Heart Rate Variability is the only real competing technology. CVT is significantly more capable than Heart Rate Variability (HRV) at measuring Fatigue, Stress and uniquely, the ability to determine when a person is about to enter stage 1 sleep.
The technology used for HRV calculations and the NeuroScope/ProCVT systems are quite different, and unlike measurement of CVT, measurement of HRV is not yet a diagnostic procedure that can be used in a wide clinical practice. In fact the Neuroscope technology (which ProCVT uses) was developed specifically to overcome all the difficulties with HRV.
The main issue is that HRV uses a surrogate index that is dependant on the variability of heart rate influenced by multiple physiological alterations in bodily functions, such as breathing rate or temperature regulation. It is based on imprecise generalisations and assumptions and is more of a measure of the ratio of sympathetic vs parasympathetic than purely a measure of the parasympathetic. It is not standard and can’t be used to compare across subjects. It has been likened to measuring the temperature of a glass of water by putting your finger in, rather than using a digital thermometer (ie the Neuroscope and ProCVT).
Other technical shortcomings of HRV in autonomic measurement can be summarized as follows:
- HRV requires a stationary condition in the autonomic nervous system which cannot be achieved in a conscious person.
- HRV requires a constant rate of data sampling which is prevented by the variability of the heart rate itself.
- HRV requires a minimum number of data points to achieve acceptable resolutions. This requires a measurement window possibly as long as 500 seconds. Therefore it is not suitable for use in real time applications.
- It is practically impossible to directly compare figures of HRV from multiple centres as there is no standardized scale of measurement and no absolute zero reference point.