Cardio‐and cerebrovascular control in men and women with furosemide‐induced hypovolemia during artificial gravity exposure by short radius centrifuge

Abstract

We tested cardio‐and cerebrovascular regulation in nine men and eight women during artificial gravity (AG) exposure using a short radius centrifuge while hypovolemic. ECG, beat‐by‐beat blood pressure, middle cerebral artery blood velocity (MCAv), and end‐tidal carbon dioxide (ETCO2) were measured in supine position during ~90‐min AG exposure. Dynamic cerebral autoregulation and arterial baroreflex sensitivity (BRS) were obtained with cross‐spectral analysis during 5‐min rest pre and post AG exposure, and during maximal AG. Plasma volume was reduced by 8.6% following furosemide infusion and a subsequent 5.7% with AG exposure. From pre AG rest to maximal AG, mean arterial pressure (MAP) increased, while mean MCAv, ETCO2 and BRS decreased significantly; oscillations in MAP and mean MCAv, and coherence between MAP and mean MCAv augmented significantly within the frequency range (0.07–0.20 Hz) while gain and phase remained unchanged. In post AG rest, MAP, BRS, and oscillations in MAP returned to control values, while mean MCAv and coherence between MAP and mean MCAv were significantly lower than pre AG rest. Similarly gain remained unchanged but phase was reduced significantly. We conclude that enhanced coherence suggests that autoregulation remained intact during AG exposure; MCAv and phase were reduced suggesting autoregulation may have been affected following AG.Supported by KY NASA EPSCoR Grant #NNX07AT58A, KY State Matching Grants, the NASA Johnson Space Center Human Research Program and the NASA Ames Research Center.