BREATHING RESPONSES OF UNANESTHETIZED MAN AND GUINEA-PIGS TO INCREASED TRANSRESPIRATORY PRESSURE

The breathing responses of unanesthetized men and guinea pigs to externally imposed shifts in lung volume produced by steady pressures applied to the body surface while the mouth remained near atmospheric pressure were compared. Lung inflation caused no consistent or significant changes in frequency or end-tidal CO2 in the 3 men. During lung inflation the guinea pigs breathed at low frequencies and smaller tidal volumes and showed consistent increases in arterial PCO2 [CO2 partial pressure] lasting up to 10 min. The changes seen immediately on application of pressure, i.e. apneic periods followed by breathing in which inspiratory duration was shortened while expiratory duration was substantially increased, indicated that conscious guinea pigs had active inflation reflexes. Reflex responses rather than mechanical factors probably account for underventilation in guinea pigs. Guinea pigs are not nearly s well equipped as is man to defend gas exchange against nonmetabolic shifts in lung volume.