Volume of isoflow in the detection of airway obstruction and abnormalities of lung elasticity in man
Abstract
In 68 healthy subjects 7 to 25 yr old and in 27 patients with chronic lung disease (cystic fibrosis, bronchiectasis, bronchial asthma, chronic bronchitis) 8 to 29 yr old, the volume of isoflow (VisoV) was measured from flow-volume curves obtained with gases of various densities. Maximum expiratory flow rates (Vmax) with room air and lung recoil pressures [Pst(I)] were also measured.
In healthy subjects the mean VisoV value was 8.6 +- 6.6% of VC. In 44% of the patients VisoV was beyond 2 standard deviations of the normal values, while Vmax(25% VC) with room air was significantly reduced in 81% and Vmax(60% TLC) in 71% of the patients.
VisoV was, therefore, less sensitive for detecting airway obstruction than Vmax measured at low lung volumes. VisoV was negatively correlated with Pst(I)(60% TLC) and depended more on Pst(I) than did maximum flows.
It is concluded that the changes in lung elasticity may be responsible for the different sensitivities of Vmax and of VisoV. The latter might reflect abnormalities of Pst(I) contributing to small airway obstruction in the authors' patients.