Comparison of two mouthpieces in the measurement of MIP and MEP in adults

Objectives: To compare and establish the degree of agreement between the values of Maximal Inspiratory Pressure (MIP) and Maximal Expiratory Pressure (MEP) measured with a plastic mouthpiece and a scuba type mouthpiece in adults. The secondary objective was to evaluate the degree of agreement between the values calculated with the equations by Evans and Whitelaw and the maximal values attained with each interface. Materials and Method: We conducted an observational, descriptive, prospective transversal study. We carried out a consecutive, non-probabilistic sampling of Argentinian subjects aged between 18 and 69 years. We measured the MIP and MEP with a unidirectional valve system and an aneroid manovacuometer, with a plastic mouthpiece and a scuba type mouthpiece. Results: A total of 240 subjects were included and completed all the measurements with both interfaces. MEP values were higher when measured with a plastic mouthpiece compared to the scuba type (p < 0.01), with an Intraclass Correlation Coefficient (ICC) between them of 0.80 (95% CI [confidence interval]: 0.74-0.84). There were no differences in the MIP between both interfaces, with an ICC of 0.88 (95% CI: 0.85-0.91). The ICC between the equations by Evans and Whitelaw and the maximal values attained by the subjects varied from -0.15 to 0.09, showing a low degree of agreement. Conclusion: MEP values attained with a plastic mouthpiece are greater than those attained with the scuba type mouthpiece. There are no differences between both interfaces for the MIP. Evans and Whitelaw equations were not successful in predicting maximal pressures in the population under study.