VALIDATION OF A NONINVASIVE TENSION-TIME INDEX OF INSPIRATORY MUSCLES

The aim of this study was to validate a noninvasive tension-time index (TT) for all the inspiratory muscles estimated from the measurement o f mouth occlusion pressure (P-0.1), i.e., TT of inspiratory muscles (T Tmus = (P) over bar I/PImax x TI/TT, where (P) over bar I is mean insp iratory pressure, PImax is maximal PI, TI is time of muscle contractio n, and TT is total time of respiratory cycle) compared with TT of the diaphragm (TTdi = (P) over bar di/Pdi(max) x TI/TT, where (P) over bar di is mean transdiaphragmatic pressure and Pdi(max) is maximal Pdi). (P) over bar I was estimated as (P) over bar I = 5 P-0.1 x TI. Eleven patients with chronic obstructive pulmonary disease and seven normal s ubjects were studied at rest in the sitting position. After 5 min of s teady state, we measured breathing pattern, gastric and esophageal pre ssures, (P) over bar di, mean inspiratory transpulmonary pressure swin g, PImax and Pdi(max). By linear regression analysis, significant posi tive correlations were found between (P) over bar I and mean inspirato ry transpulmonary pressure swing, (P) over bar I and (P) over bar di, PImax and Pdi(max) and (P) over bar I/PImax and (P) over bar di/Pdi(ma x), with P < 0.001 for all subjects combined. These led to the highly significant correlation between TTmus and TTdi for all subjects combin ed (TTmus = 2.1 TTdi + 0.012; r = 0.97; P < 0.001) and for patients on ly (TTmus = 2.0 TTdi + 0.024; r = 0.97; P < 0.001). Therefore, pattern s of breathing that lie near fatigue thresholds can be identified with TTmus or TTdi. In conclusion, noninvasive and clinically easily deter mined TTmus seems valid for situating patients of chronic obstructive pulmonary disease in reference to the inspiratory muscle fatigue.