Energy expenditure and physical activity in COPD by doubly labelled water method and an accelerometer

Abstract

Although weight loss suggests poor prognosis of COPD, only a few studies have examined total energy expenditure (TEE) or physical activity level (PAL) using the doubly labelled water (DLW) method. We evaluated TEE and PAL using the DLW method together with a triaxial accelerometer to elucidate the relationships between TEE, PAL and clinical parameters leading to a practical means of monitoring COPD physical status. This study evaluated 50- to 79-year-old male patients with mild to very severe COPD (n=28) or at risk for COPD (n=8). TEE, activity energy expenditure for 2 weeks and basal metabolic rate were measured by DLW, an accelerometer and indirect calorimetry, respectively. All patients underwent pulmonary function, chest-computed tomography, 6-min walk test, body composition and grip strength tests. Relationships between indices of energy expenditure and clinical parameters were analysed. Bland-Altman analysis was used to examine the agreement of TEE and PAL between the DLW method and the accelerometer. TEE and PAL using DLW in the total population were 2273±445 kcal·day^-1 and 1.80±0.20, respectively. TEE by DLW correlated well with that from the accelerometer and grip strength (p<0.0001), and PAL by DLW correlated well with that from the accelerometer (p<0.0001), grip strength and 6-min walk distance (p<0.001) among various clinical parameters. However, the accelerometer underestimated TEE (215±241 kcal·day^-1) and PAL (0.18±0.16), with proportional biases in both indices. TEE and PAL can be estimated by accelerometer in patients with COPD if systematic errors and relevant clinical factors such as muscle strength and exercise capacity are accounted for.

FIGURE 1

Differences in a) total energy expenditure (TEE) and b) physical activity level (PAL) between the doubly labelled water (DLW) method and measurement by accelerometer (ACC). Significant differences in TEE (all, Global Initiative for Chronic Obstructive Lung Disease (GOLD) 1 and GOLD 2) and PAL (all, GOLD 0, GOLD 1, GOLD 2 and GOLD 3,4) were observed between the two methods. *: p<0.05, **: p<0.01, ***: p<0.001, ****: p<0.0001.

FIGURE 2

Bland–Altman plots for a) total energy expenditure (TEE) and b) physical activity level (PAL), used to compare the values determined by the doubly labelled water (DLW) and accelerometer (ACC) methods, and c) basal metabolic rate (BMR), to compare the values obtained by indirect calorimetry (BMR_I) and the Ganpule (BMR_G) equation. Mean values are depicted by solid lines, while dotted lines show ranges within the 95% confidence interval. The 95% confidence interval for the difference in TEE was 133.5–296.6 kcal·day⁻¹ (p<0.0001) and that in PAL was 0.129–0.235 (p<0.0001) between the two methods. No difference in BMR (95% CI −25.8–4.1 kcal·day⁻¹, nonsignificant) was seen between measurements and the predicted values.

FIGURE 3

Correlations between a) total energy expenditure determined using the doubly labelled water method (TEE_DLW) or b) physical activity level determined using TEE_DLW (PAL_DLW) and clinical parameters. There was a good correlation between the grip strength, fat-free mass index (FFMI) and body mass index (BMI) and the TEE_DLW. 6-min walk distance (6MWD), grip strength, and the change in heart rate (ΔHR) during the 6-min walk test were well correlated with the PAL_DLW.

FIGURE 4

Correlations of a) total energy expenditure determined using the doubly labelled water method (TEE_DLW) and b) physical activity level determined using TEE_DLW (PAL_DLW) with the accelerometer (ACC) parameters. TEE_DLW was strongly correlated with TEE_ACC (r=0.854, p<0.0001), while the association between PAL_DLW and PAL_ACC was relatively modest (r=0.642, p<0.0001). Light (1.5–3.0 metabolic equivalents (METs)) and moderate (3.0–6.0 METs) daily activity times were correlated with both indices.