Effects of short-term environmental hyperthermia on patterns of cerebral blood flow.

Environmental hyperthermia is a very common risk factor for many occupations, however, its potential influences on cerebral circulation remain obscure. In this study, 20 participants underwent two simulated environmental thermal conditions (50 °C/25 °C, 1 h), and their cerebral blood flows (CBFs) were quantified using a pseudo-continuous arterial spin labeling (ASL) MR imaging. During the experiment, the physiological parameters, including rectal temperature, arterial blood pressure and weight loss, heart rate and respiration rate, were recorded, and a visual analog scale (VAS) test was performed during both conditions to evaluate the psychological state including vigilance, anxiety, vigor, confidence, anger, nervousness, drowsiness, and loquacity. After scanning, a highly-demanding attentional task--the psychomotor vigilance test (PVT) was performed for behavioral performance evaluation. Compared with that during normothermic condition, the global CBF (gCBF) during hyperthermic condition showed a tendency of decrease, but no significant differences. Regional CBFs (rCBFs) were significantly altered mainly in the prefrontal cortex, somatosensory areas and limbic system. Physiological detection revealed significantly decreased diastolic pressure and systolic pressure and accelerated respiration rate. Furthermore, linear multivariate regression analysis showed that altered rCBFs in several regions could be predicted by physiological (systolic pressure, rectal temperature) and psychological (vigilance, drowsiness, nervousness, anger) changes. And PVT revealed significantly slower attentional reaction during hyperthermia, and the longer reaction time was correlated with the altered rCBF in the left dorsolateral prefrontal cortex (DLPFC). These findings suggested that during short-term hyperthermia gCBF might remain relatively stable under the integrated effect of physiological changes and cerebral auto-regulation, rather than decreased solely dependently on hyperthermia-induced physiological changes. Furthermore, altered regional blood distribution might be accounted for neural activity of thermal sensation and regulation, mood state and cognitive changes.