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

The effect of both inspiratory and expiratory respiratory tract obstruction upon the ventilatory response to 3 and 5 per cent CO 2 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 CO 2 . 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 CO 3 seen in patients with obstructive pulmonary emphysema and hypercarbia is discussed in relation to these experimental observations.