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[Effects of repeated low body negative pressure (LBNP) exposures on LBNP tolerance]
1Department of Aerospace Biodynamics, The Fourth Military Medical University, Xi'an, China.
Objective:
To investigate variation of low body negative pressure (LBNP) tolerance and the relationship with change of heart function after repeated LBNP exposures.
Method:
Ten healthy subjects were exposed to eight min consecutive daily LBNP (-50 mmHg). Before and after this exposures, tolerance to LBNP was determined by a cumulative stress index (CSI) and duration of negative pressure (DNP).
Result:
The pre- and post repeated exposure values of CSI and DNP were 1058 +/- 216 s, 1354 +/- 233 s and 45833 +/- 12546 s mmHg, 63433 +/- 13458 s mmHg, respectively. It showed that both were increased significantly (P<0.05), and the heart function was showed to have a tendency of being enhanced.
Conclusion:
It suggested that LBNP tolerance increased after repeated exposures, which might be achieved via strengthening of ventricular contractivity, decreasing the compliance of peripheral vascular, the hypotensive [correction of hypotentive] reflex compensatory mechanisms becoming more effective, and increasing arterial blood pressure on heart level.