Experimental Biot periodic breathing in cats: effects of changes in PiO2 and PiCO2

Periodic breathing of the Biot or cluster type was induced in spontaneously breathing, pentobarbital anesthetized cats by placing bilateral lesions within the pneumotaxic system of the rostral pons. Control lesions positioned outside of the critical nuclei never resulted in Biot breathing. The periodic pattern was characterized by clusters of breaths which were separated by distinct periods of apnea and was clearly not of Cheyne-Stokes quality. Test gas challenges inducing hypoxia and hypercapnia tended to diminish the apneic breatholds, whereas hyperoxia potentiated the periodic breathing by increasing the duration of the non-ventilatory phase. Only hypercapnia significantly altered the tidal volume of Biot breaths by increasing the depth of breathing. No conclusions can be drawn as to whether the Biot pattern arises from an inherent central respiratory controller periodicity, or from oscillations in arterial blood gas tensions and peripheral chemoreceptor (and mechanoreceptor) inputs. It is suggested that the experimental model for Biot breathing may be of unique importance for studying the control of expiratory duration, particularly apnea. Also, it is of interest that similar breathing patterns and gas responses occur in the neonate and adult.