RECOVERY OF CARDIOVASCULAR RESPONSES TO LOWER BODY NEGATIVE PRESSURE (LBNP) AFTER SPACE FLIGHT 203

Abstract

We investigated the cardiovascular (CV) responses to LBNP during 5-8 d of recovery from short duration (8-14 d) space flights. Before flight, crewmembers (7 men, 3 women; 35-57 yrs) completed one LBNP to pre-syncope and two LBNP ramps. LBNP ramps were 30 min of supine rest followed by six 5-min stages of LBNP (-10, -20, -30, -40, -50, -60 mmHg). LBNP ramps were repeated on landing day (L+0) and 1-2 (L+1), 3-4 (L+3), and 5-8 (L+5) days after flight. All subjects completed ramp tests without presyncope preflight (PRE), but five were intolerant of -50 or -60 mmHg LBNP on L+0. CV responses at -50 mmHg of LBNP were compared for the tolerant (TOL) and intolerant (INT) subjects. PRE, groups were similar in age, height, weight, flight duration, and LBNP tolerance (TOL: -94±5; INT: -86±5 mmHg). HR response to LBNP (0 to -50 mmHg) on L+0 was increased (p<0.05) above PRE in both groups, but HR response in INT (53±3 bpm) was greater (p<0.05) than in TOL (29±5 bpm). Stroke volume (SV) decreased more during LBNP in both groups on L+0 than at PRE, but decreased to a greater degree in INT. The mean arterial pressure (MAP) response to LBNP was not different from PRE in either group on L+0, but in TOL the response (+3.4±2.2 mmHg) was greater (p<0.05) than INT (-2.2±1.5 mmHg). However, MAP at rest was elevated (p<0.05) in both groups on L+0. Cardiac output and calf compliance during LBNP were similar to PRE in both groups on L+0. During recovery, the HR response to LBNP in TOL (13±4 bpm) had recovered to PRE by L+1 and SV response was recovered by L+3. For INT, HR response (25±6 bpm) was still elevated (p<0.05) and SV reduced during LBNP at L+5. MAP response to LBNP were similar between groups on L+1 and resting MAP was similar to PRE by L+1 in both groups. In conclusion, some crewmembers do not completely recover CV responses to LBNP by 5-8 d after short duration space flight, and the recovery of HR, SV, and MAP occurs at different rates.