Effects of Resistance Exercise and Nutritional Supplementation on Dynamic Cerebral Autoregulation in Head-Down Bed Rest

Abstract

Head-down bed rest (HDBR) is commonly considered as ground-based analog to spaceflight and simulates the headward fluid shift and cardiovascular deconditioning associated with spaceflight. We investigated in healthy volunteers whether HDBR, with or without countermeasures, affect cerebral autoregulation (CA). Twelve men (at selection: 34 ± 7 years; 176 ± 7 cm; 70 ± 7 kg) underwent three interventions of a 21-day HDBR: a control condition without countermeasure (CON), a condition with resistance vibration exercise (RVE) comprising of squats, single leg heel, and bilateral heel raises and a condition using also RVE associated with nutritional supplementation (NeX). Cerebral blood flow velocity was assessed using transcranial Doppler ultrasonography. CA was evaluated by transfer function analysis and by the autoregulatory index (Mxa) in order to determine the relationship between mean cerebral blood flow velocity and mean arterial blood pressure. In RVE condition, coherence was increased after HDBR. In CON condition, Mxa index was significantly reduced after HDBR. In contrast, in RVE and NeX conditions, Mxa were increased after HBDR. Our results indicate that HDBR without countermeasures may improve dynamic CA, but this adaptation may be dampened with RVE. Furthermore, nutritional supplementation did not enhance or worsen the negative effects of RVE. These findings should be carefully considered and could not be applied in spaceflight. Indeed, the subjects spent their time in supine position during bed rest, unlike the astronauts who perform normal daily activities.

Alterations in Cerebral Hemodynamics During Microgravity: A Literature Review

“…Currently, no concurring results of cerebrovascular autoregulation have been reached ( Table 3 ). Dynamic cerebrovascular autoregulation was improved after 21 days of HDBR by reducing plasma volume [ 55 ], which was observed during a short-term study [ 49 ]. A study of optic nerve sheath diameter and cerebral autoregulation revealed a strong negative correlation between these factors, suggesting that a persistently elevated ICP can be attributed to poor cerebral autoregulation recovery [ 17 ].…”

Vascular and Microvascular Dysfunction Induced by Microgravity and Its Analogs in Humans: Mechanisms and Countermeasures

“…Data concerning microgravity effect on cerebral autoregulation are controversial. Indeed, bed rest has been reported to impair ( Zhang et al, 1997 ; Sun et al, 2005 ), or to maintain ( Pavy-Le Traon et al, 2002 ), or to improve ( Jeong et al, 2014 ; Kermorgant et al, 2019 ) cerebral autoregulation. Similarly, in astronauts cerebral autoregulation might be impaired ( Zuj et al, 2012a ), preserved ( Herault et al, 2000 ; Arbeille et al, 2001 ; Iwasaki et al, 2007 ), or improved ( Iwasaki et al, 2007 ).…”

Impacts of Microgravity Analogs to Spaceflight on Cerebral Autoregulation

“…Yang et al (2015) found in 10 subjects an elevation in CBFV after acute consecutive exposure to randomized 10 • , 25 • , and 55 • HDT; however, an autoregulatory correction index was applied in this study and revealed a modified but an unimpaired cerebrovascular autoregulation. Moreover, a recent work in 12 healthy male subjects who underwent 21 days of HDBR showed that autoregulatory index Mxa was reduced reflecting an enhanced dynamic CA (Kermorgant et al, 2019). Following an extensive literature search, we found only few studies that measured CA after DI.…”