Maximal Expiratory Flow and Total Respiratory Resistance During Induced Bronchoconstriction in Asthmatic Subjects1–3

Abstract

Fifteen mild to moderate attacks of asthma were induced in 12 asymptomatic asthmatic subjects by nebulization of an allergen. Serial measurements were made of maximal expiratory flow-volume curves and total respiratory resistance; both were related to absolute lung volume. At the height of the attack, total lung capacity was unchanged, vital capacity decreased, residual volume increased, maximal flows decreased, and resistance increased. Maximal flow at 60 per cent of control total lung capacity was the most sensitive indicator of response. Total respiratory resistance corrected for volume was also sensitive and tended to change with maximal flow at 60 per cent of total lung capacity. In many subjects, the first effect of the inhaled allergen was to cause a parallel shift in the maximal expiratory flow-volume curve, with no change in slope. The mechanical explanation for this behavior is uncertain. A possible explanation is that closure of susceptible lung units occurred but the mechanical behavior of uninvolved units was unaffected.