A comprehensive examination of cardiovascular autonomic response to motion sickness was studied and whether differences in cardiopulmonary function exist in high and low susceptibility groups were determined. Measurement techniques were developed as was test equipment for its ability to provide accurately new measures of interest and to test the adequately of these new measures in differentiating between susceptibility groups. It was concluded that these groups can be differentiated using simple, brief stressors and measurements of cardiodynamic function

Naifeh, K.

English

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EXPLORATORY STUDIES OF PHYSIOLOGICAL
COMPONENTS OF MOTION SICKNESS
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National Aeronautics and
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Ames Research Center
Moffett Field, California 94035
ARC275a (F«b81)
https://ntrs.nasa.gov/search.jsp?R=19860011637 2020-03-20T15:15:55+00:00Z
Enclosure III:
Project #2: Exploratory Studies of Physiological Components of
Motion Sickness
A Pilot Study of Cardiopulmonary Function Differences in
High and Low Motion Sickness Susceptibles.
PROGRESS REPORT
Project #2: Exploratory Studies of Physiological Components of Motion
Sickness: Cardiopulmonary Differences Between High and
Low Susceptibles.
Prepared by: Karen Naifeh, Ph.D./ Assoc. Professor, Pulmonary Physiology,
University of California at San Francisco.
Funding for this project was delayed, and only arrived in June. We
have therefore spent the last four months obtaining equipment and setting up
the project. The following is a report on a pilot study conducted in order to
evaluate new measures of dynamic cardiopulmonary function and begin to use
them to examine possible differences between high and low motion sickness
susceptible subjects. In a previous study (1) we demonstrated a strong
autonomic nervous system response to motion sickness, with significant changes
in heart rate (HR), finger pulse volume (FPV), which is a relative measure of
peripheral vascular resistance, respiratory rate (RR) and basal skin
resistance (BSR). The heart rate response was the strongest of these, and
differences in heart rate response emerged between susceptibility groups even
in the first two minutes of the motion sickness test. We therefore designed
the present project in order (l)to provide a more comprehensive examination of
cardiovascular autonomic response to motion sickness and (2) to determine
whether differences in cardiopulmonary function exist in high and low
PAGE 2
susceptible groups of subjects. This pilot study was performed in order to
develop new measurement techniques, test equipment for its ability to provide
accurately new measures of interest and to test the adequacy of these new
measures in differentiating between susceptibility groups.
In order to gain a more comprehensive view of dynamic cardiovascular
responses during motion sickness we have added the measures of stroke volume,
cardiac output, myocardial contractility, pre-systolic and systolic timing
intervals (all obtained by impedance cardiography); blood pressure; and total
peripheral resistance as calculated from cardiac output and blood pressure
measures. In order to assess the interaction of the respiratory and
cardiovascular systems we have added the measures of tidal volume, and rib
cage and abdominal compartmental volumes. We obtained all measures during
resting baseline conditions and during two different types of stressors which
are known to affect the cardiovascular system. These were the Valsalva
maneuver and mental arithmetic. In order to gain some notion as to whether
differences in these measures might be associated with differences in motion
sickness susceptibility, we studied subjects who had previously been
categorized as either high or low motion sickness susceptible in a standard
Coriolis (CSSI) motion sickness test.
METHODS
Subjects were six healthy males 35 to 55 years of age, three of whom
were high and three of whom were low motion sickness susceptibles.
The following impedance derived variables were obtained from a
Minnesota Impedance Cardiograph with associated microcomputer: stroke volune
(SV), cardiac index (CI) which is cardiac output adjusted for body surface
PAGE 3
area, cardiac contractility (CC), pre-ejection period (PEP) which is the
period of systole before the aortic valve opens, and ventricular ejection time
(VET) which is the period of systole during which the left ventricle is
actually ejecting blood into the aorta. For these measures, subjects were
fitted with four circumferential mylar tape bands, two around the neck and two
mid-chest; a microphone for monitoring heart sounds, and a precordial ECG. The
microcomputer automatically calculated all five impedance-related variables
for heart beats selected by the experimenter, and stored the data on cassette
tape. The microprocessor required a minimum of 8 seconds to calculate data
from each beat selected; another beat could not be selected until calculations
were completed. Blood pressure was recorded twice per minute from an automatic
cuff system (Narco Biosystems) worn on the left arm. Systolic and diastolic
pressures were derived from Karotkoff sounds picked up by microphone and
recorded, along with cuff pressure, on strip chart.
Respiratory tidal volume, and rib cage and abdominal compartmental
volumes were recorded using a Respitrace inductance plethysmography system
(Ambulatory Monitoring, Inc), calibrated by spirometry prior to each session.
A computer program for performing the calibrations, assessing the accuracy of
calibration and collecting the data was developed in this laboratory for the
project. Heart rate, respiratory rate, finger pulse volume, toe pulse volume
.and basal skin resistance were also measured as in previous studies in this
laboratory in order to compare the new measures with these older ones.
For the resting baseline session subjects sat in a reclining chair for
thirty minutes. One-minute means were computed for each variable for the
thirty minutes of the session. For the task session, a ten minute resting
baseline was recorded, following which subjects performed a Valsalva maneuver.
PAGE 4
For this, subjects held their breath in mid-inspiration, contracting abdominal
muscles against a closed glottis for 30 sec., then relaxed for a two minute
recovery period. A second Valsalva maneuver and recovery were then performed.
For the mental arithmetic condition subjects subtracted serial 17's from 500,
repeating each answer verbally, for a period of three minutes. Approximately
ten to twenty trials were carried out during the three-minute period,
depending on the mathmatical prowess of the subject. A mean for each
variable was calculated for each minute of the task session.
RESULTS
The impedance cardiography system and the Respitrace inductance
plethysmography system were found to be virtually incompatible when used
together. The frequency oscillator of the Respitrace system created large
artifacts in the impedance cardiography system which often could not be
eliminated. We did find that interrupting the mylar tape bands around the
chest so that they no longer formed a completely closed loop removed the
artifact in some individuals without degrading the impedance signal, but it
did not consistently allow us to obtain clean data from both systems. In those
instances in which it was impossible to obtain both impedance and respiratory
data, we chose to eliminate respiratory measurements. Since our N is small for
this pilot study, we did not analyze the respiratory data obtained from those
individuals whose data was artifact free. In order to overcome this
incompatibility problem we have decided to use the new piezo-electric strain
gauge system developed by this laboratory for the SL-3 flight to obtain the
pulmonary measures in our formal study. It measures pulmonary volumes using a
PAGE 5
different principle which is compatible with the impedance cardiography
system. Our software for obtaining respiratory data should require only minor
modifications in order to be used with the new transducers.
Our assessment of the impedance cardiography system is that it
provides relatively accurate data on a wide range of dynamic cardiovascular
variables and appears to be sensitive even to rapid changes in these
variables. It is therefore well suited to our purposes in the formal study.
The microprocessor designed to work with it we found to be largely unsuited to
our purposes. With the microprocessor one can obtain data from one heart beat
at a minimum of 8-sec. intervals. Thus much data is lost from the intervening
beats, especially when rapid changes in the cardiovascular system are
occurring. In the formal study, therefore, we shall tag time periods of
interst during experimental runs and obtain impedance data from all beats
of interest off-line from tape recorded data using our own software.
In spite of the above equipment limitations, valuable data were
gathered. Mean values for all variables across the resting baseline condition
for each subject are presented in Table 1. The values for all impedance
variables fall within accepted normal values as measured by classical
techniques (2).
Correlations were run between ANS variables for both the task and
baseline sessions in order to compare old and new measures of autonomic
function. Results are presented in Table 2. In general, the higher the
correlation between two measures having some relation to each other, the more
likely they are measuring identical phenomena. Thus although there is clearly
overlap, the relatively moderate correlations between old and new measures
indicates that we are measuring new aspects of autonomic function with the
PAGE 6
addition of these new variables. We were especially interested in how total
peripheral resistance (TPR), which takes into account all vascular beds,
compares with finger pulse volume (FPV), a very localized measure of relative
vascular resistance. Although relatively highly correlated under resting
conditions (r=-0.51), there is still a considerable amount of variance in TPR
which is not accounted for by FPV, and the correlation is much lower under
dynamic conditions (i.e., the presence of stressors). These latter measures
are of particular importance because vascular resistance is controlled solely
by the sympathetic arm of the ANS and may therefore be a means of dissecting
sympathetic and parasympathetic components of motion sickness. Cardiac
contractility, which is a measure of how forcefully the heart contracts
independently of ventricular filling, is also apparently solely under SNS
control. However, it is a cardiac measure, whereas peripheral resistance is a
vascular measure; the two may show differential effects depending on the
stimulus and the status of the cardiovascular system.
Next, possible differences between susceptibility groups were assessed
using analysis of variance. A three-way ANOVA (Epoch X Susceptibility X ANS
variable) was performed on the baseline data, where Epoch was each of three
consecutive ten-minute periods of the baseline session and Susceptibility was
"high" and "low". Results revealed no significant difference between
susceptibility groups on any measure, nor was there a significant change in
any variable across the session. It appears, therefore, that susceptibility
groups cannot be differentiated under resting conditions by any of the
physiologic variables we have measured.
A similar ANOVA (task X susceptibility X ANS variable) was performed
on data from the task session, where "task" was valsalva maneuver, valsalva
PAGE 7
recovery and math. There was a highly significant effect of Task (p<0.0001)
and of Susceptibility (p<0.003). Individual ANOVA's run susequently on each
separate variable revealed a significant effect of Task on stroke volume
(p<0.025), cardiac contractility (p<0.02), basal skin resistance (p<0.006)f
and finger pulse volume (p<0.025). There was a trend toward a significant
effect of Task on pre-ejection period and toe pulse volume (p<0.10). These
findings verify that the tasks administered did indeed produce changes in
dynamic cardiovascular function.
There was a significant effect of Susceptibility on stroke volume
(p<0.005) and cardiac contractility (p<0.05). Additionally, there was a
significant Task by Susceptibitlity interaction for stroke volume (p<0.007)
and BSR (p<0.01), and a trend toward significance for total peripheral
resistance (TPR) (p<0.08). Figures 1-5 present plots of all variables having
significant changes related to susceptibility.
As indicated by Figs. 1 and 2, two of the original measures, finger
pulse volume and BSR, were significantly different between susceptibility
groups. The difference in BSR appears to be attributable to the fact that the
low susceptibility group had a much higher resting BSR prior to the tasks than
did the high susceptibility group, possibly because they were more relaxed.
Paradoxically, heart rate, the measure snowing the strongest between group
difference in our original motion sickness study, was not different during
these non-motion sickness stressors. Three of our new cardiodynamic measures
did demonstrate differences, however. Although any conclusions we draw from
this small study must be very tentative, our findings may indicate that low
motion sickness susceptible subjects have a more flexible autonomic nervous
system, able to respond in either direction and return rapidly, whereas high
PAGE 8
suscptible subjects may not respond readily to more minor stressors, as the
ones in this pilot study certainly were, but respond more extremely to severe
stressors such as motion sickness itself. A larger study should help to
elucidate these issues. In summary, it appears that motion sickness
susceptibility groups can possibly be differentiated using simple, brief
stressors and measurments of cardiodynamic function. Further studies are
necessary to verify these findings; nevertheless, these results are
sufficiently promising to merit a formal study.
PROTOCOL FOR FORMAL STUDY
In the formal study, fifteen subjects previously determined to be high
and fifteen determined to be low motion sickness susceptible will participate.
They will undergo the following: two days of resting baseline, two sessions
with CSSI tests performed in the Rotating Room, and two sessions with
psychophysiologic stressors - Valsalva maneuver, cold pressor test, and 30
degree head-up tilt. We have decided to delete the mental arithmetic task
because mental arithmetic stress varies considerably across subjects and is
subject to movement artifact. Cold pressor has been added in its place.
Head-up tilt has been added as an additional pure physiologic stressor.
Measures taken during all sessions will be the old measures of HR, RR,
FPV, and BSR, plus the new measures of stroke volume, cardiac output, cardiac
contractility, systolic timing intervals, blood pressure, and transcutaneous
carbon dioxide tension (Pco2). Total peripheral resistance will be calculated
from blood pressure and cardiac output data. Estimates of rib cage and
abdominal compartmental volumes and tidal volume will be made from
piezo-electric strain gauges calibrated by spirometry. Pco2 will be included
PAGE 9
as a further monitor of ventilation, as ventilation and Pco2 are reciprocal as
long as metabolic rate is constant (3). Transcutaneous Pco2 has been shown to
accurately reflect arterial Pco2 in healthy subjects (4). Ihe transcutaneous
electrode heats the skin to 43 degrees C to provide arterialization of
capillary blood. Ihe output of the device is electronically adjusted to
reflect gas tensions at normal body temperature of 37 degrees C and to
compensate for skin metabolism of C02.
Our first priority will be to develop the software to obtain the
impedance cardiography measures and to make any modifications in our
respiratory volume software necessary to enable us to obtain volume data with
the piezo-electric strain gauge transducers. We will also attempt to modify
existing equipment to obtain EEC measures which, along with transcutaneous
Pco2, will provide information on Sopite Syndrome, the drowsiness and lethargy
often associated with motion sickness.
PAGE 10
REFERENCES
1. Cowings P, Suter S, Tbscano W, Kamiya J and Naifeh K. General autonomic
components of motion sickness. Psychophysiology (submitted).
2. Kubicek WG, Karnegis JN, Patterson RP, Witsoe DA, and Matson RH.
Development and evaluation of an impedance cardiac output system.
Aerospace Med 37:1208-1212, 1966.
3. Mitchell RA and Berger AJ. Neural regulation of respiration. Am Rev
Respir Pis vol.III, 1975, pp.206-224.
4. Hazinski TA and Severinghaus JW. Transcutaneous analysis of arterial
Pco2. Med Instrum 16:150, 1982.
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(sec)
FPV
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HR
BSR
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0.51*
-0.72*
0.11
*=significant at p<0.05
Table 3. Task session: Correlations between old and
new autonomic measures.
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(sec)
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HR
BSR
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11
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0.25
0.25
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(L/min)
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0.04
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0.41*
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-0.12
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Exploratory studies of physiological components of motion sickness: Cardiopulmonary differences between high and low susceptibles

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