Evidence suggests that cephalad fluid shifts during weightlessness stimulate arterial and cardiopulmonary baroreceptors, leading to cardiovascular readaptation syndrome. Central venous pressure (CVP) is one variable used to monitor fluid shifts. A noninvasive Doppler technique was used to document CVP during weightlessness.
APPROACH:
The subjects' jugular flow was monitored via a pocket Doppler device, which provided an audio Doppler signal. The character of the jugular flow was assessed, and after a verification trial, the target pressure was accepted as the CVP estimate. A total of 9 astronauts, 4 women and 5 men, were subjects for this investigation. They flew on 4 Shuttle flights with flight durations of 5, 5, 6, and 8 days. Preflight data were collected one or more times from all 9 subjects while they were supine, and inflight data were collected as often as possible.
RESULTS:
For the 9 subjects, absolute data, as well as data normalized using the preflight average, showed a significant decrease in CVP from early in the mission (day 1) to late in the mission (day 6). After inspection of the data, subjects were grouped according to whether or not the last in-flight data point was greater than their preflight average. The 2 groups (n=4 and n=5) were compared with respect to the relationship between CVP response and the subjects' sex, age, severity of motion sickness, body weight, and changes in body weight. The results for these factors were equivocal because of the small number of cases. The decrease in CVP agrees with earlier studies, but this study showed a different time course for the changes.