The Assessment of Maximal Respiratory Mouth Pressures In Adults

Maximal inspiratory pressure (MIP) and maximal expiratory pressure (MEP) are simple, convenient, and noninvasive indices of respiratory muscle strength at the mouth, but standards are not clearly established. We review recent literature, update the 2002 American Thoracic Society/European Respiratory Society statement, and propose as the best choice using a flanged mouthpiece for reference values and lower limit of normal (LLN) values as a function of age for adults age up to about 70 years. Because male pressures are higher than female and MEP exceeds MIP, we present 4 linear regression reference equations as a function of age for adults age up to approximately 70 years: Male MIP = 120 - (0.41 × age), and male MIP LLN = 62 - (0.15 × age). Male MEP = 174 - (0.83 × age), and male MEP LLN = 117 - (0.83 × age). Female MIP = 108 - (0.61 × age), and female MIP LLN = 62 - (0.50 × age). Female MEP = 131 - (0.86 × age), and female MEP LLN = 95 - (0.57 × age). (Pressure in cm H₂O and age in years.) We discuss normal values in older subjects, estimation of LLN values, and the relationship between vital capacity and respiratory muscle strength, and offer a guide to interpretation of maximal pressure measurements. The approach should allow direct implementation of MIP and MEP in a pulmonary function laboratory.