The Effect of Respiratory Tract Obstruction Upon the Ventilatory Response to Inhaled Carbon Dioxide in Normal Subjects

¹ The Cardio-Pulmonary Laboratory and the Department of Medicine, Mt. Sinai Hospital, Miami Beach, Florida, and the Section of Cardiology of the Department of Medicine, University of Miami School of Medicine, Coral Gables, Florida.

The effect of both inspiratory and expiratory respiratory tract obstruction upon the ventilatory response to 3 and 5 per cent CO₂ has been studied in 14 normal subjects. Three grades of obstruction were employed. In nine subjects the effects of two levels of obstruction were noted. Maximum breathing capacities were determined under both control and experimental (respiratory tract obstruction) conditions.

The results indicate that mild degrees of obstruction have relatively little effect upon the response to inhaled CO₂. A decrease in alveolar ventilation and arterial blood pH and an increase in arterial carbon dioxide tension result from interposition of more severe grades of obstruction. The etiology of the depressed ventilatory response to inhaled CO₃ seen in patients with obstructive pulmonary emphysema and hypercarbia is discussed in relation to these experimental observations.