The MW/FEV, Ratio in Normal and Asthmatic Subjects: Materials and Methods

7 Oct

Twenty nonsmoking normal subjects (ten men, ten women; mean age±SD = 37± 15 years) without history of allergic rhinitis, cardiopulmonary or systemic disease were studied. Forty stable asthmatic subjects (20 men, 20 women; age = 37 ± 13 years) also were studied. Criteria for the diagnosis of asthma were those established by the Committee of Nomenclature of the American Thoracic Society. The following criteria were considered indicative of stability: (1) ambulatory status; (2) no acute exacerbations of asthma within three months; (3) no recent change in type or dosage of medications; and (4) no appreciable change in pulmonary function tests compared with previous studies (if available). All subjects gave informed consent to participate in the study Bronchodilators were withheld for at least 12 hours prior to testing. fully

Pulmonary Function Measurements
The forced vital capacity (FVC), its subdivisions, and MW were determined using a Cardiopulmonary Instruments (CPI) model 220 rolling—seal spirometer connected to a CPI model 750A X-Y recorder. The highest of three values for FEV, and of two values for MW were used. The MW was measured by having the subject ventilate as rapidly and deeply as possible for 12 s with vigorous encouragement by the pulmonary technician. A minimum of two (and usually three) minutes of resting ventilation was allowed between MW maneuvers.

Body plethysmography was performed in all subjects. Thoracic gas volume (Vtg) at functional residual capacity and airway resistance (Raw) were measured. The results were expressed as specific conductance (SGaw = Raw • Vtg’)- To assess volume history effects, subjects avoided any deep breaths or cough for 3 min; SGaw was then obtained. Subsequently, subjects rapidly inhaled to total lung capacity (TLC) and then immediately exhaled to a lung volume near Vtg by relaxing with the glottis open. Within 5 s of this deep inspiration, Raw and Vtg were again measured and SGaw was calculated; this result was designated SGawDI.* Specific conductance was then determined within 5 s of completion of a 12-s MW maneuver; this result was designated SGawMVV.