Perfusion of the Underventilated Compartment of the Lungs in Asthmatic Children*

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Abstract
Bronchial asthma is characterized by inadequate ventilation (in respect to volume) of parts of the lung. This study was conducted in order to determine to what extent these areas were perfused and therefore contributed to the O2 unsaturation of the arterial blood. This was done by following the rate of N2 washout from alveolar gas and arterial blood during O2 breathing. In all patients, including those studied in the symptom-free interval, the underventilated compartment received more perfu-sion than ventilation. This indicates that assessment of the functional status by ventilatory study alone will underestimate the severity of the disease. In addition, the more severe cases behaved as if some parts of the lungs were perfused but not ventilated at all, and these could not be demonstrated by the alveolar gas washout technique. It is suggested that study of the N2 washout in the arterial blood is a most useful index of the lung function in this condition.