IS EXTRATHORACIC AIRWAY-OBSTRUCTION IMPORTANT IN ASTHMA

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Abstract
Pulmonary pressure-flow (P/.ovrhdot.V) curves were measured by ensemble averaging 20 breaths in 16 asthmatic patients while they were breathing air and a mixture of 80% He and 20% O2 at functional residual capacity at a frequency of 60 breaths/min. Of the patients, 14 were also studied during quiet breathing with air. Curves were analyzed according to P = K'' .ovrhdot.Va, where K'' represents the slope of the P/.ovrhdot.V curve and a its curvilinearity. Analyses were done separately for the inspiratory and expiratory limbs of the curve. Curvilinearity of inspiratory P/.ovrhdot.V curves in asthmatics is greater than normal and is abnormally flow-dependent. In contrast to normal subjects, curvilinearity was corrected by breathing the mixture of He and O2. Apparently flow dependence is in larger airways. In 7 of the 16 patients inspiratory resistance was greater than resistance during the early phase of expiration while they were panting at 60 breaths/min. During quiet breathing expiratory resistance was always greater than inspiratory resistance. These 7 patients also showed the greatest response to He during inspiration, but the effect of the He-O2 mixture during expiration was considerably less, which suggests a different site of airway obstruction on expiration as compared to inspiration. Apparently the glottis and extrathoracic trachea play an important role in some asthmatic patients.