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, FEV₁ 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_diindex, EMG_PSindex). Borg breathlessness was assessed every minute and at exhaustion.

Results EMG_PSindex and EMG_PS activity per unit ventilation (EMG_PSindex/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_diindex and breathlessness were not significantly different at exhaustion when exercise modes were compared.

Conclusion A higher EMG_PSindex/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.