Static and dynamic lung volumes and ventilation-perfusion abnormality in adult asthma

Abstract

Dynamic lung volumes (forced vital capacity, forced expiratory volume in 0·5 second and in 1·0 second), static lung volumes (total lung capacity, functional residual capacity, residual volume), and ventilation-perfusion relationships (alveolar-arterial oxygen tension difference, alveolar dead space ventilation to tidal volume ratio, arterial oxygen and carbon dioxide tension, and the fractional ventilation and perfusion relationship by the three-compartment lung model) were measured in adult asthmatics during the acute, recovery, and stable or asymptomatic phases of an asthmatic attack. Eighteen patients were studied during 20 separate asthmatic attacks. The patients behaved in one of three ways with regard to total lung capacity (TLC): group I had an elevated TLC during the acute asthmatic attack which returned to normal, group II had a normal TLC throughout the attack, and group III had an elevated TLC that did not return to normal on recovery from the asthmatic attack. With the patients separated into the three groups, the other pulmonary function measurements, especially the measurements of ventilation-perfusion abnormality, were compared. There were no statistically significant differences of ventilation-perfusion abnormality between groups I, II, or III. There was a tendency for perfusion abnormality to be less during the acute phase of the asthmatic attack in patients with an elevated TLC (group I). The three-compartment lung model revealed the major abnormality in all groups to be an increased fraction of unventilated but perfused lung.