Changes in cerebral oxygen saturation and cerebral blood flow velocity under mild +Gz hypergravity

Abstract

We previously reported that cerebral blood flow (CBF) was reduced by even mild +Gz hypergravity. Regional cerebral oxygen saturation as measured by near-infrared spectroscopy (C-rSO2) has been widely used to detect cerebral ischemia in clinical practice. For example, decreases in C-rSO2 reflect reduced CBF or arterial oxygen saturation. Thus it was hypothesized that C-rSO2 would decrease in association with reduced CBF during mild hypergravity. To test this hypothesis, we measured CBF velocity by transcranial Doppler ultrasonography and C-rSO2 during mild +Gz hypergravity while participants were in a sitting position. Among 17 male participants, 15 completed 21 min of exposure to +1.5 Gz generated by short-arm centrifuge. C-rSO2 and mean CBF velocity in the middle cerebral artery (MCBFVMCA) during centrifugation were averaged every 5 min and compared with pre-hypergravity (+1.0 Gz). C-rSO2 did not change significantly throughout centrifugation, although MCBFVMCA gradually decreased from the beginning (−1.2% at 0–5 min), and significantly decreased at 5–10 min (−4.8%), 10–15 min (−6.7%), and 15–20 min (−7.4%). Contrary to our hypothesis, decreases in C-rSO2 were not detected, despite reductions in CBF velocity during hypergravity. Since some assumptions, such as unaltered arteriovenous volume ratio, hemoglobin concentration, extracranial blood flow, and brain activity, need to be satisfied to monitor cerebral ischemia by C-rSO2, the present results suggest that these necessary assumptions for near-infrared spectroscopy are not always applicable, and that cerebral oxygenation may not precisely reflect decreases in CBF under mild +Gz hypergravity. NEW & NOTEWORTHY To our knowledge, this is the first study to evaluate simultaneously cerebral oxygenation monitored by near-infrared spectroscopy and cerebral blood flow (CBF) monitored by transcranial Doppler under +1.5 Gz hypergravity. Contrary to our hypothesis, there was no significant correlation between CBF velocity and regional cerebral oxygen saturation (C-rSO2). However, an incomplete case nearly involving syncope suggests the possibility that C-rSO2 can detect a remarkable decrease in CBF with development of presyncope during +Gz hypergravity.

Effects of targeted mild hypercapnia versus normocapnia on cerebral oxygen saturation in patients undergoing laparoscopic hepatectomy under low central venous pressure: a prospective, randomized controlled study

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Roles of Physiological Responses and Anthropometric Factors on the Gravitational Force Tolerance for Occupational Hypergravity Exposure

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Cerebral oxygenation and perfusion kinetics monitoring of military aircrew at high G using novel fNIRS wearable system

“…Near-infrared spectroscopy (NIRS) is another method that has been suggested to be capable of measuring brain activityrelated physiological changes via noninvasive monitoring of oxygenation and deoxygenation of tissues underneath the sensor (Madsen and Secher, 1999). While reduced brain oxygenation due to decreased cerebral perfusion is expected to occur under hypergravity (Pollock et al, 2021), prolonged G-exposure effects on prefrontal cortex (PFC) oxygenation have been inconsistent in past reports (Kobayashi and Miyamoto, 2000;Kobayashi et al, 2002;Smith et al, 2013;Konishi et al, 2019). Due to historical sensing limitations, there is limited knowledge about the deoxygenation kinetics responses of the brain during repeated, acute G-exposure, especially high G-exposure (> 5G).…”