Effects of oxygen breathing on regional distribution of ventilation and perfusion in hypoxemic patients with chronic lung disease.

Regional distribution of ventilation and perfusion were measured in 17 hypoxemic and 16 normoxic patients using 13N as tracer. The effect of 100% and 50% O2 breathing was tested. No variation was observed in normoxic patients. In hypoxemic patients, perfusion was not modified significantly during O2 breathing. Poorly-ventilated zones hypoventilated even more during O2 breathing. It is suggested that this effect may have been due to (1) a collapse of some alveoli, (2) a variation in the mechanical properties of the surrounding opened alveoli, or (3) a possible modification in tidal volumes and functional residual capacities during O2 breathing.