WISE‐2005: Exercise countermeasure protects against changes in cardiovascular response to sublingual nitroglycerin after 56‐d bed rest

Abstract

Cardiovascular responses to 0.3mg sublingual nitroglycerin spray (NG) were assessed before and after 56 days head-down tilt bed rest (HDT) with (EX) and without (No-EX) treadmill in LBNP and resistive exercise countermeasure. Heart rate (HR), mean arterial pressure (MAP, finger photoplethysmography), and aortic blood velocity (pulse Doppler ultrasound) were recorded before and after administration of NG. In response to NG stimulation pre HDT, MAP decreased by 5.5±3.3mmHg (mean±SD), and HR increased by 12±4bpm. The increase in HR, combined with a small increase in cardiac stroke volume (SV), resulted in cardiac output (CO) increasing by 0.97±0.55L/min. Post HDT, a trend was observed to higher resting HR and lower MAP in No-EX. Responses to NG were similar to the pre HDT condition, however, No-EX showed an augmented HR increase (11±8bpm) when compared to EX (7±4bpm, p=0.035). As SV did not change from the pre HDT condition, the increased HR response resulted in increased CO. MAP responses were similar in both groups post HDT; therefore, it would appear that No-EX had a greater reliance on the heart rate component of blood pressure regulation. This is likely the result of increased vasodilation and or lack of compensatory sympathetic vasoconstriction in the peripheral vasculature. The results of this study suggest that exercise protects against cardiovascular changes during HDT that would alter responses to NG stimulation. Supported by Canadian Space Agency, NASA, ESA, CNES