P124 Neuroventilatory uncoupling during cycle and treadmill exercise in COPD

Background It is widely accepted that neuroventilatory uncoupling drives breathlessness in COPD. COPD patients are more likely to stop exercising because of breathlessness during treadmill exercise than whilst cycling. Aim To test the hypothesis that patients exhibit higher levels of neuroventilatory uncoupling during treadmill exercise than whilst cycling. Methods Diaphragm electromyogram (EMG di ) and parasternal intercostal muscle EMG (EMG PS ) activity were recorded in 12 COPD patients (mean (SD) age 66.7 (7.0) years, FEV 1 38.7 (14.5)% predicted, 11 male), during incremental cycle and treadmill exercise to exhaustion. For each muscle, the mean peak root mean square (RMS) EMG per breath over the final 30 s of each minute was normalised to peak RMS EMG recorded during maximal inspiratory manoeuvres, and corrected for inspiratory time and respiratory rate (EMG di index, EMG PS index). Borg breathlessness was assessed every minute and at exhaustion. Results EMG PS index and EMG PS activity per unit ventilation (EMG PS index/V E ) were higher at exhaustion during treadmill exercise (Abstract P124 Table 1). A higher V E at exhaustion whilst cycling approached statistical significance. EMG di index and breathlessness were not significantly different at exhaustion when exercise modes were compared. Conclusion A higher EMG PS index/V E and lower V E at exhaustion during treadmill exercise suggest that neuroventilatory uncoupling is greater than during cycle exercise. This did not translate to greater breathlessness during treadmill exercise in this study, but warrants further investigation in a larger group of patients.