PHYSIOLOGICAL PARAMETERS THAT PREDICT ORTHOSTATIC INTOLERANCE AFTER SPACEFLIGHT
(HEART)
Research Area: Cardiovascular and Respiratory Systems
Expedition(s): 9
Principal Investigator(s): ● John M. Karemaker, University of Amsterdam, Netherlands
RESEARCH OBJECTIVES
The objective of Physiological Parameters That Predict Orthostatic Intolerance After Spaceflight
(Heart) is to predict orthostatic intolerance, ie, the inability to stand upright, of astronauts who
have spent a long period in a weightless environment. Predictions are based on measurements
of physical parameters such as blood pressure, electrocardiograms, thoracic impedance, and
brain blood flow by ultrasound. This data serve as inputs for a computer model of blood
circulation to assist in diagnosis of unexplained fainting in patients.
RESULTS
Two of 5 space explorers showed abnormal orthostatic response 1 and 2 days after spaceflight.
Although all subjects completed stand tests, 2 of 5 subjects had drastically reduced pulse
pressures and an increase in heart rate of ∼30 beats/min or more during standing. None of the
postflight results were mimicked during preflight venous occlusion. Overall, there were
indications of increased sympathetic response to standing, even though we can expect (partial)
restoration of plasma volume to have taken place. Blood pressure levels in space were not very
much changed from preflight; the circadian blood pressure rhythm seemed dampened. Only
daytime diastolic pressures (both subjects) and nighttime heart rate (1 subject) were
significantly lower in space. However, compared to the effect of a control tilt maneuver on the
ground, even lower blood pressure values might have been expected. Striking were the blood
pressure and heart rate surges during the working days in space, often related to stressful
moments like live appearances on public TV. Systemic vascular resistance dropped during the
night, unlike during bed rest research. Thus, actual spaceflight refuted earlier bed rest findings
both for blood pressure levels and for daytime to nighttime changes.
The combined observations led to the hypothesis that short-lasting spaceflight may induce
strong psychological stress in astronauts. When interpreting space-physiological observations
this must be taken into account.
PUBLICATION(S)
Karemaker JM, Berecki-Gisolf J. Twenty-four hour blood pressure in space: The dark side of
being an astronaut. Respiratory Physiology and Neurobiology. 2009;169:S55-S58. doi:
10.1016/j.resp.2009.05.006.
Karemaker JM, Berecki-Gisolf J, Stok WJ, van Montfrans GA. Twenty-four hour blood pressure in
HDT-bed rest and short-lasting space flight. Journal of Gravitational Physiology. July 2007;
14(1):49-50.