How many manoeuvres should be done to measure maximal inspiratory mouth pressure in patients with chronic airflow obstruction?

To determine the number of maximal mouth pressure manoeuvres needed to obtain a reproducible value of maximal inspiratory mouth pressure (MIP), we studied 44 patients with chronic airflow obstruction, with a mean (SD) % predicted FEV1 value of 53.9 (25), who were clinically stable. Maximal inspiratory mouth pressure was determined with an anaeroid manometer during maximal inspiratory efforts in a quasi static condition at residual volume. All patients performed 20 consecutive maximal inspiratory mouth manoeuvres, each one separated by 30-40 seconds. The mean (SD) values of MIP varied from 71.5 (25.5) cm H2O at the first measurement to 80.1 (27) cm H2O at the last measurement. Maximal values of MIP were usually achieved after nine determinations. It is concluded that to obtain a reproducible MIP value in patients with chronic airflow obstruction who are untrained and unexperienced in such manoeuvres a minimum of nine technically acceptable maximal mouth pressure manoeuvres should be performed.