What’s it all about….HRV?

Dr Nyjon Eccles BSc MBBS MRCP PhD

A young fit and well man walked into my clinic to have a stress test i.e. Heart Rate Variability (HRV) reading. Not until he was wired up did he inform me that he had a history of panic attacks when he was in doctor’s offices! Sure enough whilst the monitoring proceeded I witnessed him start to perspire, become pale and become generally agitated. As the test requires the client to remain still, this only served to increase his anxiety. What do you predict that his pulse rate was during his panic attack? All the textbooks would say his heart rate would be racing because of Sympathetic Nervous System (SNS) fight or flight activation. However, his average pulse rate during his panic was maintained at 60 beats per minute. How could this be? The analysis showed that for sure he had tremendous SNS activation but synonymously with it he also had tremendous Parasympathetic Nervous System (PNS) activation, which served to maintain his heart rate at normal levels even in the face of obvious panic!! A perfect illustration of what happens when a person has adequate Autonomic Nervous System (ANS) reserve. Ongoing stressors, physical (excessive exercise, poor diet, toxins, psychological stress, etc) seem to exhaust this ANS reserve leading, in the long run, to incompetent homeostasis.

Originating from the Russian Space program, HRV is a non-invasive simple to conduct test gives a wealth of important information about a person’s physiology and health. Although the test may take only 5 minutes to conduct it provides information about the body’s homeostatic control, the balance in the autonomic nervous system, stress reserves (ability to cope with stress), ageing stress and hormonal function.

HRV is based on the measured time difference between each heartbeat (R-wave) (as above), i.e. the beat-to-beat variability. Each R-wave represents a contraction of the heart and corresponds to the pulse. The beat-to-beat variability is affected by autonomic nervous system activity.

Normally the heartbeat should vary from beat to beat under direct control of both the SNS and PNS. These are the two components of the ANS and are like yin and yang; working to balance each other to achieve homeostasis For example, the SNS speeds and the PNS slows the heart rate. HRV is therefore the result of the interaction between these 2 systems. It is accepted by scientists that this interaction at the heart is a reflection of ANS balance or imbalance in the body in general. SNS dominance at the heart is therefore an indication of a general sympathetic dominance in the ANS. This would indicate a system under chronic stress and a vulnerability to further stresses and disease. An overactive ANS is an indicator of a system under current stress. A balanced ANS is essential for effective managing any stress.

Until recently, technology has been limited to investigation of the sympathetic division of the ANS. We have been aware of the parasympathetic branch, but it has played a limited role in our thinking. Porges (1995,1997) coined the term “Cannon’s mistake” – which is not understanding the important role that the PNS plays in physiological regulation The PNS nerve activity is critically involved in homeostatic regulation in everyday activities.

Even sustained positive mood has been shown to positively enhance ANS balance. When this happens all physiological systems work better…blood pressure drops, anxiety and stress is relieved, work is more productive and efficient; and if this more balanced autonomic nervous function is sustained, the tissues and cells work more efficiently and age less rapidly.

A healthy physiological system has the following characteristics: