Using Heart Rate Variability to Monitor the Balance of the Autonomic Nervous System

John Zhang, Ph.D., MD

Chiropractic care is concerned with the integrity of the nervous system. The sympathetic and parasympathetic nervous systems are responsible for physiological regulatory mechanisms. Heart rate variability (HRV) is a noninvasive measurement developed over the past two decades to determine the balance of the autonomic nervous system. HRV is a phenomenon where the heart rate of a normal individual changes continuously around its mean value. This constant changing in heart rate is a response to the interplay between sympathetic and vagal modulation of sinus node pacemaker activity. An increased activity in one system is accompanied by decreased activity in the other. Analysis of HRV data generates important information concerning sympatho-vagal balance. HRV measurement is a recording of ECG readings and monitoring the heart rate changes. The HRV has been used in a wide variety of clinical interests, especially to monitor stress and predict cardiovascular diseases. Research has found that lowered HRV is associated with aging and increased incidence of sudden death. Changes in HRV are associated with major depression, panic disorders, anxiety, and worry. HRV analysis has also shown that, during mental or emotional stress, sympathetic activity increases and parasympathetic activity decreases.

This cohort study was designed to investigate the reliability of HRV measurement on the balance of sympathetic and parasympathetic nervous system in the first year chiropractic student who received varying forms of chiropractic care in SCSC. The goal of the study was to determine whether their care received during the period of study had any effect on their autonomic nervous system. Twenty-seven 'normal' students, 22 to 49 years old, voluntarily participated in the study. HRV was measured four times within a twelve-month period. The first three measurements were made within three months and the fourth reading was taken after a 12 month period. The mean heart rate decreased from 80+9, 81+12, and 83+10 beats per minute in the first three tests to 73+10 beats per minute in the fourth test (the mean high frequency component that represents parasympathetic stimulation increased from 95, 121 and 67 hz in the first three measurements to 218 hz in the fourth measurement. the low frequency component that represents sympathetic stimulation showed dominant pattern in all four readings, ranging from 522, 592, 487 to 676 hz0.05). There was a slight increase in sympathetic stimulation in the fourth reading compared to the first three measurements but the change did not reach statistical significance.

A high sympathetic stimulation was found in the first year chiropractic students. A significant improvement in heart rate and increased parasympathetic stimulation was noted one year later with varying chiropractic care. Further research will assign subjects into different chiropractic care groups and isolate the effect of varying chiropractic care on the autonomic nervous system. HRV used in the study appeared to be a reliable measurement of sympathetic and parasympathetic balance.