Energy requirements of the respiratory musculature in asthma

Oxygen consumption and carbon dioxide production were measured in 29 asthmatic subjects. Minute ventilation was measured by a rib cage and abdomen-diaphragm displacement method. Expired gases were collected via a tight-fitting mask. Minute ventilation, oxygen consumption, and carbon dioxide production all increased when subjects inspired room air via a mouthpiece (when compared with a tight-fitting mask). By contrast, minute ventilation and carbon dioxide production both decreased when supplementary oxygen replaced room air via the tight-fitting mask (p less than 0.001). No consistent changes in either inspiratory work (estimated from measurement of pleural pressure during quiet breathing), airway resistance, or physiologic dead space could be seen to accompany changes in minute ventilation. It is concluded that the oxygen cost of breathing in asthma is substantial.