1 to sc4 due to the respirations of the subject S are large (or small), and thus, the respiratory amplitude of the subject S is also estimated as large (or small).
Next, the threshold value setting unit 345 sets the threshold value σth to be used in the determining step S224 on the basis of the estimated magnitude of the respiratory amplitude of the subject S. In particular, for example, if the estimated magnitude of the respiratory amplitude is larger than a predetermined threshold value μth, then the threshold value σth is set to a first threshold value σth1 whereas if the estimated magnitude of the respiratory amplitude is smaller than the predetermined threshold value μth, then the threshold value σth is set to a second threshold value σth2 (<σth1). A description will be made later on about the reason of changing the magnitude of the threshold value σth according to the magnitude of the respiratory amplitude of the subject S in this manner.
Note that without estimating the magnitude of the respiratory amplitude, any one of the calculated non-negative-valued averages μ1 to μ4 (a selected non-negative-valued average μs) may be compared with the threshold value μth. Then, if μs is larger than the threshold value μth, then the threshold value σth may be set to the first threshold value σth1 whereas if μs is smaller than the threshold value μth, then the threshold value σth may be set to the second threshold value σth2 (<σth1). In this case, practically, the threshold value σth is also set on the basis of the magnitude of the respiratory amplitude of the subject S.
Thereafter, the body motion determining unit 34 uses the set threshold value σth to perform the determining step S224 with the determining unit 346, so as to determine whether or not the subject S has a body motion. The body motion determining unit 34 is supposed to continuously use the threshold value σth until the subject S leaves the bed BD and, thereafter, may perform the determining step S224 alone but not perform the resting period determining step S222 and the threshold value setting step S223.
Whether or not the subject S has a body motion is determined, in particular for example, by comparing the threshold value σth set in the threshold value setting step S223 with any one of the standard deviations σ1 to σ4 (to be referred to below as “selected standard deviation σSE”) of the load signals sc1 to sc4 calculated constantly or continuously by the standard deviation calculating unit 342.
During the period when the subject S has a body motion, the variation of the load signals sc1 to sc4 increases in magnitude, so that the standard deviations σ1 to σ4 and, furthermore, the selected standard deviation σSE also increase (for example, during the period P2 of
In this context, a description will be made as follows on the reason for the body motion determining unit 34 of this referential embodiment to set the threshold value σth which differs according to each subject S by taking the magnitude of the respiratory amplitude of the subject S into referential consideration.
As described earlier on, the load signals s1 to s4 from the load detectors 11 to 14 vary according to the heartbeats, respirations and body motion of the subject S, and the magnitude of the oscillation changes according to the physical description of the subject S (such as the height, weight, body fat percentage, muscle mass, and the like). Then, according to the discovery and knowledge of the present inventors, there is a certain correlation between the magnitude of the load variation according to respirations (the magnitude of respiratory amplitude) and the magnitude of load variation according to the body motion.
As depicted in
In this context, according to the discovery and knowledge of the present inventors, as shown in
That is, suppose that the σth1 (
Conversely, suppose that the σth2 (
In the biological state monitoring system 200 of this referential embodiment, however, based on the magnitude of the respiratory amplitude of the subject S, the threshold value σth is set according to a specific subject S, and the set threshold value σth is used to determine whether or not there is a body motion in the subject S. By virtue of this, it is possible to determine with high precision whether or not there is a body motion in each of a plurality of subjects S who differ in the magnitude of the respiratory amplitude.
[The Respiratory Rate Calculating Step]
In the respiratory rate calculating step S23, the respiratory rate calculating unit 35 calculates the respiratory rate of the subject S on the basis of at least one of the load signals s1 to s4.
In particular, for example, the respiratory rate calculating unit 35 calculates the respiratory rate of the subject S by carrying out the Fourier analysis on at least one of the load signals s1 to s4 (or the load signals sc1 to sc4) so as to specify the peak frequency coming up in the frequency band corresponding to the respirations (from about 0.2 Hz to about 0.33 Hz because the human respiration is performed about 12 to 20 times per minute). With the specified peak frequency, it is possible to calculate (estimate) the respiratory rate of the subject S over that period.
Further, in the period when the subject S has a body motion (the period P2 of
Therefore, the respiratory rate calculating unit 35 of this referential embodiment ceases to calculate the respiratory rate for the period when the subject S has a body motion on the basis of the determination result of the body motion determining unit 34. As for the respiratory rate of this period, an estimation value may be outputted on the basis of the respiratory rate of periods before and after that period, or a message may be outputted to indicate that the respiratory rate is unknown.
[The Display Step]
In the display step S24, the control unit 3 causes the display unit 5 to display the determination result of the body motion determining step S22 and/or the calculation result of the respiratory rate calculating step S23. Further, in the display step S24, the notifying unit 6 may be used to perform a notification in addition to or instead of the display using the display unit 5. In this case, for example, when the subject S has a body motion, a notification sound may be emitted to notify the nurses, caregivers and/or others who are the users of the biological state monitoring system 200 that a body motion is arising.
The effects of the body motion determining system and the biological state monitoring system 200 including the same according to this referential embodiment are summarized as follows.
In the body motion determining system and the biological state monitoring system 200 including the same according to this referential embodiment, the body motion determining unit 34 sets a suitable threshold value σth for each subject S on the basis of the respiratory amplitude of the subject S, and uses the same to determine whether or not the subject S has a body motion. Hence, it is possible to determine whether or not there is a body motion with high precision for each of a plurality of subjects S who differ in the magnitude of the respiratory amplitude.
In the biological state monitoring system 200 of this referential embodiment, based on the determination result of the body motion determining unit 34, the respiratory rate calculating unit 35 excludes the periods difficult in calculating the respiratory rate of the subject S from the objects of calculating the respiratory rate. Therefore, there is a high reliability of the respiratory rate of the subject S calculated by the respiratory rate calculating unit 35.
The body motion determining system and the biological state monitoring system 200 including the same according to this referential embodiment use the load detectors 11 to 14 arranged under the legs BL1 to BL4 of the bed BD to monitor the biological state of the subject S. Therefore, it is not necessary to attach any measuring device to the body of the subject S so that the subject S will not feel discomfort and a sense of incongruity.
It is also possible to adopt the following modified embodiments with respect to the body motion determining system and the biological state monitoring system 200 according to the above referential embodiment.
In the body motion determining unit 34 of the above referential embodiment, whenever the determining unit 346 determines that the subject S has a body motion in the determining step S224, the resting period determining step S222 and the threshold value setting step S223 may be performed again to reset the threshold value σth for the use in the determining step S224.
The magnitude of the respiratory amplitude of the subject S depends basically on the physical description of the subject S, and thus it does not change greatly during the monitoring period. Therefore, generally speaking, as far as the subject S is not changed, it is possible to use the threshold value σth, which is once set in the threshold value setting step S23, continuously in the successive monitoring.
However, patients, et al. who are receiving terminal cares (end-of-life medical treatment and end-of-life care) change often in physical condition as much as the respiratory amplitude changes, and such kind of change in physical condition often arises along with a body motion. Therefore, for the patients, et al. who are receiving terminal cares, it is possible to reset the threshold value σth at each body motion and use the threshold value σth according to the physical condition at the timing, so as to raise the precision of determining the body motion, and the reliability of the calculated respiratory rate.
On the other hand, the non-negative-valued average calculating unit 343 of the body motion determining unit 34 of the above referential embodiment may cease to calculate the non-negative-valued averages μ1 to μ4 after the threshold value σth is set if the threshold value σth once set is to be used continuously in the determining step S224. Alternatively, the non-negative-valued averages μ1 to μ4 may be calculated only in the case where the resting period determining unit 344 determines that the subject S is in the resting period in the resting period determining step S222.
In the above referential embodiment, the standard deviation calculating unit 342 of the body motion determining unit 34 may calculate variances σ21 to σ24 instead of or in addition to the standard deviations σ1 to σ4. In this case, in the threshold value setting step S223, a threshold value σ2th is set according to the variances σ21 to σ24. Further, in the determining step S224, whether or not the subject S has a body motion is determined by comparing the threshold value σ2th to any one or the sum of any two or more of the variances σ21 to σ24.
In the above referential embodiment, the body motion determining unit 34 compares whether or not any one of the standard deviations σ1 to σ4 is smaller than the predetermined threshold value σ0, to determine that the subject S is in the resting period. However, without being limited to that, the body motion determining unit 34 may compare the sum of any two or more of the standard deviations σ1 to σ4 with the threshold value, to determine that the subject S is in the resting period.
In the above referential embodiment, the body motion determining unit 34 selects any one of the non-negative-valued averages μ1 to μ4 and, based on that one, estimates the magnitude of the respiratory amplitude of the subject S. However, without being limited to that, the body motion determining unit 34 may estimate the magnitude of the respiratory amplitude of the subject S on the basis of the sum of any two or more of the non-negative-valued averages μ1 to μ4. For example, by using the summation of the non-negative-valued averages μ1 to μ4, it is possible to estimate the magnitude of the respiratory amplitude of the subject S with high precision regardless of the position of the subject S on the bed BD.
In the above referential embodiment, the body motion determining unit 34 sets the threshold value σth to either the first threshold value σth1 or the smaller second threshold value σth2. However, without being limited to that, the body motion determining unit 34 may set the threshold value σth in a more detailed manner according to the magnitude of the respiratory amplitude of the subject S estimated from the non-negative-valued averages μ1 to μ4. In particular, the threshold value σth may be set to any of the first threshold value σth1 to an nth threshold value σthn (n is a natural number larger than two) which are different from one another.
In the above referential embodiment, the body motion determining unit 34 compares the set threshold value σth to the selected standard deviation σSE which is any one of the standard deviations σ1 to σ4, to determine whether or not the subject S has a body motion. However, without being limited to that, the body motion determining unit 34 may determine whether or not the subject S has a body motion by comparing the threshold value σth with the sum of any two or more of the standard deviations σ1 to σ4. Note that in this case, the threshold value σth set in the threshold value setting step S223 is supposed to also accord to the contents of the standard deviations used in the determining step S224.
In the above referential embodiment, the body motion determining unit 34 may include a center of gravity position calculating unit instead of or in addition to the standard deviation calculating unit 342. The center of gravity position calculating unit uses sampling values W11 to W14 of the load signals s1 to s4 (or the load signals sc1 to sc4) fed from the load detectors 11 to 14, to calculate the position (X, Y) of the center of gravity G of the subject S.
The calculation of the position (X, Y) of the center of gravity G is performed in accordance with the following operation. Coordinates X-Y are set up for the bed BD as depicted in
The center of gravity position calculating unit finds a temporal variation of the position (X, Y) of the center of gravity G, i.e., a center of gravity locus GT while calculating the position (X, Y) of the center of gravity G at a predetermined sampling period T on the basis of the formulas 2 and 3 given above. The acquired center of gravity locus GT is stored, for example, in the storage unit 4.
Here, the movement of the center of gravity G of the subject S is characterized as follows.
As described earlier on, the center of gravity G of the subject S oscillates in the direction of the body axis SA of the subject S according to the respirations of the subject S (
Therefore, the body motion determining unit 34 can determine whether or not the subject S has a body motion by comparing a predetermined threshold value with the moving distance of the center of gravity G over a predetermined period. In particular, for example, it is possible to determine that the subject S has a small body motion if the moving distance D of the center of gravity G over a predetermined period is longer than a threshold value Dth.
In this modified embodiment, too, the body motion determining unit 34 causes the threshold value setting unit 345 to perform the threshold value setting step S223 to set the threshold value Dth (for example, either a Dth1 or a smaller Dth2) according to the magnitude of the respiratory amplitude of the subject S.
In the above referential embodiment, the respiratory rate calculating unit 35 calculates the respiratory rate of the subject S by performing the Fourier transform on at least one of the load signals s1 to s4 (or the load signals sc1 to sc4). However, the present invention is not limited to that.
In particular, for example, if the body motion determining unit 34 has the center of gravity position calculating unit, then it is possible to draw a respiratory waveform BW of the subject S (
Note that in this case, too, when the subject S has a body motion, the center of gravity G of the subject S moves greatly to deviate from the oscillation due to the respirations, so that the respiratory waveform BW also departs from the state of being oscillating due only to the respirations. Therefore, when the body motion determining unit 34 determines that the subject S has a body motion, calculation of the respiratory rate is ceased.
In the above referential embodiment, the control unit 3 may display the drawn respiratory waveform BW on the display unit 5.
In the above referential embodiment, the body motion determining unit 34 first determines that the subject S is in the resting period in the resting period determining step S222, and then uses the non-negative-valued average μ in that period to estimate the magnitude of the respiratory amplitude of the subject S. However, the present invention is not limited to that.
The subject S rarely moves constantly on the bed BD (to give rise to a body motion) but, usually, the subject S is resting without body motion (only respiring) during the most part of the period of his/her being present on the bed BD. Therefore, if the non-negative-valued averages μ1 to μ4 are observed continuously over a predetermined period of time (one minute or longer for example) without determining the resting period, then the minimal value of any one of (or the sum of any two or more of) the non-negative-valued averages μ1 to μ4 obtained in that period over time is often practically a value obtainable in the resting period (in other words, although the resting period is not distinctly determined, at the point when that minimal value is obtained, there is often a case where the subject is in the resting state, and the minimal value is the non-negative-valued average in the resting period). In this manner, the body motion determining unit 34 may estimate the magnitude of the respiratory amplitude of the subject S on the basis of the minimal value of the non-negative-valued averages obtained sequentially in the predetermined period of time.
Further, in this case, if such a value is observed as even smaller than the minimal value of the non-negative-valued averages once obtained, then on the basis of this value, the magnitude of the respiratory amplitude of the subject S may be estimated anew and/or the threshold value σth, be set anew as necessary.
Alternatively, it is possible to carry out the Fourier analysis on the load signals s1 to s4 (or the load signals sc1 to sc4) fed from the load detectors s11 to s14 to extract only the signals of the respiration band, and to estimate the magnitude of the respiratory amplitude of the subject S from the non-negative-valued average calculated on the basis of the extracted signals. According to this method, because it is possible to exclude the influence of body motion on the load signals s1 to s4 (or the load signals sc1 to sc4) by way of the Fourier analysis, the magnitude of the respiratory amplitude of the subject S can be estimated at any time without determining the resting period.
In the above referential embodiment and modified embodiments, as an example of the method for estimating the magnitude of the respiratory amplitude of the subject S on the basis of the non-negative-valued average μ, it is possible to regard the same magnitude or predetermined multiples of the magnitude of the non-negative-valued average μ as the magnitude of the respiratory amplitude of the subject S.
In the above referential embodiment, the body motion determining unit 34 can also find the respiratory amplitude of the subject S without using the non-negative-valued average μ.
In particular, for example, if there is a center of gravity position calculating unit and the respiratory waveform BW is drawn, then it is possible to estimate (determine) the respiratory amplitude of the subject S from the amplitude of the respiratory waveform BW. Alternatively, it is possible to estimate (determine) the respiratory amplitude of the subject S on the basis of at least one of the amplitudes of the load signals s1 to s4 and the load signals sc1 to sc4 in the resting period.
The biological state monitoring system 200 of the above referential embodiment may further include a biological state determining unit to determine other biological states than whether or not the subject S has a body motion and the respiratory rate of the subject S. Such a biological state determining unit determines, for example, whether the subject S is present in or absent from the bed, asleep or awake, dead or alive, etc., on the basis of whether or not the subject S has a body motion, the respiratory rate of the subject S, etc.
Because the biological state monitoring system 200 of the above referential embodiment can determine the body motion of the subject S and estimate the respiratory rate of the subject S with high precision, the biological state monitoring system 200 of the modified embodiments based on the former can also determine whether the subject S is present in or absent from the bed, asleep or awake, dead or alive, etc., with high precision.
The body motion determining system 100 of the above embodiment does not need to include all of the load detectors 11 to 14 but may include only any one of the four. For example, if there are three such load detectors, then it is still possible to detect the position of the center of gravity G of the subject S on the plane of the bed BD provided that the three load detectors are not arranged on a straight line. Further, the load detectors do not need to be arranged at the four corners of the bed but may be arranged in any positions as far as they can detect the load of the subject on the bed and the variation thereof. Further, the load detectors 11 to 14 are not limited to load sensors using beam-type load cells but, for example, force sensors are also usable.
In the body motion determining system 100 of the above embodiment, the load detectors 11 to 14 are arranged respectively on the undersides of the casters C attached to the lower ends of the legs of the bed BD. However, there is no limitation thereto. Each of the load detectors 11 to 14 may be provided respectively between one of the four legs of the bed BD and the board of the bed BD. Alternatively, if each of the four legs of the bed BD can be divided into upper and lower portions, each of the load detectors 11 to 14 may be provided between the upper leg and the lower leg. Further alternatively, the load detectors 11 to 14 may be formed integral with or removable from the bed BD to construct a bed system BDS comprising the bed BD, and the body motion determining system 100 of this embodiment (
In the body motion determining system 100 of the above embodiment, between the load detecting unit 1 and the A/D converting unit 2, it is possible to provide a signal amplifying unit to amplify the load signals fed from the load detecting unit 1, and a filtering unit to eliminate the noises from the load signals.
In the body motion determining system 100 of the above embodiment, the display unit 5 may include a printer for printing out the information indicating whether or not there is a body motion, a simplified visual display means such as lamps indicating whether or not there is a body motion, and/or the like, instead of the monitor or in addition to the monitor. Further, the notifying unit 6 may include a vibration generating unit for performing the notification by way of vibration, instead of the speaker or in addition to the speaker.
It is also possible to construct a body motion determining system by use of a combination of the body motion determining system 100 of the above embodiment and the body motion determining system of the above referential embodiment. Such body motion determining system, in particular for example, determines the body motion with the body motion determining system of the above referential embodiment without depending on the respiratory waveform BW for periods after the system is started up in which it is not possible to reliably draw the respiratory waveform BW and to calculate the average amplitude AAVn. Then, when coming to the point of being able to reliably draw the respiratory waveform BW and calculate the average amplitude AAVn, the body motion determining system 100 of the above embodiment starts to determine the body motion. For example, the body motion determining unit of such body motion determining system determines the body motion of the subject S in the same manner as the body motion determining unit 34 of the above referential embodiment, by using the threshold value σth (the second threshold value) set on the basis of the non-negative-valued averages μ1 to μ4, in a period immediately after the system is started up. Then, if the subject S is determined as with no body motion, then the system calculates the average amplitude AAVn of the respiratory waveform BW of the subject S and, thereafter, determines the body motion of the subject S on the basis of a comparison between the threshold value σsTH (the first threshold value) and the simple average σsAV of the normalized standard deviations σs1 to σs4 which are normalized by the average amplitude AAVn.
The present invention is not limited to the embodiments described above provided that the feature of the present invention is maintained. Other embodiments, which are conceivable within the scope of the technical concept of the present invention, are also included in the scope of the present invention.
According to the body motion determining system of the present invention, it is possible to determine whether or not the subject has a body motion with high precision by reducing the influence of the subject's frame and respiratory depth. Therefore, by using the body motion determining system of the present invention, it is possible to provide high-quality medical treatments and caregiving services on the basis of those high-precision determinations.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018-046885 | Mar 2018 | JP | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 16980194 | Sep 2020 | US |
| Child | 18058323 | US |
