WIRELESS
HEART RATE MONITORING TECHNOLOGY
A UNIQUE PHOTO PLETHMOGRAPHY
HEART RATE SENSOR
This work was funded in part by an
NIH PHASE 1 Grant – A Phase II Grant is pending.
PGS has developed an innovative low cost infant monitoring
technology that is completely wireless and requires
no intimate patient contact. The PGS monitor combines a
state-of-the-art FDA pre-market approved wireless noninvasive
inductive respiration sensor with new photo sensor
technology for acquiring heart rate, eliminating ALL
wires and electrodes. As medical advances improve, the
survival rates of pre-term and low-birth weight infants in the
U.S. continue to rise along with the need for cost effective
monitoring.
A phase I feasibility study conducted at Children’s National
Medical Center, Washington D.C. demonstrated that a viable and
stable physiological pulse pressure waveform could reliably be
acquired at the umbilicus area of the abdomen on low
birth-weight infants in the hospital’s NICU. The
abdominal area was previously deemed inappropriate for
monitoring. We further combined the cardiac sensor
with the existing PGS wireless inductive respiration sensor.
The clinical data collected in the phase I study demonstrated
that the PGS motion artifact rejection performance was
superior to the reference pulse oximeter monitor.
CLINICAL
SNAPSHOTS (NIH PHASE I)
The figures below represent the
overall performance of the PGS Wireless Respiration and
Cardiac sensor when compared to a widely used wired
hospital reference monitor.
The NIH Phase I clinicals were very
encouraging in demonstrating the veracity of obtaining a
usable cardiac pulse pressure waveform from the umbilical
region of the infants studied. Previous to this investigation
it was generally accepted that the lack of arterial flow would
hamper the use of a photo sensor in this area of the body. The
key features to note are the stability of the base line
(middle trace) of the
PGS sensor when compared to the reference monitor, and the
relative immunity to normal respiration artifacts when
compared to the loss of signal on the reference monitor. The
most important advantage to this new location is in the
realization that the abdominal wall of the umbilical area
moves as one on a relatively large plane. This affords a far
more stable area for the sensor than on an arm or leg
producing consistent signals even when the infant’s arms or
legs are in motion. The infants ranged in weight from 2 to 4
pounds.
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RESPIRATION ARTIFACT
REJECTION EXAMPLE:
SINGLE EXCURSION |
 |
|
RESPIRATION
MOVEMENT
ARTIFACT EXAMPLE:
MULTIPLE EXCURSION |
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BLOOD PRESSURE
PGS OCCLUSIVE
DETERMINATION SYSTEMS:
FAST & ACCURATE - PGS has developed a proprietary
software driven intermittent (pump up) blood pressure
monitoring system that delivers reliable Systolic / Mean /
Diastolic / Heart Rate data within 10 seconds upon start of
measurements and under 6 seconds after the first occlusive
determination. The system meets or exceeds the AAMI standards
for Blood pressure monitors.
LINEAR BLEED - The unit incorporates a Linear Bleed
which unlike ‘stepped’ systems provides very accurate
determination as ALL waveforms are associated with real time
pressures rather than in 5 to 7 mmHg steps. There is no
skewing of the occlusion envelope. LOW POWER –
Using a state of the art pump, and extremely low power valve,
the system reflects an optimal design for long battery life in
ambulatory products.
WIRELESS CAPABILITY - This system is compatible with
the PGS RFID wireless system and can provide remote patient
data acquisition for the hospital and in home environments.
PGS CONTINUOUS BLOOD PRESSURE
SYSTEM
CVC BLOOD
PRESSURE MONITOR
An INVESTIGATIONAL CONTINUOUS
VOLUME CORRECTED NONINVASIVE BLOOD PRESSURE MONITORING SYSTEM
The PGS Medical Research & Electronic
Design CVC technology represents the first noninvasive
continuous blood pressure (NICBP) monitor with the
potential of real time arterial pressure measurement in the
presence of blood volume changes and motion artifact. The
improvement and reliability for noninvasive blood pressure
measurement afforded in using the CVC technology is
striking.. The CVC technology has the convenience and ease
of use of an inflatable occlusive cuff type monitoring system
with the added potential of being able to monitor a patient’s
arterial pressure continuously without the limitations
associated with intermittent cuff measurements. PGS has a US
patent for this technology.
PGS Medical Research with the CVC
NICBP has successfully solved two of the most serious
limitations of the current noninvasive continuous monitors.
The first limitation of other systems is their inability to
respond correctly in the continuous modality to blood
volume changes without re-calibration. The second
limitation is the inability of all current noninvasive
monitors to withstand the type of body motion artifacts
(noise) typically occurring in the patients in which blood
pressure is being measured -i.e.: shivering, muscle tremor
etc.). These motions obliterate the incoming signals used
to compute blood pressure and render the continuous function
useless- usually just when the clinician needs the information
the most.
The above limitations have severely restricted the use of the
continuous noninvasive blood pressure monitors – until now.
CVC FEATURES
-
1. The PGS CVC pressure monitor
does NOT rely on the pulse amplitude (ballistic) for the
computation of the mean arterial pressure. There is no
usable portion of the elasticity curve in the patient
population that will correlate with central or arterial
pressure with blood volume or vasoautonomous physiological
changes. Everyone's peripheral resistance changes as a
function of the impulses received from the medullary vasomotor
center of the brain, and does so continually but not
predictably. 5 This is only one of the many factors
contributing to "reverse trends" seen in monitors utilizing
amplitude ballistics for calculation.
2. ARTIFACT REJECTION - The
PGS CVC technology does not suffer from the high degree of
artifact present in other systems. The PGS NICBP requires
only an electrical gain of 3 ( instead of the 1500
utilized by most systems) to accomplish it's measurement and
therefore is immune from most of the typical motion artifact
presented in other monitors.
SCREEN
CAPTURE OF CVC – 20mm monitoring
The Screen Capture
below is described as follows:
TOP
TRACE:
represents the real time pulse pressure waveform at
approximately 20-mm. This signal clearly shows the
dichrotic notch as well as other features of the BP
waveform.
MIDDLE TRACE: is a linear display of
actual cuff pressure but at a reduced (compressed)
scroll rate. The hump 2/3 to the right represents a
pressure correction change of the cuff pressure to bring it
into the 20 mm range.
BOTTOM TRACE: represents pulse
amplitude. It is scrolled at a still slower rate. This
trace starts at the beginning of an occlusive
determination. Approximately 1/3 from the left side of the
trace you can see the occlusion is complete and pulse
amplitude is diminished to nominal 20 mm heights.
NIH PHASE 1
Clinical Investigation Status:
-
PGS is in the process of clinical evaluation of the CVC non
invasive blood pressure system.
-
In
addition an NIH grant submission has been submitted
for further funding of this technology and to establish the
veracity of the technique in preparation for FDA 510K
submission.
General
Information about Blood Pressure Measurement:
PUMP UP
OCCLUSIVE DEVICES - description
"Pump up" type devices that
periodically inflate a cuff (occlusive determination) and
display the patient’s pressure. These "pump up” type
procedures are effective on less critically ill patients but
are inadequate for OR procedures that require constant real
time monitoring of a patient's pressure. Attempts to occlude
at more frequent intervals (i.e.: Stat Mode) with the
intermittent "pump up" occlusive machines can lead to nerve
damage of the limb and other patient complications. Most
physicians prefer to see the actual pulse pressure waveform
that is generated each time the heart pumps. This information
is unavailable on automated or manual occlusive units. These
devices do not monitor continuously.
Several well known companies have
attempted to introduce noninvasive continuous monitors that
rely on the pulsatile information contained in the pulse
pressure waveform. These systems rely on measuring the
amplitude and area under the curve (integration), or
various combinations of techniques that try to extract
information based on the arterial compliance or elasticity of
the arterial wall as a predictive function of blood pressure.
A few have met with limited success in the ICU on patients
that are sedated or immobile. 3 All have
the following restrictive limitations of use:
1.
They are extremely
susceptible to motion artifact despite claims to the
contrary. These monitors will automatically go into the
occlusive determination procedure when in the presence of
motion artifact for any length of time, or stop monitoring
altogether.4
2.
Present noninvasive continuous
pressure monitors are unable to deal with normal
physiological blood volume changes. This prevents their
use during critical operations, and precludes use in the
dialysis units where large infusions of blood are occurring on
all patients.
DEFINITIONS, TECHNOLOGY, & PHYSIOLOGY
THE NON INVASIVE
MEASUREMENT OF BLOOD PRESSURE IN A REAL TIME CONTINUOUS
MODALITY -
OVERVIEW
AND TECHNICAL DISCUSSION
Central Blood Pressure has
traditionally been measured by the insertion of a hollow
needle (catheter) into a functioning artery. The needle tip
is kept clear of clotting blood by a small amount of heparin
(anticoagulant) or other similar compound that inhibits
clotting of the blood. A tube is connected from the needle and
any entrapped air is vented by way of a valve to atmosphere.
Another port on the valve connects with a traditional pressure
sensor device. This sensor outputs a direct current voltage
that can be calibrated to pressure
PULSATILE AMPLITUDE METHOD
The company states that in its view
the use of pulsatile amplitude measurement as a basis for on
line continuous computation of the vital sign of blood
pressure is dangerous, produces reversed trends, and
can lead to the administration of medication that is the
opposite of that required for critical and nominal care in
controlling blood pressure.
THE REASON
-
The following are the main
disadvantages and dangers associated with the use of pulsatile
measurement as a basis for the computation of continuous blood
pressure based on an initial occlusive determination.
1. The stress / strain curve
for the arterial wall is a complex function. If the artery
were looked at alone in space, it would still be complex. The
walls of the artery are comprised of several layers some of
which are smooth muscle susceptible to the sympathetic nervous
system responses. These walls react to various stimuli from
the body. The vasoconstrictor fibers surrounding the major
arterial and venous blood vessels can greatly change the
resistance, and compliance (elasticity) of the measured
vessel. Obviously, if the elasticity of the pulsating
(measured) artery were to change the amplitude of the
pulsations would change also. Unfortunately, if we take an
example of what happens when this occurs, the limitations of
the pulsatile amplitude method of continuous pressure
measurement are readily seen.7 It is known that
when peripheral resistance increases, that the impulses from
the medullary vasomotor center increase in rate to the
vasoconstrictor fibers mentioned above. This is known to
raise arterial pressure and is in fact the primary means that
the body utilizes to regulate pressure.8 The
importance of peripheral circulatory resistance in the body's
regulation of blood pressure can be attributed to the fact
that over 80% of the blood volume is contained in the venous
and capillary systems! 9
As the fibers constrict about their
vessels, the compliance, elasticity, and pulsatile ability
decrease past a certain pressure point (different for all
individuals but relatively low in patients with hypertension)
and compromised, i.e. (calcified, hard, old, or clogged)
vessels.) This effect will cause a lowering of pulsatility for
a rise in pressure. This is exactly the opposite of
what is supposed to happen according to the pulsatile
measurement technique. That is based on the premise - that
if the amplitude is increasing, then the pressure is
increasing. The converse is also true, that as peripheral
resistance goes lower (more compliant) , the pulsatility will
increase. This is erroneously interpreted by the
pulsatile method as an increase in pressure where in actuality
the pressure is going down.10
2. Peripheral changes in
vessel resistance produce blood volume changes in the arm or
leg. Any change in volume will cause a loss of calibration to
the original occlusive reference. If for example more blood
enters a fixed volume i.e., the upper arm, the skin acts like
a balloon being stretched. As more blood enters the arm, the
force of this interarm pressure becomes greater, acting as a
constricting force on any pulsations of the vessels in the arm
aimed back at the center of the vessel. Thus, as
interstitial fluid, or blood increase in the appendage, the
ability of the vessels to pulsate diminishes.11,12
This is again unfortunately the opposite of the desired
result, as pressure in the limb is obviously increasing. The
Colin medical device is less susceptible to this as the radial
artery in the wrist is surrounded mostly by bone, and is very
near the surface.13
3. The non linear relationship
of the arterial stress/strain curve can, as the limited
working range of the pulsatile method moves up or down on this
curve, produce trends opposite that of what is actually taking
place. These are caused whenever cardiac output (volume), or
peripheral resistance changes occur. These changes occur
frequently under anesthesia, intubation, and operating
procedures.14
4. The indigenous signal to noise
ratio is very low for the pulsatile measurements. The problem
is that the power spectrum of the typical arterial pulse as
acquired by the noninvasive pressure transducers is the same
as the muscle and motion artifacts in many cases. Therefore,
they are inseparable in either the time or frequency domains.
No amount of software or signal processing can restore
the data in these often occurring situations. The
data is therefore discontinuous in many instances i.e.,
during an operation or tremor when it is most needed.
Note: The above discussion is excerpted from another longer
document. However, the footnotes below apply.
3. De Jong MD, Tepaske MD, Ros PhD., de Lange MD, Phd, "Noninvasive
Continuous Blood Pressure Measurements With the Cortronic APM
770: An Unfortunate Application of Computing Power," VU
Academisch Ziekenhuis, Amsterdam, The Netherlands.
4. Maier WR , Noninvasive Blood Pressure Monitoring :
Monitoring in Anaesthesia and Critical Care Medicine,
New York, Churchill Livingstone, 1985, pp. 35-40.
5. Chaffee and
Lytle, Basic Physiology and Anatomy, Philadelphia,
J.B.. Lippincott Company, 1980, pp. 376-378.
7. Kalath, Satish, etal., "Non-Invasive Assessment of Aortic
Mechanical Properties, New Jersey, Annals of Biomedical
Engineering , Vol. 14, pp 513-524, 198
8. Fulton, John F., Physiology Of The Nervous System,
New York , Oxford University Press, 1943,pp.429-435.
9. Rushmer, Robert F, MD., Cardiovascular Dynamics,
Philadelphia & London, Saunders Company , 1968, pp. 8-12.
10. Vaessen, HHB, "Another Manner of Continuous Non-invasive
Blood Pressure Measurement - an investigation", University
Hospital Utracht, Institute of Anesthesiology ( 35 patient
study).
11. Geddes and Baker, Principles of Applied Biomedical
Instrumentation, New York, John Wiley and Sons, 1975,
pp. 362-365.
12. Cromwell, Weibell, And Pfieffer, Biomedical
Instrumentation and Measurements, New Jersey, Prentice
Hall, 1980, pp. 163-16.
13. Bassenge,
Eberhard, M.D., Munzel, Thomas, M.D., "Consideration of
Conduit and Resistance Vessels in Regulation of Blood Flow",
The American Journal of Cardiology, Vol. 62, No. 8 , 1988, pp.
2E-7E.
14.
Perret,
Waeber, Tardy, Meister, Burnier, and Brunner, "Compliance -
Pressure Curves of the Radial Artery In Normal Subjects Under
Prolonged Administration Of Atenolol, Lisinopril,
Nitrendipine And Placebo," Proceedings of the 4th European
Meeting on Hypertension, Ricerca Scientif., Perman. 76,676,
1989.
EKG / HEART RATE
EKG MODULES FOR CLINICAL RESEARCH
  PGS
can design and supply custom EKG modules tailored to
the specific needs of the researcher’s clinical study. The
modules can be either wired or WIRELESS and feature the
following specifications. In addition PGS can provide
software enabling display and control of EKG waveforms through
the addition of an embedded PIC microprocessor.
EKG
CUSTOMIZING
The modules can be configured to
maximize one or more desirable features. For example, it
may be necessary to acquire the transducer signal while the
subject is moving about or exercising. PGS can then design
the EKG module to maximize motion artifact rejection.
50/60 Hz. NOTCH FILTERING
Another Example is acquiring the EKG
signal in the presence of severe noise such as 50 or 60-cycle
mains interference. Below is an example of a customized
PGS module and this type of noise. The top trace is the
EKG processed out of that noise. For reference, the QRS
signal input is a .5 mV. QRS from a Dynatech Nevada
simulator. The noise was present with a dc offset of
approximately 100 mV.. Channel 2 (filtered QRS) is displayed
on top of the original signal for clarity. Channel one
represents both the .5 mV. QRS and noise.
PGS 60 Hz. Notch
Filtering of .5 mV. QRS EXAMPLE
 |
QRS : .5 mV.
NOISE: 60 Hz ,
800 mV. |
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transducing sensor developed by PGS has demonstrated a
strikingly improved method of measuring respiration and
cardiac rate on infants. In particular, the respiration
transducing system is clearly superior to the wired electrode
method currently used (thoracic impedance) in conventional
monitors. 
outperforms
the high end inductive respiration neonatal monitoring
Systems.. NIMStm. and Respitracetm inductive respiration
systems for comparison require extensive wired support
electronics to function. Those systems are confining (encircle
the body with coils woven into fabric) and require long set up
times (typically 10 – 20 minutes) combined with skilled
personnel for calibration. 
EUMOSCREEN
RESPIRATION MONITOR FEATURES: