Autonomic Nervous System Test (HRV) | Identifying the Cause of Flushing That Worsens in Specific Situations

1. What Is the Autonomic Nervous System Test?

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The autonomic nervous system test (HRV, Heart Rate Variability) analyzes variations in heartbeat intervals to assess the balance of the autonomic nervous system. At our clinic, it is used to identify the underlying cause of flushing that worsens in specific situations.

The autonomic nervous system consists of the sympathetic and parasympathetic nervous systems. The sympathetic nervous system responds to stress and excitement, while the parasympathetic nervous system is responsible for relaxation and recovery. In a healthy state, these two systems maintain balance, causing subtle variations in heart rate intervals. Greater variation indicates that the autonomic nervous system is functioning flexibly.

When the sympathetic nervous system is overactive, heart rate variability decreases and shows a more consistent pattern. The HRV test quantifies this difference.

2. Why Is It Necessary?

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There are various causes of facial redness. Among them, emotional flushing that occurs during stress or heightened emotions and neurogenic rosacea that responds to heat or spicy foods may appear similar but have different causes and treatments.

The HRV test is the first step in this differentiation. Since symptoms alone make differentiation difficult, it is necessary to determine the direction of flushing treatment.

It objectively identifies whether the sympathetic nervous system is overactive or within the normal range through quantitative measurements to determine the cause of flushing.

• Sympathetic overactivity + normal TEWL → Possible emotional flushing
• Normal autonomic nervous system + elevated TEWL → Possible neurogenic rosacea

3. How Is It Performed?

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Clip-type electrodes are attached to both wrists and ankles, and measurements are taken for 1–5 minutes while sitting in a comfortable position. No needles or medications are used, and there is no pain whatsoever.

Pre-Test Precautions

• Avoid caffeine (coffee, energy drinks) and smoking from 2 hours before the test
• Avoid vigorous exercise immediately before the test
• Rest for at least 5 minutes after arrival before measurement

The autonomic nervous system responds sensitively to caffeine, nicotine, and exercise. These precautions must be followed for accurate results.

4. How Are Results Interpreted?

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The two most important indicators in HRV test results are:

Indicator	Meaning	Interpretation
LF/HF Ratio	Balance between sympathetic and parasympathetic nervous systems	1.5 or higher indicates sympathetic dominance
RMSSD	Parasympathetic nervous system activity	Below 20 indicates reduced parasympathetic activity

If LF/HF is high and RMSSD is low, the sympathetic nervous system is overactive and the parasympathetic nervous system is not providing sufficient inhibition. In such cases, emotional flushing is likely, and beta-blockers and stress management may be helpful.

If both indicators are within normal range, flushing via the sensory nerve (TRPV1) pathway rather than the autonomic nervous system is suspected. In this case, a comprehensive assessment is made together with TEWL test results.

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References

1. Shaffer F, Ginsberg JP. An Overview of Heart Rate Variability Metrics and Norms. Front Public Health. 2017;5:258.
2. Wu C, Zhang K, Guo Y, et al. Clinical Characteristics and Serum CGRP Level Differences Between Neurogenic Rosacea and Non-neurogenic Rosacea. Int J Dermatol. 2025;64 Suppl 2:42-51.