The effect of sulfur dioxide on the response of rabbits to expiratory loads

The role of slowly adapting pulmonary stretch receptors (PSR) in the reflex control of expiratory duration was investigated in anesthetized, spontaneously breathing rabbits. Graded resistive and elastic loads were applied for single expirations to produce expiratory volume-time curves. The PSR were selectively blocked by administration of 200-400 ppm sulfur dioxide (SO2) to the inspired air of the rabbits. Volume-time curves were generated for pre-treatment, SO2 exposure, recovery and post-bilateral cervical vagotomy. SO2 exposure significantly reduced the volume-dependent modulation of expiratory duration from the pre-treatment levels. The response to the expiratory loads returned when the SO2 gas was removed. Vagotomy completely abolished any volume-dependent modulation of expiratory duration with expiratory loading. These results demonstrate that the response of rabbits to expiratory loads is vagally dependent. The hypothesis that PSR are the vagal afferents mediating this response is supported by these results.