Abstract
Ultra-short heart rate variability (HRV) analysis refers to the study of HRV features in excerpts of length <5 min. Ultra-short HRV is widely growing in many healthcare applications for monitoring individual's health and well-being status, especially in combination with wearable sensors, mobile phones, and smart-watches. Long-term (nominally 24 h) and short-term (nominally 5 min) HRV features have been widely investigated, physiologically justified and clear guidelines for analysing HRV in 5 min or 24 h are available. Conversely, the reliability of ultra-short HRV features remains unclear and many investigations have adopted ultra-short HRV analysis without questioning its validity. This is partially due to the lack of accepted algorithms guiding investigators to systematically assess ultra-short HRV reliability. This Letter critically reviewed the existing literature, aiming to identify the most suitable algorithms, and harmonise them to suggest a standard protocol that scholars may use as a reference in future studies. The results of the literature review were surprising, because, among the 29 reviewed papers, only one paper used a rigorous method, whereas the others employed methods that were partially or completely unreliable due to the incorrect use of statistical tests. This Letter provides recommendations on how to assess ultra-short HRV features reliably and proposes an inclusive algorithm that summarises the state-of-the-art knowledge in this area.
Highlights
IntroductionThe dynamic modulation of heart rate (HR) is controlled by the several voluntary and involuntary mechanisms, including respiration, thermoregulation and the interaction of the sympathetic (which has a response time in the order of a few seconds) and parasympathetic activities (which works much faster: response time 0.2–0.6 s) [1]
The dynamic modulation of heart rate (HR) is controlled by the several voluntary and involuntary mechanisms, including respiration, thermoregulation and the interaction of the sympathetic and parasympathetic activities [1]
Since clear guidelines on ultra-short HR variability (HRV) analysis are not available yet, this review aimed to explore to what extent ultra-short HRV features can be used to estimate short-term ones, which are still to be considered as a benchmark for HRV analysis
Summary
The dynamic modulation of heart rate (HR) is controlled by the several voluntary and involuntary mechanisms, including respiration, thermoregulation and the interaction of the sympathetic (which has a response time in the order of a few seconds) and parasympathetic activities (which works much faster: response time 0.2–0.6 s) [1]. A much stronger condition than correlation is required to be sure that a surrogate is valid and can be used to replace a real clinical outcome Another common misconception is that a marker X can be considered a good surrogate of a clinical outcome Y if statistical null-hypothesis tests demonstrate no-significant differences between X and Y. This is a major misconception because statistical differences may reveal themselves only in particular conditions (e.g. when a sufficient number of measures are observed). Both correlation and statistical tests are often used improperly (e.g. parametric tests used for nonnormally distributed features)
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