The effect of spontaneous versus controlled ventilation on the rate of rise of alveolar halothane concentration in dogs.

The rate of rise of the alveolar:inspired halothane concentration (F delta/F1) ratio was measured in dogs breathing spontaneously. These rates were measured at inspired concentrations of 0.3, 1.5, and 4 percent. Initially, FON (FA/F1) ratio was measured in dogs breathing spontaneously. These rates were measured at inspired concentrations of 0.3, 1.5, and 4 percent. Initially FA/F1 rose at similar rates for all 3 concentrations, but a 4 percent, the plateau attained was lower as a result of respiratory depression. In a 2nd group of dogs, FA/FI was measured for inspired concentrations of 0.3, 1.5, 4, and 6 percent during controlled ventilation. FA/FI rose at similar rates at the lower 2 concentrations but at progressively more rapid rates at inspired concentrations of 4 and 6 percent, presumably as a result of circulatory depression.