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THE EFFECTS OF ARTERIAL BLOOD PRESSURE LOADING ON THE CAROTID-CARDIAC BAROREFLEX RESPONSE AND ITS CORRELATION TO PULSE PRESSURE.  S. Koreen¹, D. Doerr², D. Ratliff³, V. Convertino^{4,  1}Monmouth University, W. Long Branch, NJ; ²NASA, Kennedy Space Center, FL; ³Bionetics, Kennedy Space Center, FL; ⁴U.S. Army Institute of Surgical Research, San Antonio, TX

     A significant percentage of astronauts develop orthostatic hypotension immediately after their return from space flight, a condition that could compromise the astronauts’ safety and performance.  Groundbased experiments have revealed an association between orthostatic hypotension and attenuated baroreflex that occurs during exposure to microgravity. Therefore, development of a treatment designed to acutely increase baroreflex sensitivity may prove to be an effective countermeasure against post-flight orthostatic intolerance.

     We hypothesized that repeated straining maneuvers (SM training) designed to load arterial baroreceptors by increasing arterial pulse pressures (arterial pressure loading) would acutely increase cardiac baroreflex responses. 

We tested this hypothesis by measuring cardiac baroreflex responses to carotid baroreceptor stimulation (neck pressures) and reductions in blood pressures induced by a 15-second Valsalva maneuver in 12 subjects at 1, 3, 6, and 24 hours after performing SM training. Cardiac baroreflex responses were also measured in each subject at 1, 3, 6, and 24 hours at the same time on a separate day without SM training (control) in a randomized, counterbalanced cross-over experimental design. Our results are consistent with our hypothesis since larger elevations in pulse pressure during SM training was related (r = +0.54) to greater increases in isolated carotid-cardiac baroreflex responses. Our data suggest that loading of arterial baroreceptors by large fluctuations in pulse pressure represents a mechanism by which baroreflex function can be acutely enhanced. We conclude that SM training similar to that conducted by high performance aircraft pilots may provide astronauts with protection from orthostatic hypotension after return from spaceflight.

(Supported by NASA- Spaceflight and Life Sciences Training Program)