Quantitative MRI volumetry, diffusivity, cerebrovascular flow, and cranial hydrodynamics during head-down tilt and hypercapnia: the SPACECOT study

To improve the pathophysiological understanding of visual changes observed in astronauts, we aimed to use quantitative MRI to measure anatomic and physiological responses during a ground-based spaceflight analog (head-down tilt, HDT) combined with increased ambient carbon dioxide (CO2). Six healthy, male subjects participated in the double-blinded, randomized crossover design study with two conditions: 26.5 h of –12° HDT with ambient air and with 0.5% CO2, both followed by 2.5-h exposure to 3% CO2. Volume and mean diffusivity quantification of the lateral ventricle and phase-contrast flow sequences of the internal carotid arteries and cerebral aqueduct were acquired at 3 T. Compared with supine baseline, HDT (ambient air) resulted in an increase in lateral ventricular volume (P = 0.03). Cerebral blood flow, however, decreased with HDT in the presence of either ambient air or 0.5% CO2 (P = 0.002 and P = 0.01, respectively); this was partially reversed by acute 3% CO2 exposure. Following HDT (ambient air), exposure to 3% CO2 increased aqueductal cerebral spinal fluid velocity amplitude (P = 0.01) and lateral ventricle cerebrospinal fluid (CSF) mean diffusivity (P = 0.001). We concluded that HDT causes alterations in cranial anatomy and physiology that are associated with decreased craniospinal compliance. Brief exposure to 3% CO2 augments CSF pulsatility within the cerebral aqueduct and lateral ventricles.
NEW & NOTEWORTHY Head-down tilt causes increased lateral v...

Source: Journal of Applied Physiology - May 9, 2017 Category: Physiology Authors: Kramer, L. A., Hasan, K. M., Sargsyan, A. E., Marshall-Goebel, K., Rittweger, J., Donoviel, D., Higashi, S., Mwangi, B., Gerlach, D. A., Bershad, E. M., SPACECOT Investigators Group Tags: RESEARCH ARTICLE Source Type: research