Physical activity limitation as measured by accelerometry in pulmonary arterial hypertension

Abstract

Background: The 6-min walk test, commonly used to assess exercise capacity and response to therapy in pulmonary arterial hypertension (PAH), has many well-described limitations. Sedentary time is associated with adverse cardiovascular outcomes and reduced quality of life, and measuring sedentary time and physical activity using accelerometry is another potential way to quantify exercise capacity in PAH. Whether sedentary time is different in patients with PAH vs control subjects is unknown.

Methods: Physical activity was measured in 20 patients with PAH and 30 matched healthy control subjects using accelerometry for 7 consecutive days. Patients with PAH completed standard 6-min walk testing, and baseline demographics were recorded for all study participants. Total daily activity counts, sedentary time, and proportion of time at various activity levels were compared between groups.

Results: Sedentary time was significantly higher in patients with PAH (mean, 92.1% daily activity; 95% CI, 89.5-94.8%) than in control subjects (mean, 79.9% daily activity; 95% CI, 76.4%-83.5%; P < .001), and all levels of physical activity were reduced in the PAH group compared with the control group ( P < .01 for all). Daily moderate to vigorous physical activity was reduced in the PAH group (7.5 min; 95% CI; 0.8-15.6 min) compared with the control group (mean, 64.7 min; 95% CI, 51.1-78.2 min; P < .001). Activity counts correlated with 6-min walk distance in the PAH group (Spearman rank correlation 5 0.72, P < .001).

Conclusions: Sedentary time is increased in patients with PAH and may lead to increased risk for metabolic and cardiovascular morbidity. Quantitation of daily activity and sedentary time using accelerometry may be a novel end point for PAH management and clinical trials.

Figures

Figure 1.

Representative single-day ActiGraph output from a patient with World Health Organization (WHO) functional class III pulmonary arterial hypertension. Activity count (y-axis) is shown as a function of time of day (x-axis). Sedentary ( 6.0 METs) activity levels are shown according to ActiGraph specifications.

Figure 2.

Daily activity in patients with PAH and control subjects. Mean percentage of daily time spent at each activity level is shown for the control and PAH groups. PAH = pulmonary arterial hypertension. See Figure 1 legend for expansion of other abbreviation.

Figure 3.

Activity counts are significantly reduced in patients with PAH compared with control subjects. For each group, the median is shown as the black bar; boxes represent the interquartile range. The open circle denotes an outlier value, and the asterisk denotes an extreme value. P < .001 by Mann-Whitney U test. See Figure 2 legend for expansion of abbreviation.

Figure 4.

Sedentary time is increased in patients with PAH compared with control subjects. Sedentary time is shown as percentage of time per day at 1.0 to 1.5 METs for patients with PAH and control subjects. For each group, the median is shown as the black bar; boxes represent the interquartile range. The open circles denote outlier values. P < .001 by Mann-Whitney U test. See Figure 1 and 2 legends for expansion of abbreviations.

Figure 5.

Low, moderate, and vigorous activity in patients with PAH and control subjects. Results are shown as mean percentage of daily activity. *P = .001 by Mann-Whitney U test. **P < .001 by Mann-Whitney U test. See Figure 1 and 2 legends for expansion of abbreviations.

Figure 6.

Physical activity by WHO functional classification. A, Total daily activity count in patients with WHO class I/II compared with class III/IV pulmonary arterial hypertension. B, Percentage of time per day at 1.0 to 1.5 MET (sedentary/rest time) in patients with WHO class I/II compared with class III/IV pulmonary arterial hypertension. The open circle denotes an outlier value, and the asterisks denote extreme values. P values shown are for comparison between groups using Mann-Whitney U test. See Figure 1 and 2 legends for expansion of abbreviations.

Figure 7.

Daily activity count correlates with 6-min walk distance in patients with pulmonary arterial hypertension.