Inflight leg cuff test does not identify the risk for orthostatic hypotension after long-duration spaceflight

Katelyn N Wood,Kevin R Murray,Richard L Hughson,Danielle K Greaves

doi:10.1038/s41526-019-0082-3

Katelyn N Wood, Kevin R Murray + Show 2 more

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https://doi.org/10.1038/s41526-019-0082-3

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Abstract

Landing day symptoms from orthostatic hypotension after prolonged spaceflight can be debilitating, but severity of these symptoms can be unpredictable and highly individual. We tested the hypothesis that an impaired baroreflex response to an inflight leg cuff test could predict orthostatic intolerance on return to Earth. Eight male astronauts (44 ± 7 years of age (mean ± SD); mean mission length: 167 ± 12 days) participated in a standardized supine-to-sit-to-stand test (5 min–30s–3 min) pre- and postflight, and a 3 min thigh cuff occlusion test pre- and inflight with continuous monitoring of heart rate and arterial blood pressure. The arterial baroreflex was not changed inflight as shown by similar reductions in mean arterial pressure (MAP) response to leg cuff deflation (preflight −19 ± 2 mmHg vs. inflight −18 ± 5 mmHg). With the sit/stand test, the nadir of MAP was lower postflight (−17 ± 9 mmHg) than preflight (−11 ± 6 mmHg, p < 0.05). A greater increase in heart rate (25 ± 7; 16 ± 3 bpm) and decrease in stroke volume (−24 ± 11; −6 ± 4 mL) occurred with sit/stand postflight than leg cuffs inflight (p < 0.001). Inflight testing was influenced by elevated cardiac output resulting in a smaller drop in total peripheral resistance. Two of eight subjects exhibited orthostatic hypotension during the postflight stand test; their responses were not predicted by the inflight leg cuff deflation test. These results suggest that the baroreflex response examined by inflight leg cuff deflation was not a reliable indicator of postflight stand responses.

Highlights

Orthostatic intolerance, a major problem for the return of astronauts to the gravitational forces of Earth,[1,2] is aggravated by long-duration spaceflight.[3]
Based on the current knowledge and understanding of cardiovascular mechanisms that are altered during exposure to microgravity, a test, administered during spaceflight, to identify individual astronauts at greatest risk for postflight orthostatic hypotension could provide input guiding the extent of near endof-flight and immediate postflight countermeasures designed to reduce the risk of impairment of performance and loss of consciousness
Two of eight male astronauts presented with orthostatic hypotension during a 3-min stand test conducted between 18 and 36 h of returning from 6 months on the International Space Station (ISS)

Summary

Introduction

Orthostatic intolerance, a major problem for the return of astronauts to the gravitational forces of Earth,[1,2] is aggravated by long-duration spaceflight.[3]. Based on the current knowledge and understanding of cardiovascular mechanisms that are altered during exposure to microgravity, a test, administered during spaceflight, to identify individual astronauts at greatest risk for postflight orthostatic hypotension could provide input guiding the extent of near endof-flight and immediate postflight countermeasures designed to reduce the risk of impairment of performance and loss of consciousness These end-of-flight countermeasures could include lower body negative pressure, as used by Russian cosmonauts, high intensity exercise, and fluid loading during re-entry; whole body cooling, and lower body compression garments alone or in combination, can provide protection against postflight orthostatic intolerance.[16] Methods to challenge the arterial blood pressure (BP) regulatory mechanisms can be applied while in microgravity

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