Diaphragmatic pressure waveform can predict electromyographic signs of diaphragmatic fatigue

To evaluate the relationship between diaphragmatic pressure (Pdi) waveform and electromyographic (EMG) signs of diaphragmatic fatigue (DF), 11 chronic obstructive pulmonary disease (COPD) subjects underwent a 12-stage graded treadmill exercise test (GXT). No COPD subjects completed the GXT; all stopped exercising due to dyspnea. We then used the crural diaphragmatic EMG (EMGdi) to divide the COPD subjects into a group that exhibited EMGdi signs of fatigue during the GXT (i.e., F group) and one that did not (i.e., NF group); three COPD subjects were classified as F, and eight COPD subjects were classified as NF. At end exercise, F and NF groups did not differ with respect to peak inspiratory Pdi swing (peak Pdi); however, they did differ with respect to percent of peak Pdi manifest at 50 and 90% of inspiratory time (TI). At 50% TI, NF = 88 +/- 3%, F = 60 +/- 1%, P less than 0.01; likewise at 90% TI, NF = 58 +/- 5%, F = 12 +/- 10%, P less than 0.01. Since peak Pdi occurred in both groups during the initial 50% of TI, these data indicate that the F group maintained Pdi less well than the NF group during the latter half of TI. Based on the above results and other data in the manuscript, we suggest that this change in Pdi waveform can predict EMG signs of DF.