Short-arm human centrifugation with 0.4g at eye and 0.75g at heart level provides similar cerebrovascular and cardiovascular responses to standing.

Abstract

Orthostatic intolerance continues to be a problem with astronauts upon return to Earth as a result of cerebral and cardiovascular adaptations to weightlessness. We tested the hypothesis that artificial gravity from a short-arm human centrifuge (SAHC) could provide cerebral and cardiovascular stimuli similar to upright posture and thereby serve as a suitable countermeasure. We compared cardiovascular and cerebrovascular responses before, during, and after exposure to hyper-G with that of standing in healthy young participants. The head was positioned such that the middle cerebral artery (MCA) was 0.46 m from the center of rotation. Two levels of hyper-G that provided 1g and 2g at foot level were investigated. Continuous blood pressure, heart rate, calf blood volume, MCA mean blood flow velocity (MFV) and end-tidal CO2 were measured. Blood pressure at the level of the MCA (BP-MCA) and MFV was reduced during stand and at 2g. The relationship between MFV and BP-MCA at 2g was different from supine and similar to standing, while 1g centrifugation was not different from supine. The cardiovascular system was also not different from supine at 1g but was similarly challenged in 2g compared to stand. Our data suggest that short-arm centrifugation 2g at the feet, with the head offset 0.5 m from the center, provides similar cardiovascular and cerebral responses to standing. This supports the hypothesis that passive 2g SAHC exposure at the feet could be used as a countermeasure for in-flight cardiovascular and cerebrovascular deconditioning.