Heart Rate Variability Analysis: A Powerful Health Assessment Technique

Autonomic nervous system and the heart

Our heart is one of the various organs whose activity is influenced by the autonomic nervous system or ANS. The autonomic nervous system is a division of the peripheral nervous system responsible for regulating the optimum functioning of various organs and systems. The ANS also helps maintain the body's homeostasis in the face of changing external and internal conditions.

Autonomic failure can cause the body's synchronized systems to break down. Autonomic failure may result from primary autonomic disorders of which autonomic nervous system degeneration is the characteristic symptom or from other 'secondary' reasons such as cardiovascular disorders, metabolic disorders and chronic stress. As the smooth functioning of the ANS is critical to good health, high immunity and a positive prognosis of future health, it becomes imperative to assess the state and functioning of the ANS on a regular basis.

Heart rate variability analysis

The heart does not beat at regular intervals. Rather, successive heartbeats are separated by slightly varying time intervals. This variability, referred to as heart rate variability, is caused by the interplay of the activities of the two branches of the ANS. The two branches, known as the parasympathetic nervous system and the sympathetic nervous system, have opposing effects on the beating of the heart.

Heart rate variability analysis serves as a non-invasive tool to give a quantitative evaluation of autonomic nervous system function, the activities of the PNS and the SNS and the balance between these two branches.

Measuring and analyzing heart rate variability
To record, measure and analyze heart rate variability, two common means are employed:

• Electrocardiograph

Electrocardiograph or ECG involves recording the electrical activity of the heart by using electrodes placed on the patient's body. The electrodes detect the tiny electrical changes in the skin that occur due to the electrical changes in the heart muscle caused during each heartbeat. As ECG is a direct reflection of the electrophysiological activity of the heart, it is considered to be the most reliable way to measure and analyze heart rate variability.

• Photoplethysmogram

Photoplethysmogram or PPG is a modality that reflects pulsatile blood transport through peripheral blood vessels. It is an indirect reflection of the heart's activity but is known to provide a fairly accurate measurement of the variation in the time intervals between successive heartbeats.