Resting ventilatory pattern, mouth occlusion pressure, and the effects of aminophylline in asthma and chronic airways obstruction.

Patients with obstruction of the airways can maintain normocapnia either by increasing the central inspiratory neuromuscular output or by altering the central timing of each breath. This point and the effects of administration of aminophylline on ventilatory regulation were studied in six normal subjects, seven asthmatic patients, and eight patients with unresponsive chronic obstruction of the airways. Spirometric and body plethysmographic values, the ventilatory pattern, and the mouth occlusion pressure did not differ between the two groups of patients. The results indicate that in these patients, normocapnia is maintained at rest by increased central inspiratory neuromuscular output; central respiratory timing is not altered. Intravenous administration of aminophylline (5.6 mg/kg of body weight) increased alveolar ventilation in all three groups, without increasing the uptake of oxygen. In normal subjects, there was no significant effect on ventilatory regulation or drive. In asthmatic patients the central timing of each breath was altered, with no significant effect on central inspiratory output. In unresponsive obstruction of the airways, the central inspiratory output increased transiently, with no effect on central timing.