Effect of 26% oxygen breathing on ventilation and perfusion distribution in patients with cold

Fourteen patients suffering from severe but stable chronic airway obstruction were studied while breathing room air and mildly hyperoxic mixture (26%). The data were collected at the end of each 30 min randomized breathing period. The multiple inert gas elimination technique was used to detect alterations in ventilation-perfusion (VA/Q) mismatching. Ventilatory, arterial and mixed venous blood gases, and hemodynamic measurements were made simultaneously. To show a possible effect of O2 on hypoxic pulmonary vasoconstriction (HPV), the fractional part of cardiac output perfusing low VA/Q areas was separated using as upper limit of VA/Q the compartments with PAO2 70, 60 and 50 mmHg while breathing oxygen, compared to the percentage of blood flow in the same areas limited by the same VA/Q unit in air breathing conditions. Only a few changes due to O2 are statistically significant: 1) a rise in PaO2 (+20.2 +/- 8.3 mmHg) and PvO2 (+4.2 +/- 2.18 mmHg) without any change in ventilation, respiratory frequency, pH, PaCO2, haemodynamics and overall criterion of distribution; 2) a moderate increase in inert gas dead space; 3) an increase in the percentage of blood flow under the limit when chosen at 50 mmHg (+3 +/- 2.8%). This change could be related to an inhibition of HPV response while breathing O2 in compartments previously placed above the limit in air. Consequently, their VA/Q decrease and their perfusions are summed with those under the limit in O2. These data suggest that mild hyperoxia has a slight but real deleterious effect on pulmonary gas exchange.