HF

HF power: respiratory sinus arrhythmia and vagal activity.

HF — high-frequency power — is the heart-rate-variability power in the band 0.15–0.40 Hz, which corresponds to normal breathing rates of about 9–24 breaths per minute. It reflects respiratory sinus arrhythmia — the rhythmic acceleration and slowing of the heart with each breath — and is the principal spectral index of vagal (parasympathetic) activity.

Heart rate variabilityFrequency domainVagal toneBreathing

Frequency band0.15–0.40 Hz

Breathing rate≈ 9–24 / min

Unitms² (or n.u.)

HF n.u., healthy, 5 min40 ± 10

Physiology

The activity of the cardiac vagus nerve rises during exhalation and falls during inhalation. Because acetylcholine acts and is removed within a single heartbeat, these changes translate into beat-to-beat changes of heart rate synchronised with breathing. The size of this respiratory modulation — and therefore HF power — is a reliable marker of vagal influence on the heart: it almost disappears after pharmacological blockade of the vagus nerve with atropine.

Figure 1. Heart-rate power spectrum. The HF band (green, 0.15–0.40 Hz) contains the respiratory oscillations produced by the vagus nerve.

Measurement and pitfalls

HF power depends strongly on breathing: slow, deep breaths increase it; fast, shallow breathing decreases it. If breathing is slower than 9 per minute, respiratory oscillations move into the LF band and HF is underestimated.
HF correlates closely with the time-domain indices RMSSD, pNN50 and SD1, which reflect the same vagal modulation.
Absolute HF (ms²) varies widely between individuals and is often log-transformed (ln HF); normalised HF (HF n.u.) is described in the separate nHF article.

Interpretation

Low HF

Reduced vagal tone, sympathetic predominance
Stress, anxiety, lack of sleep, acute illness, overtraining
Ageing, sedentary lifestyle, obesity
Persistently low values: hypertension, heart failure, coronary disease, diabetic autonomic neuropathy, depression

High HF

Strong vagal tone: rest, sleep, good aerobic fitness, youth
Slow deep breathing (within the HF band)
Falsely high values: extrasystoles, atrial fibrillation, artefacts

How to increase HF

Regular aerobic exercise, sufficient sleep, stress reduction, limiting alcohol and slow-breathing practice all increase vagal modulation over time.

When to see a doctor

Discuss your results with a doctor if HF and RMSSD remain low for your age over a long period, especially with palpitations, breathlessness, chest pain, diabetes or known heart disease.

References

Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology. Heart rate variability: standards of measurement, physiological interpretation and clinical use. Circulation. 1996;93(5):1043–1065. doi:10.1161/01.CIR.93.5.1043
Billman GE. The LF/HF ratio does not accurately measure cardiac sympatho-vagal balance. Front Physiol. 2013;4:26. doi:10.3389/fphys.2013.00026
Nunan D, Sandercock GRH, Brodie DA. A quantitative systematic review of normal values for short-term heart rate variability in healthy adults. Pacing Clin Electrophysiol. 2010;33(11):1407–1417. doi:10.1111/j.1540-8159.2010.02841.x
Shaffer F, Ginsberg JP. An overview of heart rate variability metrics and norms. Front Public Health. 2017;5:258. doi:10.3389/fpubh.2017.00258

This article is for general information and does not replace a consultation with a doctor. HRV values depend on the device, recording length and conditions.

Published on 1 July 2019

Medical Book

Showing results for: Array