Cerebral hemodynamic effects of 30-minute supine rest and postural changes at normoxia and hypoxia using near infrared spectroscopy

Abstract

We investigated the effects of hypoxia on neurophysiological parameters during rest and moderate intensity exercise to understand cerebral metabolism. 31 male (age= 31±13 yr, height= 177±5 cm, mass= 79±9 kg) and 4 female (age= 25±7 yr, height= 169±7 cm, mass= 60±5kg) participants were recruited. Near-infrared spectroscope (NIRS) was placed over the right prefrontal cortex to measure relative changes in oxy (HbO2), deoxy (HHb), total (tHb) and hemoglobin difference (HbDiff). Participants rested in a supine position for 30-minutes, followed by a 2-minute washout period before beginning a 10-second squat-stand (0.05 Hz) maneuver for 5 minutes. Thereafter participants repeated the supine and squat-stand protocol in a normobaric environmental chamber (14.8% oxygen; ~2750m). The difference from the last 5 minutes of supine rest was compared to the first 5 minutes in both conditions. The difference between the supine rest vs. squat-stand was compared in both conditions. NIRS standard deviation (SD) was compared during the 30-minutes of supine rest vs. the 5 minutes of squat-stand. A Wilcoxon signed-rank test was use to compare paired samples. Results showed a significant decrease in HbO2, tHb and HbDiff, a significant increase in HHb at the end of the supine rest in hypoxia vs. normoxia, and an increase in SD of all parameters in hypoxia. For squat-stand, there was a significant decrease in HbDiff and a significant increase in HHb in hypoxia, with a significant increase in SD of all parameters in hypoxia. These results suggest altered cerebral metabolism at altitudes about 2750m during rest and exercise.