Résumé :
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Background : The joint ATS/ERS statement on respiratory muscle testing1 states that a maximum inspiratory pressure <-80cmH20 excludes clinically significant inspiratory muscle weakness but does not specify a cut-off for maximum expiratory pressure (MEP). An MEP of less than 45 cmH2O is associated with an ineffective cough2. In our laboratory, we define inspiratory muscle weakness as mild when MIP is 41-80, moderate 20-40 and severe if <20cmH2O. Peak cough flow (PCF) is an alternative measure of expiratory function which is simple to perform using meters which are widely available; a PCF greater than 270 L/min indicates an effective cough, whereas a value less than 160 L/min means that the patient is likely to experience difficulty clearing respiratory secretions3. Aims : To define comparable cut-off values for MEP and PCF in the definition of abnormal expiratory muscle function and the assessment if its severity. Methods : MEP and PCF were compared in 100 subjects undergoing respiratory muscle testing. Results : The regression equation for the two measurements was as follows : PCF = (2.14 x MEP) + 116 (PCF in L/min, MEP in cmH2O) Using this equation, the PCF corresponding to an MEP of 80cmH2O was 287. An MEP of 20cmH2O equated to a PCF of 159, and an MEP of 40 cmH2O to a PCF of 202 L/min. Conclusions : We propose the following values in the assessment of expiratory muscle weakness : 1 Am J Respir Crit Care Med 2002;166 :518-624. 2 Bach JR et al. Prevention of pulmonary morbidity for patients with Duchenne muscular dystrophy. Chest 1997;112 :1024-1028. 3 Szeinberg A et al. Cough capacity in patients with muscular dystrophy. Chest 1988;94 :1232-1235.
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