Pattern of reduction of ventilatory and occlusion pressure response to carbon dioxide by pentazocine in man.

Mean inspiratory flow, occlusion pressure and end-tidal PCO2 were measured in six healthy, sitting subjects, during breathing air and rebreathing carbon dioxide, before and after pentazocine 0.5 mg kg-1 i.v. and again after naloxone 20 micrograms kg-1. Pentazocine reduced the occlusion pressure and inspiratory flow responses at a given PCO2 during carbon dioxide rebreathing and these effects were antagonized by naloxone. The relationship of inspiratory flow and end-tidal carbon dioxide during rebreathing was used to measure the PCO2 value at which mean inspiratory flow was 1 litres-1. Occlusion pressure at this PCO2 was reduced in all the subjects by pentazocine, suggesting that the generation of inspiratory flow required less muscle activity. This effect was antagonized by naloxone.