Abstract
Cardiovascular disease (CVD) is the leading cause of death and disability worldwide. The understanding of the risk factors for CVD may yield important insights into the prevention, etiology, course, and treatment of this major public health concern. Autonomic imbalance, characterized by a hyperactive sympathetic system and a hypoactive parasympathetic system, is associated with various pathological conditions. Over time, excessive energy demands on the system can lead to premature aging and diseases. Therefore, autonomic imbalance may be a final common pathway to increased morbidity and mortality from a host of conditions and diseases, including cardiovascular disease. Heart rate variability (HRV) may be used to assess autonomic imbalances, diseases and mortality. Parasympathetic activity and HRV have been associated with a wide range of conditions including CVD. Here we review the evidence linking HRV to established and emerging modifiable and non-modifiable CVD risk factors such as hypertension, obesity, family history and work stress. Substantial evidence exists to support the notion that decreased HRV precedes the development of a number of risk factors and that lowering risk profiles is associated with increased HRV. We close with a suggestion that a model of autonomic imbalance may provide a unifying framework within which to investigate the impact of risk factors, including psychosocial factors and work stress, on cardiovascular disease.
Keywords
Heart rate variability, Risk factors, Work stress, Heart disease, Hypertension
Introduction
Recent research has strongly suggested that negative affective states, dispositions and work stress are associated with diseases and ill health [1–7]. Work stress, in particular, has been associated with substantial economic consequences, including increased absenteeism, increased worker turnover, decreased worker job satisfaction and
associated decreases in worker productivity [8,9]. Stress at work is also a major public health risk associated with cardiovascular morbidity [10,11]. Cardiovascular disease (CVD) is the leading cause of morbidity and mortality in both men and women. This is particularly true in developed countries [12,13]. A wide range of risk factors for CVD have been identified but as yet a unified model that can account for this diversity of risk factors has not been put forward. A recent report from the Whitehall Study [11] has shown that work stress is associated with decreased heart rate variability (HRV). Decreased HRV is an independent risk factor for morbidity and mortality. The important role that the vagus nerve plays in health and disease has been known for some time [14]. However, only relatively recently have researchers and clinicians started to investigate how this knowledge can be incorporated into a greater understanding of the etiology, manifestations, course, outcomes, and treatment of disease. In this illustrative review we show that autonomic imbalance, in which vagal inhibitory influences are deficient, is associated with increased morbidity and all-cause mortality. We also review evidence linking vagal function to established and emerging risk factors including work stress, for CVD and mortality. Importantly, we discuss evidence that factors that increase HRV are associated with decreased risk and an improved health profile. Thus, the model of autonomic imbalance may provide a unified approach to the understanding of the role of HRV in the risk for cardiovascular disease and all-cause mortality.
Summary
In this paper we have tried to provide an overview of some of the evidence for the role of HRV in cardiovascular disease risk and mortality. Although not exhaustive, this review shows that there is a large body of data to suggest that decreased vagal function is an independent risk factor for all-cause mortality. In addition, we examine evidence that decreased vagal function is a common factor in all of the major risk factors for CVD, both modifiable and non-modifiable. Furthermore, we showed that decreased vagal function characterizes emerging psychosocial risk factors. Importantly, the evidence presented here also strongly suggests that work stress is associated with decreased HRV. Work stress itself is a major risk factor for cardiovascular morbidity and research suggests that one of the major pathways involves decreased HRV. We also note that the effects of modifiable risk factors might be prevented or minimized by engaging in behaviors that might increase HRV. Moreover, studies that include indices of both sympathetic and parasympathetic activity are necessary to provide a more complete picture of the role of the ANS in health and disease [89]. Finally, we suggested that autonomic imbalance might be the final common pathway linking a host of disorders and conditions to death and disease. Thus, behaviors that alter this autonomic imbalance toward a more salubrious profile may serve to prevent or at least minimize the effects of certain factors on the risk for cardiovascular disease and death.
Acknowledgements
We would like to thank Tammy N. Sadle for her assistance with the tables. The authors of this manuscript have certified that they comply with the Principles of Ethical Publishing in the International Journal of Cardiology [90].