Medical Book

LANGUAGE
English Español 中文 Українська
Search

Showing results for: Array

    Medical Book

    LANG
    English Español 中文 Українська
    nHF
    Home > Parameters

    nHF

    Normalised HF power (HF n.u.): relative share of respiratory vagal oscillations.

    nHF — normalised high-frequency power (HF n.u.) — expresses HF power as a percentage of the sum of LF and HF power. It shows the relative share of respiratory, vagally mediated oscillations in the heart-rate spectrum and is often used, together with LF n.u., to describe changes of autonomic modulation with posture, sleep stages and mental load.

    Heart rate variabilityFrequency domainNormalised unitsVagal modulation
    FormulaHF / (LF + HF) × 100
    Unitn.u.
    Healthy adults, 5 min40 ± 10 n.u.
    Usual range≈ 16–60 n.u.

    How it is calculated

    HF n.u. = HF / (TP − VLF) × 100 = HF / (LF + HF) × 100 = 100 − LF n.u.

    HF n.u. and LF n.u. are complementary: when one rises, the other falls by the same amount. Normalisation makes values comparable between people with very different total power, but it also hides whether a change was caused by HF, by LF, or by both.

    Power spectrum of heart rate variability with very low frequency band up to 0.04 hertz, low frequency band 0.04 to 0.15 hertz and high frequency band 0.15 to 0.40 hertz; total power is the area under the whole curve VLFLFHF ≈ 0.1 Hz: baroreflex≈ 0.25 Hz: breathing (vagus) 00.040.150.40 Frequency, HzPower, ms²/Hz
    Figure 1. Heart-rate power spectrum. HF n.u. is the share of the HF band (green) in the combined LF + HF power.

    Interpretation

    Low HF n.u.

    • Respiratory (vagal) oscillations make up a small share of variability
    • Standing, mental and emotional stress, REM sleep
    • Slow breathing near 6 breaths per minute (respiratory power moves to LF)
    • Reduced vagal modulation in chronic stress, heart failure, diabetic autonomic neuropathy

    High HF n.u.

    • Predominance of respiratory modulation: lying at rest, deep non-REM sleep, relaxation
    • Well-trained endurance athletes at rest
    • Fast breathing (which reduces LF) or artefacts
    Interpret with caution

    HF n.u. describes proportions, not the absolute strength of vagal activity. A person with very low total HRV can still have a "normal" HF n.u. Always read it with absolute HF power, RMSSD, heart rate and breathing rate.

    When to see a doctor

    Discuss persistent abnormalities of HRV with a doctor, particularly when accompanied by palpitations, fainting, high blood pressure, poor sleep or chronic fatigue.

    References

    1. 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
    2. 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
    3. 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

    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 24 June 2019