HOW MANY MANEUVERS ARE REQUIRED TO MEASURE MAXIMAL INSPIRATORY PRESSURE ACCURATELY

Objective: To determine whether performing more maximal inspiratory pr essure (MIP) maneuvers per test provides a more accurate assessment of the true maximal inspiratory strength. Design: Review of MIP data fro m 367 tests. Each subject was encouraged to perform 20 MIP maneuvers p er test, unless the patient reached the highest measurable pressure th ree times, or because of poor cooperation, fatigue, or respiratory dis tress. From the same raw data, MIP was calculated in two ways: (1) the ''short MIP'' was defined as the average of the first three highest v alues with less than or equal to 5% variability; the results from furt her maneuvers were ignored; and (2) the ''long MIP'' is defined as the average of the three highest values with less than or equal to 5% var iability from all recorded maneuvers. Setting: Pulmonary Physiology La boratory, Childrens Hospital Los Angeles. Participants: One hundred se venty-eight pediatric and adult subjects (age, 14 +/- 3 [SD] years; 53 % male) with suspected inspiratory muscle weakness. Measurements and r esults: The long MIP (91 +/- 39 cm H2O) was significantly greater than the short MIP (82 +/- 39 cm H2O) (p < 0.000005). In 177 of 367 tests, the short MIP underestimated the peak performance. Conclusions: From the same raw data, the long MIP was significantly greater than the sho rt MIP. In 48% of the tests, the short MIP method underestimated the p eak performance determined by the long MIP method. We speculate that t he difference between the long MIP and the short MIP can be attributed to a learning effect.