ELECTROMYOGRAPHIC EVIDENCE FOR EXERCISE-INDUCED DIAPHRAGM FATIGUE IN PATIENTS WITH CHRONIC CERVICAL CORD INJURY OR PRIOR POLIOMYELITIS INFECTION

The purpose of this study was to determine, in exercising patients, ho w much diaphragm force increases before electromyographical evidence o f diaphragm fatigue occurs. The study was performed in ten male patien ts with complete cervical cord injury (CCI) at the C5 to C8 levels, an d five male patients with prior poliomyelitis infection (PPI) requirin g chronic treatment with intermittent positive pressure ventilation (I PPV) at night, We studied the time course of the diaphragmatic tension -time index (TTdi), the centre frequency (CFdi) of the diaphragm elect romyogram (EMGdi) power spectrum, and the ventilatory parameters, duri ng steady-state submaximal arm/leg exercise. During exercise, early si gns of diaphragm fatigue were present in seven out of 10 CCI patients and in four out of five PPI patients, as indicated by a reduction in C Fdi, The increase in TTdi achieved before reductions in CFdi occurred was twofold in both the CCI and PPI patients. All patients except for the PPI patients, who demonstrated a reduction in CFdi, showed an incr ease in minute ventilation (V-E), achieved by increasing both their ti dal volume (V-t) and the breathing frequency (f(b)). The PPI patients demonstrating reductions in CFdi during exercise also increased their V-E however, this was achieved by increasing fb while Vt remained cons tant. Following the reductions in CFdi, the CCI patients further incre ased their TTdi throughout the exercise test, while the PPI patients r educed their TTdi values. In conclusion: (1) During exercise, electrom yographical evidence for diaphragmatic fatigue frequently occurred in the CCI and PPI patients studied; (2) Compared to the eightfold increa se in TTdi seen in healthy subjects before reductions in CFdi occur, t he TTdi values increased only two-fold before electromyographical evid ence of diaphragm fatigue was present in these patients. (3) There is a clear discrepancy between the CCI and PPI patients who demonstrate e lectromyographical evidence of diaphragm fatigue, in terms of their ve ntilatory and TTdi responses.