MAXIMAL INSPIRATORY PRESSURE AND INSPIRATORY MUSCLE ENDURANCE TIME INASTHMATIC-CHILDREN - REPRODUCIBILITY AND RELATIONSHIP WITH PULMONARY-FUNCTION TESTS

Respiratory muscle strength, assessed by maximal inspiratory mouth pre ssure (PImax), and endurance, assessed as the length of time a subject could breathe against inspiratory resistance with a target mouth pres sure greater than or equal to 70% of PI,max (Tlim), were measured in 2 0 symptomless asthmatic children, in order to assess the reproducibili ty of such measurements and their relationship to traditional pulmonar y function tests or tests of bronchial hype,responsiveness. After reco rding lung volumes and bronchial response to methacholine, PI,max and Tlim were measured twice in the same morning, with a 30-minute interva l between each experimental trial. Mean (+/-SD) values of PI,max were 72.2 +/- 20.6 cmH(2)O in the first and 75.8 +/- 22.9 cmH(2)O in the se cond trial. Tlim was 154 +/- 65 and 164 +/- 66 seconds in the first an d in the second trial respectively. A tack of agreement between differ ent measurements was seen for both PI,max and Tlim. The coefficient of repeatability was 24.8 for PI,max and 92.3 for Tlim. A significant co rrelation between age and Pi,max as well as between body mass index an d PI,max were shown; no similar correlation was found for Tlim. No cor relation was found between PI,max and Tlim in either of the two succes sive runs or between either PI,max or Tlim and lung volumes or bronchi al response to methacholine. Our study shows that at this time the rep roducibility of PI,max or Tlim in children with asthma in remission se ems to be poor, although PI,max has a better reproducibility than Tlim . A standardized procedure to measure PI,max, should be obtainable in the near future. This would improve its clinical usefulness since PI,m ax is the only noninvasive test to assess respiratory muscle strength that can identify subjects at risk to develop respiratory muscle fatig ue during an acute asthmatic attack. (C) 1997 Witey-Liss, Inc.