Patent Application
20090156946
This invention relates generally to blood pressure monitoring and more particularly to blood pressure monitoring apparatus including motion artifact sensing.
Non-invasive blood pressure (NIBP) monitors typically use a blood pressure cuff. To measure a person's blood pressure, a blood pressure cuff of an appropriate size can be affixed to a person's limb, typically to the upper portion of an adult's arm or to an infant's leg. The blood pressure cuff generally includes at least one inflatable bladder. Blood pressure measurements are made by inflating the bladder and then monitoring the pressure of the bladder using a pressure sensor as the bladder is deflated. Because the person's heart is pumping blood through arteries in the limb constrained by the blood pressure cuff, the bladder pressure measured by the pressure sensor includes pressure changes caused by pumping blood superimposed on the changing bladder pressure.
Systolic pressure is the maximum arterial pressure during contraction of the left ventricle of the heart. Diastolic pressure is the minimum arterial pressure during relaxation and dilatation of the ventricles of the heart when the ventricles fill with blood. Systolic pressure and diastolic pressure readings are two of the blood pressure parameters that a non-invasive blood pressure monitor can measure. Using the well known oscillometric method, the blood pressure cuff is initially inflated to a pressure higher than the highest expected systolic reading and then deflated to a pressure lower than the lowest expected diastolic reading. Above the systolic pressure, the pressure sensor signal reflects only the dominant cuff pressure. When the bladder pressure falls to a pressure near the systolic pressure, the pressure sensor signal begins to indicate cuff pressure oscillations superimposed on the deflating cuff pressure signal. When the cuff bladder pressure falls below the lower diastolic pressure, the cuff pressure oscillations are no longer present. An additional parameter, mean arterial pressure (MAP), can also be measured using the oscillometric method by further analysis of the cuff pressure oscillations that occur between the systolic pressure and diastolic pressure.
Most types of blood pressure monitors can produce reasonably accurate readings if the person's limb is substantially motionless during the deflation of the blood pressure cuff bladder. However, if the limb to which the blood pressure cuff is affixed is in motion during the blood pressure cuff bladder deflation, the pressure sensor can respond to additional motion induced pressure artifacts. In addition to conscious movement of the limb, motion artifact can be caused by involuntary motion such as can be caused by shivering and tremors. In many cases the magnitude of the motion can cause significant error in the blood pressure measurement results. For example, we have observed persons in a hospital setting where motion of limbs caused repeated errors in blood pressure measurements. In some cases, particularly where the NIBP measurement equipment is fully automatic, a clinician might be distracted and not realize that a blood pressure measurement has been corrupted by excessive patient motion. NIBP motion artifact can also be problematic during patient vehicular transport motion.
One solution to the motion artifact problem in NIBP monitors has been implemented under the trade name Smartcuf® technology by the Welch Allyn Corporation. The Smartcuf technology combines NIBP with ECG information. The Smartcuf technology can identify and disregard as attributable to motion artifact, pressure oscillations that occur at incorrect times with respect to heart pumping as monitored by the ECG. NIBP-ECG motion artifact detection and correction can be very effective, as indicated in the 1998 Revision Labs study, “Noninvasive Blood Pressure Measurement and Motion Artifact: A Comparative Study.” The NIBP-ECG motion artifact solution, however, is most cost effective when associated with a multifunction medical monitor already including both NIBP and ECG measurements. The problem is that ECG measurement signals are not typically available in the context of many stand alone NIBP clinical monitors as well as in most home use applications. Also, NIBP-ECG motion artifact detection and correction is cost prohibitive in the context of low cost NIBP single function instruments.
Another solution to the motion artifact problem in NIBP monitors studied by the Welch Allyn Corporation was described in U.S. patent application Ser. No. 10/619,380, “Motion management in a fast blood pressure measurement device” published as U.S. Published Patent Application No. 2005/0033188. In this solution, motion artifact was detected by analyzing a pressure signal indicative of the pressure of a bladder in a blood pressure cuff. The '380 application is incorporated herein by reference in its entirety.
What is needed is a blood pressure monitor that can better indicate when a blood pressure measurement has been corrupted by motion artifact. What is also needed is a blood pressure monitor that can correct blood pressure readings by removing the effects of motion artifact.
In one aspect, the invention relates to a blood pressure monitor for measuring the blood pressure of a person including a blood pressure cuff. The blood pressure cuff includes at least one bladder. The blood pressure monitor also includes an electro-pneumatic package. The electro-pneumatic package includes a pump, a valve, a pressure sensor, and one or more accelerometers. The blood pressure monitor also includes a pneumatic mechanical coupling. The pneumatic mechanical coupling is configured to pneumatically and mechanically directly couple the blood pressure cuff to the electro-pneumatic package, wherein a signal from the one or more accelerometers configured to indicate an activity level of the person during a blood pressure measurement. The blood pressure monitor also includes a display. The display is configured to display an indication of the activity level.
In one embodiment the signal from the one or more accelerometers indicates an activity level of the person during a blood pressure measurement and an algorithm running on a microcomputer is configured to receive one or more values representative of the signal from the one or more accelerometers and the algorithm rejects at least one pressure value representative of a pressure signal from the pressure sensor as cause to be in error by the activity level of the person.
In another embodiment, the signal from the one or more accelerometers indicates an activity level of the person during a blood pressure measurement and an algorithm running on a microcomputer is configured to receive one or more values representative of the signal from the one or more accelerometers and the algorithm corrects at least one pressure value representative of a pressure signal from the pressure sensor to substantially remove motion induced error caused by the activity level of the person.
In yet another embodiment, the signal from the one or more accelerometers indicates an activity level of the person during a blood pressure measurement, the activity level of the person causing a motion induced error, and an algorithm running on a microcomputer is configured to receive one or more values representative of the signal from the one or more accelerometers and the algorithm corrects the blood pressure of the person to substantially remove the motion induced error.
In another aspect, the invention relates to a blood pressure monitor including a blood pressure cuff including at least one bladder. The blood pressure cuff also includes a first half of a mechanical pneumatic connector. The blood pressure monitor also includes a pump. The pump is pneumatically coupled to the bladder and configured to inflate the bladder. The blood pressure monitor also includes a valve. The valve is pneumatically coupled to the bladder and configured to cause a controlled deflation of the bladder. The blood pressure monitor also includes a pressure sensor. The pressure sensor is pneumatically coupled to the bladder and configured to measure a bladder pressure. The blood pressure monitor also includes one or more accelerometers. The one or more accelerometers are electrically and mechanically configured to provide a motion signal from the one or more accelerometers responsive to and representative of a movement of the at least one blood pressure inflatable bladder. The blood pressure monitor also includes an electronics circuit. The electronics circuit is electronically coupled to the valve, the pump, the pressure sensor, and the one or more accelerometers, wherein the pump, the valve, the pressure sensor, the one or more accelerometers, and the electronics circuit are disposed within an electro-pneumatic package, and the electro-pneumatic package include a second half of a mechanical pneumatic connector and wherein the first half of the mechanical pneumatic connector is configured to mechanically connect to the second half of a mechanical pneumatic connector to provide a substantially air-tight semi-rigid mechanical and pneumatic direct coupling between the electro-pneumatic package and the blood pressure cuff and wherein the electronics circuit is configured to receive the motion signal from the one or more accelerometers during a blood pressure measurement.
In one embodiment, the electronics circuit is configured to cause an indication of excessive motion based on the motion signal from the one or more accelerometers representative of the movement of the at least one bladder when the motion signal exceeds a pre-determined threshold.
In another embodiment, the indication of excessive motion includes one of a visual indication and an audio indication.
In yet another embodiment, the indication of excessive motion is configured to indicate that the blood pressure measurement should be repeated.
In yet another embodiment, the electronics circuit further comprises a microcomputer, the microcomputer configured to receive the motion signal from the one or more accelerometers and to correct the blood pressure measurement based on the motion signal.
In yet another embodiment, the one or more accelerometers comprise a MEMS accelerometer.
In yet another embodiment, the MEMS accelerometer includes a three axis accelerometer.
In yet another embodiment, the at least one accelerometer is mechanically disposed on or in a blood pressure monitor housing.
In yet another embodiment, the motion signal includes one or more analog signals from the one or more accelerometers and wherein the indication of excessive motion is based at least in part upon the motion signal and the motion signal threshold.
In yet another embodiment, the motion signal includes one or more analog signals from the one or more accelerometers and the electronics circuit includes at least one analog to digital converter (ADC), the at least one ADC configured to digitize the one or more analog signals from the one or more accelerometers, and wherein the indication of excessive motion is based at least in part upon the motion signal in a digital form and the motion signal threshold in a digital form.
In yet another embodiment, the electronics circuit is additionally configured to provide a correction to substantially correct the blood pressure measurement for a blood pressure cuff motion induced error.
In yet another embodiment, the correction to the blood pressure measurement includes a correction based on analog signals or a correction based on digital signals.
In yet another embodiment, the correction is configured to be applied to a digital representation of a pressure signal from the pressure sensor.
In yet another embodiment, the correction is configured to be applied as part of a digital computation used to calculate the blood pressure measurement.
In another aspect, the invention features a method for detecting a motion artifact in a non-invasive blood pressure measurement comprising the steps of: providing a blood pressure cuff having at least one bladder, providing a blood pressure monitor pneumatically coupled to the blood pressure cuff, providing at least one accelerometer mechanically disposed such that the at least one accelerometer substantially measures a motion of the at least one bladder, attaching the blood pressure cuff to a person, performing an oscillometric procedure using the blood pressure cuff, measuring a pressure and a motion of the at least one bladder during the oscillometric procedure, determining an effect of the motion on the non-invasive blood pressure measurement, and whereby a motion artifact greater than a pre-determined threshold is detected when present during a non-invasive blood pressure measurement.
In one embodiment, the step of determining an effect includes the step of determining an effect of the motion on the non-invasive blood pressure measurement and providing an indication to the person to reduce movement of a limb to which the blood pressure cuff is attached.
In another embodiment, the step of determining an effect includes the step of determining an effect of the motion on the non-invasive blood pressure measurement and indicating to an Operator of the blood pressure monitor to do the non-invasive blood pressure measurement over again where an excessive motion has been detected.
In yet another embodiment, further including, following the step of determining an effect, the step of correcting the non-invasive blood pressure measurement based on the measurement of the motion of the at least one bladder.
For a further understanding of these and objects of the invention, reference will be made to the following detailed description of the invention which is to be read in connection with the accompanying drawing, where:
The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the drawings, like numerals are used to indicate like parts throughout the various views.
A blood pressure monitor 100 according to the invention can provide information indicative of a patient's activity level as measured by the one or more accelerometers 101. Such information can be for use solely by the instrument, or transmitted by wired or wireless means to another instrument or computer. Typically a blood pressure monitor as shown in the embodiments of
Beyond general monitoring of a person's motion or activity, information from the one or more accelerometers 101 can be used by an algorithm running on a microcomputer in blood pressure monitor 100 to discriminate undesired patient motion from the person's heart signal as monitored through pressure measurements of bladder 103. The discrimination feature can be used to enable an alert mechanism for a clinician. In some embodiments, in response to an alert, a clinician can act as needed to settle a patient exhibiting excessive activity. In other embodiments improved performance NIBP algorithms running on a microcomputer, such as microcomputer 107, can ignore or reject pressure signals adversely affected by a person's motion. In still other more sophisticated embodiments, improved performance NIBP algorithms running on a microcomputer, such as microcomputer 107, can cancel patient motion from the corresponding pressure signal used in the blood pressure measurement.
According to the inventive system and method, a blood pressure cuff is first attached to the limb of a person, typically around the person's arm. In a home setting, generally a monitor having a single suitably sized cuff is used. In a clinical setting, there can be a range of cuff sizes available to accommodate different limb sizes and different ages, such as baby, pediatric, and adult. Once attached to the limb, a bladder in a blood pressure cuff can be inflated to a pressure above the highest expected systolic blood pressure, typically to a pressure of on the order of 160 mmHg (1 PSI˜50.17 mmHg). A valve can then be opened and the pressure of the bladder monitored as the bladder deflates. While unimportant to the inventive use of an accelerometer to monitor motion of the bladder, typically in modern blood pressure monitors, a pressure sensor generates an analog or a digital pressure signal over time as the bladder inflates and/or deflates. In the case of such a microcomputer based blood pressure monitor, the blood pressure parameters, such as the systolic pressure, diastolic pressure, and mean arterial pressure, can then be calculated from the pressure data and displayed, such as on a LCD display.
We define the term “oscillometric procedure” herein as including known techniques and algorithms for measuring blood pressure using, for example, a blood pressure cuff having at least one inflatable bladder. It is unimportant for the inventive technique or associated apparatus whether the bladder pressure measurements used to determine the desired blood pressure parameters, are taken, recorded, digitized, or measured during inflation, deflation, or during a combination of inflation and deflation. For example, one useful oscillometric technique, the Welch Allyn FastBP® system, measures blood pressure cuff bladder pressure during inflation. U.S. patent application Ser. No. 11/347,889, published as U.S. Published Patent Application No. 2007/0185401, “Blood Pressure Measurement”, describes one such oscillometric technique. The '889 application is incorporated herein by reference in its entirety.
Returning now to
Here it can be seen that in some embodiments, a semi-rigid pneumatic coupling 110 can be configured to provide rotation or swivel feature such that when blood pressure cuff 102 is affixed on the limb of a person, electro-pneumatic package 125 can be rotated 130 to a convenient operating and viewing angle. While pneumatic coupling 110 is not visible in
In the most basic embodiments, it might only be possible to include a motion warning indication, such as by a warning light visible display indication, or audible sound or some combination of audio and/or visual warnings. In embodiments having more sophisticated electronics, there can be a display indicating through icons and/or text that there is excessive motion of a person's limb (patient activity) to which a blood pressure cuff 102 is affixed. In still more sophisticated embodiments using electronics packages including microcomputers, such as the apparatus illustrated in
In the exemplary flow charts that follow, we describe various embodiments of such NIBP algorithms in more detail. Turning to the flow charts of
In one embodiment of an inventive blood pressure monitor, as illustrated by the flow chart of
Another embodiment, similar to that illustrated in
In the embodiment illustrated by the exemplary flow chart of
example: We now describe a compact wearable blood pressure monitor according to the invention. The wearable blood pressure monitor includes both an electronics/pneumatic package (the NIBP monitor) and a blood pressure cuff having an inflatable bladder. In the exemplary blood pressure monitor, the blood pressure cuff attaches directly to the electronics/pneumatic package by a FLEXIPORT (a substantially rigid mechanical and pneumatic connection of the cuff to the NIBP monitor). A FLEXIPORT connection is described in more detail in two related U.S. patent applications Ser. No. 11/230,117, entitled Blood Pressure Measuring Apparatus”, and U.S. patent applications Ser. No. 11/513,608, entitled “Blood Pressure Measuring Apparatus”, both applications also assigned to the Welch Allyn Corporation. The Ser. No. 11/230,117 and the Ser. No. 11/513,608 applications are both incorporated herein by reference in their entirety. In addition, to accomplish the inventive technique, one or more accelerometers are mounted on or in the electronics/pneumatic package. The accelerometer can be mounted on a printed circuit board (PCB), elsewhere in or on the enclosure, or in or on the FLEXIPORT. Since the electronics/pneumatic package is mechanically coupled to the blood pressure cuff by the relatively rigid FLEXIPORT connection, any motion of the blood pressure cuff is substantially transmitted to the accelerometer disposed in or on the electronics/pneumatic package or in or on the FLEXIPORT.
In the exemplary NIBP monitor, the blood pressure cuff need only be FLEXIPORT compatible, otherwise the cuff itself does not need to include an accelerometer. One advantage of system a NIBP monitor is that there need only be one version of FLEXIPORT blood pressure cuffs, albeit in various sizes where multiple persons having different limb sizes are monitored. Also, since in this example the accelerometer is not disposed in the blood pressure cuff, there is no need for electrical connections between the FLEXIPORT compatible cuff and the FLEXIPORT connection or port.
While in the exemplary embodiment of
A portion of pump 105 including a motor (cylindrical portion) and pump head (adjacent to the motor) can also be seen
Display 109 can be seen represented as an exemplary LCD display and can be of various useable resolutions and monochromatic such as black or blue or a color display. A symbolic power source can be seen to be represented by battery 410 including for example, one or more button batteries. A pressure sensor 106 (not shown in
Accelerometer 101 can be any type of accelerometer suitable for use to detect motion of a bladder 103 of a blood pressure cuff 102. Typical suitable accelerometers include solid state accelerometers such as those using MEMS technologies. MEMS accelerometers are available from a number of companies including: Freescale Semiconductor of Austin, Tex., Analog Devices or Norwood, Mass., Infineon Technologies of Los Angeles, Calif., Memsic of Andover, Mass. and China, Bosch Sensortec of Reutlingen, Germany, Hitachi Metals of Tokyo, Japan, Oki Electric Industries of Tokyo, Japan, and Kionix of Ithaca, N.Y. While it may be possible to detect blood pressure cuff motion using an accelerometer having one or two sensitive axis to successfully, full three axis (x,y,z) sensitivity can be preferable. It is unimportant to the invention whether three separate analog or digital signals are received from an accelerometer 101 and further processed, such as to generate a motion vector having a magnitude and/or direction, or if the output from an accelerometer 101 is a single analog or digital magnitude and/or direction. It is also unimportant whether a single multi-axis accelerometer or two or more single axis accelerometers are mechanically disposed to be sensitive in two or more axis.
A person's or patient's activity level as measured by the one or more accelerometers is defined as a physical motion of some part of a person's body where that motion transmits to the part of the person's body to which a blood pressure cuff is affixed, typically a person's limb. The motion can be in another part of the body, such as the torso and mechanically transmitted to the relevant limb, or the motion can be caused by motion of the limb itself. Such a motion can result in a motion artifact error in a blood pressure measurement, typically by causing an acceleration of a bladder in a blood pressure cuff. The acceleration of the cuff can cause a pressure signal related to the motion that can distort the pressure reading (pressure sensor signal) from the blood pressure cuff that otherwise could produce an accurate measurement of the person's blood pressure. We define such errors interchangeably herein by the terms and phrases including, but not limited to, motion error, motion induced error, motion artifact error, excessive motion error, and motion induced artifact error.
We define “microcomputer” herein as synonymous with microprocessor, microcontroller, and digital signal processor (“DSP”). It is understood that memory used by the microcomputer, including for example blood pressure monitor “firmware”, can reside in memory physically inside of a microcomputer chip or in memory external to the microcomputer or in a combination of internal and external memory. Similarly, analog signals can be digitized by one or more stand alone analog to digital converter (“ADC”) or one or more ADCs or multiplexed ADC channels can reside within a microcomputer package. It is also understood that field programmable array (“FPGA”) chips or application specific integrated circuits (“ASIC”) chips can perform microcomputer functions, either in hardware logic, software emulation of a microcomputer, or by a combination of the two. Blood pressure monitors having any of the inventive features described herein can operate entirely on one microcomputer or can include more than one microcomputer.
A wireless connection made by a blood pressure monitor 100 can be 802.11 compliant, or can use a lighter-weight (simpler) protocol that can be more energy efficient. A suitable lighter weight protocol can be proprietary, or standards-based, such as ZigBee or Bluetooth. A blood pressure monitor 100 having wireless capability can be used in hospital environment as part of an integrated wireless monitoring network. The details of such monitoring networks are disclosed in U.S. patent application Ser. No. 11/031,736 entitled, “Personal Status Physiological Monitor System and Architecture and Related Monitoring Methods”, which is incorporated by reference herein in its entirety.
