Heart Rate Variability (HRV) Analysis Heart Rate Variability (HRV) analysis measures the variations in time intervals between heartbeats, which reflect autonomic nervous system activity. Here’s how to perform HRV analysis step-by-step:

1. Step-by-Step Procedure for HRV Analysis

1.1 Preparation:

• Ensure a quiet environment with minimal disturbances.
• The subject should be relaxed and avoid caffeine, heavy meals, and strenuous exercise for at least 2 hours before the test.
• Explain the procedure to the subject to reduce anxiety.

1.2 Equipment Needed:

• Electrocardiogram (ECG) machine or a portable HRV monitoring device.
• HRV analysis software (such as Kubios HRV, HRV4Training, or other specialized software).

1.3 Electrode Placement (if using ECG):

• Clean the skin with alcohol wipes where electrodes will be placed.
• Place electrodes according to standard ECG lead placement. Typically, for HRV, you can use:
• Lead I (right arm and left arm).
• Or a simpler two-electrode placement on the chest.

1.4 Recording the Data:

• Record a continuous ECG or pulse waveform for at least 5 minutes. Longer recordings (up to 24 hours) can provide more comprehensive data.
• Ensure the subject remains still and breathes normally during the recording.

1.5 Data Analysis:

• Transfer the recorded data to the HRV analysis software.
• Perform the following analyses:

1.5.1 a. Time-Domain Measures:

1.5.1.1 SDNN (Standard Deviation of NN intervals):

Measures the overall variability in heart rate.

• Normal value: Typically > 50 ms.

1.5.1.2 RMSSD (Root Mean Square of Successive Differences):

Measures short-term variability.

• Normal value: Higher values indicate good parasympathetic activity.

1.5.2 b. Frequency-Domain Measures:

1.5.2.1 LF (Low Frequency):

0.04 to 0.15 Hz, reflects both sympathetic and parasympathetic activity. Normal value: Higher values can indicate more sympathetic activity.

1.5.2.2 HF (High Frequency):

0.15 to 0.40 Hz, reflects parasympathetic (vagal) activity. Normal value: Higher values indicate stronger parasympathetic activity.

1.5.2.3 LF/HF Ratio:

Reflects the balance between sympathetic and parasympathetic activity. Normal value: Usually between 1.5 to 2.5.

1.6 Interpreting the Results:

• High HRV: Indicates good autonomic regulation and cardiovascular health.
• Low HRV: May indicate stress, fatigue, or underlying health issues like cardiovascular diseases or autonomic dysfunction.

1.7 Documenting and Reporting:

• Summarize the findings in a report, including time-domain and frequency-domain measures.
• Provide interpretations and possible implications based on the HRV data.

Definitions for time and frequency domain measures of heart period variability

Variable	Units	Definition
TimeDomain–Statisticalmeasures
Night-day difference	ms	Difference between the average of all the normal RR intervals at night (24:00 to 05:00) and the average of all the normal RR intervals during the day (07:30 to 21:30).
SDNN	ms	Standard deviation of all normal RR intervals in the entire 24-hour ECG recording.
SDANN	ms	Standard deviation of the average normal RR intervals for all 288 5- minute segments of a 24-hour ECG recording (each average is weighted by the fraction of the 5 minutes that has normal RR intervals).
ASDNN	ms	Average of the standard deviations of normal RR intervals for all 288 5- minute segments of a 24-hour ECG recording.
r-MSSD	ms	Root mean square successive difference, the square root of the mean of the squared differences between adjacent normal RR intervals over the entire 24-hour ECG recording.
pNN50	percent	Percent of differences between adjacent normal RR intervals that are greater than 50 ms computed over the entire 24-hour ECG recording.
NN50	none	Number of adjacent normal RR intervals that are greater than 50 ms counted over the entire 24-hour ECG recording.
TimeDomain–Geometricmeasures
HRV triangular index	none	Total number of NN intervals divided by the number of NN intervals in th modal bin of a histogram of all NN intervals with a bin width of 7.8125 msec (for a sampling rate of 128/sec).
TINN	ms	Baseline width of the minimum square difference triangular interpolation of the highest peak of the histogram of all NN intervals.
FrequencyDomainMeasures
Total power	ms2	The energy in the heart period power spectrum up to 0.40 Hz.
Ultra low frequency (ULF) power	ms2	The energy in the heart period power spectrum up to 0.0033 Hz.
Very low frequency (VLF) power	ms2	The energy in the heart period power spectrum between 0.0033 and 0.04 Hz.
Low frequency (LF) power	ms2	The energy in the heart period power spectrum between 0.04 and 0.15 Hz.
High frequency (HF) power	ms2	The energy in the heart period power spectrum between 0.15 and 0.40 Hz.
LF/HF ratio	none	The ratio of low to high frequency power.
beta	none	Slope of log (power) on log (frequency) between 0.01 and 0.0001 Hz on a log-log plot.

2. Example of HRV Analysis Software Kubios HRV:

2.1 Steps:

• Import ECG data into Kubios HRV.
• The software automatically detects R-peaks and calculates NN intervals.
• Review and edit the R-peak detections if necessary to correct any artifacts.
• Perform the HRV analysis to obtain time-domain, frequency-domain, and nonlinear measures.
• Generate a report summarizing the HRV metrics.

2.2 Practical Tips

• Ensure the subject is in a consistent state during the recordings (e.g., same time of day, similar environment).
• Check for and correct artifacts (e.g., ectopic beats, noise) in the ECG data to ensure accurate HRV analysis.
• Consider the context of the measurements (e.g., health status, lifestyle factors) when interpreting HRV results.

By following these steps, you can perform a comprehensive HRV analysis to assess autonomic function and overall cardiovascular health.