Heart rate variability is a test that looks to measure the short and long-term fluctuations that occur in normal heart functioning. Despite common use of ‘steady state’ heart rate, there is actually no such thing. And actually, the more steady state the heart, the worse that is for your health. The normal resting rhythm of the heart is irregular and based on a series of complex interaction of neural, hormonal, mechanical and cellular control systems.
HRV looks to gauge the small changes in heart rate from beat-to-beat by analysing the gaps in the R waves, which is the contraction of the ventricles, or lower heart chambers, from an ECG signal.
HRV has long been associated with the detection of illness. Back in 1965 it was noted that foetal distress was preceded by a period of altercations in beat-to-beat anaylsis – this being prior to any change in actual heart rate. Since then, the technology has come much further and we can use it guide clinicians to certain pathologies and appropriate treatments as well as enhancing risk for sudden cardiac death.
HRV is a large and growing subject and certainly not easy to master or even explain clearly and concisely. To understand basically how this works, the PNS (Parasympathetic Nervous System), which if you remember from the first article in this series is the ‘rest and digest’ branch, has an immediate impact on the heart rate due to the role of something called the vagus nerve (a nerve that runs from the brain directly into the heart). The SNS (Sympathetic Nervous System) or ‘flight or fight’ branch has a delayed impact on the heart – it takes around 5 seconds – this does not have a direct route to the heart.
So by measuring beat-to-beat analysis over a period of time, or even, right here in the now, we can see how hard each branch is working and functioning. As heart rate fluctuates from each beat, this tells a story as to how each branch of the ANS is influencing the physiology.
We want, in general physiology terms, an equal functioning of both systems – you want to be able to react to stress, but also be able to ‘unwind’ as well. This will maintain things such as the resting heart rate in what is considered a healthy range. When stress occurs, we want the SNS to kick in and do its job – helping the body to overcome whatever it is that requires action. However, higher SNS activity is linked to such things as ventricular fibrillation (a condition where the heart rhythm is altered that can be life threatening), higher heart rates and blood pressures. The PNS is cardio-protective, so quite quickly you can figure out which system you don’t want to be prevalent in.
In a vast array of medical conditions HRV can become deranged. For example, diabetes, hypertension and even obesity are know to diminish HRV, equalling increased sympathetic drive. It is now becoming clear that even amongst people who appear to be healthy, abnormal patterns of HRV can develop and as a result represent a predisposition to disease.
Mental stress is now recognised at disturbing normal patterns of HRV, which results in increased SNS activity and diminished PNS influence. How many people do we know that have mental stress!!? How many of ourselves have mental stress?
Ok, clearly not all of us have fell into puddles of stress related heart attacks, which later on in the series I will address why. However, Cardiovascular Disease (CVD) in the Western World is massive, and HRV is the first step to understanding if you are at risk, and more importantly, what lifestyle changes are working to reverse that back whilst its still possible.
During the next part, as we delve a bit deeper, I will be talking in more detail about SNS dominance and what that can lead to in regards to digestion, sex, hormones and much more.