SKIN SHEAR DETECTION FOR HOSPITAL BEDS

Abstract

A patient support apparatus comprises a plurality of load cells, a frame supported on the load cells, a mattress, a plurality of air pressure sensors, and a control system. The mattress includes a plurality of inflatable zones positioned on the frame, the mattress and frame cooperating to direct any patient load through the mattress and frame to the load cells. Each of the plurality of air pressure sensors measures the pressure in a respective inflatable zone of the mattress. The control system includes a controller operable to receive a separate signal from each of the plurality of load cells and each of the plurality of air pressure sensors and process the signals to identify motion of the patient. The motion of the patient is further processed by the controller to characterize the nature of the patient motion as a high shear motion or a low shear motion, and based on the characterization of the patient motion, the controller automatically updates a patient profile in a patient record or communicates the information with a caregiver.

Description

BACKGROUND

The present disclosure relates to the use of sensors in a patient support apparatus, such as a hospital bed, for example, to detect patient motion and characterize the patient motion. More specifically, the present disclosure is directed to detecting shear to skin and using shear to skin as a determinant for an incidence of increase in pressure injuries.

The use of load cells in patient support apparatuses, such as hospital beds, for example, to measure patient weight is known. Over time, approaches to using the information from the load cells to detect patient movement and to issue an alert or notification when the patient moves beyond a particular threshold have been developed. The use of load cells to make these determinations and inferences based on the motion is limited by the potential for external influences, such as the addition of equipment to the frame supported on the scale. When this is done, the existing information regarding the position of the patient is compromised as the weight distribution is changed unexpectedly.

The pressure sensors used to measure air pressure in zones of an inflatable mattress are used to control the inflation pressure in the zones to control the interface pressure experienced by a patient supported on the mattress. However, because of transient effects and lack of precision, air pressure sensors associated with mattress zones are not regularly used to measure patient information. The challenges of using air pressure sensors are exacerbated by the variability between the anthropometric characteristics of patients. People with completely different body types sometimes have similar weights. The variations in the surface area of bodies can vary the pressure and volume effects applied to inflatable zones. Still further, the variability in the construction of chambers in the zones makes every application necessary to characterize.

In addition, caregivers or visitors may intermittently apply pressure to the mattress, thereby changing air pressure measurements and the distribution of the weight on the frame. Motion algorithms generally rely on changes in the distribution of weight over multiple sensors to determine patient location and relative movement. These transient and external forces confound the algorithms used to determine patient movement and motion.

It is useful to determine if patient movement relative to the patient support apparatus may indicate shear to skin. Movement in this context may be a determinant of an incidence of a pressure related injury or may be used to determine the frequency of pressure related injuries. There is a need to improve the approaches to measuring and characterizing such patient movement in real-time. Improving the characterization of patient movement allows for a more fulsome predictive analysis of patient actions and evaluation of patient conditions. Detection of specific types of patient movement may be used to inform a caregiver about patient health.

SUMMARY

The present disclosure includes one or more of the features recited in the appended claims and/or the following features which, alone or in any combination, may comprise patentable subject matter.

According to a first aspect of the present disclosure, a patient support apparatus comprises a plurality of load cells, a frame supported on the load cells, a mattress including a plurality of inflatable zones positioned on the frame, the mattress and frame cooperating to direct any patient load through the mattress and frame to the load cells, a plurality of air pressure sensors, each air pressure sensor measuring the pressure in a respective inflatable zone of the mattress, and a control system including a controller, the controller operable to receive a separate signal from each of the plurality of load cells and each of the plurality of air pressure sensors, process the signals to identify, based on transient changes in the signals, motion of the patient that does not result in relative movement of the patient relative to the frame, the motion of the patient being further processed to characterize the nature of the patient motion and, based on the characterization of the patient motion, automatically determine if the patient motion is a high shear motion or a low shear motion.

In one embodiment, the controller is operable to monitor the energy detected by each of the load cells and each of the air pressure sensors and compare the change in total energy measured by the load cells and air pressure sensors to determine if external energy has acted on the patient support apparatus, and, if a change in total energy measured is indicative that external energy has acted on the patient support apparatus, utilize the resulting change in total energy to modify the characterization of the patient motion that is used to update the patient profile. In another embodiment, the transient changes in the signals are indicative of motion of a least a portion of the patient in a vertical direction.

In one embodiment, the controller is operable to calculate the work done by the patient in the vertical direction to characterize the patient motion. In another embodiment, the controller is operable to compare the air pressure sensor signal for each of two adjacent zones and use the relative changes in the pressure in the adjacent zones during a potential patient movement event to confirm the characterization of the patient motion.

In one embodiment, the controller is operable to monitor the energy detected by each of the load cells and each of the air pressure sensors and compare the change in total energy measured by the load cells and air pressure sensors to determine if external energy has acted on the patient support apparatus, and, if a change in total energy measured is indicative that external energy has acted on the patient support apparatus, utilize the resulting change in total energy to modify the characterization of the patient motion that is used to update the patient profile. In another embodiment, the controller is operable to determine that the patient motion is the low shear motion if the patient motion is characterized as a self-offloading motion in which a patient readjusts their position on the mattress without any external influence.

In one embodiment, the controller is operable to determine that the patient motion is the high shear motion if the patient motion is characterized as a lateral motion in which a patient readjusts their position by dragging themselves on the patient support apparatus. In some embodiments, center of gravity of the patient changes in an x-y direction due to the patient motion. In another embodiment, there is no momentary change in the force due to the patient motion.

In one embodiment, a momentary change in force is determined by measuring an integral of the absolute value of total forces on the load cells minus the patient's weight, and wherein if the integral is less than a threshold, the patient motion is determined to be the high shear motion. In some embodiments, there is a dampened oscillation in a z direction, and wherein center of gravity of the patient changes in an x-y direction due to the patient motion.

According to a second aspect of the present disclosure, a system comprises a patient support surface including a plurality of inflatable zones, a plurality of load cells supporting the patient support surface, a plurality of air pressure sensors, each pressure sensor measuring the pressure in a respective inflatable zone of the patient support surface, and a controller operable to receive a separate signal from each of the plurality of load cells and each of the plurality of air pressure sensors, process the signals to identify motion of the patient, the motion of the patient being further processed to characterize the nature of the patient motion and, based on the characterization of the patient motion, automatically determine if the patient motion is a high shear motion or a low shear motion.

In one embodiment, the controller is operable to monitor the energy detected by each of the load cells and each of the air pressure sensors and compare the change in total energy measured by the load cells and air pressure sensors to determine if external energy has acted on the system, and, if a change in total energy measured is indicative that external energy has acted on the system, utilize the resulting change in total energy to modify the characterization of the patient motion that is used to update the patient profile. In another embodiment, the signals are indicative of motion of a least a portion of the patient in a vertical direction.

In one embodiment, the controller is operable to calculate the work done by the patient in the vertical direction to characterize the patient motion. In another embodiment, the controller is operable to compare the air pressure sensor signal for each of two adjacent zones and use the relative changes in the pressure in the adjacent zones during a potential patient movement event to confirm the characterization of the patient motion. In a further embodiment, the controller is operable to monitor the energy detected by each of the load cells and each of the air pressure sensors and compare the change in total energy measured by the load cells and air pressure sensors to determine if external energy has acted on the system, and, if a change in total energy measured is indicative that external energy has acted on the system, utilize the resulting change in total energy to modify the characterization of the patient motion that is used to update the patient profile.

In one embodiment, the controller is operable to determine that the patient motion is the low shear motion if the patient motion is characterized as a self-offloading motion in which a patient readjusts their position on the mattress without any external influence. In another embodiment, the controller is operable to determine that the patient motion is the high shear motion if the patient motion is characterized as a lateral motion in which a patient readjusts their position by dragging themselves on the patient support apparatus.

In one embodiment, center of gravity of the patient changes in an x-y direction due to the patient motion. In some embodiments, there is no momentary change in the force due to the patient motion.

In one embodiment, a momentary change in force is determined by measuring an integral of the absolute value of total forces on the load cells minus the patient's weight, and wherein if the integral is less than a threshold, the patient motion is determined to be the high shear motion. In some embodiments, there is a dampened oscillation in a z direction, and wherein center of gravity of the patient changes in an x-y direction due to the patient motion.

According to a third aspect of the present disclosure, a method of characterizing motion of a person on an inflatable mattress having multiple inflatable zones comprises the steps of monitoring signals from a plurality of pressure sensors, each pressure sensor providing a signal indicative of the pressure in a respective inflatable zone; monitoring signals from a plurality of load cells, the plurality of load cells supporting inflatable mattress; processing the signals from the load cells and pressure sensors to identify motion of the person; upon detection of a potential motion of the person, further processing the signals to characterize the nature of the person's motion and, based on the characterization of the motion; and automatically determining if the patient motion is a high shear motion or a low shear motion.

In one embodiment, the method comprises monitoring the energy detected by each of the load cells and each of the air pressure sensors; comparing the change in total energy measured by the load cells and air pressure sensors to determine if external energy other than the person supported on the mattress has acted on the mattress; and, if a change in total energy measured is indicative that external energy has acted on the mattress, utilizing the resulting change in total energy to modify the characterization of the motion that is used to update the record.

In one embodiment, the method comprises determining that the signals are indicative of motion of a least a portion of the person in a vertical direction. In another embodiment, the method comprises calculating the work done by the person in the vertical direction to characterize the motion.

In one embodiment, the method comprises comparing the air pressure sensor signal for each of two adjacent zones; and using the relative changes in the pressure in the adjacent zones during a potential person movement event to confirm the characterization of the motion. In another embodiment, the method comprises monitoring the energy detected by each of the load cells and each of the air pressure sensors; comparing the change in total energy measured by the load cells and air pressure sensors to determine if external energy has acted on the mattress; and if a change in total energy measured is indicative that external energy has acted on the mattress, utilizing the resulting change in total energy to modify the characterization of the motion that is used to update the record.

In one embodiment, the method comprises characterizing the patient motion is the low shear motion if the patient motion is characterized as a self-offloading motion in which a patient readjusts their position on the mattress without any external influence. In another embodiment, the method comprises characterizing the patient motion is the high shear motion if the patient motion is characterized as a lateral motion in which a patient readjusts their position by dragging themselves on the patient support apparatus.

In one embodiment of the method, center of gravity of the patient changes in an x-y direction due to the patient motion. In another embodiment of the method there is no momentary change in the force due to the patient motion.

In one embodiment of the method, a momentary change in force is determined by measuring an integral of the absolute value of total forces on the load cells minus the patient's weight, and wherein if the integral is less than a threshold, the patient motion is determined to be the high shear motion. In another embodiment of the method, there is a dampened oscillation in a z direction, and wherein center of gravity of the patient changes in an x-y direction due to the patient motion.

Additional features, which alone or in combination with any other feature(s), such as those listed above and/or those listed in the claims, can comprise patentable subject matter and will become apparent to those skilled in the art upon consideration of the following detailed description of various embodiments exemplifying the best mode of carrying out the embodiments as presently perceived.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description particularly refers to the accompanying figures in which:

FIG. 1 is a perspective view of a patient support apparatus including a control system operable to measure signals from a plurality of sensors and process those signals according to the present disclosure;

FIG. 2 is a block diagram of a portion of the control system of the patient support apparatus of FIG. 1, the control system in communication with a hospital information system;

FIG. 3 is a diagrammatic illustration of the interaction between a first frame of the patient support apparatus of FIG. 1 and a second frame supported on load cells supported from the first frame;

FIG. 4 is a graphical representation of a time series of a sensor signal from a group of sensors of the patient support apparatus of FIG. 1;

FIG. 5A is a graph showing the change in the position of a patient's center of gravity in the x and y direction due to a lateral patient motion (LPM);

FIG. 5B is a graph showing the integral of the absolute value of the total forces due to a lateral patient motion (LPM);

FIG. 5C is a graph showing no momentary change of forces due to a lateral patient motion (LPM);

FIG. 6A is a graph showing the change in center of gravity in the x and y direction due to a self-offloading patient movement (SO);

FIG. 6B is a graph showing the integral of the absolute value of the total forces due to a self-offloading patient movement (SO);

FIG. 6C is a graph showing dampened oscillations due to a self-offloading patient movement (SO);

FIG. 7 is an illustration of how change in a patient's center of gravity is assessed in relationship to the position of the patient on the bed; and

FIG. 8 is a diagrammatic representation of an algorithm for characterizing sensor signals from the patient apparatus of FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

An illustrative patient support apparatus 10 embodied as a hospital bed is shown in FIG. 1. The bed 10 of FIG. 1 has a frame 20 which includes a base frame 22 supported on casters 24. The stationary base frame 22 further supports a weigh frame 30 that an adjustably positionable mattress support upper frame 34 supporting a mattress 18. The illustrative mattress 18 is an inflatable patient support surface which includes inflatable zones including a head zone 36, a seat zone 38, thigh zone 40, and a foot zone 42. The bed 10 further includes a headboard 12 at a head end 46 of the bed 10, a footboard 16 at a foot end 48 of the bed 10, and a movable siderails 14 coupled to the upper frame 34 of the bed 10. The bed 10 also includes a user interface 54 positioned on one of the siderails 14. The bed 10 of the embodiment of FIG. 1 is conventionally configured to adjustably position the upper frame 34 relative to the base frame 22 to adjust the position of a patient supported on the mattress 18.

Conventional structures and devices may be provided to adjustably position the upper frame 34, and such conventional structures and devices may include, for example, linkages, drives, and other movement members and devices coupled between base frame 22 and the weigh frame 30, and/or between weigh frame 30 and upper frame 34. Control of the position of the upper frame 34 and mattress 18 relative to the base frame 22 or weigh frame 30 is controlled, for example, by a patient control pendant 56 or user interface 54. The upper frame 34 may, for example, be adjustably positioned in a general incline from the head end 46 to the foot end 48 or vice versa. Additionally, the upper frame 34 may be adjustably positioned such that the head section 44 of the mattress 18 is positioned between minimum and maximum incline angles, e.g., 0-65 degrees, relative to horizontal or bed flat, and the upper frame 34 may also be adjustably positioned such that a seat section (not shown) of the mattress 18 is positioned between minimum and maximum bend angles, e.g., 0-35 degrees, relative to horizontal or bed flat. Those skilled in the art will recognize that the upper frame 34 or portions thereof may be adjustably positioned in other orientations, and such other orientations are contemplated by this disclosure. A bed 10 that is adjustably positionable consistent with the structures contemplated by the disclosure is disclosed in PCT No. WO2016196403A1, titled “PATIENT SUPPORT APPARATUS”, which is incorporated in its entirety for the detailed disclosure of the structural elements of a bed consistent with the bed 10 of this disclosure.

In one illustrative embodiment shown diagrammatically in FIG. 2, the bed 10 has a control system 26 that includes a controller 28, a scale module 50, an air module 52, and the user interface 54. In the illustrative embodiment each of the controller 28, scale module 50, air module 52, and user interface 54 includes a processor 62 and a memory device 64. The memory device 64 includes instructions that, when executed by the processor 62, cause the processor 62 to perform functions associated with the particular one of the controller 28, scale module 50, air module 52, and user interface 54. The components of the control system 26 communicate amongst themselves to share information and distribute the functions of the bed 10. The processor 62 of each of the controller 28, scale module 50, air module 52, and user interface 54 is also operable, based on instructions from the memory device 64, to communicate with the others of the controller 28, scale module 50, air module 52, and user interface 54 using a standard communications protocol. It should be understood that the term processor here includes any microprocessor, microcontroller, processor circuitry, control circuitry, preprogrammed device, or any structure capable of accessing the memory device and executing non-transient instructions to perform the tasks, algorithm, and processed disclosed herein. In the illustrative embodiment, the control system 26 employs a conventional controller area network (CAN) for communications between subsystems, but it should be understood that any of a number of networking and communications solutions could be employed in the control system 26.

The scale module 50 includes four load cells 66, 68, 70, and 72. To determine a weight of a patient supported on the mattress 18, the load cells 66, 68, 70, and 72 are positioned between the weigh frame 30 and the upper frame 34 as illustrated in FIG. 3. Each load cell 66, 68, 70, 72 is configured to produce a signal indicative of a load supported by the respective load cell 66, 68, 70, 72 from the upper frame 34 relative to the weigh frame 30. Some of the structural components of the bed 10 will be designated hereinafter as “right”, “left”, “head” and “foot” from the reference point of an individual lying on the individual's back on the mattress 18 with the individual's head oriented toward the head end 46 of the bed 10 and the individual's feet oriented toward the foot end 48 of the bed 10. Following this convention, the load cell 66 is designated as the right head load cell (RHLC) in the figures to represent that the load cell 66 is positioned at the right side of the bed 10 at the head end 46. The load cell 68 is designated at the left head load cell (LHLC), the load cell 70 is designated as the right foot load cell (RFLC), and the load cell is designated left foot load cell (LFLC), each following the same convention.

The scale module 50 includes the processor 62 that is in communication with each of the respective load cells 66, 68, 70, and 72 and operable to process the signals from the load cells 66, 68, 70, and 72. The memory device 64 is also utilized by the controller 28 to store information corresponding to features and functions provided by the bed 10.

A weight distribution of a load among the plurality of load cells 66, 68, 70, and 72 may not be the same depending on variations in the structure of the bed 10, variations in each of load cells 66, 68, 70, and 72 and the position of the load on the mattress 18 relative to the particular load cell 66, 68, 70, or 72. Accordingly, a calibration constant for each of the load cells 66, 68, 70, and 72 is established to adjust for differences in the load cells 66, 68, 70, and 72 in response to the load borne by each. Each of the load cells 66, 68, 70, and 72 produces a signal indicative of the load supported by that load cell 66, 68, 70, or 72. The loads detected by each of the respective load cells 66, 68, 70, 72 are adjusted using a corresponding calibration constant for the respective load cell 66, 68, 70, 72. The adjusted loads are then combined to establish the actual weight supported on the bed 10. In the present disclosure, the independent signals from each of the load cells 66, 68, 70, 72 is used to draw inferences about the movement and motion of the patient.

The air module 52 is the functional controller for the mattress 18 and includes processor 62 and a memory device 64. The processor 62 is in communication with a blower 106, a manifold 58, and an air pressure sensor assembly 60. The air module 52 is a conventional structure with the manifold 58 operating under the control of the processor 62 to control the flow of air from the blower 106 into and out of the head zone 36, seat zone 38, thigh zone 40, and foot zone 42 to control the interface pressure experienced by the patient supported on the mattress 18. However, the present disclosure is directed to using the information from sensor assembly 60 to make further inferences regarding motion by the patient supported on the mattress 18. The sensor assembly 60 includes separate sensors for measuring the air pressure in each of the head zone 36, seat zone 38, thigh zone 40, and foot zone 42. The pressure sensor assembly includes a head zone sensor 82, a seat zone sensor 84, a thigh zone senor 86, and a foot zone sensor 88. While signals from the sensors 82, 84, 86, and 88 are used to control the pressure in the respective zones, applying the principles of the present disclosure, the signals are also useful in making inferences regarding patient movement and, when used synergistically with the information gleaned from the signals from the load cells 66, 68, 70, and 72, provide a more fulsome and accurate analysis of patient movement and/or motion.

Thus, the present disclosure is directed to utilizing the bed 10, and specifically the scale module 50 and air module 52, as an instrument for measuring the motions of a patient that occupies the bed 10 and characterizing that motion to make inferences about the patient's health. The motion may be characterized as causing shear to the patient's skin.

Like all biomedical sensing systems, error can be introduced when the sensor output is affected by various sources of noise. Some sources of noise, such as electrical or stray environmental noise can be mitigated through robust design.

Experimental studies indicated that motion can be classified as one of three types: lateral patient motions (LPMs); vertical or self-offloading patient movements (SOs); or non-patient motion artifacts (NPMAs). It has also been observed that load cell signals varied when there was no patient movement. These artifacts were designated as non-movements (NMs). Permutations of these categories, called “complex movements”, also including further categorization into combinations including different directionality of the simple movements was also established.

The present disclosure is directed to the identification of offloading patient movements (SOs) in real-time. Once determined, offloading patient movements (SOs) are used to determine if the patient experienced skin shear. Such identification requires determining the difference between the different motion types.

A centroid/center-of-gravity (CG) approach is one approach used to infer patient motion. Signals from the load cells of a bed 10, such as load cells 66, 68, 70, and 72 are used to determine the equivalent centroid of vertical load supported by the load cells 66, 68, 70, and 72. Through empirical analysis, a determination of motion in the x/y horizontal plane of a range of speeds and magnitudes of motion that are associated with patient motions is determined. Thus, this allows for the detection of lateral patient motions (LPMs), which are, by definition, detected patient motions which have no vertical component. Any lateral movement will cause the center of gravity of the bed 10 to change during a unit-time interval, proportionally to ratio of the displacement of the amount of mass moved to the amount of mass that remained stationary. Due to this, this feature is self-normalized by patient weight. Note that CG movement in the x and y axis is merged by typical vector addition and the directionality is ignored to establish a factor called CGspeed. It is understood that both patient and non-patient movements will cause the CG to move, for these reasons, and the classifiers and inference models discussed below, any motion that imparts its force to the weigh frame 30 is considered to be a motion.

In a first approach at discriminating NPMAs from LPMs, the patient and the bed 10 are treated as a closed system. The total energy of the closed system is determined to be constant and conserved over time of typical patient movements. Any energy that is created by the patient as a result of them moving does not change the overall loading of all four load cells 66, 68, 70, and 72, but simply changes the proportion the total load that each load cell 66, 68, 70, or 72 is carrying at any given time. There is no total gain of loads, the loads simply shift around the four load cells 66, 68, 70, and 72 as the patient moves laterally.

In contrast, when a caregiver pushes or pulls on the patient or bed 10 (a NPMA), the closed-system is corrupted by an external energy source and the net load on the load cells 66, 68, 70, and 72 is increased or decreased. This is the case for both transient touches of the bed 10, such as when a person hugs the patient, and in sustained touches of the bed 10, such as when a caregiver leans on bed 10 while doing a long procedure. In either case, an additional load is introduced to the load cells 66, 68, 70, and 72 resulting in a material change from the sum of the loads on each load cell 66, 68, 70, and 72 when the transient load is applied to the bed 10. The value of the transient load, designated as total transient load (TTL) is calculated by subtracting the detected load from the total load measured by the load cells 66, 68, 70, and 72 that the closed-system load measured before the transient event; the closed-system load which is effectively the patient's static weight, designated as the DC sum of beams (DCSB) which can be determined using known techniques, such as that disclosed in U.S. Pat. No. 10,054,479 titled “BED WITH AUTOMATIC WEIGHT OFFSET DETECTION AND MODIFICATION,” which is incorporated herein for the disclosure of monitoring and updating a patient load to establish a static patient weight, DCSB.

Once the DCSB is established, a simple threshold can be tested to determine whether a TTL is an NPMA or not. The units here are forces, measured in kg, also called kg-force. As part of the test of the threshold, an oscillation in the location of the CG and an effective return of the TTL to zero can be considered to confirm the transient nature of the load to help confirm that the event is a TTL.

Relying just on thresholding TTL moment-by-moment is confounded by self-offloading patient movements (SOs). SOs are large vertical shifts that are an artifact of a patient quickly lifting their core body up using the strength in his legs or arms and then returning to a starting or near starting position. These self-movements cause large momentary changes in TTL and may appear to be an NPMA. Although SOs can cause momentary large shifts from the patient's weight in the closed system, appearing to break it, the closed system is not broken if the response of the system through the entire duration of the motion is considered.

A self-offloading patient movement (SO) occurs when a patient momentarily “pops” themselves up to break the friction between their body and the bed 10, then laterally thrust themselves. On the other hand, a LPM occurs when a patient is dragged or drags themselves across the bed 10. A lateral movement may be described as a high friction or a high shear movement, as a self-offloading movement may be described as a low shear or a low friction movement.

Referring to FIG. 4, the phenomenon of an SO event is illustrated with reference to the variation the sum of the signals from the load cells 66, 68, 70, and 72 over time. The initial forces imparted to move the trunk of the patient create a spike in the measured load as the movement begins to occur in a preload phase designated as 1 on the graph in FIG. 4. The forces oscillate after the movement occurs in a reaction phase, designated as 2 on the graph in FIG. 4. This is a result of a sort of conservation of energy. The integral or sum of TTL over this event is approximately zero when an SO event is experience, where TTL is negative at points in time, such as the designation 2. Under this conservation of energy approach, the SO is detected when any loads induced by the motion of the patient are offset by reactionary loads.

Using empirically generated test data, an approach was developed to model the absolute total transient load (ATTL), which is defined as:

ATTL=|[Σ(RHLC,LHLC,RFLC,LFLC)−DCSB]/DCSB|  (EQ. 1)

Where RHLC, LHLC, RFLC, and LFLC are the values in kg, of the four load cells 66, 68, 70, and 72 and DCSB, which is defined above. This approach provides an absolute value of the TTL, recognizing that transient loads may also unload the weigh frame 30 in some situations.

The conservation of energy theory was modeled using an integral approach and taking the absolute value of the integral as shown below.

centInt=|∫_L^−L[(sum(RHLC,LHLC,RFLC,LFLC)−DCSB)/DCSB]|  (EQ. 2)

A third modeling equation was derived to calculate CGspeed, which is discussed in theory above, and these equations were used:

$\begin{array}{cc}\mathrm{CGspeed}=\frac{\left(\sqrt{\Delta {\mathrm{CGx}}^2+\Delta {\mathrm{CGy}}^2}\right)}{t}& \left(\mathrm{EQ}.3\right)\end{array}$ $\begin{array}{cc}\mathrm{CGx}=X*\left(\mathrm{LHLC}+\mathrm{LFLC}\right)/\mathrm{sum}\left(\mathrm{RHLC},\mathrm{LHLC},\mathrm{RFLC},\mathrm{LFLC}\right)& \left(\mathrm{EQ}.4\right)\end{array}$ $\begin{array}{cc}\mathrm{CGy}=Y*\left(\mathrm{RHLC}+\mathrm{RFLC}\right)/\mathrm{sum}\left(\mathrm{RHLC},\mathrm{LHLC},\mathrm{RFLC},\mathrm{LFLC}\right)& \left(\mathrm{EQ}.5\right)\end{array}$

Where t, is the time interval over which the change in the position of the CG moves and where X is the distance between the left load cells 68, 72 and the right load cells 66, 70, and Y is the distance between head load cells 66, 68 and the foot load cells 70, 72.

Having successfully established that the features under study could be extracted and applied with confidence in an inference model, a generalized algorithm 78 for processing sensor data from existing sensors from a bed 10 was developed as shown in FIG. 8. At a pre-processing step 90, bed status data and sensor data obtained from the sensors 60 are pre-processed. The sensor data from the sensors 60 includes data from head zone sensor 82, a seat zone sensor 84, a thigh zone senor 86, and a foot zone sensor 88. The sensor data is filtered, such as through a low-pass filter 120. Additional testing is confirmed at step 92 where data being transferred into an inference engine 94 is validated. At step 92, validation include a determination that sensor data being received is consistent with the environment of the bed 10 and patient. In some examples, information may be received from a hospital information system 32 which indicates an expected sensor signal range. For example, validation may test the DCSB against the weight of the patient in the hospital information system 32 to validate that the signals from the load cells 66, 68, 70, 72 are reasonable. The hospital information system 32 may include an admission/discharge/transfer (ADT) management system, an electronic medical records system, or a nurse call system. Each of these units of the hospital information system 32 may regularly communicate with others of the systems or may be stand-alone systems. The validation step 92 may also use other sensors to confirm that a patient is in the bed 10 and generating meaningful data to confirm the validity of the algorithm 78 in real time. The filtered data is provided to the inference engine 94 where at step 96 a first feature extraction is conducted. From the example above, a first feature is extracted to confirm whether there is a threshold state, such as motion or no motion. The CGspeed and ATTL analysis were each proven to be a useful to establish the presence of motion or no motion. In other embodiments, other first features may extracted as the first step in a serial classification approach. Upon extraction of the first feature, the serial classification approach is continued with the features extracted in step 96 advanced to step 98 where baseline data is tested against an extracted first feature to determine whether a threshold has been met that is indicative of motion. If no motion is detected, the algorithm 78 loops at step 98 until motion is identified and classification can be conducted.

Once motion is identified at step 98, the motion is discriminated at step 80 between NPMA and patient motion of either LPM or SO. If NPMA is identified at step 80, then the signal data is disregarded. However, confirmation and characterization of LPM or SO at step 80 is further analyzed at step 102 to establish a degree of motion. At step 102, in the illustrative embodiment, the motion can be distinguished between an egress, a large self-offloading patient movement (SO), a major lateral patient motion (LPM) and/or a small self-offloading patient movement (SO), or a slight lateral patient motion.

If the patient is determined to move themselves, a major lateral patient motion (LPM) is observed. As shown in FIG. 5A, the patient's center of gravity changes in the x and y dimension of the bed 10 from a position time to t₀ a position in time t_n. Such a motion is determined to be a high shear movement. As shown in FIG. 5C, no momentary change of forces is observed during such movement. The motion is completely orthogonal to the direction the orientation of the load cells 66, 68, 70, 72 in the bed 10.

In case of a self-offloading patient movement (SO), the movement may have some vertical component. This is shown in FIGS. 6A-C. Momentary change of forces are observed during such movement. There is some forcing and the resultant reaction forces cause dampened oscillations (FIG. 6C). The dampened oscillations may be caused by the patient moving or popping momentarily in the z dimension. Such motion might not be entirely vertical, but may have some vertical component and some movement in the x and y direction (FIG. 6A). Such a movement may be deemed a low-shear or a low friction movement. The occurrence of a high shear movement may be determined by measuring the integral of the absolute value of the total forces (all beams summed) minus the known patient weight (see FIGS. 5B, 6B). If this integral is under a certain threshold, the motion that caused the center of gravity to change may be deemed a major lateral patient motion (LPM) or a high friction or shear movement. FIG. 7 illustrates how change in the patient's center of gravity is assessed in relationship to the position of the patient on the bed 10.

Once the inference as to the type of patient motion is complete at step 102, the information is then moved to a database associated with the patient as step 104. For example, at step 104 the patient's medical record can be updated, based on the inference identify, objectively, the patient's motion and behavior such as regular self-offloading patient movement, major LPMs, slight LPMs, or ingress or egress with or without caregiver assistance.

If the motion is determined to be a LPM, it may be noted as a high shear motion. The occurrence and frequency of such motion may be monitored and used to identify high or low shear events. Such identification is critical to inform caregivers about the onset of pressure injuries. The high or low shear events can be used as determinants into a model that calculates the overall risk of pressure injury formation to the patient.

In addition to simple characterization of the patient motion, between an LPM, SO, egress, or ingress, the data from the load cells 66, 68, 70, 72 may be processed further to provide a higher level of sensitivity to the characterization of the patient movement. While the discussion above addresses the inference and characterization of the patient motion, by calculating the work done by the patient during the motion, other methods may be used to monitor and identify the type of patient movement, possibility of high shear or low shear events, and provide insights as to the patient's medical progression, whether it be positive or negative.

While the algorithm 78 of FIG. 8 has been established as a successful approach to drawing inferences regarding the characterization of patient motion, considering the entire structure of the bed 10, additional information is available that may be fused with the load cell signal data to provide and even more accurate indication of the status of the patient and assist in improving the inferences drawn. Specifically, the patient is supported on the mattress 18 and portions of the patient are supported on the inflated zones 36, 38, 40, and 42. As shown in FIG. 2, the respective head zone sensor 82, a seat zone sensor 84, a thigh zone senor 86, and a foot zone sensor 88 are each gathering data in real time and the air module 52 is in communication with the scale module 50 and controller 28 so that data can be shared to further inform the analysis. The analysis may include the determination of high shear or show shear patient movement.

Still further, it should be understood the closed-system conservation of energy principles discussed above with regard to the load cells 66, 68, 70, and 72 hold with regard to the collective air pressure sensors 82, 84, 86, 88 and the load cells 66, 68, 70, 72 all-together. In other words, changes in energy at one inflatable zone 36, 38, 40, or 42 should be conserved, but may not be conserved as measure only by the air pressure sensors 82, 84, 86, 88, but some of the energy may be transferred away from the sensors 82, 84, 86, 88 and measured at one or more of the load cells 66, 68, 70, 72. Similarly, energy transferred away from one of the load cells 66, 68, 70, 72 and be effectively measured by one or more of the air pressure sensors 82, 84, 86, 88. This is best understood with an appreciation for the relative flexibility of the inflatable zones 36, 38, 40, or 42 and mattress 18 in total. The ability of the mattress 18 to absorb “shocks” without transferring the concomitant energy change to the load cells 66, 68, 70, 72 by transferring the energy to stretching fabric or compressing air within the zones 36, 38, 40, 42 confounds the analysis.

However, following the basic principles of conservation of energy, for movements considered to be NPMAs, a simple test to monitor for net changes in energy in the entire system of sensors will provide a high confidence level that the detected movement is, or is not, a true patient movement. In effect, the net kinetic energy being measured by the air pressure sensors 82, 84, 86, 88 and load cells 66, 68, 70, 72 should stay relatively constant, other than the theoretical variations due to heat transfer.

Finally, the implementation requires the controller 28 to account for energy added to the system by the operation of components of the bed 10 such as the blower 106 or various drive motors that move components of the frame 34, such as the head section 44.

With this in mind, we return to the control system 26 shown in FIG. 2. The control system 26 further includes a communications interface 108 that is operable, under the control of the controller 28, to communicate with the hospital information system 32 through a communications infrastructure 110 to share the patient health characterization, whether that be occurrence of a high shear movement, a mobility score, an activity score, a consciousness score, or any other objective score based on the output from the bed 10 acting as a sensor to objectively measure the motions made by the patient and characterizing the type of motions patient is making.

Still further, it is contemplated that if the controller 28 detects an adverse condition, the controller 28 may communicate that adverse condition through the communications interface 108 to the hospital information system 32 for action by caregivers. Similarly, the controller 28 may communicate an adverse event to the user interface 54 which may issue an audible or visual alert of the adverse condition. The adverse condition may be based on an acceptable threshold of motion or work. In addition, the adverse condition evaluation may rely solely on a rate of change of patient motion or work. For example, a significant drop in the motion of or work being done by a patient may be an indicator of the deterioration of a patient due to, for example, sepsis, delirium, or a loss of consciousness. Additionally, the controller 28 may issue an audible or visual alert if the frequency of high shear movements exceeds a certain threshold.

Although this disclosure refers to specific embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the subject matter set forth in the accompanying claims.

Claims

1. A patient support apparatus comprising a plurality of load cells,a frame supported on the load cells,a mattress including a plurality of inflatable zones positioned on the frame, the mattress and frame cooperating to direct any patient load through the mattress and frame to the load cells,a plurality of air pressure sensors, each air pressure sensor measuring the pressure in a respective inflatable zone of the mattress, anda control system including a controller, the controller configured to receive a separate signal from each of the plurality of load cells and each of the plurality of air pressure sensors, process the signals to identify, based on transient changes in the signals, motion of the patient that does not result in relative movement of the patient relative to the frame, the motion of the patient being further processed to characterize the nature of the patient motion and, based on the characterization of the patient motion, automatically determine if the patient motion is a high shear motion or a low shear motion.

2. The patient support apparatus of claim 1, wherein the controller is configured to monitor the energy detected by each of the load cells and each of the air pressure sensors and compare the change in total energy measured by the load cells and air pressure sensors to determine if external energy has acted on the patient support apparatus, and, if a change in total energy measured is indicative that external energy has acted on the patient support apparatus, utilize the resulting change in total energy to modify the characterization of the patient motion that is used to update the patient profile.

3. The patient support apparatus of claim 2, wherein the transient changes in the signals are indicative of motion of a least a portion of the patient in a vertical direction.

4. The patient support apparatus of claim 3, wherein the controller is operable to calculate the work done by the patient in the vertical direction to characterize the patient motion.

5. The patient support apparatus of claim 1, wherein the controller is configured to compare the air pressure sensor signal for each of two adjacent zones and use the relative changes in the pressure in the adjacent zones during a potential patient movement event to confirm the characterization of the patient motion.

6. The patient support apparatus of claim 5, wherein the controller is configured to monitor the energy detected by each of the load cells and each of the air pressure sensors and compare the change in total energy measured by the load cells and air pressure sensors to determine if external energy has acted on the patient support apparatus, and, if a change in total energy measured is indicative that external energy has acted on the patient support apparatus, utilize the resulting change in total energy to modify the characterization of the patient motion that is used to update the patient profile.

7. The patient support apparatus of claim 5, wherein the controller is configured to determine that the patient motion is the low shear motion if the patient motion is characterized as a self-offloading motion in which a patient readjusts their position on the mattress without any external influence.

8. The patient support apparatus of claim 5, wherein the controller is configured to determine that the patient motion is the high shear motion if the patient motion is characterized as a lateral motion in which a patient readjusts their position by dragging themselves on the patient support apparatus.

9. The patient support apparatus of claim 8, wherein the center of gravity of the patient changes in an x-y direction due to the patient motion.

10. The patient support apparatus of claim 1, wherein a momentary change in force is determined by measuring an integral of an absolute value of a total of all forces on the load cells minus the patient's weight, and wherein if the integral is less than a threshold, the patient motion is determined to be the high shear motion.

11. The patient support apparatus of claim 1, wherein there is a dampened oscillation in a z direction, and wherein center of gravity of the patient changes in an x-y direction due to the patient motion.

12. A system comprising a patient support surface including a plurality of inflatable zones,a plurality of load cells supporting the patient support surface,a plurality of air pressure sensors, each pressure sensor measuring the pressure in a respective inflatable zone of the patient support surface, anda controller configured to receive a separate signal from each of the plurality of load cells and each of the plurality of air pressure sensors, process the signals to identify motion of the patient, the motion of the patient being further processed to characterize the nature of the patient motion and, based on the characterization of the patient motion, automatically determine if the patient motion is a high shear motion or a low shear motion.

13. The system of claim 12, wherein the controller is configured to monitor the energy detected by each of the load cells and each of the air pressure sensors and compare the change in total energy measured by the load cells and air pressure sensors to determine if external energy has acted on the system, and, if a change in total energy measured is indicative that external energy has acted on the system, utilize the resulting change in total energy to modify the characterization of the patient motion that is used to update the patient profile.

14. The system of claim 12, wherein the signals are indicative of motion of a least a portion of the patient in a vertical direction.

15. The system of claim 12, wherein the controller is configured to calculate the work done by the patient in the vertical direction to characterize the patient motion.

16. The system of claim 12, wherein the controller is configured to compare the air pressure sensor signal for each of two adjacent zones and use the relative changes in the pressure in the adjacent zones during a potential patient movement event to confirm the characterization of the patient motion.

17. The system of claim 12, wherein the controller is configured to monitor the energy detected by each of the load cells and each of the air pressure sensors and compare the change in total energy measured by the load cells and air pressure sensors to determine if external energy has acted on the system, and, if a change in total energy measured is indicative that external energy has acted on the system, utilize the resulting change in total energy to modify the characterization of the patient motion that is used to update the patient profile.

18. The system of claim 17, the controller is operable to determine that the patient motion is the low shear motion if the patient motion is characterized as a self-offloading motion in which a patient readjusts their position on the mattress without any external influence.

19. The system of claim 17, wherein the controller is configured to determine that the patient motion is the high shear motion if the patient motion is characterized as a lateral motion in which a patient readjusts their position by dragging themselves on the patient support apparatus.

20. The system of claim 19, wherein center of gravity of the patient changes in an x-y direction due to the patient motion.