Posthyperventilation isocapnic hyperpnea.

Subjects voluntarily hyperventilated for 10 breaths. A dynamic end-tidal forcing technique manipulated inspired gases to hold end-tidal CO2-O2 tensions at normal values during the voluntary ventilation period and the postvoluntary ventilation recovery period when the subjects returned to spontaneous breathing. Six of the seven subjects studied exhibited a hyperpnea during the recovery period. Although intersubject and intrasubject variations were evident, the average response for 30 experiments in the six subjects was characterized by an initial drop to 32% of the hyperventilation magnitude followed by an exponential-like decrease with a time constant of 22 s. This recovery period response is consistent with theoretical properties of neural network and physical oscillators where there is a persistence in the amplitude response after the removal of the stimulus. Thus, such oscillator properties may govern the respiratory center behavior in man. Furthermore, since isocapnic voluntary ventilation increases cardiac output, the recovery period response may be a consequence of cardiodynamic hyperpnea.