Arterial and venous cerebral blood flow responses to long‐term head‐down bed rest in male volunteers

Abstract

In this study, we investigated the whole cerebral haemodynamic response to long-term headdown bed rest (HDBR). We hypothesized that long-term exposure to weightlessness influences cerebral blood flow (CBF) or CBF distribution among cerebral arteries and veins because of the different physiological roles of each cerebral vessel. To test this hypothesis, 10 male volunteers were exposed to −6 deg HDBR for 60 days. Blood flows in the internal carotid artery, external carotid artery and vertebral artery or internal jugular vein and vertebral vein were measured using ultrasonography before and on days 30 and 57 of the HDBR. The internal carotid artery blood flow was reduced on day 30 (P = 0.019) and had returned to the baseline level by day 57. In contrast, the vertebral artery blood flow remained unaltered throughout the HDBR (P = 0.626). The internal jugular vein blood flow was reduced on day 30 (P = 0.009), whereas the vertebral vein blood flow remained unaltered (P = 0.397). These findings suggest that long-term HDBR causes a heterogeneous CBF response between the anterior and posterior cerebral circulation in the both arteries and veins. The posterior arterial and venous CBFs were well maintained throughout HDBR, and these CBF responses to HDBR were different from the anterior cerebral circulation.

The effect of microgravity on the human venous system and blood coagulation: a systematic review

“…All studies in the present systematic review reported increased venous distension (venous cross-sectional area), increased venous pressure and decreased or even retrograde venous flow states, in cephalad regions of the body, both in microgravity (Arbeille et al, 2015;Fortrat et al, 2017;Herault et al, 2000;Marshall-Goebel et al, 2019;Martin et al, 2016) and in ground-based analogues (Arbeille et al, 2001;Bleeker et al, 2004;Marshall-Goebel et al, 2016;Moreva, 2008;Navasiolava et al, 2010;Ogoh et al, 2020). These findings may be associated with increased cyclical stretch forces and reduced shear forces, which may lead to a pro-thrombotic state, and thus increased VTE risk in spaceflight.…”

“…Furthermore, ground-based analogues have also been shown to induce decreased venous flow, including DI (Moreva, 2008;Navasiolava et al, 2010), HDT (Marshall-Goebel et al, 2016) and HDBR (Arbeille et al, 2001;Bleeker et al, 2004;Ogoh et al, 2020).…”

Effect of jump exercise training on long‐term head‐down bed rest‐induced cerebral blood flow responses in arteries and veins

“…For the first time, our previous study (Ogoh et al., 2020) recently demonstrated a differentiated effect of long‐term bed rest (60 days) among blood flows of cerebral arteries and veins. In particular, the anterior cerebral arterial (ICA) and venous (IJV) blood flows decreased, but the posterior cerebral arterial (VA) and venous (VV) blood flows were well maintained around the baseline value during the HDBR.…”

“…Our previous report (Ogoh et al., 2020) demonstrated that the ICA blood flow decreased by the 30th day of HDBR; thereafter, the decreased ICA blood flow returned to the baseline level until the 57th day. This finding indicates that the anterior CBF decreased within 1 month, which is consistent with the finding of middle cerebral artery blood velocity reported in the previous studies during short‐term microgravity of less than 3 weeks (Frey et al., 1993; Sun et al., 2002, 2005; Yao et al., 2001).…”

Going against the flow: are venous thromboembolism and impaired cerebral drainage critical risks for spaceflight?

“…Cerebral blood flow is governed by cerebral autoregulation through intricate myogenic, neurogenic, and metabolic mechanisms ( 13,14). Due to the rigid skull, overall cerebral arterial inflow must be perfectly matched beat-to-beat by venous outflow to maintain intracranial pressures (ICP) within life-sustaining range (15)(16)(17). Cerebral arterial flow is narrowly maintained relative to changes in posture, blood pressures, and ICP (22).…”