Cerebral Circulation and Brain Temperature during an Ultra-Short Session of Dry Immersion in Young Subjects

Abstract

The primary aim of the study was to assess cerebral circulation in healthy young subjects during an ultra-short (45 min) session of ground-based microgravity modeled by "dry" immersion (DI), with the help of a multifunctional Laser Doppler Flowmetry (LDF) analyzer. In addition, we tested a hypothesis that cerebral temperature would grow during a DI session. The supraorbital area of the forehead and forearm area were tested before, within, and after a DI session. Average perfusion, five oscillation ranges of the LDF spectrum, and brain temperature were assessed. Within a DI session, in the supraorbital area most of LDF parameters remained unchanged except for a 30% increase in respiratory associated (venular) rhythm. The temperature of the supraorbital area increased by up to 38.5 °C within the DI session. In the forearm area, the average value of perfusion and its nutritive component increased, presumably due to thermoregulation. In conclusion, the results suggest that a 45 min DI session does not exert a substantial effect on cerebral blood perfusion and systemic hemodynamics in young healthy subjects. Moderate signs of venous stasis were observed, and brain temperature increased during a DI session. These findings must be thoroughly validated in future studies because elevated brain temperature during a DI session can contribute to some reactions to DI.

Keywords: Laser Doppler Flowmetry (LDF); blood perfusion; cerebral circulation; microgravity; temperature; weightlessness; “dry” immersion.

Figure 1

Device “LASMA PF” placement for LFD measurements of supraorbital regions.

Figure 2

Blood pressure in subjects during “dry” immersion session (median and interquartile range). Study points: before (baseline test—preDI); on the 15, 30, 40 min of DI session (15′DI, 30′DI and 40′DI, correspondingly); and 3 min after DI (post-DI). SBP, systolic blood pressure; DBP, diastolic blood pressure. The significance of ANOVA *** p < 0.001; the difference from preDI value # p < 0.001 (Duncan post-hoc test).

Figure 3

The temperature of the suborbital area (a) and forearm area (b).