Role of parasympathetic (vagal) cardiac control in elevated heart rates of smokers

A healthy heart is not a metronome: an integrative review of the heart's anatomy and heart rate variability

Heart rate variability (HRV), the change in the time intervals between adjacent heartbeats, is an emergent property of interdependent regulatory systems that operate on different time scales to adapt to challenges and achieve optimal performance. This article briefly reviews neural regulation of the heart, and its basic anatomy, the cardiac cycle, and the sinoatrial and atrioventricular pacemakers. The cardiovascular regulation center in the medulla integrates sensory information and input from higher brain centers, and afferent cardiovascular system inputs to adjust heart rate and blood pressure via sympathetic and parasympathetic efferent pathways. This article reviews sympathetic and parasympathetic influences on the heart, and examines the interpretation of HRV and the association between reduced HRV, risk of disease and mortality, and the loss of regulatory capacity. This article also discusses the intrinsic cardiac nervous system and the heart-brain connection, through which afferent information can influence activity in the subcortical and frontocortical areas, and motor cortex. It also considers new perspectives on the putative underlying physiological mechanisms and properties of the ultra-low-frequency (ULF), very-low-frequency (VLF), low-frequency (LF), and high-frequency (HF) bands. Additionally, it reviews the most common time and frequency domain measurements as well as standardized data collection protocols. In its final section, this article integrates Porges' polyvagal theory, Thayer and colleagues' neurovisceral integration model, Lehrer et al.'s resonance frequency model, and the Institute of HeartMath's coherence model. The authors conclude that a coherent heart is not a metronome because its rhythms are characterized by both complexity and stability over longer time scales. Future research should expand understanding of how the heart and its intrinsic nervous system influence the brain.

Preliminary evidence of parasympathetic influence on basal heart rate in posttraumatic stress disorder

OBJECTIVE

Evidence of elevated basal heart rate (HR) in posttraumatic stress disorder (PTSD) has been interpreted in terms of elevated sympathetic cardiac activity, as have possible increased cardiovascular disease risks and outcomes associated with elevated HR. Yet it is well-established that the parasympathetic branch of the autonomic nervous system not only influences HR independently of the sympathetic branch, but makes a greater contribution to HR, including resting HR. Additionally, abnormally low tonic parasympathetic activity on the heart has been implicated in cardiovascular disease and hypertension. This study addressed a potential parasympathetic contribution to elevated basal HR in PTSD.

METHODS

We used a descriptive and subgroup differences approach to investigate relationships between parasympathetic activity and basal HR in 59 adults (50 females) with PTSD, all of whom were participants in a treatment outcome study and assessed prior to exposure to trauma-related script-driven imagery. Consistent with the well-known relationship between parasympathetic activity and HR, we hypothesized that basal respiratory sinus arrhythmia (RSA), a measure of parasympathetic cardiac activity, would be negatively correlated with basal HR. More important, we predicted that pathologically elevated HRs previously associated with PTSD would only characterize a low-RSA subgroup. Potential confounds of age, respiration rate, and aerobic fitness were addressed.

RESULTS

As predicted, mean HR was 80.5 bpm in the low-RSA tercile group, similar to mean HRs of PTSD groups in prior research and significantly higher than 69 and 65 bpm in the middle- and high-RSA groups, respectively, which are typical of non-PTSD controls.

CONCLUSION

These findings suggest that a substantial proportion of those with PTSD may not have elevated basal HRs. Furthermore, among those who do exhibit elevated HR, there may be a parasympathetic contribution that is independent of any sympathetic one. Only measuring both branches at once, ideally with autonomic blockades, can definitively address these issues.

Increased resting heart rate with pollutants in a population based study

BACKGROUND

Air pollution is associated with cardiovascular mortality. Changes in the autonomic nervous system may contribute to cardiac arrhythmias and cardiovascular mortality. This study investigated the relations between air pollutant concentrations of sulphur dioxide (SO(2)), ozone (O(3)), nitric dioxide (NO(2)), and resting heart rate (RHR) in a population based study.

METHODS

A sample of 863 middle aged men and women, living in Toulouse (MONICA centre) area, was randomly recruited. A cross sectional survey on cardiovascular risk factors was carried. RHR was measured twice in a sitting position after a five minute rest. Multivariate analyses with quintiles of RHR were performed using polytomous logistic regression. Models were adjusted for temperature, season, relative humidity, sex, physical activity, blood pressure, C reactive protein, and cardiovascular drugs.

RESULTS

For NO(2), the OR (odds ratio) (95% CI) associated with an increase of 5 microg/m(3) in the current day of medical examination was 1.14 (1.03 to 1.25) in quintile Q5 of RHR compared with Q1, p for trend = 0.003. For SO(2), OR was 1.16 (0.94 to 1.44) in Q5 compared with Q1, p for trend = 0.05, and for O(3), OR was 0.96 (0.91 to 1.01) in Q5 compared with Q1, p for trend = 0.11. No significant association was seen when the daily mean concentration of NO(2), SO(2), and O(3) was considered during the previous day as well as when day lag 2 or 3 was considered. The cumulative concentration (three consecutive days) of O(3) is negatively associated with RHR (p for trend = 0.02).

CONCLUSION

Changes in pulse rate could reflect cardiac rhythm changes and may be part of the pathophysiological link between pollution and cardiovascular mortality.