Analysis of Heart Rate Variability
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Abstract:
The practice of medicine has long been an art of managing snapshots in time. Clinically, daily decisions are based on labs, x-rays, and ECGs. These studies work well to diagnose many acute illnesses, such as infections, fractures, and heart attacks. As clinicians, we focus on these isolated snapshots of single systems. Given technologic advances in data collection, storage, and analysis, we should be able to extract more information by considering the complex nature of health.
A central problem in medicine is the early recognition of illness. Health is not a single state but is dynamically complex in its robustness to physiologic stressors. Loss of robustness, or decomplexification, appears to forecast deterioration of health.
To date, assessments of robustness and outcome (APACHE scores, SOFA scores, etc) have been made largely through population statistics. I seek to find the earliest evidence of loss of robustness in individuals. In other words, I hope to explore the relationship between dynamic complexity and health in a single individual, and to use this information to make predictions about his or her outcome. Subtle disruption of physiologic complex systems may yield prognostic information helpful in early intervention and the design of novel treatment algorithms.
Our hypothesis is that robustness, namely the ability to compensate for a physiologic stress, can be inferred from the dynamics of a free-running physiologic system in the basal state. Using a set of approximately 300 cardiac exercise stress tests, we aim to predict the response to the stress (specifically rate of heart rate increase and loss of heart rate variability) from the initial (basal, free-running) segment, predict the rate of recovery (rate of heart rate decrease, recovery of variability) when the stress is removed, and be able to classify the results of the stress test as "normal" or "abnormal" based solely on analysis of the dynamic complexity, using the official interpretation as the gold standard.