Activity monitoring reflects cardiovascular and metabolic variations in COPD patients across GOLD stages II to IV

We investigated whether activity monitoring reliably reflects variations in oxygen transport and utilization during walking in COPD patients. Forty-two patients (14 in each GOLD stage 11,111 and IV) performed an incremental treadmill protocol to the limit of tolerance. Breath-by-breath gas exchange, central hemodynamic variables and activity monitoring were simultaneously recorded. Physiological variables and accelerometer outputs rose linearly with walking speeds. Strong correlations (r[interquartile range, IQR]) were found between treadmill walking intensity (WI: range 0.8-2.0 m s(-2)) and oxygen consumption (0.95 [IQR 0.87-0.97]), (range 7.6-15.5 ml kg(-1) min(-1)); minute ventilation (0.95 [IQR 0.86-0.98]), (range 20-37l min(-1)); cardiac output (0.89 [IQR 0.73-0.94]), (range 6.8-11.5l min(-1)) and arteriovenous oxygen concentration difference (0.84 [IQR 0.76-0.90]), (range 7.7-12.1 ml O-2 100 ml(-1)). Correlations between WI and gas exchange or central hemodynamic parameters were not different across GOLD stages. In conclusion, central hemodynamic, respiratory and muscle metabolic variations during incremental treadmill exercise are tightly associated to changes in walking intensity as recorded by accelerometry across GOLD stages II to IV. Interestingly, the magnitude of these associations is not different across GOLD stages.