Changes in heart rate variability pre and postoperative coronary artery bypass grafting

Introduction and objectives: Previous studies have shown that after coronary artery bypass grafting (CABG), heart rate variability (HRV) becomes decreased. The loss of the peripheral autonomic sympathetic and parasympathetic control in Sinoatrial Node in the form of an autonomic cardioneuropathy syndrome is the predictor of the pre and postoperative complications after CABG. The aim of this study was to establish the temporal pattern of change in the decrease of HRV observed after CABG. Methods: The study involved 119 consecutive patients who underwent the first CABG operation with sinus rhythm. All subjects underwent assessed with 24-hour Holter recordings 2 days preoperative and 7 days, 3 months, 6 months postoperative at Hanoi Heart Hospital from 6/2016 to 8/2018. Main results: All indicators of heart rate variability decreased to the lowest level after surgery 7 days, recovers to the preoperative values within three to six months of the procedure. The incidence of pre and postoperative low HRV varies from 28.6% (preop) to 51.8% (postop 7 days), 19.6% (postop 3 months) and 12.7% (postop 6 months). Conclusions: This study have showed that CABG surgery generally leads to significant reduction in HRV. HRV gradually recovers to the preoperative values within three to six months of the procedure.

Sensitivity to changes in rate of heartbeats as a measure of interoceptive ability

Individuals vary in their ability to perceive, as conscious sensations, signals like the beating of the heart. Tests of such interoceptive ability are, however, constrained in nature and reliability. Performance of the heartbeat tracking task, a widely used test of cardiac interoception, often corresponds well with individual differences in emotion and cognition, yet is susceptible to reporting bias and influenced by higher order knowledge, e.g. of expected heart rate. The present study introduces a new way of assessing cardiac interoceptive ability, focusing on sensitivity to short-term, naturalistic changes in frequency of heartbeats. At rest, such heart rate variability typically reflects the dominant influence of respiration on vagus parasympathetic control of the sinoatrial pacemaker. We observed an overall tendency of healthy participants to report feeling fewer heartbeats during increases in heart rate, which we speculate reflects a reduction in heartbeat strength and salience during inspiratory periods when heart rate typically increases to maintain a stable cardiac output. Within-participant performance was more variable on this measure of cardiac interoceptive sensitivity relative to the 'classic' heartbeat tracking task. Our findings indicate that cardiac interoceptive ability, rather than reflecting the veridical monitoring of subtle variations in physiology, appears to involve more interpolation wherein interoceptive decisions are informed by dynamic working estimates derived from the integration of afferent signalling and higher order predictions.

Study of sympathetic and parasympathetic control of haemodynamics in mid pregnancy by cardiac autonomic neuropathy analyzer

Pregnancy is associated with substantial changes in cardiovascular system. The action of autonomic nervous system is essential for circulatory adaptations in pregnancy and nourishing growing fetus. The study was conducted to assess the significance of autonomic function tests amongst women of mid pregnancy and non pregnant women. A comparative study was caried out amongst pregnant and non pregnant women in Department of Physiology. A total of 60 women (30 pregnant as study group and 30 non pregnant healthy women as control group) aged between 18- 30 years were included in study. The results indicated that there was statistically significant change in resting heart and highly statistically significant change to deep breathing in mid pregnancy reflecting higher parasympathetic activity in study group (pregnant female) as compared to control group (non pregnant female) while sympathetic activity assessed by isometric hand grip test didn’t show any statistically significant change among pregnant as compared to non pregnant. Our study showed role of parasympathetic activity in controlling haemodynamics in mid pregnancy and it may help to return the arterial pressure to non pregnant level by causing haemodilution, although when the increase in activity is excessive, hypertension may ensue.

Renal, Cardiac, and Autonomic Effects of Catheter-Based Renal Denervation in Ovine Heart Failure

A growing number of clinical studies suggest that in heart failure renal denervation (RDN) has beneficial effects on the autonomic control of the heart. There is also experimental evidence that surgical RDN improves sodium handling and clearance in heart failure. The aim of this study was to determine the effects of catheter-based RDN on the sympathetic and parasympathetic control of the heart, and salt and water handling capacity of the kidneys, in sheep with established heart failure. A randomized, controlled study was conducted in 10 sheep with heart failure (ejection fraction<40%) induced by rapid ventricular pacing. Sheep underwent either bilateral RDN using the Symplicity denervation system or sham denervation and were studied 1 and 6 weeks after RDN. In established ovine heart failure, at 6 weeks after catheter-based RDN, heart rate significantly decreased, estimates of resting and maximal parasympathetic control of heart rate increased, and cardiac sympathetic nerve activity decreased. Compared with sham denervation, there was an increase in the resting sodium and water excretion 6 weeks after catheter-RDN and an improved ability of the kidneys to excrete a nonhypertensive saline load. After catheter-based RDN, renal norepinephrine levels were reduced by 70% compared with sham denervation. In established heart failure, RDN induced a beneficial shift in both arms of the autonomic nervous control of the heart and improved the ability of the kidneys to excrete sodium and water. Thus, effective catheter-based RDN may be beneficial to both the heart and kidneys in heart failure.

Inhibition of G-protein signalling in cardiac dysfunction of intellectual developmental disorder with cardiac arrhythmia (IDDCA) syndrome

BackgroundPathogenic variants of GNB5 encoding the β5 subunit of the guanine nucleotide-binding protein cause IDDCA syndrome, an autosomal recessive neurodevelopmental disorder associated with cognitive disability and cardiac arrhythmia, particularly severe bradycardia.MethodsWe used echocardiography and telemetric ECG recordings to investigate consequences of Gnb5 loss in mouse.ResultsWe delineated a key role of Gnb5 in heart sinus conduction and showed that Gnb5-inhibitory signalling is essential for parasympathetic control of heart rate (HR) and maintenance of the sympathovagal balance. Gnb5−/− mice were smaller and had a smaller heart than Gnb5+/+ and Gnb5+/−, but exhibited better cardiac function. Lower autonomic nervous system modulation through diminished parasympathetic control and greater sympathetic regulation resulted in a higher baseline HR in Gnb5−/− mice. In contrast, Gnb5−/− mice exhibited profound bradycardia on treatment with carbachol, while sympathetic modulation of the cardiac stimulation was not altered. Concordantly, transcriptome study pinpointed altered expression of genes involved in cardiac muscle contractility in atria and ventricles of knocked-out mice. Homozygous Gnb5 loss resulted in significantly higher frequencies of sinus arrhythmias. Moreover, we described 13 affected individuals, increasing the IDDCA cohort to 44 patients.ConclusionsOur data demonstrate that loss of negative regulation of the inhibitory G-protein signalling causes HR perturbations in Gnb5−/− mice, an effect mainly driven by impaired parasympathetic activity. We anticipate that unravelling the mechanism of Gnb5 signalling in the autonomic control of the heart will pave the way for future drug screening.

GENDER-SPECIFIC DIFFERENCES OF CARDIAC VEGETATIVE CONTROL IN ADRENALINE-INDUCED NECROSIS AND LIGHT DEPRIVATION

Background. Cardiovascular disease is the main cause of morbidity predominantly in males. Stress is one of the crucial factors, especially with light desynchronosis. Objective of the study was to assess gender-specific characteristics of cardiac vegetative control in myocardial necrosis in cases of light deprivation. Methods. Cardiac vegetative control in adrenaline-induced myocardial necrosis (AIMN) in a setting of light deprivation (LD) was assessed in 72 mature white rats of both sexes. The animals were divided into 2 groups: G1 – the animals kept under day/night cyclic balance (12 hours/12 hours); G2 – the animals kept at LD (illumination 0.5-1 LX) for 10 days. On Day 11, AIMN caused by adrenaline (0.5 mg/kg) and heart rate variability (HRV) was assessed in 1 hour and 24 hours. Results. The development of AIMN at LD in the ♂G2 led to HRV increase that was caused by augmentation of parasympathetic and reduction of sympathetic cardiac effects. In cases of AIMN, changes of CVC in the ♀G2 were similar to the ♀G1. However, in 1 hour of AIMN, parasympathetic cardiac effects were more significant than in the ♀G1. While the ♀G2 AIMN animals experienced balanced sympathetic and parasympathetic actions, the predominance of the sympathetic component was evidenced in the ♀G1 AIMN animals. Conclusions. Light deprivation has different effects on baseline sympathetic/parasympathetic balance in males and females, i.e. increased parasympathetic control of heart rhythm in males and maintenance of sympathetic/ parasympathetic balance in females.

A common neural substrate for elevated PTSD symptoms and reduced pulse rate variability in combat-exposed veterans

BackgroundPrevious studies have identified reduced heart rate variability (HRV) in posttraumatic stress disorder (PTSD), which may temporally precede the onset of the disorder. A separate line of functional neuroimaging research suggests that the ventromedial prefrontal cortex (vmPFC) — a key aspect of a descending neuromodulatory system that exerts inhibitory control over heart rate — shows functional and structural abnormalities in PTSD. No research to date, however, has simultaneously investigated whether altered vmPFC activation is associated with reduced HRV and elevated PTSD symptoms in the same individuals.MethodsWe collected fMRI data during alternating conditions of threat of shock and safety from shock in 51 male, combat-exposed veterans with either high or low levels of PTSD symptoms. Pulse rate variability (PRV) – an HRV surrogate calculated from pulse oximetry – was assessed during a subsequent resting scan. Correlational analyses tested for hypothesized relationships between vmPFC activation, PRV, and distinct dimensions of PTSD symptomatology.ResultsRe-experiencing PTSD symptoms were inversely associated with high-frequency (HF)-PRV, thought to primarily reflect parasympathetic control of heart rate, in veterans with elevated PTSD symptoms. Lower HF-PRV was associated with reduced vmPFC activation for the contrast of safety-threat in a region that also showed an inverse relationship with re-experiencing symptoms.ConclusionsReduced vmPFC responses to safety vs. threat were associated with both reduced HF-PRV and increased re-experiencing symptoms. These results tie together previous observations of reduced HRV/PRV and impaired vmPFC function in PTSD and call for further research on reciprocal brain-body relationships in understanding PTSD pathophysiology.

Evaluating the Effectiveness of Graduated Stress Exposure in Virtual Spaceflight Hazard Training

Psychological and physiological stress experienced by astronauts can pose risks to mission success. In clinical settings, gradually increasing stressors help patients develop resilience. It is unclear whether graduated stress exposure can affect responses to acute stressors during spaceflight. This study evaluated psychophysiological responses to potentially catastrophic spaceflight operation, with and without graduated stress exposure, using a virtual reality environment. Twenty healthy participants were tasked with locating a fire on a virtual International Space Station (VR-ISS). After orientation, the treatment group ( n = 10) practiced searching for a fire while exposed to a low-level stressor (light smoke), while the control group ( n = 10) practiced without smoke. In the testing session, both groups responded to a fire while the VR-ISS unexpectedly filled with heavy smoke. Heart rate variability and blood pressure were measured continuously. Subjective workload was evaluated with the NASA Task Load Index, stress with the Short Stress State Questionnaire, and stress exposure with time-to-complete. During the heavy smoke condition, the control group showed parasympathetic withdrawal, indicating a mild stress response. The treatment group retained parasympathetic control. Thus, graduated stress exposure may enhance allostasis and relaxation behavior when confronted with a subsequent stressful condition.