Objective: To determine whether performing more maximal inspiratory pressure (MIP) maneuvers per test provides a more accurate assessment of the true maximal inspiratory strength.
Design: Review of MIP data from 367 tests. Each subject was encouraged to perform 20 MIP maneuvers per test, unless the patient reached the highest measurable pressure three times, or because of poor cooperation, fatigue, or respiratory distress. 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 values with < or = 5% variability; the results from further maneuvers were ignored; and (2) the "long MIP" is defined as the average of the three highest values with < or = 5% variability from all recorded maneuvers.
Setting: Pulmonary Physiology Laboratory, Childrens Hospital Los Angeles.
Participants: One hundred seventy-eight pediatric and adult subjects (age, 14 +/- 3 [SD] years; 53% male) with suspected inspiratory muscle weakness.
Measurements and results: 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 short MIP. In 48% of the tests, the short MIP method underestimated the peak performance determined by the long MIP method. We speculate that the difference between the long MIP and the short MIP can be attributed to a learning effect.