Efficacy of a Commercial Physical Activity Monitor in Longitudinal Tracking of Patients With Pulmonary Hypertension: A Pilot Study

Abstract

Background: Patients with pulmonary arterial hypertension have quality-of-life limitations, decreased exercise capacity, and poor prognosis if the condition is left untreated. Standard exercise testing is routinely performed to evaluate patients with pulmonary arterial hypertension but may be limited in its ability to monitor activity levels in daily living.

Objective: To evaluate the validity of the commercial Fitbit Charge HR as a tool to assess real-time exercise capacity as compared with standard exercise testing.

Methods: Ambulatory pediatric and adult patients were enrolled and given a Fitbit with instructions to continuously wear the device during waking hours. Patients underwent a 6-minute walk test, cardiopulmonary exercise test, and a 36-Item Short Form Health Survey on the day of enrollment and follow-up. Twenty-seven ambulatory patients with pulmonary arterial hypertension were enrolled, and 21 had sufficient data for analyses (median age, 25 years [range, 13-59 years]; 14 female participants).

Results: Daily steps measured by the Fitbit had a positive correlation with 6-minute walk distance (r = 0.72, P = .03) and an inverse trend with World Health Organization functional class. On the 36-Item Short Form Health Survey, 77% of patients reported improvement in vitality (P = .055). At follow-up, there was a strong correlation between number of steps recorded by Fitbit and role limitations because of physical problems (r = 0.88, P = .02) and weaker correlations with other quality-of-life markers.

Conclusion: The findings of this pilot study suggest activity monitors may have potential as a simple and novel method of assessing longitudinal exercise capacity and activity levels in patients with pulmonary hypertension. Further study in larger cohorts of patients is warranted to determine which accelerometer measures correlate best with outcomes.

Keywords: Pulmonary hypertension; accelerometry; exercise tolerance; physical activity.

Fig. 1

The average daily step count of each participant was plotted over the first 2 weeks of monitoring and graphed against World Health Organization functional classes I, II, and III. The average daily steps for each respective functional class are represented by the X and connected blue lines to represent the trend of daily steps across functional classes. The median is represented by the horizontal line inside each box, with the upper and lower edges representing the upper and lower quartiles, respectively. The horizontal lines on the top and bottom of each whisker represent the upper and lower end of the range, respectively. The blue circle above the upper limit of functional class II represents an upper bound outlier.

Fig. 2

Self-reported vitality scores, as measured by the 36-Item Short Form Health Survey, were compared in 13 participants at baseline and follow-up.

Fig. 3

A) 6-Minute walk distance in meters was graphed in a scatterplot against median steps at baseline (first 2 weeks of Fitbit monitoring). B) 6-Minute walk distance in meters was graphed in a scatterplot against median steps at follow-up (2 weeks of Fitbit monitoring after 3-4 months). 6MWD, 6-minute walk distance.

Fig. 4

Median Fitbit-measured steps at follow-up (2 weeks of Fitbit monitoring after 3-4 months) was graphed in a scatterplot against 36-Item Short Form Health Survey self-reported vitality. SF-36, 36-Item Short Form Health Survey.