INCREMENTAL THRESHOLD LOADING - A STANDARD PROTOCOL AND ESTABLISHMENTOF A REFERENCE RANGE IN NAIVE NORMAL SUBJECTS

Incremental threshold loading (TTL) has been proposed as a test of ins piratory muscle strength and endurance, To date, however, there has be en no standardized protocol for an ITL test, and no reference range, w ith different investigators using a variety of different pressure incr ements in small numbers of subjects. We developed an ITL test using th e weighted plunger (WP) principle, which uses standard increments of p ressure. In our protocol subjects inspire through the WP generating an initial threshold opening pressure of 10 cmH(2)O. This pressure is ra ised at 2 min intervals in increments of 5 cmH(2)O until they fail to lift the plunger on two consecutive attempted breaths. Sixty healthy v olunteers (30 males and 30 females) aged 20-80 yrs performed the ITL t est, Twelve subjects (sis females and six males) performed the test tw ice to assess reproducibility and repeatability, Using stepwise multip le linear regression, we regressed the maximum threshold pressure sust ained for a full 2 min (Pmaz) against age, height, weight and static m aximum inspiratory mouth pressure (MIP). Pmax was significantly relate d to age but not to either height or weight, the regression equation f or males was Pmax (cmH(2)O)=103.8 - (1.0 x age in gears), and for fema les was Pmax (cmH(2)O)=93.7 - (1.0 x age in Sears). The within-subject standard deviation for those repeating the ITL test was 5.4 cmH(2)O. Incremental threshold loading is a simple technique with good reproduc ibility, which most naive subjects can use without difficulty. By usin g standard pressure increments and performing the test in a large numb er of naive subjects, we have established a reference range that shoul d be applicable wherever similar pressure increments are used.