A selective suppression of human pain sensitivity by carbon dioxide: central mechanisms implicated

Eur J Appl Physiol Occup Physiol. 1994;68(1):74-9. doi: 10.1007/BF00599245.


The effect of breathing CO2 on somatic sensitivity was studied in human subjects. Healthy humans breathed room air, 100% O2, or CO2 (5% or 8% in O2). Thresholds to heat pain, mechanical pain, electrically evoked pain, and electrically evoked perception were measured using psychophysical techniques. Also, the effects on sensory and affective components of experimental ischaemic pain, alertness and on cardiovascular parameters were observed. In addition, the effect of CO2 on heat pain threshold was determined in the ischaemic limb to exclude the possibility that the threshold elevation was due to an action on primary afferent fibres. Naloxone (0.8 mg), dexamethasone (0.1 mg) or placebo (0.9% NaCl) were applied intravenously in double blind tests to reverse the threshold elevations. In an electrophysiological experiment the effect of CO2 on a spinal nociceptive flexion reflex evoked by an electric stimulus was measured. The CO2 produced a dose-dependent elevation of the heat pain threshold. Similarly, the sensory and affective components of experimental ischaemic pain were attenuated by CO2. The heat pain threshold was significantly elevated by CO2 in the ischaemic limb, also. However, there was no effect on thresholds to mechanically or electrically induced pain or perception thresholds to electrically evoked sensations. One hundred percent O, did not elevate the heat pain threshold. In double blind tests the heat pain threshold elevation was not significant when the naloxone or dexamethasone was administered. The threshold to electrically evoked spinal flexion reflex was not elevated by CO2. The CO2 at the current dose produced sedation, an increase in blood pressure but no change in heart rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Publication types

  • Clinical Trial
  • Controlled Clinical Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Arousal / drug effects
  • Arousal / physiology
  • Blood Pressure / drug effects
  • Blood Pressure / physiology
  • Carbon Dioxide / pharmacology*
  • Carbon Dioxide / physiology
  • Dexamethasone / pharmacology
  • Electroshock
  • Female
  • Heart Rate / drug effects
  • Heart Rate / physiology
  • Hot Temperature
  • Humans
  • Hypercapnia / physiopathology
  • Ischemia / physiopathology
  • Male
  • Middle Aged
  • Naloxone / pharmacology
  • Pain Threshold / drug effects*
  • Pain Threshold / physiology
  • Perception / drug effects
  • Perception / physiology
  • Physical Stimulation


  • Carbon Dioxide
  • Naloxone
  • Dexamethasone