Effect of G-suit protection on carotid-cardiac baroreflex function.
BACKGROUND
To test the hypothesis that G-suit inflation could increase cardiac chronotropic responses to baroreceptor stimulation and enhance baroreflex buffering of BP, the carotid-cardiac baroreflex response of 12 subjects was measured across two levels of lower body negative pressure (LBNP = 0 and 50 mm Hg) and two levels of G-suit inflation (0 and 50 mm Hg) in random order.


METHODS
Carotid-cardiac baroreflex stimulation was delivered via a silastic neck pressure cuff and responsiveness quantified by determination of the maximum slope of the stimulus-response function between R-R intervals (ms) and their respective carotid distending pressures (mmHg).


RESULTS
Mean +/- SE baseline control baroreflex responsiveness was 3.8+/-0.4 ms x mm Hg(-1). LBNP reduced the baroreflex response to 2.7+/-0.4 ms x mm Hg(-1), but G-suit inflation with LBNP restored the baroreflex response to 4.3+/-0.6 ms x mm Hg(-1).


CONCLUSIONS
These results suggest that, in addition to increased venous return and elevated peripheral resistance, G-suit inflation may provide protection against the debilitating effects of blood distribution to the lower extremities during orthostatic challenges such as standing or high +Gz acceleration by increasing cardiovascular responsiveness to carotid baroreceptor stimulation.
Convertino
V A
VA
U.S. Army Institute of Surgical Research, Fort Sam Houston, TX 78234-6315, USA.
Reister
C A
CA
D000328:Adult; D002339:Carotid Arteries / Q000502:physiology*; D005676:Gravity Suits; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D011311:Pressoreceptors / Q000502:physiology*; D011897:Random Allocation; D013318:Stroke Volume / Q000502:physiology; D014655:Vascular Resistance / Q000502:physiology