Sympathetic neurohemodynamic transduction is attenuated in older males independent of aerobic fitness

Clinical Autonomic Research -     

Impact of sampling duration on spontaneous sympathetic transduction

Clinical Autonomic Research -     

Case study: a health check-up for the corporate IT department

As advances such as the electronic charting, closed-loop medication safety, physician order entry, consumer portals, electronic collaboration, and wireless access become the norm, central IS organizations are finding it difficult to keep pace. This challenge is exacerbated by declining margins, severe cost pressures, increased regulation, and added public scrutiny. Is your centralized IS organization healthy enough to meet the challenges presented by today's complex, demanding, dynamic healthcare delivery environments? How do you know? What factors do you consider?     

Cardiac mechanoreceptor function implicated during premature ventricular contraction

In a premature ventricular contraction (PVC), a systolic blood pressure peak is missing during the affected cardiac cycle, leading to a prolonged reduction in blood pressure which is then followed by a large burst of sympathetic outflow. In a normal ventricular contraction, it is generally believed that peak carotid and aortic distensions associated with systolic pressure is the neural feedback that terminates sympathetic outflow through a baroreflex mechanism. Yet, the characteristically large sympathetic burst following a PVC is terminated without a systolic pressure and evidently without this mechanism. To address this anomaly, we examined the possible role of cardiac receptors in providing an alternative mechanism for the termination of sympathetic outflow in a PVC. For this purpose, recordings of electrocardiogram (ECG), arterial blood pressure (ABP), and muscle sympathetic neural activity (MSNA) were made in a human subject during repeated PVC episodes. The time intervals, or "latencies", from key events within the PVC to the peak of the associated MSNA burst were calculated and compared with the latency in a normal ventricular contraction which is associated with central baroreceptor function. It was found that the only event in a PVC that corresponds with a physiologically plausible latency is that which marks the end of ventricular filling. We conclude with the hypothesis that in the unique circumstances of a PVC, where the systolic pressure peak required to trigger arterial baroreceptors to terminate sympathetic outflow is absent, mechanoreceptors in the heart appear to "step in" to perform this sympathoinhibitory function.     

Meeting international aerobic physical activity guidelines is associated with enhanced cardiovagal baroreflex sensitivity in healthy older adults

Clinical Autonomic Research - Cardiovagal baroreflex sensitivity (cvBRS) reflects the efficiency of modulating heart rate in response to changes in systolic blood pressure. International guidelines...     

Ventral medial prefrontal cortex and cardiovagal control in conscious humans

The autonomic nervous system plays a critical role in regulating the cardiovascular responses to mental and physical stress. Recent neuroimaging studies have demonstrated that sympathetic outflow to the heart is modulated by the activity of the anterior cingulate cortex (ACC). However, the cortical modulation of cardiovagal activity is still unclear in humans. The present study used functional MRI to investigate the cortical network involved in cardiovagal control. Seventeen healthy individuals performed graded handgrip exercise while heart rate (HR) and cortical activity were recorded. Muscle sympathetic nerve activity (MSNA), mean arterial pressure (MAP) and HR were measured while participants repeated the same protocol in a parallel experiment session. The handgrip exercise elevated HR and MAP without concurrent elevations in MSNA supporting earlier conclusions that the cardiovascular responses are mainly modulated by vagal withdrawal. The imaging data showed activation in the insular cortex, thalamus, parietal cortices and cerebellum during the exercise period. Consistently across all the participants, the HR response correlated with the deactivation in the ventral medial prefrontal cortex (vMPFC), which has substantial anatomical connection with the subcortical autonomic structures. The deactivation of the vMPFC was independent of the motor control and was observed commonly in both left and right hand exercise. Stronger vMPFC deactivation was observed when participants completed a higher intensity exercise that elicited a larger HR response. Our findings support the hypothesis that the vMPFC is involved in modulating the vagal efferent outflow to the heart and the suppression of its activity elevates cardiovascular arousal in conscious humans.     

The relationship between aerobic fitness and low-flow-mediated constriction in older adults

European Journal of Applied Physiology - Aerobic fitness is directly related to favorable vasodilatory (i.e., flow-mediated dilation; FMD) and vasoconstrictor functions (i.e., low-flow-mediated...