Changes in operating lung volume and symptoms during daily activity in COPD

Patients with moderate-severe COPD perform low levels of daily physical activity and both breathlessness and leg fatigue are important symptoms limiting exercise. It is now possible to accurately measure daily physical activity using accelerometers. Less is known about symptoms and hyperinflation measured during laboratory exercise testing relate to daily activity. We studied 20 stable COPD patients (15 male, mean (SD) age 67 (7) yrs, FEV1 0,96 (0,4) l, 36 (12) % predicted, IC 1,7 (0,4) l, 62 (14) % predicted during a time-limited endurance cycle exercise test at 70 % VO2 max. IC, dyspnoea intensity and leg fatigue on a Borg scale were recorded every 2 minutes. We calculated the individual slope of the change in these variables expressed as IC absolute. We assessed daily physical activity using both AW (Actiwatch) and SW (SenseWear) that subjects wore for 3-4 consecutive days from waking until going to bed. There was a good relationship between AW mean activity score and AW mean activity moving (r2=0,7; p<0,01) and a close relationship between SW step count and AW mean activity score (r2=0,8; p<0,001). We found a good relationship between the AW mean activity score and the rate of increase of dyspnoea (r2=0,5; p<0,05) but no correlation between AW mean activity score and the rate of rise of leg discomfort (r2=0,2; p=NS). There was no relationship between the baseline IC expressed as absolute and the AW mean activity score (r2=0,03; p=NS) and the SW number of steps (r2=0,1; p=NS). Activity levels measured by these different devices worn on the lower and upper limb are similar and data registered with the same uniaxial leg accelerometer give similar level of the typical daily activity. Baseline level of hyperinflation did not predict daily activity and the individual’s perception of breathlessness as lung volume rises is the important factor limiting daily activity. Changes in symptoms related to peripheral muscle dysfunction did not limit the daily activity in our COPD patients.