In the past decade, heart rate variability (HRV) has emerged as an intriguing parameter for interrogation of autonomic nervous system functioning. It relies on the physiologic phenomenon of changing heart rate with respiration, a process heavily reliant on input from the parasympathetic and sympathetic nervous systems. A decrease in this variability has been shown in various studies to predict mortality and other adverse outcomes in certain populations (such as post-MI patients, critically ill neurosurgery patients, and severe sepsis), and correlates with pathologies of autonomic dysfunction.
HRV is commonly measured using spectral analysis of R-R intervals from an EKG tracing. Time and frequency domain analyses generate parameters which can be used to assess the ratio of sympathetic to parasympathetic tone.
Intellewave was designed as a stand-alone fully automated cardiac monitoring device that utilizes frequency domain analysis to provide real-time quantitative assessment of HRV. It utilizes artificial intelligence technology to differentiate between high frequency (HF) and low frequency (LF) components, which respectively represent parasympathetic and mixed sympathetic/parasympathetic tone. How best to interpret the parameters generated by HRV analysis requires further research to define.
The novelty of Intellewave’s Nerve Express algorithm lies in its accessibility. It was compared to the gold standard CHRONOS algorithm and found to be similar, but had the benefit of not relying on Holter monitoring and technician-dependent data gathering. Instead it is a stand-alone automated system that could be used in an office setting.
Potential applications for Intellewave in the perioperative setting are varied and largely unexplored. There is potential use for preoperative risk stratification of patients who may be more likely to suffer cardiovascular instability intraoperatively on the basis of dysfunctional autonomic activity, allowing the anesthesiologist to better plan to counteract these events. Postoperatively, there is potential for predicting which patients may suffer poor outcomes and being more aggressive about their prevention.
There are many confounding influences on HRV which limit its applications. Medications, a litany of pathologies and stressors all influence the autonomic nervous system, which in turn has broad effects on so many physiologic functions. It would be difficult to interpret HRV parameters given these confounders. Nonetheless, ongoing research is underway in attempt to better understand its possible applications.