BACKGROUND: Measurement of maximal respiratory pressures and vital capacity are essential in evaluating respiratory function. However, methodological variations may interfere with the interpretation of results. OBJECTIVE: To compare values obtained using mouthpiece and face-mask evaluation methods in the measurement of maximal respiratory pressures and vital capacity. METHOD: We studied 30 patients (16 male), with a mean age of 55.9 ± 15.7, in the preoperative phase of abdominal surgery. Maximal inspiratory pressure and maximal expiratory pressure, as well as vital capacity, were evaluated using either a rigid flanged mouthpiece or a face mask, in randomized order. RESULTS: Evaluation with a face mask did not significantly alter vital capacity and maximal inspiratory pressure values, although maximal expiratory pressure values were significantly lower than when measured using a rigid mouthpiece. During measurement of maximal expiratory pressure, air leakage from around the mask was observed in 60% of cases. When maximal expiratory pressure measurements in which there was no such leakage were considered in isolation, face-mask values were higher than those obtained with the moutpiece CONCLUSION: With a face mask, maximal inspiratory pressure and vital capacity can be accurately evaluated. Maximal expiratory pressure can also be adequately evaluated using a face mask, provided that air leakage from the mask edges can be avoided. However, such leakage and the consequent reduction in the values obtained are common and limit the use of this method of evaluation.
Respiratory function tests; Maximal voluntary ventilation; Respiratory muscles
