Diaphragmatic fatigue under inspiratory resistive load in healthy subjects and the effect of several selections of frequency bands on the H/L (high/low) ratio

Abstract

In seven normal adult males the authors studied diaphragmatic fatigue by analysis of the power spectrum of the diaphragmatic electromyogram obtained with an esophageal electrode, and of the change of transdiaphragmatic pressure. Diaphragmatic fatigue was produced by inspiring through a resistive load, and mean value of the index of the tension time of the diaphragm (TTdi) maintained until fatigue was 0.33 +/- 0.09, which has been known to produce fatigue. The mean value of ratios of power at high frequencies to power at low frequencies (H/L) decreased to 61.2 +/- 16.8% of the initial value at just before breaking time. Breaking time was 4.88 +/- 1.37 minutes in average. The selection of low and high band widths for analysis of H/L ratio has differed slightly in the literature, but such differences do not have any substantial influence on the estimation of the changes of H/L ratio.