D28-07 Function-on-scalar Regression Models for Assessing Associations Between Daily Physical Activity Profiles and Clinical Measures in Pulmonary Arterial Hypertension

Rationale

Pulmonary arterial hypertension (PAH) is a progressive disease in which patients commonly experience marked exertional intolerance and impaired functional capacity. Total physical activity levels have been shown to be significantly associated with disease severity and functional status. ACTiPH, an ancillary study of the Pulmonary Hypertension Association Registry (PHAR), uses actigraphy to capture real-world physical activity. We examined time-specific associations between daily physical activity patterns and clinical measures, including exercise capacity, functional class, and health-related quality of life (HRQoL).

Methods

Participants in ACTiPH wore a tri-axial hip-based accelerometer during waking hours for 7 consecutive days. Minute-level vector magnitude counts were extracted and aggregated into functional activity curves. Demographic and clinical data, including the six-minute walk distance (6MWD), HRQoL scores, and WHO functional class were obtained from linked PHAR assessments. Function-on-scalar mixed-effects regression models were used to evaluate time varying associations between the clinical variables and daily physical activity profiles, adjusting for age, PAH etiology, sex, BMI, race, and average daily wear time. Only baseline visits were included in this analysis.

Results

2297 valid wear-days of data were available across 438 individuals, the majority of whom were female (74.9%), non-Hispanic (85.8%), and diagnosed with idiopathic or heritable PAH (40%), and with WHO FC I/II (70.8%). Higher 6MWD was associated with greater morning activity, particularly between 7 AM and 11 AM. Participants in worse WHO functional class showed reduced activity from 10 AM to 5 PM. Higher SF-12 physical and mental component scores were associated with increased activity early in the day (5-8 AM) and lower evening activity (6-10 PM). Similarly, lower EmPHasis-10 scores (better HRQoL) were linked to higher early morning activity and lower evening activity during the same windows.

Conclusion

Daily physical activity profiles in PAH are differentially associated with clinical and HRQoL metrics across the day. These time-specific patterns may reflect behavioral adaptations to symptoms such as fatigue or exertional limitation. Identifying periods of activity vulnerability may inform personalized strategies for activity promotion and improve our understanding of functional status in PAH.

This abstract is funded by: NHLBI – R01 – HL159997 (PI: Kawut), NHLBI – K23 – HL169930 (PI: Minhas)