24-HOUR PATTERN OF BLOOD PRESSuRE AND HEART RATE IN WEIGHTLESSNESS (CIRCA)
Research Area: Cardiovascular and Respiratory Systems
Expedition(s): 9
Principal Investigator(s): ● John M. Karemaker, University of Amsterdam, Netherlands
● Claude Gharib, Lyon Grange Blanche, Lyon, France
RESEARCH OBJECTIVES
24-hour Pattern of Blood Pressure and Heart Rate in Weightlessness (Circa) aims to measure
the pattern of blood pressure and heart rate during a 24-hour period in an astronaut. The
combined data from 2 instruments used in this experiment enables the science team to unravel
the underlying physiology of circadian cardiovascular control in weightlessness.
RESULTS
This study showed that astronauts on short-duration
missions may be subject to strong psychological
stimuli. In particular, official moments like press
conferences can induce surges of blood pressure
and heart rate. The initial hypothesis is that
spaceflight would show the same day/night changes
as had been observed earlier in ground-based bed
rest studies. However, unlike the simulations, blood
pressure and heart rate were not very much
changed inflight from preflight. Only daytime
diastolic pressures and nighttime heart rate were
significantly lower inflight than preflight. Actual
spaceflight did not confirm the earlier bed rest
findings for blood pressure levels and for daytime to
nighttime changes. Daytime blood pressure levels
were definitely higher than was expected. Strikingly,
blood pressure and heart rate surges during the
working days in space were often related to stressful
moments like live media events but were not
restricted to these moments. The authors
hypothesized that the busy work schedule of short-
stay astronauts added to the general level of
excitement that was apparent from the
measurements. Systemic vascular resistance dropped during the night, unlike bed rest study
findings. Thus, actual spaceflight refuted earlier findings in bed rest studies both for blood
pressure levels and for daytime to nighttime changes.
None of the postflight results were duplicated during preflight venous occlusion. In conclusion,
some crew members showed abnormal orthostatic response 1 and 2 days after spaceflight.
Overall, there were indications of increased sympathetic response to standing, even though it
was expected that (partial) restoration of plasma volume may have taken place.
Spanish European Space Agency astronaut
Pedro Duque is wearing the experiment
equipment. ESA image.