Pressure enhancement of the depressant effect of halothane on cilial beat.

In order to test the applicability of the critical volume hypothesis of anaesthetic action to the side effects of anaesthesia, we have studied the pressure-anaesthetic interactions on cilial beat. The swimming speed of Tetrahymena pyriformis was determined at one and 137 atmospheres with 0 to 4 per cent halothane. The pressure and anaesthetic effects were synergistic with the halothane dose-response curve being shifted to the left and increased in slope at the high pressure, although high pressure alone had no significant effect. These results are contrary to the predictions of the critical volume hypothesis and appear to demarcate the narcotic effect of anaesthetics from the type of molecular interaction which is concerned in the effect on cilial beat.