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Selected LifeShirt details and medical references from web page www.lifeshirt.com added 12/24/00
Overview of LifeShirt© Configuration
Introduction. The LifeShirt© system is based upon a low turtleneck, sleeveless,
loose-fitting, hand washable, reusable, elastic shirt onto which have been sewn
an array of physiologic sensors to monitor cardiorespiratory functions. The
sensors are cinched at their locations to snugly fit them to the body contours.
The shirt also incorporates two accelerometers, one placed over the breastbone,
the other just below the hip on the upper thigh to record body posture and
activity. The electrocardiogram is recorded by means of three electrodes placed
directly onto the skin. All sensors are attached via electrically conductive
wires to a custom designed, battery powered electronic module (Spingboard©)
that is incorporated into a commercial, palmtop computer (Handspring Visor©)
worn on a belt. The monitored subject can enter symptoms, activities and
medications into the Handspring Visor© that becomes part of the digital data
stream. A pulse oximeter can be inputted into the electronic module for
recordings during sleep or defined activities. Intermittent blood pressure
readings, body weight, and body temperature can be entered into the Handspring
Visor© via a menu and become part of the digital data stream. The purpose of
this system is to collect, trend, store and send cardiac, respiratory, blood
pressure, posture, activity, and emotional measures annotated with symptoms,
types of activities and a medication diary to an Internet hub. This is
accomplished by uploading data from the Handspring Visor© to a personal
computer as an offline mode of operation. As such, the LifeShirt© can be
considered as an analogue of a multichannel Holter digital recorder. Technicians
directed by physicians, who review quality of information for subsequent
distribution to patients and their doctors, staff the Internet hub. The system
addresses several populations, among which are patients who utilize health care
information portals for diagnosed or self-perceived diseases, physician referred
patients that require extensive continuous monitoring, and patients
participating in clinical drug trials. The manufacturer, Non-Invasive Monitoring
Systems bases the sensor components and software of the LifeShirt© system upon
25 years of experience. The individual sensors and software making up the
LifeShirt© system have received FDA 510(k) approval for marketing as
respiratory, electrocardiographic, and central station recording devices. In
addition, these systems have been approved for clinical polysomnography, i.e.,
sleep studies. The LifeShirt© system provides the greatest number of
non-invasive, clinically relevant, parameters in a single system ever made
available to ambulatory patients. With capability of continuous monitoring over
hours, days and weeks, application of the LifeShirt© system becomes a metaphor
for making a movie of health and/or disease whereas the standard history and
physical examination conducted in a physician's office can be considered a
snapshot.
Inductive Plethysmography
The uniqueness of LifeShirt© over other systems for ambulatory monitoring
relates in large part to its incorporation of Non-Invasive Monitoring SystemsÕ
inductive plethysmographic sensors and software for monitoring cardiorespiratory,
physiological signals. These sensors consist of a sinusoidal arrangement of
electrical wires that are excited through an extremely low current, electrical
oscillator circuit; no electricity passes through the monitored subject.
Movements of the body covered by the sensors within LifeShirt© generate
magnetic fields that are converted into voltage changes over time, i.e.,
waveforms, by the technology. These waveforms, that are proportional to changes
in cross sectional area, can be displayed as raw signals referenced to time on a
computer screen and processed as instantaneous numerical values or one-minute
median trends. The location of the sensors over the body part determines the
type of waveform collected, e.g., breath, vascular or cardiac.
Thoracocardiograph.
This measure (TCG) derives from a single inductive plethysmographic sensor
placed transversely at the level just below or at the xiphoid process. Under
resting conditions, respiratory movement dominates its waveform with only
approximately 3 to 5% of its content consisting of oscillations synchronous with
the heartbeat. The oscillations are extracted from the respiratory waveform
by combining a high pass digital filter to suppress respiratory content and an
ECG triggered ensemble average. This provides a trace that depicts an averaged
ventricular volume curve. The amplitude of this curve permits computation of
stroke volume and cardiac output. Analyses of this waveform provide measures of
systolic and diastolic function. Shortening of the preejection period (PEP) and
increased percent of stroke volume ejected in the first third of systole signify
enhanced systolic function. The mathematical derivative of the ventricular
volume curve depicts a trace that strongly resembles the Doppler trace of
transmitral blood flow. Pertinent parameters of diastolic function that can be
measured from this trace include the ratios of peak early filling to atrial
filling ratio (E/A), PFR/SV, and deceleration time of the 'E' wave. Deceleration
time in combination with impaired systolic function correlates inversely with
the level of pulmonary capillary wedge pressure. Finally, TCG depicts
ventricular wall motion that may be limited or paradoxical in the presence of
myocardial ischemia.
Heart Rate Variability - - - - - - - - - -
Berntson GG, Stowell JR. ECG artifacts and heart period
variability: don't miss a beat! Psychophysiology 1998;35:127-32.
The impact of artifacts on estimates of heart period variability were evaluated
by modeling the effects of missed R-waves and spurious R-wave detections in
actual and simulated heart period series. Results revealed that even a single
artifact, occurring within a 128-s interbeat interval series, can impart
substantial spurious variance into all commonly analyzed frequency bands,
including that associated with respiratory sinus arrhythmia. In fact, the
spurious variance introduced by a single artifact may be greater than that
associated with true basal heart period variability and can far exceed typical
effect sizes in psychophysiological studies. The effects of artifacts are not
related to a specific analytical method and are apparent in both frequency and
time domain analyses. Results emphasize the importance of artifact detection and
resolution for studies of heart period variability.
Casolo G, Balli E, Taddei T, Amuhasi J, Gori C. Decreased
spontaneous heart rate variability in congestive heart failure. Am.J.Cardiol.
1989;64:1162-67.
Heart rate (HR) variability is a noninvasive index of the neural activity of the
heart. Although also dependent on the sympathetic activity of the heart, HR
variability is mainly determined by the vagal outflow of the heart. Several HR
abnormalities have been described in patients with congestive heart failure (CHF);
however, there are no data on HR variability in CHF patients. In the present
study HR variability was assessed in 20 CHF patients and 20 control subjects
from 24-hour Holter tapes. HR variability was evaluated by calculating the mean
hourly HR standard deviation and by analyzing the 24-hour RR histogram. Mean
hourly HR standard deviation was markedly and significantly reduced in CHF
patients both over the 24-hour period (97.5
+/- 41 vs
233.2
+/- 26 ms, p less
than 0.001) as well as during most of the individual hours examined. The 24-hour
RR histogram of CHF patients had a different shape and had a decreased variation
compared to control subjects (total variability 356 +/- 102 vs 757 +/- 156 ms, p
less than 0.001). Thus, CHF patients with depressed ejection fraction (less than
30%) have a low HR variability compared to normal individuals. This result can
be interpreted as adjunctive evidence for decreased parasympathetic activity to
the heart during CHF. The authors analyzed hourly heart rate variability in the
time domain from 24 hour Holter recorders. They found reduced variability over
the entire 24 hour period.
Kleiger RE, Stein PK, Boser MS, Rottman JN. Time domain
variability measurements of heart rate variability. Card.Clinics
1992;10:487-98.
This is a review article on the subject. The authors discuss the two approaches
used to minimize erroneous calculations and the degree of human overediting. One
excludes from analysis intervals that are more than 20% different from the
preceding intervals and the other derives bounds for all the parameters of HRV
that incorporate all cycles, including those with ectopic beats. The latter
assumes that such intervals represent a insubstantial minority of the total
number of intervals and only marginally affect the final calculation. However,
the authors believe that the assumption is valid only when ectopic beats are
< 10 per hour. The 20% rule will exclude some sinus intervals in which there
are sudden changes in sinus rate.
Sekioka K, Takaba H, Nakano T. Parallel recording of
physical activity on commercial Holter recorders. Front Med.Biol.Eng
1997;8:253-68.
To accurately interpret heart rate variability (HRV) including circadian rhythm
from Holter ECG, the simultaneous assessment of physical activity, which
significantly affects HRV, is essential. In this study, to obtain this
simultaneous assessment, the fundamental problems in implementing an
accelerometer in a commercial Holter recorder were studied. In a treadmill
exercise, three axial outputs of an accelerometer showed highly linear
correlations with the running speed (correlation coefficient; vertical 0.94,
forward-backward 0.97, sideways 0.97, three-dimensional amplitude 0.96, n = 8).
The vertical acceleration showed a slightly sigmoidal increase with speed.
Against a slope change, no significant increase in acceleration was observed
except in the forward-backward direction. Individual calibration was found to be
needed for the accurate estimation of physical load from body acceleration. A
simplified calculation with the sum of the three axial absolute values
correlated highly with the three-dimensional (3D) acceleration which shows the
most reliable response to motions in any direction (r = 0.98, the slope of the
regression line = 0.97) and, with this relation, the estimated 3D amplitude
showed a sufficient degree of agreement. This substituted calculation was used
in the Holter recordings. To know the posture of subjects, a piezoresistive
accelerometer with the function of clinometer was used in another study. From
played-back Holter recordings, the R-R interval and body acceleration were
simultaneously sampled. The serial changes of both the power spectra of HRV and
the body acceleration were observed over a 24 h period. Some cases with an
abnormally reduced high-frequency component (HF) of HRV at night or an unusually
high HF in the daytime were explained by physical conditions estimated with the
accelerometer. The simultaneous assessment of patients' physical state by the
present method provides the accurate interpretation of circadian rhythm in HRV.
Chakko S, Mulingtapang RF, Huikuri HV, Kessler KM, Materson
BJ, Myerburg RJ. Alterations in heart rate variability and its circadian
rhythm in hypertensive patients with left ventricular hypertrophy free of
coronary artery disease. Am.Heart J. 1993;126:1364-72.
Heart rate variability (HRV) and its circadian rhythm were evaluated in 22
patients with treated hypertension and left ventricular hypertrophy in whom
coronary artery disease was excluded by stress thallium or angiography. By using
24-hour Holter monitoring, HRV and its spectral components were measured.
Findings were compared with 11 age-matched normal controls. The difference
between mean R-R intervals during sleep (11 PM to 7 AM) and while awake (9 AM to
9 PM) (73 +/- 33 vs 263 +/- 63 msec, p < 0.0001) and the mean 24-hour SD of
the R-R intervals (55 +/- 6.3 vs 93 +/- 11, p < 0.0001) were lower among the
hypertensive patients compared with controls. The percentage of difference
between successive R-R intervals that exceeded 50 msec, a measure of
parasympathetic tone, was also lower among the hypertensive patients (6.8 +/-
7.1 vs 13.6 +/- 8.9, p < 0.002); it increased at night and decreased during
the day among the controls, and this circadian rhythm was blunted among the
patients. Spectral analysis showed that power in the high-frequency range (0.15
to 0.40 Hz) was lower among the hypertensive patients during 21 of 24 hours but
that the difference was statistically significant only during 9 hours (p ranging
from < 0.05 to 0.009). Power in the low-frequency range (0.04 to 015 Hz) was
lower at night, increased in the morning, and higher during the day among
controls; this circadian rhythm was absent among hypertensive patients. From 24
hour Holter recordings, authors plotted hourly RR intervals and SD for normal
subjects and patients with hypertension and left ventricular hypertrophy. For
hourly RR intervals, the hypertensive
Das G. Cardiovascular effects of cocaine abuse.
Int.J.Clin.Pharmacol.Ther. Toxicol. 1993;31:521-28.
Cocaine abuse is widespread in North America. It is estimated that almost one in
every four Americans has used cocaine at least once in his/her lifetime. In the
past two decades, cocaine related cardiovascular complications have mushroomed
because cocaine has become cheaper and more readily available. The fundamental
effects of cocaine on cardiovascular system are similar to those observed
following an intense, sympathetic stimulation. Cocaine intake results in marked
increase in blood pressure, myocardial oxygen demand and heart rate. Coronary
blood flow, which increases in response to exercise (endogenous sympathetic
stimulation) however, is decreased by cocaine intake. Increased demand of oxygen
by the myocardium in the face of decreased supply in subjects with cocaine use,
leads to myocardial ischemia, which in turn forms a substrate for most of the
cardiovascular complications, namely, myocardial infarction, cardiac arrhythmias
and acute pulmonary edema. Hypertension related complications, dissection and
rupture of aortic aneurysm, hemorrhagic stroke, in addition to infective
endocarditis, myocarditis, cardiomyopathy all occur more frequently in cocaine
addicts. In this review, pertinent clinical pharmacology and cardiovascular
risks associated with cocaine abuse are presented.
Garfinkel A, Raetz SL, Harper RM. Heart rate dynamics
after acute cocaine administration. J.Cardiovasc.Pharmacol. 1992;19:453-59.
We examined heart rate (HR) patterns after a bolus intravenous (i.v.)
administration of a high (10 mg/kg) dose of cocaine in unrestrained cats. Mean
R-R intervals, SD, and other measures of variability were assessed in three
periods: waking baseline, early postcocaine administration, and later recovery
periods. Cocaine resulted in initial tachycardia and reduced HR variability.
This reduction in variability was independent of changes in the average rate:
during the recovery period, HR returned to baseline values, but the reduced
variability persisted. Nonlinear methods of assessment yielded additional
results: Cocaine introduces a high correlation between one beat and the next and
a tendency for cardiac accelerations to be followed immediately by decelerations
and vice versa. The overall effect of the drug is to restrict deviation from a
fixed rate.