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Chest, Vol 77, 741-748, Copyright © 1980 by American College of Chest Physicians

ARTICLES

Determining changes in airway caliber in asthma: the role of submaximal expiratory flow rates

SA Lonky and GM Tisi

Sixteen patients with suspected reversible airway obstruction who had previously demonstrated an increase in specific airway conductance after isoproterenol, but who had not demonstrated an increase in forced expiratory flow were studied using a measurement of submaximal flow. Flow during tidal breathing (VTV) was measured spirometrically, and VTV increased in all 16 patients from a value of 0.61 L/sec before isoproterenol to 0.80 L/sec after isoproterenol. In addition, each of these 16 patients experienced a significant increase in vital capacity and a significant decompression of functional residual capacity after isoproterenol. If plethysmography is not available, the measurement of VTV may provide evidence of bronchodilatation. The mechanism responsible for the dichotomy between maximal and submaximal flow is the compression of airways by high positive pleural pressure which is present during maximal, but not submaximal maneuvers.




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Copyright © 1980 by the American College of Chest Physicians.