Influence of high ambient temperatures on the physiological responses and body sway in healthy young adults after quickly standing.

This study was aimed to compare the variations in cerebral oxygenation, blood pressure and center-of-foot pressure after standing from sitting and supine positions at normal (22 degrees C) and high (32 degrees C) room temperatures. Thirty young adults stood up from a resting posture (sitting or supine position) and kept the static standing posture for 90 sec. Meanwhile, their center-of-foot pressure (COP), blood pressure, and cerebral oxygenation kinetics were measured in continuity. The change of the frequency domain low-to-high frequency (LF/HF) ratio of the R-R interval before and after standing from a supine position was significantly higher than that from a sitting position under both temperature conditions. Blood pressure as well as total and oxygenated hemoglobin levels decreased immediately after standing up and the ratio of blood pressure change when moving from a supine position to standing at high room temperature was the largest as compared with the other conditions. Total hemoglobin (Hb) volume was found to temporarily decrease after standing and required 22-24 sec to recover when the subject started from the sitting position and 33-36 sec when the subject started from the supine position. Cerebral oxygenation kinetics tended to be larger under high, rather than normal, temperature conditions. All COP parameters after standing were significantly larger in the high temperature condition than in the normal temperature condition. Body sway after standing was larger in the high temperature condition than in the normal temperature condition and after standing from a supine position than from a sitting position. In conclusion, cerebral oxygenation kinetics and blood pressure measured after the subject moved to the standing position changed dramatically under high temperature conditions, and variations in this parameter may influence body sway.