Effect of novel short-arm human centrifugation-induced gravitational gradients upon cardiovascular responses, cerebral perfusion and g-tolerance

Abstract

Artificial gravity (AG) through short-arm human centrifugation (SAHC) has been proposed as a holisticspaceflight countermeasure.Movement of the rotational axis position (RAP) from above the head towards the heart may reduce central hypovolaemia, aid cerebral perfusion, and thus promote g-tolerance. This study determined the effect of RAP upon cardiovascular responses, peripheral blood displacement (i.e. central hypovolaemia), cerebral perfusion and g-tolerance, and their inter-relationships. Twenty (10 male) healthy participants (26.2 ± 4.0 years) underwent nine (following a familiarization run) randomized 10 min passive SAHC runs with RAP set above the head (P1), at the apex of the head (P2), or at heart level (P3) with foot-level Gz at 1.0 g, 1.7 g and 2.4 g. Cerebral tissue saturation index (cTSI, cerebral perfusion surrogate), calf circumference (CC, central hypovolaemia), heart rate (HR) and digital heart-level mean arterial blood pressure (MAP) were continuously recorded, in addition to incidence of pre-syncopal symptoms (PSS). CC and HR increases were attenuated from P1 to P3 (CC: 5.46 ± 0.54 mm to 2.23±0.42 mm; HR: 50±4 bpm to 8±2 bpm, P < 0.05).In addition, cTSI decrements were also attenuated (cTSI: −2.85 ± 0.48% to −0.95 ± 0.34%, P < 0.05) and PSS incidence lower in P3 than P1 (P < 0.05). A positive linear relationship was observed between CC and HR with increasing +Gz, and a negative relationship between CC and cTSI, both independent of RAP. Our data suggest that movement of RAP towards the heart (reduced g-gradient), independent of foot-level Gz, leads to improved g-tolerance. Further investigations are required to assess the effect of differential baroreceptor feedback (i.e. aortic–carotid g-gradient).