The PWP measures the variations in heart rate of a patient in a resting state. Under resting conditions, the ECG of healthy individuals exhibits periodic variation in the interbeat intervals.
- Many clinicians view the heart as a periodic oscillator whose rate varies according to the demands of the organism. However, there is growing evidence that under physiologic conditions, the heart is not a periodic oscillator.
- Variability in heart rate reflects the vagal and sympathetic function of the autonomic nervous system, and has been used as a monitoring tool in clinical conditions characterized by altered autonomic nervous system function. Spectral analysis of beat-to-beat variability is a simple, noninvasive technique to evaluate autonomic dysfunction.
- Heart rate variability analysis has been used in the assessment of diabetic neuropathy and to predict the risk of arrhythmic events following myocardial infarction. The technique has also been used to investigate autonomic changes associated with neurotoxicity, physical exercise anorexia nervosa, brain infarction, angina, and panic disorder.
- Normative data on heart rate variability have been collected. This technology appears to hold promise for assessing overall fitness. Gallagher et al compared age-matched groups with different lifestyles. These were smokers, sedentary persons, and aerobically fit individuals. They found that smoking and a sedentary lifestyle reduces vagal tone, whereas enhanced aerobic fitness increases vagal tone. Dixon et al reported that endurance training modifies heart rate control through neurocardiac mechanisms. In occupational health, the effects of various stresses of the work environment of heart patients and asymptomatic workers may be evaluated using heart rate variability analysis.
Heart Rate Variability and Vertebral Subluxation
Zhang and Dean (20) reported the results of an study involving 520 subjects in a single-visit group, and 111 subjects in a four-week group. The purpose of the study was to investigate the effect of chiropractic care in a multi-clinic setting on the balance of the sympathetic and parasympathetic nervous system using HRV analysis. The study demonstrated consistent changes in HRV. The authors reported, “The decreased heart rate and increased total power from the HRV analysis indicated a healthy autonomic nervous system balance after correction of vertebral subluxation.”
