Hemodynamic and hormonal correlates with exposure to lower body negative pressure after 12 hours head-down tilt.
Hemodynamic and hormonal responses to lower body negative pressure (LBNP) after 12-h head-down tilt (HDT) were examined to investigate the mechanism of orthostatic intolerance following spaceflight. Ten young healthy male volunteers participated in the experiment. After 6 degrees HDT for 12 h, the tolerance to 1 h continuous -30 mm Hg LBNP was tested. Variables were measured before and after HDT, during LBNP, and 1 and 10 min after LBNP. Significant reduction in leg volume and plasma volume were observed at the end of 12-h HDT (500 ml and 5.5%, respectively). In the tolerant group, stroke volume index (SI) was decreased by 35% after 15 min LBNP, and carotid arterial blood flow (CBF), by 27% at the end of LBNP compared to the pre-LBNP value. Of the 10 subjects, 5 developed presyncope during LBNP; they exhibited remarkable reduction in SI, CBF, and heart rate, and increased secretion of ADH and adrenaline during or just prior to presyncope. This non-tolerant group tended to be hemo-concentrated from the start of the experiment. However, it will require a prospective study to determine if this variable is a reliable predictor of the outcome of the post-HDT LBNP test from data collected at the end of HDT.
Sekiguchi
C
C
Space Station Program Office, National Space Development Agency of Japan, Tokyo.
Yumikura
S
S
Murai
T
T
Miyamoto
A
A
Yajima
K
K
D000222:Adaptation, Physiological; D000328:Adult; D009320:Atrial Natriuretic Factor / Q000097:blood; D002320:Cardiovascular Physiological Phenomena; D002395:Catecholamines / Q000097:blood; D006439:Hemodynamics; D006728:Hormones / Q000097:blood*; D006801:Humans; D008150:Lower Body Negative Pressure; D008297:Male; D011187:Posture / Q000502:physiology*; D013026:Space Flight; D013575:Syncope / Q000209:etiology / Q000503:physiopathology; D014893:Weightlessness / Q000009:adverse effects
D002395:Catecholamines; D006728:Hormones; D009320:Atrial Natriuretic Factor