Hyperbaric oxygen therapy increases free radical levels in the blood of humans

Free Radic Res Commun. 1993;19(2):71-80. doi: 10.3109/10715769309056501.


It has been postulated that exposure to high concentrations of oxygen results in increased oxygen radical production which may account for the toxic effects of excessive exposure to oxygen. Examination of blood from persons undergoing hyperbaric oxygen (HBO) exposure, by low temperature electron spin resonance (ESR) spectroscopy, demonstrated a marked increase in the magnitude of a signal with properties consistent with a free radical (g = 2.006). The signal diminished to baseline levels within 10 minutes of cessation of HBO exposure. Further in vitro studies of blood revealed an ESR signal generated in red blood cells by oxygen, and dependent on oxyhaemoglobin, which had characteristics indistinguishable from those of the ESR signal of ascorbate radical and the signal in blood from persons undergoing HBO exposure. It is postulated that HBO exposure increases ascorbate radical levels in blood, which is likely to reflect increased ascorbate turnover in human red blood cells.

MeSH terms

  • Adult
  • Ascorbic Acid / blood
  • Carboxyhemoglobin / metabolism
  • Electron Spin Resonance Spectroscopy
  • Erythrocytes / drug effects
  • Erythrocytes / metabolism*
  • Ethylmaleimide / pharmacology
  • Free Radicals / blood
  • Glutathione / blood
  • Glutathione Reductase / blood
  • Humans
  • Hyperbaric Oxygenation*
  • Male
  • Middle Aged
  • Oxyhemoglobins / metabolism*


  • Free Radicals
  • Oxyhemoglobins
  • Carboxyhemoglobin
  • Glutathione Reductase
  • Glutathione
  • Ethylmaleimide
  • Ascorbic Acid