title: Determining changes in airway caliber in asthma: the role of submaximal expiratory flow rates.
abstract: 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.
mesh_terms: D000293:Adolescent; D000328:Adult; D000403:Airway Resistance; D001249:Asthma / Q000188:drug therapy / Q000503:physiopathology*; D005260:Female; D005540:Forced Expiratory Flow Rates; D006801:Humans; D007545:Isoproterenol / Q000627:therapeutic use; D008297:Male; D008450:Maximal Midexpiratory Flow Rate; D008875:Middle Aged; D010993:Plethysmography, Whole Body; D013147:Spirometry; D013990:Tidal Volume; D014797:Vital Capacity
chemical_list: D007545:Isoproterenol