Unidirectional Expiratory Valve Method to Assess Maximal Inspiratory Pressure in Individuals without Artificial Airway

INTRODUCTION: Maximal Inspiratory Pressure (MIP) is considered an effective method to estimate strength of inspiratory muscles, but still leads to false positive diagnosis. Although MIP assessment with unidirectional expiratory valve method has been used in patients undergoing mechanical ventilation, no previous studies investigated the application of this method in subjects without artificial airway. OBJECTIVES: This study aimed to compare the MIP values assessed by standard method (MIP(sta)) and by unidirectional expiratory valve method (MIP(uni)) in subjects with spontaneous breathing without artificial airway. MIP(uni) reproducibility was also evaluated. METHODS: This was a crossover design study, and 31 subjects performed MIP(sta) and MIP(uni) in a random order. MIP(sta) measured MIP maintaining negative pressure for at least one second after forceful expiration. MIP(uni) evaluated MIP using a unidirectional expiratory valve attached to a face mask and was conducted by two evaluators (A and B) at two moments (Tests 1 and 2) to determine interobserver and intraobserver reproducibility of MIP values. Intraclass correlation coefficient (ICC([2,1])) was used to determine intraobserver and interobserver reproducibility. RESULTS: The mean values for MIP(uni) were 14.3% higher (-117.3 ± 24.8 cmH(2)O) than the mean values for MIP(sta) (-102.5 ± 23.9 cmH(2)O) (p<0.001). Interobserver reproducibility assessment showed very high correlation for Test 1 (ICC([2,1]) = 0.91), and high correlation for Test 2 (ICC([2,1]) = 0.88). The assessment of the intraobserver reproducibility showed high correlation for evaluator A (ICC([2,1]) = 0.86) and evaluator B (ICC([2,1]) = 0.77). CONCLUSIONS: MIP(uni) presented higher values when compared with MIP(sta) and proved to be reproducible in subjects with spontaneous breathing without artificial airway.