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We analyzed the results of interrupter mechanics tests of 73 consecutive patients who were admitted to a chronic ventilator dependency unit. The purposes of this study were (1) to establish guidelines for grading the severity of airway obstruction based on interrupter mechanics measurements; (2) to estimate the prevalence of airway obstruction in this population; (3) to compare interrupter test results with the clinical assessment of airway function; and (4) to characterize the distribution of bronchodilator-induced changes in isorecoil flow. Measurements from 65 of 73 patients (89%) were considered technically adequate. Of 65 patients, 29 (45%) showed signs of flow limitation during passive expiration. All patients with severe obstruction documented with spirometry during clinical stability were flow-limited and achieved maximal flows < or = 0.45 L/s at recoil pressures of 10 cm H2O. In contrast to measures of expiratory dynamics, the inspiratory resistance of the respiratory system was a poor index of severity of obstruction. In seven of 12 patients, interrupter testing failed to substantiate a clinical diagnosis of severe obstruction while revealing unsuspected obstruction in six of 25 (24%) patients. The administration of 270 micrograms of albuterol increased flows at comparable recoil pressures by > or = 0.1 L/s in 29% of 41 patients. Changes in flow were unimodally distributed and were not correlated with severity of obstruction.(ABSTRACT TRUNCATED AT 250 WORDS)

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