title: Cerebral oxygenation declines at exercise intensities above the respiratory compensation threshold.
abstract: During incremental exercise PaCO2 and PETCO2 begin to decline at the respiratory compensation threshold (RCT-GEX). Since PaCO2 alters cerebral blood flow it was hypothesized that there would be a systematic decline in cerebral oxygenation (Cox) measured by near infrared spectroscopy above the RCT (RCT-NIRS). Cardiorespiratory and NIRS responses were simultaneously monitored from the left frontal lobe during incremental exercise in 17 men. All subjects showed a decline in Cox above the RCT-GEX with a 20-40 s delay. Significant differences (P<0.01) were observed between the RCT-GEX and RCT-NIRS for time (9.83 versus 10.39 min), power (198 versus 212 W) and oxygen uptake (2.31 versus 2.43 L min-1). Intra-class correlations for power and absolute VO2 were 0.97 and 0.98, respectively. Bland-Altman analysis revealed no outliers for any of the variables. The results suggested that the decrease in Cox observed above the RCT was most likely due to a reduction in cerebral blood flow mediated by a decline in PaCO2. This decline in Cox could reduce neuronal activation thereby limiting maximal exercise capacity in healthy subjects.
authors.affiliation: Faculty of Rehabilitation Medicine, University of Alberta, Edmonton, Canada. yagesh.bhambhani@ualberta.ca
authors.forename: Yagesh
authors.initials: Y
authors.lastname: Bhambhani
authors.forename: Rohit
authors.initials: R
authors.lastname: Malik
authors.forename: Swapan
authors.initials: S
authors.lastname: Mookerjee
mesh_terms: D000222:Adaptation, Physiological; D000328:Adult; D015308:Anaerobic Threshold / Q000502:physiology; D001921:Brain / Q000098:blood supply* / Q000378:metabolism; D002245:Carbon Dioxide / Q000097:blood*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D005080:Exercise Test; D017079:Exercise Tolerance / Q000502:physiology*; D005221:Fatigue / Q000097:blood; D006801:Humans; D008297:Male; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology; D012123:Pulmonary Ventilation / Q000502:physiology; D012016:Reference Values; D015656:Respiratory Mechanics / Q000502:physiology*; D018709:Statistics, Nonparametric
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen