Intrinsic variability is a characteristic of all complex systems and is a feature of all oscillating physiological processes. Variability is measured then mapped using different mathematical models. These models reveal underlying patterns and their relationships to other variables.
It turns out that the nature and structure of intrinsic variability in physiological processes can be an indicator of health status and a predictor of disease risk.
Perhaps the most well understood and clinically significant intrinsic variable in human physiology is Heart Rate Variability (HRV). HRV is a measurement of the beat-to-beat changes in heart rate. HRV was identified by Western physiologists about 100 years ago. At that time there was a clear understanding that this phenomena was related to respiratory movements – so called Respiratory Sinus Arrhythmia (RSA). RSA refers to the effect of, fluctuations in breathing, on cardiac pacemaker cells which regulate heartbeat.
In more recent times our understanding of HRV has been enriched by polyvagal theory which connects physiology to social engagement.
Original measurements of HRV were thought to be artefacts and dismissed by some prominent psychophysiologists. However the advent of analytical computational algorithms, polygraphic recording and later the cardiotachograph enabled precise quantification of beat-to-beat fluctuations in heart rate. Subsequent research has demonstrated that HRV is a ‘superimposed sum of several rhythmic heart rate oscillations and slow trends..covarying with metabolic demand’ (Stephen Porges, 2007).
The interdependence and interactions between intrinsic variables, like those seen in HRV, are common to all complex systems and processes. Development and growth, metabolic regulation, climate and ocean currents are all expressions of multiple oscillating, interacting and interdependent intrinsic variables. Complex systems are self-regulating, resilient and non-deterministic. Intrinsic variability is the ‘stuff’ that integrates multiple physiological systems and enables novel, emergent and adaptive responses.
FEATURED IMAGE:
Renart & Machens. Variability in neural activity and behaviour (2014).