This literature review was carried out according to a systematic protocol, commonly used ( 2, 3).

These categories will be detailed and a synthesis of the links between them will be further presented with a diagram of influences. Actually, with the specific methodology described below, the categorization phases of this study could point out five main themes among the counted elements: physiological and pathological factors, lifestyle factors, non-modifiable factors, neuropsychological factors and environmental factors. Knowing all the environmental and physiological factors and how they can influence amongst themselves will help to build more precise research protocols and also help clinicians in their daily practice for treatment and recommendations to their patients. The originality of this literature review is to analyze the numerous previous reviews and meta-analyses in order to present an overview of the problem, to create a comprehensive map of the main factors influencing HRV. There were very numerous studies, such that HRV is now commonly used as a health indicator.ĭespite all of these numerous studies and reviews, none was carried out to regroup all the information.

Actually, many specific reviews already focused on HRV in order to described in precise details how specific brain areas are affecting HRV, how heart dysfunctions can influence individual health, how respiration induces heart acceleration or deceleration, how stress factors act on the heart, and so on.

One can therefore wonder what kind of factors can directly influence HRV. Among the pathologies affecting HRV the most, there are the cardiovascular diseases (CVD) and depressive disorders. Alternatively, a reduced HRV is a symptom of health problems and can affect immune functions, self-regulation and psychosocial abilities ( 1). A high HRV is the sign that the heart is healthy since it has more flexibility to react to any stress (physiological or environmental). This adaptation is called heart rate variability (HRV) and can also be characterized in terms of amplitude: weak, normal or high. It reacts to any stimulus by increasing or decreasing its rhythm so that the body can adapt to any change. Because of the influence of many factors, the heart does not maintain the exact same rhythm from one heartbeat to the next. With its strategic position, the heart acts not only as the main pump but also as a global coordinator in synchronism with the other body functions. We vibrate, our hearts are pumping blood, we are a rhythm machine, that’s what we are.” - Mickey Hart. This diagram can therefore serve as a basis to improve daily clinical practice as well as help design even more precise research protocols. The direct interrelationships between these factors and HRV can be regrouped into an influence diagram. The system of these factors affecting HRV can be divided into the following five categories: physiological and pathological factors, environmental factors, lifestyle factors, non-modifiable factors and effects. The primary objective of this research is therefore to conduct a literature review in order to get a comprehensive overview of the subject. In order to better understand how this adaptation takes place, it is necessary to examine which factors directly influence HRV, whether they have a physiological or environmental origin. Consequently, HRV is now widely used as an index of health. In fact, among the pathologies affecting HRV the most, there are the cardiovascular diseases and depressive disorders, which are associated with high medical cost in Western societies.

Heart rate variability (HRV) corresponds to the adaptation of the heart to any stimulus.

Heart rate coherence pro