Internal carotid, external carotid and vertebral artery blood flow responses to 3 days of head‐out dry immersion

Abstract

What is the central question of this study? The extent to which weightlessness associated with a fluid shift from the peripheral to the central circulation influences the blood flow in each cerebral artery remains unknown. The present study was designed to explore the effect of short-term weightlessness conditions on both anterior and posterior cerebral blood flow. What is the main finding and its importance? Short-term weightlessness affects both anterior and posterior cerebral vasculature. However, a heterogeneous cerebral blood flow response in each cerebral artery did not occur during 3 days of dry immersion. We have recently demonstrated that a heterogeneous cerebral blood flow (CBF) response in each cerebral artery might contribute to the maintenance of circulatory homeostasis in the brain. However, the extent to which weightlessness associated with a fluid shift from the peripheral to the central circulation influences the distribution of CBF in each cerebral artery remains unknown. We hypothesized that a dry immersion-induced fluid shift (weightlessness conditions) would cause a heterogeneous CBF response in each cerebral artery. During and after 3 days of dry immersion, the blood flows in the internal carotid (ICA), external carotid (ECA) and vertebral arteries (VA) were measured by Doppler ultrasonography using an 8 MHz linear transducer. Although the 3 days of dry immersion and the 2 days recovery period did not change the blood flow in each cerebral artery, the conductance in both ICA and VA decreased during dry immersion on days 2 and 3 (ICA, 2.95 and 3.23 ml min mmHg ; VA, 1.10 and 1.05 ml min mmHg , respectively) from the baseline (ICA, 3.47 ml min mmHg , P = 0.027; VA, 1.23 ml min mmHg , P = 0.004). In addition, Pearson correlation analysis demonstrated that the 3 days of dry immersion induced a decrease in cardiac output (P = 0.004) that was associated with changes in ICA (P = 0.046) and VA blood flow (P = 0.021), but not ECA blood flow (P = 0.466). These findings suggest that short exposures to weightlessness, acting via a cephalad redistribution of fluid volume and blood flow in the human body, influenced the cerebral vasculature in each cerebral artery but did not cause a heterogeneous CBF response in each cerebral artery.

Reduced regional cerebral blood flow measured by 99mTc-HMPAO SPECT in microgravity simulated by 5-day dry immersion

“…failed to observe any variation in CBF as measured by Doppler ultrasound. However, they did observe an increase in CVR [25]. Compared with the literature, our results showing a decrease in CBF after 5-day DI are consistent with the increase in CVR measured during the rst week in simulated microgravity.…”

“…CPP is the result of mean arterial pressure (MAP) and ICP, according to the equation CPP = MAP -ICP [24]. Studies have shown that MAP does not seem to vary signi cantly in studies in HDBR [3] and after 3-day DI [25], consistent with our nding that blood pressure remained unchanged.…”

Dry Immersion as a Ground-Based Model of Microgravity Physiological Effects

“…Other authors, however, reported an increase of middle cerebral vein velocity and jugular vein, portal vein and thyroid volume, but these findings were obtained only during the first 2 h of DI (Arbeille et al, 2017). Another recent study failed to reveal changes in blood flow in either cerebral artery, but internal carotid and vertebral arteries conductance decreased significantly on the 2nd and 3rd day of DI (Ogoh et al, 2017).…”

Impacts of Microgravity Analogs to Spaceflight on Cerebral Autoregulation

“…Indeed, a decrease in autoregulatory index Mxa associated with an increase in the cross-spectral phase shift were observed in 12 healthy male subjects. Ogoh et al (2017) showed in the same study that DI affected both anterior and posterior cerebral vasculature, but did not provoke a heterogeneous CBF response in each cerebral artery (internal carotid, external carotid, common carotid, and vertebral arteries) measured by Doppler ultrasonography. As previously suggested for spaceflight, one suggestion for CA improvement is that microgravity could increase the responsiveness of cerebral vascular smooth muscle to changes of transmural pressure (Iwasaki et al, 2007).…”