Decreases in arterial baroreflex function after space flight may be related to changes in blood pressure and heart rate patterns during flight. Ambulatory blood pressure and heart rate were measured for 24 hours, in fourteen astronauts on two occasions before flight, two to three occasions in flight, and 2 days after landing on Shuttle missions lasting 4 to 14 days. Blood pressure and heart rate were recorded every 20minutes during awake periods and every 30 minutes during sleep. In pre- and postflight studies, the 24-hour ambulatory measurements were followed by studies of carotid baroreceptor-cardiac reflex responses. Carotid baroreceptors were stimulated using a sequence of neck pressure and suction from +40 to -65 mmHg

Boettcher, Sheila W.

Charles, John B.

Fritsch-Yelle, Janice M.

English

NASA Technical Reports Server

14'gUi-,Js'5 
EXTENDED DURATION ORBITER MEDICAL PROJECT
N95-14223
VARIABILITY OF BLOOD PRESSURE AND HEART RATE - STS-50/USML-1
Janice M. Fritsch-Yelle*, John B. Charles* and Sheila W. Boettcher +
*NASA JSC, Houston, Texas
+ KRUG Life Sciences, Houston, Texas
ABSTRACT
Decreases in arterial baroreflex function after space flight may be related to changes in
blood pressure and heart rate patterns during flight. Ambulatory blood pressure and heart rate was
measured for 24-hours, in 14 astronauts on two occasions before flight, 2-3 occasions in flight, and
two days after landing on Shuttle missions lasting 4 to 14 days. Blood pressure and heart rate
were recorded every 20 minutes during awake periods and every 30 minutes during sleep. In pre-
and postflight studies, the 24-hour ambulatory measurements were followed by studies of carotid
baroreceptor-cardiac reflex responses. Carotid baroreceptors were stimulated using a sequence of
neck pressure and suction from + 40 to -65 mmHg.
Carotid baroreceptor-cardiac reflex responses were reduced postflight. The variability of
blood pressure and heart rate are both reduced in flight. None of the changes in blood pressure and
heart rate patterns in-flight related to postflight reductions in baroreflex parameters.
NOMENCLATURE
ABPM
Carotid Baroreceptors
Diastolic Blood Pressure
Systolic Blood Pressure
Barocuff
Valsalva Maneuver
Automatic Blood Pressure Monitor
Blood pressure sensors located in the neck region
used to regulate blood pressure and heart rate.
Amount of pressure in the arteries during the (mmHg)
relaxation phase of the heart cycle.
Amount of pressure in the arteries during the (mmHg)
contraction phase of the heart cycle.
Inflatable cuff applied to the neck. Pressure in the cuff can
be increased and decreased according to the protocol.
Forced exhalation against the mouthpiece
preventing exhaled air from escaping.
Joint "L+ 1" Science Revietu for USML-I and USMP-1 u_th the Microgravity Measurement Group, September
22-24, 1993, Huntsville, Alabama, USA. 383
https://ntrs.nasa.gov/search.jsp?R=19950007809 2020-06-16T10:17:13+00:00Z
INTRODUCTION
Postflight alterations in cardiovascular responses to exercise and standing are initiated
during flight, however, they are not known to impair cardiovascular performance in space (2).
Functional problems become apparent on landing day, when most crew members have reduced
exercise capacity and orthostatic tolerance (1). The cause of the orthostatic intolerance may be
partly related with loss of plasma volume during weightlessness (5). Blood pressure variations in
flight may also contribute to the orthostatic intolerance on landing. Data received from crew
members on shorter flight durations (4-5 days) demonstrated significant reductions in vagal control
of the sinus node that may contribute in part to orthostatic intolerance (3).
This investigation measured the cardiovascular responses (heart rate and blood pressure) of
14 astronauts on Shuttle flights lasting 4-14 days. Blood pressure and heart rate were recorded
every 20 minutes during wake periods and every 30 minutes during sleep. Data sessions included
preflight, in-flight, and postflight. The pre and postflight activity involved 24-hour ambulatory
monitoring followed by studies of carotid baroreceptor-cardiac reflex responses. Baroreflex testing
occurred six times postflight for crew members on missions greater than 10 days. Carotid
baroreceptors were stimulated using a sequence of neck pressure and suction from +40 to -65
mmHg.
The data from the two subjects from USML-1 will be analyzed with the other 12 subjects to
maintain the privacy of their medical data.
I. RESULTS
Daily means and standard deviations of arterial pressure and heart rate were averaged.
Carotid distending pressures (systolic neck pressure) were plotted against R-R intervals.
Calculated variables were minimum, maximum, and range of R-R interval responses, maximum
slope, and operational point. Maximum slopes were identified with linear regression analyses
applied to each set of three consecutive data pairs on the stimulus-response relation. Operational
points were defined as [(R-R intervals at 0 mmHg neck pressure minus minimum R-R interval)/R-R
interval range] x 100%.
Variability of blood pressure and heart rate were both reduced in flight. Carotid
baroreceptor-cardiac reflex responses were reduced postflight. Preflight slope was 4.9 + 0.3
msec/mmHg, range was 250 ± 22 msec, and operational point was 40.0 + 3.8%. On landing
day, slope was 3.9 ± 0.4, range was 180 -+ 17 msec, and operational point was 27.8 ± 4.2% (p
< 0.05 from preflight). Three days after landing the slope was 4.8 ± 0.6, range was 230 ± 22,
and operational point was 35.2 + 2.5%. No values three days after landing were different from
384
1
preflight. None of the changes in blood pressure and heart rate patterns in flight related to
postflight reductions in baroreflex parameters.
I1. DISCUSSION
A series of measurements to assess autonomic control of the cardiovascular system on 14
astronauts were performed before and after Shuttle missions lasting 4-14 days. Resting vagal
control of R-R intervals as estimated by power spectral analyses was not altered after space flight.
The balance between sympathetic and vagal R-R interval control shifted toward greater sympathetic
influences on landing day, and for several days after landing. Abnormalities of carotid baroreceptor-
cardiac reflexes found after shorter duration missions (4-5 days) were also found after longer
missions, but were not greater. In fact, reduction of baroreceptor slope was less after the longer
flights. Reductions of range of the R-R interval response were similar after the short and long
missions. Systolic and diastolic pressure reductions during, and increases after Valsalva straining
were greater on landing day than preflight. In four astronauts, preflight and in-flight "square wave"
blood pressure responses changed to sinusoidal patterns on landing day (Figure 4). Several
astronauts had orthostatic intolerance both before leaving the Shuttle and later during the stand
tests in the clinic. Postflight reductions in standing arterial pressures and postflight reductions in
baroreflex operational points were significantly correlated.
The four subjects mentioned above routinely exercised (running 20 to 25 miles per week).
It has been suggested that these subjects had expanded plasma volume before flight as a result of
their normal daily intense aerobic exercise regimens (4), and the change to a sinusoidal response on
landing day is at least partially due to loss of blood volume during flight. Recent studies by the
investigator have demonstrated that normal responders become square-wave responders when
blood volume is increased by intravenous saline. These same subjects develop exaggerated
sinusoidal responses after dehydration. Postural changes reducing central blood volume could also
contribute to this phenomena (6).
Twenty-five percent of the 14 crew members experienced severe orthostatic symptoms
while in the Shuttle after wheels stop and/or during the stand test later in the clinic. Systolic
pressures decreased dramatically with standing on landing day after the longer missions (10 - 14
days) unlike the non-significant changes seen after shorter flights. Changes in diastolic pressures
were similar to the short flights.
385
CONCLUSIONS
While the variability of blood pressure and heart rate are both reduced in flight, those
reductions did not relate to changes in baroreflex function after landing for crew members. While
this study was useful in systematically documenting for the first time changes in blood pressure and
heart during space flight, the original hypothesis of long duration flights reducing the variability was
not proven. Blood pressure and heart rate exhibited diurnal variation in flight, however this variation
was reduced from preflight data.
ACKNOWLEDGMENTS
The EDOMP team would like to thank the crew members of USML-1 who participated in this
study, with the discomforts of 24-hour monitoring and neck suction. We appreciate your
dedication to collecting this scientific data and your contribution to the future of long duration space
flights. We also thank the personnel of Marshall Space Flight Center whose efforts on this
investigation have contributed to the future of long duration space flights.
REFERENCES
1. Bungo, M. W., and P.C. Johnson, Jr. Cardiovascular examinations and observations of
deconditioning during the space shuttle orbital flight test program. Aviation Space
Environmental Medicine 54:1001-1004, 1983.
2. Dietlein, L. F. Skylab: A Beginning. In: Biomedical Results from Skylab, edited by R.S.
Johnston and L. F0 Dietlein. Washington, DC; NASA, 1977, p. 408-418.
, Fritsch, Janice M., Charles, J.B., Bennett, B.S., Jones, M.M., and Eckberg, D.L.,
Short-duration spaceflight impairs human carotid baroreceptor-cardiac reflex responses. Journal
of Applied Physiology 73(2): 664-671, 1992.
. Green, H. G., J.R. Sutton, G. Coates, M. All, and S. Jones. Response of red cell and plasma
volume to prolonged training in humans. Journal of Applied Physiology 70:1810 - 1815,
1991.
. Johnson, P. C., T. B. Driscoll, and A.D. Leblanc. Blood volume changes. In: Biomedical Results
from Skylab, edited by R. S. Johnston and L. F. Dietlein. Washington, DC; NASA, 1977, p.
235-241.
, Ten Harkel, A.D., J.J. Van Lieshout, E.J. Van Lieshout, and W. Wieling. Assessment of
cardiovascular reflexes: influence of posture and period of preceding rest. Journal of Applied
Physiology 68:147-153, 1990.
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Extended duration orbiter medical project variability of blood pressure and heart rate (STS-50/USML-1)

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