ASER index

ASER, amplitude of the mode (AMo): conditional indicator of sympathetic activity.

ASER — the conditional index of activity of the sympathetic element of regulation — is the amplitude of the mode (AMo) of the heartbeat-interval histogram in R. M. Baevsky's variational pulsometry. It shows what percentage of all heartbeats fall into the most frequent interval range. The more uniform ("stabilised") the rhythm, the higher ASER — and the stronger the sympathetic influence on the heart.

Heart rate variabilityBaevsky indicesSympathetic activityAMo

DefinitionAMo — % of intervals in the modal bin

Unit%

Approximate norm at rest≈ 30–50 %

Suggests sympathetic dominance> 50 %

What ASER shows

The sympathetic nervous system acts on the sinus node like a "stabiliser": it speeds up the heart and suppresses the beat-to-beat fluctuations produced by breathing and the vagus nerve. As a result, more heartbeats have almost the same length, and the tallest bar of the interval histogram grows. Baevsky called its height — AMo — a conditional indicator of sympathetic activity: conditional, because it describes the shape of the rhythm, not a direct measurement of nerve traffic.

Figure 1. ASER is the height of the tallest histogram bar (AMo, red): the percentage of all NN intervals that fall into the modal 50-ms bin.

ASER = AMo = (number of intervals in the modal bin / all valid NN intervals) × 100 %

The classical calculation uses a 5-minute recording and histogram bins of 50 ms. With narrower bins AMo becomes smaller, with wider bins larger, so only values obtained by the same method are comparable.

Reference values and interpretation

Approximate guide values from Russian-language methodological literature for 5-minute recordings with 50-ms bins.
ASER (AMo)	Interpretation
< 30 %	Low — strong vagal modulation; typical of rest, sleep and trained people; very low values with slow pulse may mean excessive vagal tone
30–50 %	Normal at rest — balanced regulation (in people under 25 usually ≤ 40 %; tends to rise by about 1 % every 5 years)
> 50 %	High — prevalence of sympathetic regulation: stress, fatigue, pain, illness, overtraining, hypertension, heart failure

ASER is one of the three building blocks of other Baevsky indices: together with Mo and ΔX it enters the stress index (SI), the index of adequacy of regulatory processes (ARP) and the autonomic balance index (AB). It is best interpreted together with them.

What affects ASER

Emotional and physical load, standing position, talking during the recording.
Caffeine, nicotine, alcohol, a heavy meal, lack of sleep.
Fever, pain, dehydration, thyroid overactivity.
Age — sympathetic dominance gradually increases.
Medicines: beta-blockers lower AMo; stimulants and some antidepressants raise it.

When to see a doctor

A persistently high ASER at rest — especially with palpitations, high blood pressure, anxiety, insomnia or exhaustion — is a reason to consult a doctor.

References

Baevsky RM, Chernikova AG. Heart rate variability analysis: physiological foundations and main methods. Cardiometry. 2017;(10):66–76.
Baevsky RM, Ivanov GG, Chireykin LV, et al. Analysis of heart rate variability using different electrocardiographic systems (methodological recommendations). Vestnik Aritmologii. 2001;(24):65–86.
Tarvainen MP, Niskanen JP, Lipponen JA, Ranta-aho PO, Karjalainen PA. Kubios HRV — heart rate variability analysis software. Comput Methods Programs Biomed. 2014;113(1):210–220. doi:10.1016/j.cmpb.2013.07.024
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. Reference values of Baevsky indices are approximate and depend on the device, histogram settings and recording conditions.

Published on 5 June 2019

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