U.S. patent application number 11/165735 was filed with the patent office on 2006-03-23 for passive physiological monitoring (p2m) system.
This patent application is currently assigned to Hoana Medical, Inc.. Invention is credited to Ken C.K. Cheung, Paul Pernambuco-Wise, Christopher J. Sullivan, Patrick K. Sullivan.
Application Number | 20060063982 11/165735 |
Document ID | / |
Family ID | 35517760 |
Filed Date | 2006-03-23 |
United States Patent
Application |
20060063982 |
Kind Code |
A1 |
Sullivan; Patrick K. ; et
al. |
March 23, 2006 |
Passive physiological monitoring (P2M) system
Abstract
Passive physiological monitoring apparatus and method has a
sensor for sensing physiological phenomenon. A converter converts
sensed data into electrical signals and a computer receives and
computes the signals and outputs computed data for real-time
interactive display. The sensor is a piezoelectric film of
polyvinylidene fluoride. A band-pass filter filters out noise and
isolates the signals to reflect data from the body. A pre-amplifier
amplifies signals. Signals detected include mechanical, thermal and
acoustic signatures reflecting cardiac output, cardiac function,
internal bleeding, respiratory, pulse, apnea, and temperature. A
pad may incorporate the PVDF film and may be fluid-filled. The film
converts mechanical energy into analog voltage signals. Analog
signals are fed through the band-pass filter and the amplifier. A
converter converts the analog signals to digital signals. A Fourier
transform routine is used to transform into the frequency domain. A
microcomputer is used for recording, analyzing and displaying data
for on-line assessment and for providing realtime response. A
radio-frequency filter may be connected to a cable and the film for
transferring signals from the film through the cable. The sensor
may be an array provided in a MEDEVAC litter or other device for
measuring acoustic and hydraulic signals from the body of a patient
for field monitoring, hospital monitoring, transport monitoring,
home, remote monitoring.
Inventors: |
Sullivan; Patrick K.;
(Honolulu, HI) ; Cheung; Ken C.K.; (Honolulu,
HI) ; Sullivan; Christopher J.; (Honolulu, HI)
; Pernambuco-Wise; Paul; (Honolulu, HI) |
Correspondence
Address: |
FULWIDER PATTON
6060 CENTER DRIVE
10TH FLOOR
LOS ANGELES
CA
90045
US
|
Assignee: |
Hoana Medical, Inc.
|
Family ID: |
35517760 |
Appl. No.: |
11/165735 |
Filed: |
June 24, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09662006 |
Sep 14, 2000 |
6984207 |
|
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11165735 |
Jun 24, 2005 |
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Current U.S.
Class: |
600/301 ;
600/481 |
Current CPC
Class: |
A61B 5/113 20130101;
A61B 5/7257 20130101; A61B 5/11 20130101; A61B 5/08 20130101; A61B
5/0205 20130101; A61B 5/0002 20130101; A61B 2562/0247 20130101;
A61B 5/02125 20130101; A61B 5/024 20130101; A61B 5/7203 20130101;
A61B 5/021 20130101; A61B 2562/043 20130101 |
Class at
Publication: |
600/301 ;
600/481 |
International
Class: |
A61B 5/00 20060101
A61B005/00; A61B 5/02 20060101 A61B005/02 |
Claims
1. Passive physiological monitoring apparatus comprising at least
one sensor for sensing data by placing the at least one sensor on a
body, a converter communicating with the at least one sensor for
converting sensed data into signals, a computing device
communicating with the converter for receiving and computing the
voltage signals and for outputting computer data, and
instrumentation communicating with the computing device for
real-time interaction with the device and for display of the
computed data.
2-46. (canceled)
Description
BACKGROUND OF THE INVENTION
[0001] Minimization of the time between injury occurrence and
transport to the appropriate level of medical care is necessary to
ensure that wounded and sick soldiers obtain the prompt medical
attention essential for their survival. During that time,
aeromedical care in a MEDEVAC helicopter environment is used to
identify and transport casualties.
[0002] Military units conduct aeromedical evacuations daily during
times of war and peace, exposing the patient and flight/medical
crew to noise or environmental stress and difficult monitoring
conditions. As in the civilian community, military nurses depend on
reliable and efficient monitoring devices to provide accurate
patient care in various environments, some of which are hostile and
obtrusive to the use of conventional monitoring instrumentation.
While aeromedical evacuation is a life-saving process for many, it
is nearly impossible for medical personnel to monitor vital signs
in a high noise environment.
[0003] 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, and electromagnetic interference with aircraft
systems caused by some medical equipment. The additional complexity
of leads and electrodes compounds the noise and environmental
problems. The physiological parameters of vital signs fall within
the helicopter-generated frequencies. Helicopter frequencies have a
much greater power in those frequencies as well. Vibrational and
acoustic artifacts are also major problems. The signal to noise
problem must therefore be solved by other means in addition to low
and high band pass filtering approaches. Due to the limiting work
conditions, medical personnel cannot use a stethoscope to
accurately monitor heart activity or blood pressure.
[0004] 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.
[0005] 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.
[0006] 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.
[0007] 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. In combination with ultrasound, piezoelectric methods
have been used to assess coronary hemodynamics, elastic tensor,
intra-arterial imaging, and receptor field dimensions. In addition,
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, and piezoelectric disks
have been used for recording muscle sounds and qualitative
monitoring of the neuromuscular block.
[0008] 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. However, 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.
[0009] 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.
[0010] Unfortunately, the extremely high noise and vibration
inherent in the helicopter environment prevents nursing and medical
personnel from accurately measuring vital signs. Not only are
electronic medical monitors rendered ineffective with the high
vibrations; traditional methods of measuring pulse and blood
pressure using a stethoscope become unreliable in the high noise.
Cramped working conditions and bulky gear during air evacuation
exacerbate these problems.
[0011] Most conventional methods use devices that employ
electrodes, leads, wires, and cuffs to measure one or more vital
signs, for example, blood pressure machine, ECG monitor, pulse
oximeter. Existing monitors require some sort of attachment and
thus are not passive. In addition, conventional equipment is highly
sensitive to noise, such as a helicopter or airplane engines and
rotors.
[0012] Clearly, what is needed for this common situation is a
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. With the added capability of
telemetry for remote monitoring and communication, information may
be forwarded in real-time via wireless communication to the
destination where medical personnel and other caregivers are
located.
[0013] Needs exist to develop better methods and apparatus for
physiological monitoring.
SUMMARY OF THE INVENTION
[0014] The present invention is known as Passive Physiological
Monitoring, P.sup.2M, 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.
[0015] Recent developments in materials science and data processing
have created the potential for a new monitoring device using
piezoelectric film, an electrically active fluoropolymer. Although
the medical applications of piezoelectric film are still at the
infant stage, the testing of medical instruments is promising.
[0016] 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.
[0017] "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: c = 1 .rho. * d P d V ( 1
) ##EQU1##
[0018] where
[0019] c=speed of the compression wave (ft/sec);
[0020] dV=change in velocity (V.sub.initial-V.sub.final);
[0021] .rho.=density of the fluid; and
[0022] dP=change in pressure.
[0023] 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.
[0024] Womersly (1957) had applied those principles to a single
uniform tube representing an arterial segment and compared the
results to the experimental data taken in a dog, prior to Skalak's
theory. Good agreement was reported between the measured flow and
the flow computed from the measured pressure gradient.
[0025] Anliker (1968) showed that the dispersion phenomena
associated with waves propagating in blood vessels are potential
measures of the distubility of the vessels and other cardiac
parameters. Anliker assumed that vessels behave like thin-walled
cylindrical shells filled with inviscid compressible fluid. More
complete models have provided good agreement.
[0026] 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.
[0027] 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).
[0028] 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. Since
the sympathetic tone may influence blood pressure measurement
accuracy, 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.
[0029] Once velocity (v) is known, the relation between systolic
and diastolic blood pressure (2) and the Bernoulli equation (3) is
used to measure blood pressure. The Bernoulli equation is a
fundamental relationship in fluid mechanics that is derived from
Newtonian mechanics and the principle of conservation of energy. A
more compressive version of the same equation can be developed to
reflect more complicated non-steady flows. p = pD + 1 3 * ( pS + pD
) ( 2 ) ##EQU2##
[0030] where
[0031] pS=systolic pressure;
[0032] pD=diastolic pressure; and
[0033] p=average pressure. p=.rho.gh+1/2*.rho.*V.sup.2 (3)
[0034] where
[0035] .rho.=fluid density,
[0036] g=gravitational constant, and
[0037] h=height, head energy term.
[0038] From these equations we can develop expressions for pD and
pS, both as a function of the pulse wave velocity (c), flow
velocity (v) and pulse wave pressure (dP):
pD=1/2*.rho.*v.sup.2-.rho.*C*dV (4) pS=pD+.rho.*C*dv (5)
[0039] P2M is well-suited to assist medical personnel in several
areas including, but not limited to, the following situations:
[0040] (1) Medical monitoring of vital signs of severely injured
persons in high noise and vibration environments such as rescue
helicopter where current monitoring techniques are cumbersome or
impossible;
[0041] (2) Monitoring casualties resulting from major disasters
such as aircraft accidents, earthquakes and floods;
[0042] (3) Physiological monitoring of large numbers of patients
through a "smart stretcher" easily deployed for field use by
medical personnel;
[0043] (4) Continuous military hospital bed monitoring without
disturbing patients; and
[0044] (5) Patient monitoring when treatment is delayed due to
temporary overload of medical facilities.
[0045] The development of the P2M or a passive sensor array
(multi-sensor system) is a significant innovation in passive
monitoring. Through the use of 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. Additionally, the significance of a
passive multi-sensor system is that it affords the opportunity to
more comprehensively monitor a patient. As a tool, 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.
[0046] The main components of the Passive Physiological (P.sup.2M)
system are the passive sensor, hardware for amplification,
filtering, data-acquisition, and signal-analysis software. In a
preferred embodiment, the single passive sensor has dimensions
8''.times.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.
[0047] 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 FIG. 6. Among 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.
[0048] It is an object of the present invention to provide the
military medical community with an inexpensive, non-restrictive,
portable, light-weight, accurate, and reliable device that can be
used in field or fixed facilities to provide an accurate
measurement of heart rate, respiration and blood pressure in high
noise and vibration environments and thus improve medical care in
mass casualty situations, aeromedical evacuations and hospital
settings.
[0049] It is an object of the present invention to adjust the
signal noise to enable the use of piezoelectric instruments in
aeromedical transport of patients, hospital bed monitoring, and
other applications in the military and civilian medical
environment.
[0050] It is an object of the present invention to develop a
prototype physiological monitor using piezoelectric film in various
field environments. The variables of accuracy, precision, user
characteristics, and patient comfort determine the value of a field
instrument for collection data on vital signs.
[0051] It is an object of the present invention to provide a
non-invasive means for monitoring vital functions without the use
of electrical leads or wiring on the patient. The use of the human
body's acoustic and electromagnetic signals to determine heart
rate, respirations, and blood pressure.
[0052] These and further and other objects and features of the
invention are apparent in the disclosure, which includes the above
and ongoing written specification, with the claims and the
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0053] FIG. 1 is a schematic of the P2M system components.
[0054] FIG. 2 is a perspective view of the P2M system.
[0055] FIG. 3 is a graphical comparison of the P2M bench test
results and the human evaluator measurements.
[0056] FIG. 4 is a front view of the front panel display and user
interface of the P2M system in Acquire Mode.
[0057] FIG. 5 is a front view of the front panel display of the P2M
system in Monitor Mode.
[0058] FIG. 6 is a schematic view of a preferred embodiment of the
P2M sensor.
[0059] FIG. 7 shows one of the graphical user interfaces (GUI) of
the P2M system.
[0060] FIG. 8 shows the graphical user interface of the P2M system
showing time-series and frequency-domain representations of
physiological data.
[0061] FIG. 9 shows measurement of Pulse-Wave Travel Time (PWTT)
FIG. 10 shows a system test and evaluation results in a graph.
[0062] FIG. 11 high noise and vibration testing of the P2M at
Wheeler Army Air Field.
[0063] FIG. 12 shows the measurement through a body armor.
[0064] FIG. 13 shows testing through body armor and MOPP gear
combined.
[0065] 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.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0066] 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.
[0067] FIG. 1 shows a schematic of the system, and FIG. 2 shows a
perspective view of the system. First, 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. Second, 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.
[0068] 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.
[0069] 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 (.times.200-.times.5000) 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). The system uses a microcomputer 9 for
recording, analysis and presentation of data, which allows for
on-line assessment of data and realtime decisions.
[0070] In its simplest mode of operation 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. Although
similarities to a strain gage exist, current need not be applied
since the device is electrically self-generating. Unlike the strain
gage, 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.
[0071] 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.
[0072] 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.
[0073] Several techniques reduce noise and vibration interferences.
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.
[0074] 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.
[0075] Additionally, 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.
[0076] Cardiac action analysis uses a bandpass frequency limit of
0.1-4.0 Hz, and 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.
[0077] Once the signal produced by the film sensor is converted to
voltages, amplified and filtered, it is processed through the P2M
instrumentation. 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.
[0078] For system operation, a master program 17 combines the three
separate software modules of data acquisition/control, signal
processing/analysis, and data display/user interface. The
LabVIEW.TM. "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.
[0079] For protection and ease of transport, 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 FIG. 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
setup.
[0080] Significant field and analysis testing was conducted to
confirm the workability and accuracy of the P2M system. The
piezoelectric film measures mechanical, thermal and acoustic
signals. That high sensitivity is necessary to measure vital
signals non-intrusively. For 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.
[0081] 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.
[0082] To increase resolution, a large number of high sampling rate
data points were selected and re-sampled at a lower rate to
simplify computation for accurate analysis. The minimum sampling
interval was thirty seconds.
[0083] FIG. 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.
[0084] 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.
[0085] The 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.
[0086] 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
re-calculated 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.
[0087] 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.
[0088] In another preferred embodiment, FIG. 6 shows a schematic
view of the P2M system with a single passive sensor 61 positioned
on a patient 63. FIG. 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.
[0089] In a preferred method of blood pressure measurement passive
measurement of blood pressure (systolic and diastolic) 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. Thus, plural sensors are required for
measurements in different locations. The sensors may measure
pulse-wave characteristics, for example, along the brachial artery,
along with other measurements described herein.
[0090] 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).
This value can be used to correlate systolic and diastolic blood
pressure. As such, 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.
[0091] Testing and evaluation of the P2M system was performed at
TAMC in February, 1998. Simultaneous measurements of pulse and
respiration were performed with the P2M, an electronic monitor, and
by human evaluation. FIG. 9 shows a photograph of the testing
performed at TAMC. A total of 11 volunteers were monitored
following the project's testing protocol.
[0092] FIG. 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. In addition,
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.
[0093] Testing of the P2M system for pulse and respiration in a
high noise and vibration environment was performed at Wheeler Army
Air Field, on Mar. 5, 1999. Tests were-performed during static
display of a MEDEVAC helicopter. The main purpose of the test was
to characterize the high noise/vibration environment using the P2M,
microphones and accelerometers. Results showed that through
filtering and signal analyses, the P2M was able to discern
physiological signals from the high amplitude and frequency noise
caused by the helicopter to output accurately pulse and
respiration. No conventional methods were performed at this test
due to the high-noise environment, which would render those methods
useless.
[0094] FIG. 11 shows the high noise and vibration testing of P2M at
Wheeler Army Air Field, on Mar. 5, 1999.
[0095] Next, in response to inquiries made by the flight medics
during the Mar. 5, 1999 testing at Wheeler, the ability of P2M
system to accurately monitor pulse and respiration through layers
of clothing and gear was tested. Fragmentation protective body
armor, Military Oriented Protective Posture (MOPP) gear, and a
combination of the two were tested using the P2M system. Results
showed that the P2M performed with higher fidelity with the
additional layers between the subject and the sensor, which is
largely due to the increased contact area and efficient
transmission of mechanical and acoustic signals through the solid
layers.
[0096] The single-sensor P.sup.2M configuration that has been
demonstrated to accurately measure pulse and respiration is very
sensitive to the patient position relative to the main sensor pad.
The quality and magnitude of the physiological signals received by
the system depends on this positioning. 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. Thus, 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.
[0097] In a preferred embodiment, 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.
[0098] Passive monitoring of such parameters as cardiac output,
cardiac function, and internal bleeding are within the scope of
this invention. 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. In addition, 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.
[0099] With the development of a reliable multi-sensor monitoring
system for such rugged and noisy operation, the application to the
hospital ICU environment, where noise is substantially lower, is
considerably more straightforward. Completely non-invasive,
passive, pulse, respiration, blood pressure (and detection of
cardiac output, internal bleeding, shock, etc.) measurements using
a sensor system that is undetectable to the patient have
considerable intrinsic value even in noise-free surroundings. The
passive and autonomous operation of such a system is suitable for
telemetry and real-time remote monitoring, and the final feature of
the invention is a telemetry design feature for distance and remote
monitoring.
[0100] 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 FIG. 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.
[0101] 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.
[0102] 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.
[0103] 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. For the interface between sensor and patient either solid,
fluidized (air) or fluid layer may be used, as for example, gel,
water, foam, rubber, plastic, etc. The interface facilitates
transmittal of physiological signals.
[0104] The invention has great medical value for field monitoring,
hospital monitoring, transport monitoring, and home/remote
monitoring. For example, 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.
[0105] While the invention has been described with reference to
specific embodiments, modifications and variations of the invention
may be constructed without departing from the scope of the
invention.
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