Changes in cerebral blood flow during hyperventilation and CO2-breathing measured transcutaneously in humans by a bidirectional, pulsed, ultrasound Doppler blood velocitymeter

Acta Physiol Scand. 1980 Oct;110(2):167-73. doi: 10.1111/j.1748-1716.1980.tb06647.x.


We have used a bidirectional pulsed ultrasound doppler system which measures the instantaneous mean velocity across the lumen of a blood vessel in order to determine the relationship between alveolar PCO2 (PACO2) and blood flow in the four arteries supplying the brain in humans. Both high and low PACO2-values were explored. Six subjects, 3 males and 3 females (22-40 years) were studied by use of this non-invasive technique. To increase the PACO2 the subjects were breathing 4, 6 and 8% CO2 in air. PACO2 was reduced by voluntary hyperventilation down to a chosen end-expiratory PCO2 value of about 2.2 kPa. We found a linear relationship between arterial blood flow expressed as a percentage of control level and PACO2 in the range from 3.3 to 7.3 kPa. At the very lowest PACO2 values a levelling off of the response, with flow values of 40 to 45%, was observed. The CO2-reactivities in the 6 persons varied between 28.1 and 30.0%/kPa. The time course and the magnitude of the flow response were similar in all four arteries.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Blood Flow Velocity*
  • Carbon Dioxide*
  • Carotid Artery, Internal / physiology
  • Cerebrovascular Circulation*
  • Doppler Effect
  • Female
  • Humans
  • Hyperventilation / physiopathology*
  • Male
  • Methods
  • Regional Blood Flow
  • Ultrasonics / instrumentation
  • Vertebral Artery / physiology


  • Carbon Dioxide