Background: Airway resistance (RAW) and specific airway conductance (sGAW) are measures that reflect the patency\nof airways. Little is known of the variability of these measures between different lung diseases. This study\ninvestigated the contribution of RAW and sGAW to a diagnosis of obstructive airways disease and their role in\ndifferentiating asthma from COPD.\nMethods: 976 subjects admitted for the first time to a pulmonary practice in Belgium were included. Clinical\ndiagnoses were based on complete pulmonary function tests and supported by investigations of physicians�\ndiscretion. 651 subjects had a final diagnosis of obstructive diseases, 168 had another respiratory disease and 157\nsubjects had no respiratory disease (healthy controls).\nResults: RAW and sGAW were significantly different (p < 0.0001) between obstructive and other groups. Abnormal\nRAW and sGAW were found in 39 % and 18 % of the population, respectively, in which 81 % and 90 % had\ndiagnosed airway obstruction. Multiple regression revealed sGAW to be a significant and independent predictor of\nan obstructive disorder. To differentiate asthma from COPD, RAW was found to be more relevant and statistically\nsignificant. In asthma patients with normal FEV1/FVC ratio, both RAW and sGAW were more specific than sensitive\ndiagnostic tests in differentiating asthma from healthy subjects.\nConclusions: RAW and sGAW are significant factors that contribute to the diagnosis and differentiation of obstructive\nairways diseases
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