Noninvasive assessment of inspiratory muscle function during exercise

The use of esophageal and gastric: balloons limits measurement of the tensi on-time index of inspiratory muscles (T-TI) during exercise. The aim of thi s study was to assess whether a noninvasive tension-time index, TT0.1, give n by P-0.1/PImax x TI/Ttot (where P-0.1 is mouth occlusion pressure, PImax is maximal inspiratory pressure, and TI/Ttot is duty cycle) could reliably assess TTI during exercise. In seven healthy young men and nine patients wi th COPD we measured TT0.1 and TTL (i.e., Pes/Pes(max) x Tl/Ttot where Pes i s mean esophageal pressure and Pes(max) is maximal static Pes) at rest and during an incremental exercise test. A significant linear correlation (p < 0.02) was found between TT0.1 and TTL in all normal subjects and patients w ith COPD. An equation for estimating TTI from TT0.1 was established for eac h group. In the normal subjects there was good agreement between estimated and observed data. In five additional normal males studied prospectively, t he agreement was also satisfactory and reproducible. In the COPD patients t he agreement was poor. In conclusion, in young healthy subjects the changes in TT0.1 during exercise reflect the changes in TTI, allowing satisfactory estimation of TTI from noninvasive measurements of TT0.1.