Multiple inert gas elimination technique to demonstrate the changes in ventilation/perfusion () relations between awake (A) and anesthetized (B) states. Patients anesthetized with halothane or enflurane. In B, note the widening of spread as a result of more areas of both high and low , and the increase in shunt (s) with increased perfusion of atelectatic lung regions ( <0.01). (Based on data from reference 89.)