# The clinical value of circadian biofeedback in chronic heart failure

## TL;DR

A wearable tool called CircAlign-HF helps improve autonomic function and sleep in chronic heart failure patients by aligning activities with their circadian rhythms.

## Contribution

The study introduces a novel circadian biofeedback tool and demonstrates its specific benefits for nocturnal autonomic function in CHF.

## Key findings

- General advice improved 24-hour autonomic regulation, with increases in rMSSD and SDNN during exertion.
- Circadian alignment specifically enhanced nocturnal autonomic function, with significant gains in SDNN, rMSSD, LF, and HF power during sleep.
- Over half of participants reported better sleep quality and steadier energy levels with circadian-aligned recommendations.

## Abstract

Chronic heart failure (CHF) is characterized by impaired autonomic regulation and disrupted sleep–wake cycles, limiting recovery and daily function. CircAlign-HF, a wearable-guided circadian biofeedback tool providing personalized timing recommendations on activity, naps, and sleep, was developed. This study evaluated its physiological and clinical value in CHF.

Twenty-one patients with stable CHF (median age 68 years, 90.5% male, NYHA II–III) completed a 3-week crossover protocol. Week 1 served as baseline, in Week 2 participants received general advice (30 min daily walk, 20 min nap, sleep hygiene), and in Week 3, participants were guided to align their walk, nap, sleep, and wake times with their circadian rhythm. Autonomic regulation was assessed using HRV over 24 h, and within 15 min windows centred on each participant’s peak daytime activity (diurnal acrophase) and deepest nocturnal rest (nocturnal nadir), capturing activity-related and sleep-related autonomic function. Patient-centred outcomes and adherence were evaluated using a structured questionnaire.

General advice improved 24 h autonomic regulation: the root mean square of successive differences (rMSSD) increased from baseline to Week 2 (+18.2 ms, P = 0.037), with concurrent gains in standard deviation of normal-to-normal intervals (SDNN) and rMSSD during exertion windows (+47.3 ms and +56.8 ms, both P = 0.037). Adding circadian alignment yielded specific nocturnal benefits: SDNN (+56.7 ms, P = 0.039), rMSSD (+47.6 ms, P = 0.0078), low-frequency (LF) power (+6236 ms², P = 0.039), and high-frequency (HF) power (+6812 ms², P = 0.0078) during sleep increased from Week 1 to Week 3. Adherence was 68% for walks, 74% for naps, and 47% for circadian timing; over half perceived better sleep quality and steadier energy levels.

General advice improved overall autonomic regulation, whereas circadian-aligned recommendations specifically enhanced nocturnal autonomic function. These short-term physiological and perceived gains support the potential relevance of circadian biofeedback as a behavioural strategy in chronic heart failure.

Graphical Abstract