Cerebral oxygenation declines at exercise intensities above the respiratory compensation threshold

Respir Physiol Neurobiol. 2007 May 14;156(2):196-202. doi: 10.1016/j.resp.2006.08.009. Epub 2006 Aug 30.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptation, Physiological
  • Adult
  • Anaerobic Threshold / physiology
  • Brain / blood supply*
  • Brain / metabolism
  • Carbon Dioxide / blood*
  • Cerebrovascular Circulation / physiology*
  • Exercise Test
  • Exercise Tolerance / physiology*
  • Fatigue / blood
  • Humans
  • Male
  • Oxygen / blood
  • Oxygen Consumption / physiology*
  • Physical Exertion / physiology
  • Pulmonary Ventilation / physiology
  • Reference Values
  • Respiratory Mechanics / physiology*
  • Statistics, Nonparametric

Substances

  • Carbon Dioxide
  • Oxygen