Cerebral blood flow sensitivity to CO2 measured with steady-state and Read's rebreathing methods

Respir Physiol Neurobiol. 2003 Aug 14;137(1):1-10. doi: 10.1016/s1569-9048(03)00089-2.


The ventilatory response to carbon dioxide (CO2) measured by the steady-state method is lower than that measured by Read's rebreathing method. A change in end-tidal P CO2 (PET CO2) results in a lower increment change in brain tissue P CO2 (Pt CO2) in the steady-state than with rebreathing: since Pt(CO2) determines the ventilatory response to CO2, the response is lower in the steady-state. If cerebral blood flow (CBF) responds to Pt CO2, the CBF-CO2 response should be lower in the steady-state than with rebreathing. Six subjects undertook two protocols, (a) steady-state: PET CO2 was held at 1.5 mmHg above normal (isocapnia) for 10 min, then raised to three levels of hypercapnia, (8 min each; 6.5, 11.5 and 16.5 mmHg above normal, separated by 4 min isocapnia). End-tidal P O2 was held at 300 mmHg; (b) rebreathing: subjects rebreathed via a 6 L bag filled with 6.5% CO2 in O2. Transcranial Doppler-derived CBF yielded a higher CBF-CO2 sensitivity in the steady-state than with rebreathing, suggesting that CBF does not respond to Pt CO2.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Breath Tests / methods
  • Carbon Dioxide / physiology*
  • Cerebrovascular Circulation / drug effects*
  • Cerebrovascular Circulation / physiology
  • Humans
  • Hypercapnia
  • Oxygen / blood
  • Partial Pressure
  • Respiration
  • Respiratory Center / chemistry
  • Respiratory Center / physiology*
  • Tidal Volume
  • Ultrasonography, Doppler, Transcranial


  • Carbon Dioxide
  • Oxygen