Hyperoxia Reversibly Alters Oxygen Consumption and Metabolism

Aim . Ventilation with pure oxygen (hyperoxic ventilation: HV) is thought to decrease whole body oxygen consumption (VO 2 ). However, the validity and impact of this phenomenon remain ambiguous; until now, under hyperoxic conditions, VO 2 has only been determined by the reverse Fick principle, a method with inherent methodological problems. The goal of this study was to determine changes of VO 2 , carbon dioxide production (VCO 2 ), and the respiratory quotient (RQ) during normoxic and hyperoxic ventilation, using a metabolic monitor. Methods . After providing signed informed consent and institutional acceptance, 14 healthy volunteers were asked to sequentially breathe room air, pure oxygen, and room air again. VO 2 , VCO 2 , RQ, and energy expenditure (EE) were determined by indirect calorimetry using a modified metabolic monitor during HV. Results . HV reduced VO 2 from 3.4 (3.0/4.0) mL/kg/min to 2.8 (2.5/3.6) mL/kg/min ( P < 0.05), whereas VCO 2 remained constant (3.0 [2.6/3.6] mL/kg/min versus 3.0 [2.6/3.5] mL/kg/min, n.s.). After onset of HV, RQ increased from 0.9 (0.8/0.9) to 1.1 (1.0/1.1). Most changes during HV were immediately reversed during subsequent normoxic ventilation. Conclusion . HV not only reduces VO 2 , but also increases the respiratory quotient. This might be interpreted as an indicator of the substantial metabolic changes induced by HV. However, the impact of this phenomenon requires further study.