EP1494586A1 - Systeme de surveillance physiologique passive (p2m) - Google Patents

Systeme de surveillance physiologique passive (p2m)

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Publication number
EP1494586A1
EP1494586A1 EP02739108A EP02739108A EP1494586A1 EP 1494586 A1 EP1494586 A1 EP 1494586A1 EP 02739108 A EP02739108 A EP 02739108A EP 02739108 A EP02739108 A EP 02739108A EP 1494586 A1 EP1494586 A1 EP 1494586A1
Authority
EP
European Patent Office
Prior art keywords
signals
sensor
patient
physiological
data
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP02739108A
Other languages
German (de)
English (en)
Other versions
EP1494586A4 (fr
Inventor
Patrick K. Sullivan
Ken C.K. Cheung
Christopher J. Sullivan
Paul Pernambuco-Wise
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Hoana Medical Inc
Original Assignee
Hoana Medical Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Hoana Medical Inc filed Critical Hoana Medical Inc
Publication of EP1494586A1 publication Critical patent/EP1494586A1/fr
Publication of EP1494586A4 publication Critical patent/EP1494586A4/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/103—Detecting, measuring or recording devices for testing the shape, pattern, colour, size or movement of the body or parts thereof, for diagnostic purposes
    • A61B5/11—Measuring movement of the entire body or parts thereof, e.g. head or hand tremor, mobility of a limb
    • A61B5/113—Measuring movement of the entire body or parts thereof, e.g. head or hand tremor, mobility of a limb occurring during breathing
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/02—Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
    • A61B5/0205—Simultaneously evaluating both cardiovascular conditions and different types of body conditions, e.g. heart and respiratory condition
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/103—Detecting, measuring or recording devices for testing the shape, pattern, colour, size or movement of the body or parts thereof, for diagnostic purposes
    • A61B5/11—Measuring movement of the entire body or parts thereof, e.g. head or hand tremor, mobility of a limb
    • A61B5/1102—Ballistocardiography
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/48—Other medical applications
    • A61B5/4806—Sleep evaluation
    • A61B5/4818—Sleep apnoea
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/68—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient
    • A61B5/6887—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient mounted on external non-worn devices, e.g. non-medical devices
    • A61B5/6892—Mats
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/72—Signal processing specially adapted for physiological signals or for diagnostic purposes
    • A61B5/7203—Signal processing specially adapted for physiological signals or for diagnostic purposes for noise prevention, reduction or removal
    • A61B5/7207—Signal processing specially adapted for physiological signals or for diagnostic purposes for noise prevention, reduction or removal of noise induced by motion artifacts
    • A61B5/7214—Signal processing specially adapted for physiological signals or for diagnostic purposes for noise prevention, reduction or removal of noise induced by motion artifacts using signal cancellation, e.g. based on input of two identical physiological sensors spaced apart, or based on two signals derived from the same sensor, for different optical wavelengths
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/74—Details of notification to user or communication with user or patient ; user input means
    • A61B5/742—Details of notification to user or communication with user or patient ; user input means using visual displays
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B2505/00—Evaluating, monitoring or diagnosing in the context of a particular type of medical care
    • A61B2505/01—Emergency care
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B2562/00—Details of sensors; Constructional details of sensor housings or probes; Accessories for sensors
    • A61B2562/04—Arrangements of multiple sensors of the same type
    • A61B2562/046—Arrangements of multiple sensors of the same type in a matrix array
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/02—Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
    • A61B5/021—Measuring pressure in heart or blood vessels
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/02—Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
    • A61B5/021—Measuring pressure in heart or blood vessels
    • A61B5/02108—Measuring pressure in heart or blood vessels from analysis of pulse wave characteristics
    • A61B5/02125—Measuring pressure in heart or blood vessels from analysis of pulse wave characteristics of pulse wave propagation time
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/02—Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
    • A61B5/024—Detecting, measuring or recording pulse rate or heart rate
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/02—Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
    • A61B5/026—Measuring blood flow
    • A61B5/029—Measuring or recording blood output from the heart, e.g. minute volume
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/68—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient
    • A61B5/6887—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient mounted on external non-worn devices, e.g. non-medical devices
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61G—TRANSPORT, PERSONAL CONVEYANCES, OR ACCOMMODATION SPECIALLY ADAPTED FOR PATIENTS OR DISABLED PERSONS; OPERATING TABLES OR CHAIRS; CHAIRS FOR DENTISTRY; FUNERAL DEVICES
    • A61G1/00—Stretchers
    • A61G1/04—Parts, details or accessories, e.g. head-, foot-, or like rests specially adapted for stretchers
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61G—TRANSPORT, PERSONAL CONVEYANCES, OR ACCOMMODATION SPECIALLY ADAPTED FOR PATIENTS OR DISABLED PERSONS; OPERATING TABLES OR CHAIRS; CHAIRS FOR DENTISTRY; FUNERAL DEVICES
    • A61G2203/00—General characteristics of devices
    • A61G2203/30—General characteristics of devices characterised by sensor means

Definitions

  • Vital signs monitoring is normally a simple and routine procedure involving collection of pulse, respiration and blood pressure data. In a relatively quiet environment, these parameters are easily detected. However, acquisition of physiological signals of interest in a helicopter environment is a challenging problem for several reasons. Limitations on vital signs collection include high noise, vibration, auditory distractions, ineffective monitoring equipment, cramped working conditions, bulky gear during air evacuation, a ⁇ electromagnetic
  • the military medical system needs a portable, non-invasive device capable of monitoring a soldier's vital signs in the field environment under less than ideal circumstances.
  • This system needs to be useful to military medical personnel across the spectrum of care delivery, such as in mass casualty situations, aeromedical evacuations, ground ambulance transports, hospital wards, and intensive care units.
  • a recent study found that thirty-two percent of aircraft medical devices flown onboard a rotor-wing MEDEVAC aircraft failed at least one environmental test.
  • Quartz crystals are minerals that create an electric field known as piezoelectricity when pressure is applied. Materials scientists have found other materials with piezoelectric properties. The versatility and potential uses for piezoelectric materials have been known but cost-prohibitive for some time. However, recent decreases in the cost of manufacturing now permit greater application by engineers and researchers. The advantageous qualities of piezoelectric materials have been applied to medicine, security, acoustics, defense, geology and other fields. Development of applications with piezoelectric materials is in its infancy.
  • piezoelectric-based instrumentation The medical practice and research application of piezoelectric-based instrumentation is gaining momentum.
  • Piezoelectric methods have been successfully used in plethysmography, blood pressure monitoring by piezoelectric contact microphone, heart rate monitoring in avian embryos and hatchlings and piezoelectric probes.
  • Piezoelectric materials are used as detectors of sensitive motion to measure human tremor, small body movements of animals in response to pharmacological manipulation, and respiratory motion for nuclear magnetic resonance (NMR) animal experiments.
  • NMR nuclear magnetic resonance
  • piezoelectric methods In combination with ultrasound, piezoelectric methods have been used to assess coronary hemodynamics, elastic tensor, intra-arterial imaging, and receptor field dimensions.
  • piezoelectric transducers have been attached to the chest wall and used with automated auscultation devices and microcomputers for lung sound analysis.
  • Piezoelectric film has been applied and studied to determine joint contact stress
  • piezoelectric disks have been used for recording muscle sounds and qualitative monitoring of the neuro
  • Stochastic wave theory as commonly used in ocean engineering to analyze pseudo-periodic phenomena, indicates spectral peaks from respiration and heart rate.
  • Human heartbeats, respiration, and blood pressure are repetitive in nature, reflecting complex mechano-acoustical events.
  • various problems with piezoelectric instrumentation development prevent its full realization. Measurement of human tremor only works well when the environment is absolutely silent. In fact, extraneous noise such as equipment, fans, people talking, and the patient's own voice routinely exists in most hospital rooms. That noise masks and distorts the signal of interest, thus limiting the practicality of piezoelectric instrumentation. Animal noises make data collection difficult in laboratory animal studies. In non-laboratory environments, medical uses of piezoelectric instrumentation for humans remains a problem because of the inherent signal-noise problem.
  • a primary mission of military nurses is to ensure that wounded and sick soldiers obtain prompt medical attention and/or evacuation to definitive medical care.
  • the actions performed during the time period between a battlefield injury and the transfer of casualties to appropriate medical treatment is critical for the welfare of the soldier, and can be the difference between life and death. It is during this critical time period where diagnosis and treatment begins and also when evacuation - for example via MEDEVAC helicopter - occurs.
  • monitor that can consistently and accurately measure vital signs during a medical evacuation where there is high noise and vibration.
  • the monitor being relatively autonomous intervention by a nurse or technician is not required.
  • information may be forwarded in real-time via wireless communication to the destination where medical personnel and other caregivers are located.
  • the present invention is known as Passive Physiological Monitoring, p , or simply P2M.
  • Data records with vast information, such as blood pressure, are measured, recorded, and may later be delineated to determine the physical condition of the subject being monitored.
  • the cardiovascular system is modeled as a system of pipes, pumps, and other appendices, with the engineering phenomenon known as "water hammer” as the basis for a working model for data analysis in the calculation of blood pressure.
  • Water hammer is a compression wave transmitted through the household plumbing network of pipes and valves when household water is abruptly shut off. The result is a noticeable sound and the deterioration of the plumbing system. Water hammer is caused by the increase in pipe pressure caused by sudden velocity change, typically after water is shut off during a valve closing.
  • the compression wave is described as follows:
  • Skalak (1966) applied the linearized theory of viscous flow to develop a basis for understanding the main waveform features in arteries and veins.
  • the vascular system is equivalent to a network of non-uniform transmission lines.
  • Karr (1982) studied pressure wave velocity on human subjects and developed a method to determine the pulse propagation speed. The invention recognizes that such information may be used to determine plaque buildup, cholesterol concentration on the arterial wall, and arterial wall thickness.
  • Equation (1) allows for determination of pressure change (dP) from the heart pulsing based on the dispersion relationship between pulse wave velocity (c) and flow velocity (v) .
  • Karr's method measures flow velocity to determine dP, which is related to systolic pressure (pS) and diastolic pressure (pD) .
  • the new invention measures the pressure energy from heartbeat and respiration collectively.
  • the heart contribution to the energy spectrum is determined by removing the respiration contribution to the energy spectrum.
  • Respiration energy is filtered out by comparing the energy spectrum calculations of velocity with velocity measures using electromagnetic and doppler methods.
  • the new monitor can be configured for one of its piezoelectric sensors to serve as a dedicated doppler sensor that uses ultrasonics to adjust interpretations of data as a function of the sympathetic tone of the patient.
  • the selective omission of P2M signals and the selective comparison of P2M sensor data with data from other parts of the body, as well as comparisons between two or more simultaneously triggered sensors isolates energy contributions from the heart.
  • P2M energy spectra determined from the foot differs from spectra derived from the chest area, which provides a means for isolating heart energy as the foot spectra is largely void of energy from respiration.
  • P2M is well-suited to assist medical personnel in several areas including, but not limited to, the following situations:
  • the development of the P2M or a passive sensor array is a significant innovation in passive monitoring.
  • a grid of passive sensors noise can be reduced through correlating signals from different pads to discern noise from biological signals. This is very important in high-noise environments.
  • the significance of a passive multi-sensor system is that it affords the opportunity to more comprehensively monitor a patient.
  • the grid of passive sensors provides an innovative way to monitor patients in adverse ambient conditions.
  • the system provides a tool whereby parameters other than blood pressure, heart rate, and respiration can be measured. These parameters include, but are not limited to, patient movement and sleep habits, pulse strength over various portions of the body, relative blood flow volumes, and cardiac output, among others.
  • the main components of the Passive Physiological (P 2 M) system are the passive sensor, hardware for amplification, filtering, data-acquisition, and signal-analysis software.
  • the single passive sensor has dimensions 8" x 10" and is preferably encased in a protective covering. Leads from the sensor attach to the electronics (amplifier, filter, data-acquisition card, desktop computer) where the raw analog voltage signal is filtered and amplified and converted to digital form. Digital filtering and software manipulation of the data in the form of frequency analyses are then performed. Finally, signal processing techniques are then used to extract physiological information from the digital signal.
  • the sensor pad is preferably placed directly beneath the back of a patient lying supine on a MEDEVAC litter.
  • the mechanical/acoustic signals created by cardio-pulmonary function are transmitted through the body onto the passive sensor, which converts the signal into an analog voltage.
  • An illustration of the existing P2M setup is shown in Figure 6.
  • the major hardware used for the laboratory setup are: desktop computer, a multi-function programmable charge amplifier and roll-around rack to encase all of the hardware. To maintain versatility for initial research and development, most of the equipment were chosen for functionality at the expense of space efficiency.
  • the variables of accuracy, precision, user characteristics, and patient comfort determine the value of a field instrument for collection data on vital signs.
  • Figure 1 is a schematic of the P2M system components.
  • Figure 2 is a perspective view of the P2M system.
  • Figure 3 is a graphical comparison of the P2M bench test results and the human evaluator measurements.
  • Figure 4 is a front view of the front panel display and user interface of the P2M system in Acquire Mode.
  • Figure 5 is a front view of the front panel display of the P2M system in Monitor Mode.
  • Figure 6 is a schematic view of a preferred embodiment of the P2M sensor.
  • FIG. 7 shows one of the graphical user interfaces (GUI) of the P2M system.
  • Figure 8 shows the graphical user interface of the P2M system showing time-series and frequency-domain representations of physiological data.
  • FIG. 9 shows measurement of Pulse-Wave Travel Time (PWTT)
  • Figure 10 shows a system test and evaluation results in a graph.
  • Figure 12 shows the measurement through a body armor.
  • Figure 13 shows testing through body armor and MOPP gear combined.
  • FIG 14 shows a schematic view of the Passive Physiological Monitoring (P2M) System Using a passive sensor array and microelectronics incorporated into a MEDEVAC litter.
  • P2M Passive Physiological Monitoring
  • the preferred P2M system is a monitoring device with two major subsystems, one to measure signals and the other to process data into meaningful information.
  • Figure 1 shows a schematic of the system
  • Figure 2 shows a perspective view of the system.
  • the piezoelectric film, an electrically active fluoropolymer converts mechanical energy such as movement caused by a heartbeat into voltage measurements capable of supporting time series analysis techniques.
  • the voltage is recorded by and analyzed using a microcomputer controlled system, the purpose of which is to discriminate the signal from background noise and display it on a screen or printout.
  • Techniques such as preamplifying and preconditioning through the use of high and low-band pass filters reduces noise.
  • the piezoelectric material 1 used is the polymer polyvinylidene fluoride (PVDF) , which can be shaped into cables, thin film, or thick tiles.
  • PVDF piezoelectric film is environmentally rugged, lightweight, flexible, inherently reliable, sturdy, easily repairable and transportable with excessive assembly or disassembly. Since the material is inert, it may be used inside the human body. Ultraviolet radiation passes harmlessly through the PVDF film, which may be produced in varying thicknesses. In addition, the piezoelectric film is waterproof, operates between 0 and 145 degrees Centigrade, and does not tear under stress. PVDF may convert a temperature reading into an electric output.
  • the PVDF film is incorporated into a fluid-filled vinyl pad, approximately 10 cm by 10 cm in surface area. This is placed on/under/above various locations of the patient.
  • P2M detects cardiac and respiratory motion, and monitors pulse, respiration and apnea episodes 3. Cardiac and respiratory movements are simultaneously recorded by selective filtering of original signal.
  • the piezoelectric element 1 is a pressure - sensing detector acting as a highly sensitive strain gage providing high dynamic range and linearity.
  • Analog signals are fed through a band-pass filter into an amplifier (x200 - x5000) 5 and are visually displayed.
  • Analog acoustic signals are converted to digital values using a multi-channel converter 7 at a sampling rate of up to 5 kHz. Data is transformed to the frequency domain using Fast Fourier Transform (FFT) .
  • FFT Fast Fourier Transform
  • PVDF piezoelectric film 1 acts as a piezoelectric strain gage.
  • the voltage output is up to four orders of magnitude higher than that produced by a nonamplified signal from circuitry used with resistive wire. Linearity and frequency response are excellent.
  • current need not be applied since the device is electrically self-generating.
  • the present invention does not produce an electric charge ad infinitum with sustained stress.
  • the slowest frequency the polymer film detects is a thousand seconds for an electrical event to occur, and the highest is one gigahertz (microwave) .
  • the piezoelectric film is passive and biologically non-hazardous, as opposed to traditional strain gages that require an applied current.
  • PVDF sheets are commercial off-the-shelf (COTS) products, the type and specifications of which were chosen based on optimum sensitivity range and resilience. Each sheet contains seven-foot attached shielded twisted-pair (for noise rejection) leads 11 to transmit the charge produced by the sheets.
  • COTS commercial off-the-shelf
  • the piezoelectric sheets 1 are placed under a patient's chest and foot or at similarly remote areas of the body, or may be put on like a wrapped cuff.
  • the change in pressure exerted by the patient's respiration and heartbeat causes the piezoelectric film to generate voltages, which is carried via nonmagnetic miniature coaxial cable 11 through a radio frequency filter 13.
  • the signal is then directed to a high input-impedance amplifier 5 and computer system 7 for data processing.
  • a conventional oscilloscope and a chart recorder displays the output. Respiration and heart rate 15 are then calculated by the energy spectrum from the time series data.
  • Active cancellation uses two piezoelectric sensors, one of which is not in contact with the body.
  • the sensor not attached to the body is exposed to environmentally acoustic and vibrational signals, while the sensor attached to the body is exposed to environmental as well as body signals. Subtraction of one output from the other output yields the body signal of interest.
  • band- pass filtering/band-stop filtering Another preferred technique to reduce noise involves band- pass filtering/band-stop filtering. By identifying the extraneous electronic or acoustic noise and its particular frequencies, band-pass or band-stop filtering eliminates extraneous signals from the overall signal.
  • signal processing techniques that use a prior knowledge of the expected signals extract the desired information from the piezoelectric signal. Spectral techniques help to identify the frequencies and amplitudes of the events of interest and discern them from extraneous noise.
  • Cardiac action analysis uses a bandpass frequency limit of 0.1-4.0 Hz
  • respiration analysis uses a frequency limit from 0.01-3.0 Hz.
  • the filtered cardiac and respiration signals are fed to a recording system.
  • Body movements are analyzed by bandpass filtering the original signal with frequency limits from 0.1-20 Hz.
  • the hardware equipment includes, but is not limited to, a 586 processor computer 9 with enhanced RAM and disk capacity to handle large amounts of data.
  • a board with a range that includes acoustic frequencies facilitates data acquisition, signal conditioning and signal processing.
  • a master program 17 combines the three separate software modules of data acquisition/control, signal processing/analysis, and data display/user interface.
  • the LabVIEWTM "G" graphical programming language was used for all three subroutine programs.
  • the analog voltage signal is digitized and analyzed in time and frequency domains. Routines developed for signal conditioning and analysis include digital filtering, spectral analysis, auto correlation, and noise - rejection programs.
  • the data is displayed real-time in either Monitor or Acquisition mode. Monitor mode displays the current data and discards old readings as new updates are processed, while Acquisition mode saves data for future analysis.
  • the voluminous data must not exceed the disk-storage capacity of the computer in Acquisition mode.
  • the entire P2M system 19 is encased in a metal technical enclosure 21 with casters (not shown) and locking glass door (not shown), as shown in Figure 2.
  • the equipment also includes a MEDEVAC stretcher 23 on which the sensor is mounted. This device may be incorporated into a litter to eliminate the need for patient attachment or miniaturized as a portable field device in a purse with a wireless communication setu .
  • the piezoelectric film measures mechanical, thermal and acoustic signals. That high sensitivity is necessary to measure vital signals non-intrusively.
  • pulse rate the physical beating of the heart is transmitted through the body into the piezo-film sensor pad as mechanical impulses.
  • the respiration is measured by the mechanical impulse transmitted to the sensor based on chest movements.
  • the sensitive piezo-film sensor pad measures all extraneous movement and speech, resulting in a voltage signal output that is superimposed upon the physiological signals. As a result, movement or speech by the subject may cause a reading error.
  • the P2M sensor measures all physical impulses in the measuring environment, including the patient's physiological signals, nearby human noise and activity signals, noise and vibration from the machinery, and electromagnetic (EM) noise emitted from the lights and instrumentation. While the output signal includes all of these signals, many are too weak to affect the measurement while others such as EM noise corrupt the reading.
  • Running the signal through filters and other signal - processing algorithms removes the noise.
  • the conditioned signal is then analyzed through routines, including a fast Fourier transform (FFT) which identifies the primary signal frequencies. For a still, speechless patient, the primary frequency is usually respiration, and the second highest frequency is heart rate. Patient positioning and frequency harmonics may complicate the distinction, requiring additional logic to separate and identify the heart and respiration frequency peaks.
  • the logic algorithms must be robust enough to define the respiration and heart peaks for a variety of conditions.
  • the minimum sampling interval was thirty seconds.
  • Figure 3 shows the results for the twenty respiration/pulse- rate measurements performed with the P2M system. Human evaluator measurements were performed simultaneously as a control. P2M accurately measured pulse 25 and respiration 27 under ideal conditions, but patient movement or speech interfered with accurate measurement. Heart rate measurement quality was not reduced by the absence of respiration, and P2M matched the control measurement results 29, 31 with an error of less than beat per minute.
  • FIG. 4 shows the P2M front panel in Acquisition mode.
  • the upper graph 33 displays a thirty-second window of time-series measurements of all physiological signals. Heartbeat spikes are shown in the upper (time series) graph 33, along with a lower- frequency sinusoidal function which corresponds to the respiration signal.
  • the lower graph 35 shows the same data in the frequency domain.
  • the first and largest spike 37 corresponds to approximately 16.4 respirations per minute.
  • the control group 31 measured 17+2 respirations per minute.
  • the large amplitude of the spike indicates that respiration is the largest impulse measured by the sensor pad.
  • the second-largest spike 39 is sixty times per minute, which was identical to the actual heart rate measured by a fingertip-clip heart-rate monitor.
  • the power as measured by the amplitude is less than one-third of that found in the respiration frequency, but the ratio varies based on the physiology and sensor pad positioning of the patient.
  • the smaller spikes 41 in the lower graph represent respiration and heart-rate harmonics, a result of the harmonics not being a perfect sinusoidal function. Since the heart rate might fall at exactly the same frequency as a respiration harmonic, it is necessary for logic algorithms to check for harmonics.
  • the heart rate and respiration harmonics may be differentiated by comparing signals taken from different parts of the body.
  • buttons and menus 43 on the front panel of the interface program enables the control of data acquisition and analysis routines.
  • the thirty-second data records may be saved to file for archiving or additional evaluation.
  • FIG. 5 shows the P2M system in Monitor mode.
  • the top graph 45 shows the time-series data, with the characteristic higher-frequency heartbeat spikes 47 superimposed over a lower - frequency respiration wave 49.
  • the middle graph 51 shows heart rate 53 and respiration 55 as updated every five seconds. As a new five-second data string is acquired, the oldest five seconds of data is discarded, and the heart rate and respiration are recalculated by analyzing the thirty-second data string with the new data.
  • the upper curve 53 is colored red to signify heart rate, while the lower curve 55 is colored blue to signify respiration. Heart rate appears steady in the mid-50s range, with respiration in the mid-teens. Both compare favorably ( ⁇ 2) with human control measurements.
  • the anomaly 57 after 25 updates is attributable to patient movement or an extraneous and errant noise/vibration event.
  • the bottom graph 59 shows an FFT of the time-series signal.
  • Regular voltage signals of heart beat provide strength signals as voltage levels that are related to blood pressure. Times between signals at varied parts of the body or patterns of secondary signals provide information on circulation or blockage or interference with blood flow.
  • Figure 6 shows a schematic view of the P2M system with a single passive sensor 61 positioned on a patient 63.
  • Figure 7 shows one of the graphical user interfaces (GUI) of the P2M system.
  • the upper chart 65 shows a 30-second window of digital voltage data, where the low-frequency oscillations are caused by respiration and the higher-frequency spikes are the result of heartbeat measurements of the patient on the litter.
  • the time-series signal is converted to frequency data via a Fourier transform and displayed as a power spectrum, shown in the middle chart 67. From this data, pulse and respiration can be extracted by examining the power associated with the dominant frequencies 69.
  • passive measurement of blood pressure may be conducted using pulse wave analyses.
  • Measurement and characterization of the pulse-wave velocity (PWV) or alternately, the pulse-wave travel time (PWTT) , inherently requires more than one measurement location.
  • PWV pulse-wave velocity
  • PWTT pulse-wave travel time
  • the sensors may measure pulse-wave characteristics, for example, along the brachial artery, along with other measurements described herein.
  • FIG 8 shows measurement results of the pulse at two locations along the arm.
  • the temporal separation between the two corresponding peaks 71, 73 gives the Pulse-Wave Travel Time (PWTT) .
  • PWTT Pulse-Wave Travel Time
  • This value can be used to correlate systolic and diastolic blood pressure.
  • the calibration must be performed simultaneously for several measurements of PWTT and blood pressure to construct a calibration curve. Barschdorff & Erig showed that the relationship between blood pressures (systolic and diastolic) are approximately linear with PWV and PWTT.
  • Figure 10 displays the results of the testing.
  • the P2M was over 95% accurate as compared to conventional methods, and the several instances where the P2M was not in agreement with conventional methods proved to be very valuable in subsequent modifications and improvements to the system software.
  • 12 volunteer nurses performed physiological monitoring of pulse and respiration using the P2M, electronic monitor, and human evaluation. Following the monitoring, the nurses completed a survey comparing and ranking the usage of the three methods.
  • Figure 11 shows the high noise and vibration testing of P2M at Wheeler Army Air Field, on March 5, 1999.
  • the preferred optimum placement is to situate the sensor directly beneath the center of the patient's chest. If the sensor is moved from this placement, or if the patient position changes, the integrity of the incoming signal also changes.
  • a preferred configuration uses multiple sensors in a pattern that covers the entire region of the litter on which the patient would lie so that regardless of patient movement and position, there will always be one or more active sensors in optimum measurement placements.
  • the invention is a passive system using an array of distributed sensors (or "multi-sensor") capable of accurately and robustly monitoring certain physiological signals of the human body. These signals, in turn, may be processed for determination of vital signs that are currently used by nurses and other caregivers, for example, heart rate, respiration, and systolic/diastolic blood pressure.
  • the invention uniquely provides a device that is passive (completely non-invasive) , unobtrusive, and autonomous; i.e., the apparatus in no way interferes either with the patient's mobility or with other monitoring equipment, and is capable of functioning with a minimum of technical expertise.
  • the equipment functions reliably in high-noise environments and other situations that render alternative and existing methods ineffective. These environments include, but are not limited to, medical evacuation (MEDEVAC) by helicopter or ambulance, and operation through Military Oriented Protective Posture (MOPP) gear and body armor.
  • MEDEVAC medical evacuation
  • MOPP Military Oriented Protective Posture
  • FIG 14 shows a schematic of the P2M using a passive sensor array and microelectronics incorporated into a MEDEVAC litter.
  • a schematic of the inventive technology, incorporated into a MEDEVAC litter, is shown in Figure 14 below.
  • the litter 75 is covered in an array 77 of 32 sensors, each of which can measure acoustic and hydraulic inputs from the patient 63.
  • Each of these signals contains a measure of physiologically generated signal and environmental noise.
  • the environmental noise on each pad will be similar, whereas the physiologically generated signals may be position dependent. This information is used to separate the signal from the noise using proven techniques.
  • Position dependent physiological signals are used to determine patient position, heart rate, respiration, blood pressure, pulse strength distribution, and potentially some measure of cardiac output.
  • the invention may be incorporated into a wide range of applications apart from the MEDEVAC litter.
  • the passive sensor array may be configured without much change to operate on a hospital bed or an ordinary mattress used at home. Of particular note is the area of premature infant care. In this case, the attachment of sensor leads to the infant may often be difficult, causing irritation of sensitive skin and entanglement in leads.
  • the sensor may be incorporated into equipment for use in both civilian and military sectors.
  • the sensor may be incorporated into field equipment, clothes and uniforms. This includes, but is not limited to, cervical collars, body armor, biological and/or chemical hazard protection suits, extraction devices, clothes, cushions on seats and seatbacks.
  • Exercise equipment such as stationary bicycles, treadmills or steppers may benefit by incorporating sensors into the supports.
  • Physiological indicators such as heart rate may be detected through handholds as an aid to regulating the exercise regime.
  • Other useful applications might include the use of a passive sensor system in a chair or couch used for psychological examinations. Scrutiny of the subject's physiological signs may give indications of emotional disturbance caused by trigger words or events during counseling.
  • the size of each sensor, number of sensors in the array, and configuration of the sensor array may be tailored, without much experimentation, to particular needs and situations. For a mattress, for example, 32 or more sensors in a rectangular array may be required.
  • the preferred passive sensor may use piezo-electric films and ceramics, hydrophones, microphones or pressure transducers.
  • Amplification hardware may include signal amplification circuitry and hardware, e.g., charge amplifier.
  • Data acquisition hardware and signal processing hardware (circuitry) and software are used in the system.
  • solid, fluidized (air) or fluid layer may be used, as for example, gel, water, foam, rubber, plastic, etc. The interface facilitates trans ittal of physiological signals.
  • the invention has great medical value for field monitoring, hospital monitoring, transport monitoring, and home/remote monitoring.
  • the invention may have application in every hospital for passive monitoring of patients.
  • the invention being undetectable to the patient, which adds comfort to the monitoring process.

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  • Health & Medical Sciences (AREA)
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  • Veterinary Medicine (AREA)
  • Biophysics (AREA)
  • Biomedical Technology (AREA)
  • Heart & Thoracic Surgery (AREA)
  • Medical Informatics (AREA)
  • Molecular Biology (AREA)
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  • Animal Behavior & Ethology (AREA)
  • Physics & Mathematics (AREA)
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  • Pathology (AREA)
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  • Cardiology (AREA)
  • Dentistry (AREA)
  • Oral & Maxillofacial Surgery (AREA)
  • Signal Processing (AREA)
  • Artificial Intelligence (AREA)
  • Computer Vision & Pattern Recognition (AREA)
  • Psychiatry (AREA)
  • Pulmonology (AREA)
  • Measuring And Recording Apparatus For Diagnosis (AREA)
  • Measuring Pulse, Heart Rate, Blood Pressure Or Blood Flow (AREA)

Abstract

L'invention concerne un appareil et un procédé de surveillance physiologique passive, l'appareil étant équipé d'un capteur conçu pour capter le phénomène physiologique. Un convertisseur convertit les données captées en signaux électriques et un ordinateur reçoit et calcule les signaux, puis sort les données calculées en vue de leur affichage interactif en temps réel. Le capteur est un film piézo-électrique en fluorure de polyvinylidène. Les signaux captés comportent des signatures mécaniques, thermiques et acoustiques reflétant le débit et la fonction cardiaques, l'hémorragie interne, le régime respiratoire, le régime impulsionnel, l'apnée et la température. Le capteur peut être un réseau (77) fourni dans une civière MEDEVAC (73) ou autre dispositif permettant de mesurer les signaux acoustiques et hydrauliques émanant du corps d'un patient (63) pour la surveillance sur le terrain, dans les hôpitaux, pendant le transport, à domicile ou à distance.
EP02739108A 2002-03-25 2002-03-25 Systeme de surveillance physiologique passive (p2m) Withdrawn EP1494586A4 (fr)

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CN1625368A (zh) 2005-06-08
CN100518638C (zh) 2009-07-29
EP1494586A4 (fr) 2009-07-22
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HK1075190A1 (en) 2005-12-09
AU2002311781B2 (en) 2009-09-03

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