The yin and yang of cardiac autonomic control: vago-sympathetic interactions revisited

Drowning incidents precipitated by unusual causes (DIPUCs): A narrative review of their diagnoses, evaluation and management

Drowning is a cause of significant morbidity and mortality worldwide. In most circumstances, the proximate cause is attributable to human factors, such as inexperience, fatigue, intoxication, or hazardous water conditions. The phenomenon of drowning incidents precipitated by unusual circumstances (DIPUCs) - either fatal or nonfatal - involving otherwise healthy individuals under generally safe conditions has not been comprehensively addressed in the medical and drowning literature to date. In this review, we discuss etiologies of DIPUCs, diagnostic clues, suggested workup, suggested postmortem testing, and implications for surviving patients and families. Identifying the cause of a drowning incident can be extremely challenging for the initially treating physician, relying perforce on historical context, environmental clues, physical exam, medical history, eyewitness accounts or video recordings. If no clear explanation for a drowning incident emerges despite a thorough investigation, clinicians should consider some of the less common diagnoses we describe in this paper, and, when appropriate, refer for an autopsy with postmortem molecular genetic testing. While time-consuming, these efforts can prove life-saving for some non-fatal drowning victims and the families of all victims of DIPUCs.

Linking brain-heart interactions to emotional arousal in immersive virtual reality

The subjective experience of emotions is linked to the contextualized perception and appraisal of changes in bodily (e.g., heart) activity. Increased emotional arousal has been related to attenuated high-frequency heart rate variability (HF-HRV), lower EEG parieto-occipital alpha power, and higher heartbeat-evoked potential (HEP) amplitudes. We studied emotional arousal-related brain-heart interactions using immersive virtual reality (VR) for naturalistic yet controlled emotion induction. Twenty-nine healthy adults (13 women, age: 26 ± 3) completed a VR experience that included rollercoasters while EEG and ECG were recorded. Continuous emotional arousal ratings were collected during a video replay immediately after. We analyzed emotional arousal-related changes in HF-HRV as well as in BHIs using HEPs. Additionally, we used the oscillatory information in the ECG and the EEG to model the directional information flows between the brain and heart activity. We found that higher emotional arousal was associated with lower HEP amplitudes in a left fronto-central electrode cluster. While parasympathetic modulation of the heart (HF-HRV) and parieto-occipital EEG alpha power were reduced during higher emotional arousal, there was no evidence for the hypothesized emotional arousal-related changes in bidirectional information flow between them. Whole-brain exploratory analyses in additional EEG (delta, theta, alpha, beta and gamma) and HRV (low-frequency, LF, and HF) frequency bands revealed a temporo-occipital cluster, in which higher emotional arousal was linked to decreased brain-to-heart (i.e., gamma→HF-HRV) and increased heart-to-brain (i.e., LF-HRV → gamma) information flow. Our results confirm previous findings from less naturalistic experiments and suggest a link between emotional arousal and brain-heart interactions in temporo-occipital gamma power.

Neurocardiology: translational advancements and potential

In our original white paper published in the The Journal of Physiology in 2016, we set out our knowledge of the structural and functional organization of cardiac autonomic control, how it remodels during disease, and approaches to exploit such knowledge for autonomic regulation therapy. The aim of this update is to build on this original blueprint, highlighting the significant progress which has been made in the field since and major challenges and opportunities that exist with regard to translation. Imbalances in autonomic responses, while beneficial in the short term, ultimately contribute to the evolution of cardiac pathology. As our understanding emerges of where and how to target in terms of actuators (including the heart and intracardiac nervous system (ICNS), stellate ganglia, dorsal root ganglia (DRG), vagus nerve, brainstem, and even higher centres), there is also a need to develop sensor technology to respond to appropriate biomarkers (electrophysiological, mechanical, and molecular) such that closed-loop autonomic regulation therapies can evolve. The goal is to work with endogenous control systems, rather than in opposition to them, to improve outcomes.

Vasopressin and cardiovascular autonomic adjustment in chronic hypertensive pregnancy

Chronic hypertensive pregnancy (CHP) is a growing health issue with unknown etiology. Vasopressin (VP), a nonapeptide synthesized in paraventricular (PVN) and supraoptic nucleus (SON), is a well-known neuroendocrine and autonomic modulator of the cardiovascular system, related to hypertension development. We quantified gene expression of VP and its receptors, V1aR and V1bR, within the PVN and SON in CHP and normal pregnancy, and assessed levels of secreted plasma VP. Also, we evaluated autonomic cardiovascular adaptations to CHP using spectral indices of blood pressure (BPV) and heart rate (HRV) short-term variability, and spontaneous baroreflex sensitivity (BRS). Experiments were performed in female spontaneously hypertensive rats (SHRs) and in normotensive Wistar rats (WRs). Animals were equipped with a radiotelemetry probe for continuous hemodynamic recordings before and during pregnancy. BPV, HRV and BRS were assessed using spectral analysis and the sequence method, respectively. Plasma VP was determined by ELISA whilst VP, V1aR, and V1bR gene expression was analyzed by real-time-quantitative PCR (RT-qPCR). The results show that non-pregnant SHRs exhibit greater VP, V1aR, and V1bR gene expression in both PVN and SON respectively, compared to Wistar dams. Pregnancy decreased VP gene expression in the SON of SHRs but increased it in the PVN and SON of WRs. Pregnant SHRs exhibited a marked drop in plasma VP concentration associated with BP normalization. This triggered marked tachycardia, heart rate variability increase, and BRS increase in pregnant SHRs. It follows that regardless of BP normalization in late pregnancy, SHRs exhibit cardiovascular vulnerability and compensate by recruiting vagal mechanisms. Pregnant SHR dams have reduced expression of VP in SON associated with increased V1bR expression, lower plasma VP, normal BP during late pregnancy and marked signs of enhanced sympathetic cardiac stimulation (increased HR and LFHR variability) and recruitment of vagal mechanisms (enhancement of BRS and HFHR variability).

More efficient adaptation of cardiovascular response to repeated restraint in spontaneously hypertensive rats: the role of autonomic nervous system

We hypothesized that sympathetic hyperactivity and parasympathetic insuficiency in spontaneously hypertensive rats (SHR) underlie their exaggerated cardiovascular response to acute stress and impaired adaptation to repeated restraint stress exposure compared to Wistar-Kyoto rats (WKY). Cardiovascular responses to single (120 min) or repeated (daily 120 min for 1 week) restraint were measured by radiotelemetry and autonomic balance was evaluated by power spectral analysis of systolic blood pressure variability (SBPV) and heart rate variability (HRV). Baroreflex sensitivity (BRS) was measured by the pharmacological Oxford technique. Stress-induced pressor response and vascular sympathetic activity (low-frequency component of SBPV) were enhanced in SHR subjected to single restraint compared to WKY, whereas stress-induced tachycardia was similar in both strains. SHR exhibited attenuated cardiac parasympathetic activity (high-frequency component of HRV) and blunted BRS compared to WKY. Repeated restraint did not affect the stress-induced increase in blood pressure. However, cardiovascular response during the post-stress recovery period of the 7th restraint was reduced in both strains. The repeatedly restrained SHR showed lower basal heart rate during the dark (active) phase and slightly decreased basal blood pressure during the light phase compared to stress-naive SHR. SHR subjected to repeated restraint also exhibited attenuated stress-induced tachycardia, augmented cardiac parasympathetic activity, attenuated vascular sympathetic activity and improved BRS during the last seventh restraint compared to single-stressed SHR. Thus, SHR exhibited enhanced cardiovascular and sympathetic responsiveness to novel stressor exposure (single restraint) compared to WKY. Unexpectedly, the adaptation of cardiovascular and autonomic responses to repeated restraint was more effective in SHR.

Nocturia and obstructive sleep apnoea

Nocturia, the need to urinate at night, is a common symptom in patients with obstructive sleep apnoea (OSA). Continuous positive airway pressure treatment can reduce nocturia in some patients, but the underlying mechanisms are complex and not fully understood. OSA affects the autonomic nervous system, oxidative stress and endothelial damage. Furthermore, the commonly held theory attributing polyuria to a false signal of cardiac overload and response natriuresis has limitations. A comprehensive approach to the management of nocturia in OSA, considering factors such as comorbidities, medication use, alcohol consumption and lifestyle, is needed. Effective management of nocturia in OSA requires a multidisciplinary approach, and urologists should be aware of the potential effect of OSA on physiology and refer patients for further testing at a sleep centre. In addition to continuous positive airway pressure, other interventions such as oral appliances and surgical obstruction treatment could be beneficial for some patients. Overall, understanding the complex interplay between OSA and nocturia is crucial for optimizing patient outcomes.

Cold stimulation of the oral cavity redistributes blood towards the brain in healthy volunteers

BACKGROUND

The aim of this study was to analyze cold stimulation-induced changes in cerebral and cardiac hemodynamics.

METHODS

Upon ingestion of an ice cube, the changes in resistance index, mean flow velocity and flow index of the middle cerebral arteries (MCA) were assessed using transcranial Doppler sonography. Extracranial duplex sonography was used to measure the mean flow velocity and resistance index of the right internal carotid artery (ICA). The change in mean arterial pressure, heart rate, root mean square of successive differences (RMSSD) and end-tidal carbon dioxide pressure were analyzed additionally. These changes were compared to sham stimulation.

RESULTS

Compared with sham stimulation, cooling of the oral cavity resulted in significant changes in cerebral and cardiac hemodynamics. The cold stimulation decreased the resistance index in the MCA (-4.5% ± 5.4%, p < 0.0001) and right ICA (-6.3% ± 15.6%, p = 0.001). This was accompanied by an increase in mean flow velocity (4.1% ± 8.0%, p < 0.0001) and flow index (10.1% ± 43.6%, p = 0.008) in the MCA. The cardiac effects caused an increase in mean arterial pressure (1.8% ± 11.2%, p = 0.017) and RMSSD (55% ± 112%, p = 0.048), while simultaneously decreasing the heart rate (-4.3% ± 9.6%, p = 0.0001).

CONCLUSION

Cooling of the oral cavity resulted in substantial changes in cerebral and cardiac hemodynamics resulting in a blood flow diversion to the brain.

From Psychostasis to the Discovery of Cardiac Nerves: The Origins of the Modern Cardiac Neuromodulation Concept

This review explores the historical development of cardiology knowledge, from ancient Egyptian psychostasis to the modern comprehension of cardiac neuromodulation. In ancient Egyptian religion, psychostasis was the ceremony in which the deceased was judged before gaining access to the afterlife. This ritual was also known as the "weighing of the heart" or "weighing of the soul". The Egyptians believed that the heart, not the brain, was the seat of human wisdom, emotions, and memory. They were the first to recognize the cardiocentric nature of the body, identifying the heart as the center of the circulatory system. Aristotle (fourth century BC) considered the importance of the heart in human physiology in his philosophical analyses. For Galen (third century AD), the heart muscle was the site of the vital spirit, which regulated body temperature. Cardiology knowledge advanced significantly in the 15th century, coinciding with Leonardo da Vinci and Vesalius's pioneering anatomical and physiological studies. It was William Harvey, in the 17th century, who introduced the concept of cardiac circulation. Servet's research and Marcello Malpighi's discovery of arterioles and capillaries provided a more detailed understanding of circulation. Richard Lower emerged as the foremost pioneer of experimental cardiology in the late 17th century. He demonstrated the heart's neural control by tying off the vagus nerve. In 1753, Albrecht von Haller, a professor at Göttingen, was the first to discover the heart's automaticity and the excitation of muscle fibers. Towards the end of the 18th century, Antonio Scarpa challenged the theories of Albrecht von Haller and Johann Bernhard Jacob Behrends, who maintained that the myocardium possessed its own "irritability", on which the heartbeat depended, and was independent of neuronal sensitivity. Instead, Scarpa argued that the heart required innervation to maintain life, refuting Galenic notions. In contemporary times, the study of cardiac innervation has regained prominence, particularly in understanding the post-acute sequelae of SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus 2) infection (PASC), which frequently involves cardiorespiratory symptoms and dysregulation of the intrinsic cardiac innervation. Recently, it has been recognized that post-acute sequelae of acute respiratory infections (ARIs) due to other pathogens can also be a cause of long-term vegetative and somatic symptoms. Understanding cardiac innervation and modulation can help to recognize and treat long COVID and long non-COVID-19 (coronavirus disease 2019) ARIs. This analysis explores the historical foundations of cardiac neuromodulation and its contemporary relevance. By focusing on this concept, we aim to bridge the gap between historical understanding and modern applications. This will illuminate the complex interplay between cardiac function, neural modulation, cardiovascular health, and disease management in the context of long-term cardiorespiratory symptoms and dysregulation of intrinsic cardiac innervations.

Facial fanning reduces heart rate but not tolerance to a simulated hemorrhagic challenge following exercise heat stress in young healthy humans

We investigated whether reducing face skin temperature alters arterial blood pressure control and lower body negative pressure (LBNP) tolerance after exercise heat stress. Eight subjects (1 female; age, 27 ± 9 yr) exercised at ∼63% V̇o2max until core temperature had increased ∼1.5°C before undergoing LBNP to presyncope either with fanning to return face skin temperature to baseline (Δ-5°C, Fan trial) or without (No Fan trial). LBNP tolerance was quantified as cumulative stress index (CSI; mmHg·min). Before LBNP, whole body and face skin temperatures were elevated from baseline in both trials (38.0 ± 0.5°C and 36.3 ± 0.5°C, respectively, both P < 0.001). During LBNP, face skin temperature decreased in the Fan trial (30.9 ± 1.0°C) but was unchanged in the No Fan trial (36.1 ± 0.6°C, between trials P < 0.001). Mean arterial pressure was not different between trials (P = 0.237) and was similarly reduced at presyncope in both trials (from 82 ± 7 to 67 ± 8 mmHg, P < 0.001). During LBNP, heart rate was attenuated in the Fan trial at Mid LBNP (146 ± 16 vs. 158 ± 12 beats/min, P = 0.036) and at peak heart rate (158 ± 15 vs. 170 ± 15 beats/min; P < 0.001). LBNP tolerance was not different between trials (321 ± 248 vs. 328 ± 115 mmHg·min, P = 0.851). In exercise heat-stressed individuals, lowering face skin temperature to normothermic values suppressed heart rate thereby altering cardiovascular control during a simulated hemorrhagic challenge without reducing tolerance.

Clinical potential of sensory neurites in the heart and their role in decision-making

The process of decision-making is quite complex involving different aspects of logic, emotion, and intuition. The process of decision-making can be summarized as choosing the best alternative among a given plethora of options in order to achieve the desired outcome. This requires establishing numerous neural networks between various factors associated with the decision and creation of possible combinations and speculating their possible outcomes. In a nutshell, it is a highly coordinated process consuming the majority of the brain's energy. It has been found that the heart comprises an intrinsic neural system that contributes not only to the decision-making process but also the short-term and long-term memory. There are approximately 40,000 cells present in the heart known as sensory neurites which play a vital role in memory transfer. The heart is quite a mysterious organ, which functions as a blood-pumping machine and an endocrine gland, as well as possesses a nervous system. There are multiple factors that affect this heart ecosystem, and they directly affect our decision-making capabilities. These interlinked relationships hint toward the sensory neurites which modulate cognition and mood regulation. This review article aims to provide deeper insights into the various roles played by sensory neurites in decision-making and other cognitive functions. The article highlights the pivotal role of sensory neurites in the numerous brain functions, and it also meticulously discusses the mechanisms through which they modulate their effects.

Subdiaphragmatic vagal nerve stimulation attenuates the development of hypertension and alters nucleus of the solitary tract transcriptional networks in the spontaneously hypertensive rat

Augmented vagal signaling may be therapeutic in hypertension. Most studies to date have used stimulation of the cervical vagal branches. Here, we investigated the effects of chronic intermittent electric stimulation of the ventral subdiaphragmatic vagal nerve branch (sdVNS) on long-term blood pressure, immune markers, and gut microbiota in the spontaneously hypertensive rat (SHR), a rodent model of hypertension characterized by vagal dysfunction, gut dysbiosis, and low-grade inflammation. We evaluated the effects of sdVNS on transcriptional networks in the nucleus of the solitary tract (NTS), a major cardioregulatory brain region with direct gut vagal projections. Male juvenile SHRs were implanted with radiotelemetry transmitters and vagal nerve cuffs for chronic intermittent electric sdVNS, applied three times per day for 7 consecutive weeks followed by 1 wk of no stimulation. Blood pressure was measured once a week using telemetry in the sdVNS group as well as age-matched sham-stimulated SHR controls. At the endpoint, colonic and circulating inflammatory markers, corticosterone, and circulating catecholamines were investigated. Bacterial 16 s sequencing measured gut bacterial abundance and composition. RNA sequencing evaluated the effects of sdVNS on transcriptional networks in the NTS. SHRs that received sdVNS exhibited attenuated development of hypertension compared with sham animals. No changes in peripheral inflammatory markers, corticosterone, or catecholamines and no major differences in gut bacterial diversity and composition were observed following sdVNS, apart from decreased abundance of Defluviitaleaceale bacterium detected in sdVNS SHRs compared with sham animals. RNA sequencing revealed significant sdVNS-dependent modulation of select NTS transcriptional networks, including catecholaminergic and corticosteroid networks.NEW & NOTEWORTHY We show that stimulation of the ventral subdiaphragmatic vagal nerve branch may be a promising potential approach to treating hypertension. The data are especially encouraging given that rodents received only 30 min per day of intermittent stimulation therapy and in view of the potential of long-term blood pressure effects that are not stimulus-locked.

Immediate and sustained increases in the activity of vagal preganglionic neurons during exercise and after exercise training

AIMS

The brain controls the heart by dynamic recruitment and withdrawal of cardiac parasympathetic (vagal) and sympathetic activity. Autonomic control is essential for the development of cardiovascular responses during exercise, however, the patterns of changes in the activity of the two autonomic limbs, and their functional interactions in orchestrating physiological responses during exercise, are not fully understood. The aim of this study was to characterize changes in vagal parasympathetic drive in response to exercise and exercise training by directly recording the electrical activity of vagal preganglionic neurons in experimental animals (rats).

METHODS AND RESULTS

Single unit recordings were made using carbon-fibre microelectrodes from the populations of vagal preganglionic neurons of the nucleus ambiguus (NA) and the dorsal vagal motor nucleus of the brainstem. It was found that (i) vagal preganglionic neurons of the NA and the dorsal vagal motor nucleus are strongly activated during bouts of acute exercise, and (ii) exercise training markedly increases the resting activity of both populations of vagal preganglionic neurons and augments the excitatory responses of NA neurons during exercise.

CONCLUSIONS

These data show that central vagal drive increases during exercise and provide the first direct neurophysiological evidence that exercise training increases vagal tone. The data argue against the notion of exercise-induced central vagal withdrawal during exercise. We propose that robust increases in the activity of vagal preganglionic neurons during bouts of exercise underlie activity-dependent plasticity, leading to higher resting vagal tone that confers multiple health benefits associated with regular exercise.

Mapping of Neuro-Cardiac Electrophysiology: Interlinking Epilepsy and Arrhythmia

The interplay between neurology and cardiology has gained significant attention in recent years, particularly regarding the shared pathophysiological mechanisms and clinical comorbidities observed in epilepsy and arrhythmias. Neuro-cardiac electrophysiology mapping involves the comprehensive assessment of both neural and cardiac electrical activity, aiming to unravel the intricate connections and potential cross-talk between the brain and the heart. The emergence of artificial intelligence (AI) has revolutionized the field by enabling the analysis of large-scale data sets, complex signal processing, and predictive modeling. AI algorithms have been applied to neuroimaging, electroencephalography (EEG), electrocardiography (ECG), and other diagnostic modalities to identify subtle patterns, classify disease subtypes, predict outcomes, and guide personalized treatment strategies. In this review, we highlight the potential clinical implications of neuro-cardiac mapping and AI in the management of epilepsy and arrhythmias. We address the challenges and limitations associated with these approaches, including data quality, interpretability, and ethical considerations. Further research and collaboration between neurologists, cardiologists, and AI experts are needed to fully unlock the potential of this interdisciplinary field.

Cardiac Vagal Nerve Activity Increases During Exercise to Enhance Coronary Blood Flow

BACKGROUND

The phrase complete vagal withdrawal is often used when discussing autonomic control of the heart during exercise. However, more recent studies have challenged this assumption. We hypothesized that cardiac vagal activity increases during exercise and maintains cardiac function via transmitters other than acetylcholine.

METHODS

Chronic direct recordings of cardiac vagal nerve activity, cardiac output, coronary artery blood flow, and heart rate were recorded in conscious adult sheep during whole-body treadmill exercise. Cardiac innervation of the left cardiac vagal branch was confirmed with lipophilic tracer dyes (DiO). Sheep were exercised with pharmacological blockers of acetylcholine (atropine, 250 mg), VIP (vasoactive intestinal peptide; [4Cl-D-Phe6,Leu17]VIP 25 µg), or saline control, randomized on different days. In a subset of sheep, the left cardiac vagal branch was denervated.

RESULTS

Neural innervation from the cardiac vagal branch is seen at major cardiac ganglionic plexi, and within the fat pads associated with the coronary arteries. Directly recorded cardiac vagal nerve activity increased during exercise. Left cardiac vagal branch denervation attenuated the maximum changes in coronary artery blood flow (maximum exercise, control: 63.5±5.9 mL/min, n=8; cardiac vagal denervated: 32.7±5.6 mL/min, n=6, P=2.5×10-7), cardiac output, and heart rate during exercise. Atropine did not affect any cardiac parameters during exercise, but VIP antagonism significantly reduced coronary artery blood flow during exercise to a similar level to vagal denervation.

CONCLUSIONS

Our study demonstrates that cardiac vagal nerve activity actually increases and is crucial for maintaining cardiac function during exercise. Furthermore, our findings show the dynamic modulation of coronary artery blood flow during exercise is mediated by VIP.

Sudden unexpected death in epilepsy: A critical view of the literature

Sudden unexpected death in epilepsy (SUDEP) is a sudden, unexpected, witnessed or unwitnessed, non-traumatic and non-drowning death, occurring in benign circumstances, in an individual with epilepsy, with or without evidence for a seizure and excluding documented status epilepticus in which postmortem examination does not reveal other causes of death. Lower diagnostic levels are assigned when cases met most or all of these criteria, but data suggested more than one possible cause of death. The incidence of SUDEP ranged from 0.09 to 2.4 per 1000 person-years. Differences can be attributed to the age of the study populations (with peaks in the 20-40-year age group) and the severity of the disease. Young age, disease severity (in particular, a history of generalized TCS), having symptomatic epilepsy, and the response to antiseizure medications (ASMs) are possible independent predictors of SUDEP. The pathophysiological mechanisms are not fully known due to the limited data available and because SUDEP is not always witnessed and has been electrophysiologically monitored only in a few cases with simultaneous assessment of respiratory, cardiac, and brain activity. The pathophysiological basis of SUDEP may vary according to different circumstances that make that particular seizure, in that specific moment and in that patient, a fatal event. The main hypothesized mechanisms, which could contribute to a cascade of events, are cardiac dysfunction (included potential effects of ASMs, genetically determined channelopathies, acquired heart diseases), respiratory dysfunction (included postictal arousal deficit for the respiratory mechanism, acquired respiratory diseases), neuromodulator dysfunction, postictal EEG depression and genetic factors.

Heart Rate Variability as a Translational Dynamic Biomarker of Altered Autonomic Function in Health and Psychiatric Disease

The autonomic nervous system (ANS) is responsible for the precise regulation of tissue functions and organs and, thus, is crucial for optimal stress reactivity, adaptive responses and health in basic and challenged states (survival). The fine-tuning of central ANS activity relies on the internal central autonomic regulation system of the central autonomic network (CAN), while the peripheral activity relies mainly on the two main and interdependent peripheral ANS tracts, the sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS). In disease, autonomic imbalance is associated with decreased dynamic adaptability and increased morbidity and mortality. Acute or prolonged autonomic dysregulation, as observed in stress-related disorders, affects CAN core centers, thereby altering downstream peripheral ANS function. One of the best established and most widely used non-invasive methods for the quantitative assessment of ANS activity is the computerized analysis of heart rate variability (HRV). HRV, which is determined by different methods from those used to determine the fluctuation of instantaneous heart rate (HR), has been used in many studies as a powerful index of autonomic (re)activity and an indicator of cardiac risk and ageing. Psychiatric patients regularly show altered autonomic function with increased HR, reduced HRV and blunted diurnal/circadian changes compared to the healthy state. The aim of this article is to provide basic knowledge on ANS function and (re)activity assessment and, thus, to support a much broader use of HRV as a valid, transdiagnostic and fully translational dynamic biomarker of stress system sensitivity and vulnerability to stress-related disorders in neuroscience research and clinical psychiatric practice. In particular, we review the functional levels of central and peripheral ANS control, the main neurobiophysiologic theoretical models (e.g., polyvagal theory, neurovisceral integration model), the precise autonomic influence on cardiac function and the definition and main aspects of HRV and its different measures (i.e., time, frequency and nonlinear domains). We also provide recommendations for the proper use of electrocardiogram recordings for HRV assessment in clinical and research settings and highlight pathophysiological, clinical and research implications for a better functional understanding of the neural and molecular mechanisms underlying healthy and malfunctioning brain-heart interactions in individual stress reactivity and psychiatric disorders.

Dissecting the contributions of the peripheral chemoreflex and myocardial hypoxia to fetal heart rate decelerations in near-term fetal sheep

Brief repeated fetal hypoxaemia during labour can trigger intrapartum decelerations of the fetal heart rate (FHR) via the peripheral chemoreflex or the direct effects of myocardial hypoxia, but the relative contribution of these two mechanisms and how this balance changes with evolving fetal compromise remain unknown. In the present study, chronically instrumented near-term fetal sheep received surgical vagotomy (n = 8) or sham vagotomy (control, n = 11) to disable the peripheral chemoreflex and unmask myocardial hypoxia. One-minute complete umbilical cord occlusions (UCOs) were performed every 2.5 min for 4 h or until arterial pressure fell below 20 mmHg. Hypotension and severe acidaemia developed progressively after 65.7 ± 7.2 UCOs in control fetuses and 49.5 ± 7.8 UCOs after vagotomy. Vagotomy was associated with faster development of metabolic acidaemia and faster impairment of arterial pressure during UCOs without impairing centralization of blood flow or neurophysiological adaptation to UCOs. During the first half of the UCO series, before severe hypotension developed, vagotomy was associated with a marked increase in FHR during UCOs. After the onset of evolving severe hypotension, FHR fell faster in control fetuses during the first 20 s of UCOs, but FHR during the final 40 s of UCOs became progressively more similar between groups, with no difference in the nadir of decelerations. In conclusion, FHR decelerations were initiated and sustained by the peripheral chemoreflex at a time when fetuses were able to maintain arterial pressure. After the onset of evolving hypotension and acidaemia, the peripheral chemoreflex continued to initiate decelerations, but myocardial hypoxia became progressively more important in sustaining and deepening decelerations. KEY POINTS: Brief repeated hypoxaemia during labour can trigger fetal heart rate decelerations by either the peripheral chemoreflex or myocardial hypoxia, but how this balance changes with fetal compromise is unknown. Reflex control of fetal heart rate was disabled by vagotomy to unmask the effects of myocardial hypoxia in chronically instrumented fetal sheep. Fetuses were then subjected to repeated brief hypoxaemia consistent with the rates of uterine contractions during labour. We show that the peripheral chemoreflex controls brief decelerations in their entirety at a time when fetuses were able to maintain normal or increased arterial pressure. The peripheral chemoreflex still initiated decelerations even after the onset of evolving hypotension and acidaemia, but myocardial hypoxia made an increasing contribution to sustain and deepen decelerations.

The Influence of Trigeminocardiac Reflex on Postoperative Cardiac Adverse Events in Patients Undergoing Cerebellopontine Angle Tumor Resections: A Case-Control Study

OBJECTIVE

To assess the potential impact of the trigeminocardiac reflex (TCR) on postoperative adverse cardiac events and to identify predictors of the TCR in cerebellopontine angle surgery.

METHODS

Patients undergoing elective cerebellopontine angle surgery from October 1, 2015, to September 30, 2020, were recruited consecutively for this retrospective case-control study. The TCR was evaluated by reviewing electronic anesthesia records and defined as a drop in heart rate was >20%. Controls were identified from the same retrospective cohort and matched by age, sex, and similar (±5 days) surgery date in the ratio of 1:2.

RESULTS

Of 2446 patients, 68 (2.78%) experienced TCR episodes. A total of 97 TCR episodes occurred among the 68 patients. In 2 TCR episodes, severe cardiac complications developed after surgery-myocardial injury in one case and cardiac arrest in the other case. The prevalence of adverse cardiovascular events was higher in the TCR group (60.3% vs. 36.0%, P = 0.001) than in the control group. The independent risk factor for the TCR in the multivariate condition logistic regression was tumor compression of the brainstem (odds ratio = 2.36, 95% confidence interval 1.40-3.95; P = 0.001).

CONCLUSIONS

Intraoperative TCR episodes seemed to be associated with postoperative adverse cardiac events in patients undergoing cerebellopontine angle surgery. Moreover, tumor compression of the brainstem might be a risk factor for TCR episodes.

Sleep Loss Influences the Interconnected Brain-Body Regulation of Cardiovascular Function in Humans

OBJECTIVE

Poor sleep is associated with hypertension, a major risk factor for cardiovascular disease. However, the mechanism(s) through which sleep loss affects cardiovascular health remains largely unknown, including the brain and body systems that regulate vascular function.

METHODS

Sixty-six healthy adults participated in a repeated-measures, crossover, experimental study involving assessments of cardiovascular function and brain connectivity after a night of sleep and a night of sleep deprivation.

RESULTS

First, sleep deprivation significantly increased blood pressure-both systolic and diastolic. Interestingly, this change was independent of any increase in heart rate, inferring a vasculature-specific rather than direct cardiac pathway. Second, sleep loss compromised functional brain connectivity within the vascular control network, specifically the insula, anterior cingulate, amygdala, and ventral and medial prefrontal cortices. Third, sleep loss-related changes in brain connectivity and vascular tone were not independent, but significantly interdependent, with changes within the vascular control brain network predicting the sleep-loss shift toward hypertension.

CONCLUSIONS

These findings establish an embodied framework in which sleep loss confers increased risk of cardiovascular disease through an impact upon central brain control of vascular tone, rather than a direct impact on accelerated heart rate itself.

Feasibility of Ultra-Short-Term Analysis of Heart Rate and Systolic Arterial Pressure Variability at Rest and during Stress via Time-Domain and Entropy-Based Measures

Heart Rate Variability (HRV) and Blood Pressure Variability (BPV) are widely employed tools for characterizing the complex behavior of cardiovascular dynamics. Usually, HRV and BPV analyses are carried out through short-term (ST) measurements, which exploit ~five-minute-long recordings. Recent research efforts are focused on reducing the time series length, assessing whether and to what extent Ultra-Short-Term (UST) analysis is capable of extracting information about cardiovascular variability from very short recordings. In this work, we compare ST and UST measures computed on electrocardiographic R-R intervals and systolic arterial pressure time series obtained at rest and during both postural and mental stress. Standard time-domain indices are computed, together with entropy-based measures able to assess the regularity and complexity of cardiovascular dynamics, on time series lasting down to 60 samples, employing either a faster linear parametric estimator or a more reliable but time-consuming model-free method based on nearest neighbor estimates. Our results are evidence that shorter time series down to 120 samples still exhibit an acceptable agreement with the ST reference and can also be exploited to discriminate between stress and rest. Moreover, despite neglecting nonlinearities inherent to short-term cardiovascular dynamics, the faster linear estimator is still capable of detecting differences among the conditions, thus resulting in its suitability to be implemented on wearable devices.

Carotid body stimulation as a potential intervention in sudden death in epilepsy

OBJECTIVE

To investigate carotid body (CB) mechanisms related to sudden death during seizure. Ictal activation of oxygen-conserving reflexes (OCRs) can trigger fatal cardiorespiratory collapse in seizing rats, which presents like human sudden unexpected death in epilepsy (SUDEP). The CB is strongly implicated in OCR pathways; we hypothesize that modulating CB activity will provide insight into these mechanisms of death.

METHODS

Long-Evans rats were anesthetized with urethane. Recordings included: electrocorticography, electrocardiography, respiration via nasal thermocouple, and blood pressure (BP). The mammalian diving reflex (MDR) was activated by cold water delivered through a nasal cannula. Reflex and stimulation trials were repeated up to 16 times (4 pre-intervention, 12 post-intervention) or until death. In some animals, one or both carotid bodies were denervated. In some animals, the CB was electrically stimulated, both with and without MDR. Seizures were induced with kainic acid (KA).

RESULTS

Animals without seizure and with no CB modulation survived all reflexes. Non-seizing animals with CB denervation survived 7.1 ± 5.4 reflexes before death, and only 1 of 7 survived past the 12-trial threshold. Electrical CB stimulation without seizure and without reflex caused significant tachypnea and hypotension. Electrical CB stimulation with seizure and without reflex required higher amplitudes to replicate the physiological responses seen outside seizure. Seizing animals without CB intervention survived 3.2 ± 3.6 trials (per-reflex survival rate 42.0% ± 44.4%), and 0 of 7 survived past the 12-trial threshold. Seizing animals with electrical CB stimulation survived 10.5 ± 4.7 ictal trials (per-reflex survival rate 86.3% ± 35.0%), and 6 of 8 survived past the 12-trial threshold.

SIGNIFICANCE

These results suggest that, during seizure, the ability of the CB to stimulate a restart of respiration is impaired. The CB and its afferents may be relevant to fatal ictal apnea and SUDEP in humans, and CB stimulation may be a relevant intervention technique in these deaths.

Endothelin System and Ischemia-Induced Ventricular Tachyarrhythmias

Despite the contemporary treatment of acute coronary syndromes, arrhythmic complications occurring prior to medical attendance remain significant, mandating in-depth understanding of the underlying mechanisms. Sympathetic activation has long been known to play a key role in the pathophysiology of ischemia-induced arrhythmias, but the regulating factors remain under investigation. Several lines of evidence implicate the endothelin system (a family of three isopeptides and two specific receptors) as an important modulator of sympathetic activation in the setting of acute coronary syndromes. Such interaction is present in the heart and in the adrenal medulla, whereas less is known on the effects of the endothelin system on the central autonomic network. This article summarizes the current state-of-the-art, placing emphasis on early-phase arrhythmogenesis, and highlights potential areas of future research.

Physiologic Effects of Housing Rats in Metabolic Cages

Currently, metabolic cages (MC) are the only way to achieve serial sampling of urine and feces in rodents. However, the use of this caging creates a dramatic change from an animal's usual microenvironment. Here we sought to examine the effect of MC on physiologic parameters that are stress-responsive in rats. We surgically implanted 8 male Wistar rats (weight, 150 to 175 g) with telemetric transmitters and allowed them to recover for at least 2 wk. At the beginning of the study, the rats were moved to conventional open-top cages, and telemetry recording was initiated. After 24 h, the rats were moved to MC or to another conventional cage and the recording continued for another 24 h. Finally, the rats were returned to their home cages, and telemetry recording was performed for a final 24 h. After 10 days, this process was then repeated, with MC and conventional assignments switched. During the 78-h monitoring period, we recorded heart rate, arterial blood pressure, locomotor activity, body weight, and food and water consumption. Heart rate and arterial blood pressure showed transient but significant changes. Locomotor activity during the dark phase was greatly decreased in MC compared with conventional cages, perhaps due to space constraints. In addition, when the rats were housed in MC, they showed a small but significant weight loss. Food consumption did not differ between housing environments, but water consumption was lower when rats were in MC. In conclusion, the housing of rats in MC for 24 h can elicit mild and reversible cardiovascular changes. This finding is consistent with European Directive 2010/63/EU, which considers short-term (less than 24 h) restraint in MC a procedure of mild severity.

QT interval alterations in epilepsy: A thorough investigation between epilepsy subtypes

OBJECTIVES

Cardiac disturbances and rhythm abnormalities which potentially lead sudden unexpected death in epilepsy, have been extensively studied in focal epilepsies. However, studies including generalized epilepsies are scarce and it is not clear whether electrocardiogram parameters reflecting vulnerability to ventricular arrhythmias differ between these groups.

METHODS

Medical records of patients who were followed in epilepsy department of a tertiary center between October 2015 and September 2016 were retrospectively reviewed. 66 generalized and 64 focal epilepsy patients with eligible electrophysiological data were analyzed. QTc interval, QTcd and other electrocardiographic indices were compared between patients with focal vs generalized epilepsy. Another analysis was performed in order to disclose any difference between patients with epilepsy (n:130) and psychogenic non-epileptic seizures. A two-tailed p value < 0.05 was considered significant.

RESULTS

There was no difference in terms of QTc and QTcd between patients with focal and generalized epilepsy [median: 406 ms vs 404 ms, p = 0.119; and median: 46 ms vs 44 ms, p = 0.497, respectively]. However patients with epilepsy were found to have longer QTc and QTcd when compared to ones with psychogenic non-epileptic seizures (p = 0.035 and p < 0.001, respectively).

CONCLUSION

Current findings demonstrate that patients with epilepsy have longer QTc and QTcd than patients with pure psychogenic non-epileptic seizures. Since there was no difference between patients with focal and generalized epilepsy; QTc interval, QTcd and potential susceptibility to cardiac arrhythmias as a result, could be a consequence of epilepsy itself regardless of origin.

Freezing revisited: coordinated autonomic and central optimization of threat coping

Animals have sophisticated mechanisms for coping with danger. Freezing is a unique state that, upon threat detection, allows evidence to be gathered, response possibilities to be previsioned and preparations to be made for worst-case fight or flight. We propose that - rather than reflecting a passive fear state - the particular somatic and cognitive characteristics of freezing help to conceal overt responses, while optimizing sensory processing and action preparation. Critical for these functions are the neurotransmitters noradrenaline and acetylcholine, which modulate neural information processing and also control the sympathetic and parasympathetic branches of the autonomic nervous system. However, the interactions between autonomic systems and the brain during freezing, and the way in which they jointly coordinate responses, remain incompletely explored. We review the joint actions of these systems and offer a novel computational framework to describe their temporally harmonized integration. This reconceptualization of freezing has implications for its role in decision-making under threat and for psychopathology.

Acute Cardiovascular and Metabolic Effects of Different Warm-Up Protocols on Dynamic Apnea

The aim of this study was to evaluate the acute physiological response to different warm-up protocols on the dynamic apnea performance. The traditional approach, including a series of short-mid dives in water (WET warm-up), was compared to a more recent strategy, consisting in exercises performed outside the water (DRY warm-up). Nine athletes were tested in two different sessions, in which the only difference was the warm-up executed before 75m of dynamic apnea. Heart rate variability, baroreflex sensitivity, hemoglobin, blood lactate and the rate of perceived exertion were recorded and analyzed. With respect to WET condition, DRY showed lower lactate level before the dive (1.93 vs. 2.60 mmol/L, p = 0.006), higher autonomic indices and lower heart rate during the subsequent dynamic apnea. A significant correlation between lactate produced during WET with the duration of the subsequent dynamic apnea, suggests that higher lactate levels could affect the dive performance (72 vs. 70 sec, p = 0.028). The hemoglobin concentration and the rate of perceived exertion did not show significant differences between conditions. The present findings partially support the claims of freediving athletes who adopt the DRY warm-up, since it induces a more pronounced diving response, avoiding higher lactate levels and reducing the dive time of a dynamic apnea.

Turn it off and on again: characteristics and control of torpor

Torpor is a hypothermic, hypoactive, hypometabolic state entered into by a wide range of animals in response to environmental challenge. This review summarises the current understanding of torpor. We start by describing the characteristics of the wide-ranging physiological adaptations associated with torpor. Next follows a discussion of thermoregulation, control of food intake and energy expenditure, and the interactions of sleep and thermoregulation, with particular emphasis on how those processes pertain to torpor. We move on to review the evidence for the systems that control torpor entry, including both the efferent circulating factors that signal the need for torpor, and the central processes that orchestrate it. Finally, we consider how the putative circuits responsible for torpor induction integrate with the established understanding of thermoregulation under non-torpid conditions and highlight important areas of uncertainty for future studies.

Advancing respiratory-cardiovascular physiology with the working heart-brainstem preparation over 25 years

Twenty‐five years ago, a new physiological preparation called the working heart–brainstem preparation (WHBP) was introduced with the claim it would provide a new platform allowing studies not possible before in cardiovascular, neuroendocrine, autonomic and respiratory research. Herein, we review some of the progress made with the WHBP, some advantages and disadvantages along with potential future applications, and provide photographs and technical drawings of all the customised equipment used for the preparation. Using mice or rats, the WHBP is an in situ experimental model that is perfused via an extracorporeal circuit benefitting from unprecedented surgical access, mechanical stability of the brain for whole cell recording and an uncompromised use of pharmacological agents akin to in vitro approaches. The preparation has revealed novel mechanistic insights into, for example, the generation of distinct respiratory rhythms, the neurogenesis of sympathetic activity, coupling between respiration and the heart and circulation, hypothalamic and spinal control mechanisms, and peripheral and central chemoreceptor mechanisms. Insights have been gleaned into diseases such as hypertension, heart failure and sleep apnoea. Findings from the in situ preparation have been ratified in conscious in vivo animals and when tested have translated to humans. We conclude by discussing potential future applications of the WHBP including two‐photon imaging of peripheral and central nervous systems and adoption of pharmacogenetic tools that will improve our understanding of physiological mechanisms and reveal novel mechanisms that may guide new treatment strategies for cardiorespiratory diseases.

Regulation of heart rate in vertebrates during hypoxia: A comparative overview

Acute exposure to low oxygen (hypoxia) places conflicting demands on the heart. Whilst an increase in heart rate (tachycardia) may compensate systemic oxygen delivery as arterial oxygenation falls, the heart itself is an energetically expensive organ that may benefit from slowing (bradycardia) to reduce work when oxygen is limited. Both strategies are apparent in vertebrates, with tetrapods (mammals, birds, reptiles, and amphibians) classically exhibiting hypoxic tachycardia and fishes displaying characteristic hypoxic bradycardia. With a richer understanding of the ontogeny and evolution of the responses, however, we see similarities in the underlying mechanisms between vertebrate groups. For example, in adult mammals, primary bradycardia results from the hypoxic stimulation of carotid body chemoreceptors that are overwhelmed by mechano-sensory feedback from the lung associated with hyperpnoea. Fish-like bradycardia prevails in the mammalian foetus (which, at this stage, is incapable of pulmonary ventilation), and in fish and foetus alike, the bradycardia ensues despite an elevation of circulating catecholamines. In both cases, the reduced heart rate may primarily serve to protect the heart. Thus, the comparative perspective offers fundamental insight into how and why different vertebrates regulate heart rate in different ways during periods of hypoxia.

Cardiovascular Reactivity to a Novel Stressor: Differences on Susceptible and Resilient Rats to Social Defeat Stress

Prolonged and heightened responses to stress are known factors that influence the development of mood disorders and cardiovascular diseases. Moreover, the coping strategies related to the experience of adverse events, i.e., resilience or the susceptibility to stress, are determinants for the individual risk of developing such diseases. Susceptible rats to the social defeat stress (SDS), identified by the social interaction test (SIT), show behavioral and cardiovascular alterations after SDS exposure that are not found in resilient rats. However, it is not elucidated yet how the cardiovascular system of susceptible and resilient phenotypes responds to a new stressor after SDS exposure. Thus, using the SDS exposure followed by the SIT, we evaluated heart rate, blood pressure (BP), tail skin temperature, and circulating corticosterone responses to an acute session of restraint stress in susceptible and resilient rats to SDS. Susceptible rats showed resting tachycardia and exaggerated BP response to restraint stress, while resilient rats did not present such alterations. In contrast, both phenotypes showed increased plasma corticosterone and a drop in tail skin temperature to restraint stress, which was similar to that observed in control animals. Our results revealed an increased cardiovascular reactivity in response to a new stressful stimulus in susceptible rats, which might be related to a greater risk for the development of cardiovascular diseases.

Forebrain corticosteroid receptors promote post-myocardial infarction depression and mortality

Myocardial infarction (MI) with subsequent depression is associated with increased cardiac mortality. Impaired central mineralocorticoid (MR) and glucocorticoid receptor (GR) equilibrium has been suggested as a key mechanism in the pathogenesis of human depression. Here, we investigate if deficient central MR/GR signaling is causative for a poor outcome after MI in mice. Mice with an inducible forebrain-specific MR/GR knockout (MR/GR-KO) underwent baseline and follow-up echocardiography every 2 weeks after MI or sham operation. Behavioral testing at 4 weeks confirmed significant depressive-like behavior and, strikingly, a higher mortality after MI, while cardiac function and myocardial damage remained unaffected. Telemetry revealed cardiac autonomic imbalance with marked bradycardia and ventricular tachycardia (VT) upon MI in MR/GR-KO. Mechanistically, we found a higher responsiveness to atropine, pointing to impaired parasympathetic tone of 'depressive' mice after MI. Serum corticosterone levels were increased but-in line with the higher vagal tone-plasma and cardiac catecholamines were decreased. MR/GR deficiency in the forebrain led to significant depressive-like behavior and a higher mortality after MI. This was accompanied by increased vagal tone, depleted catecholaminergic compensatory capacity and VTs. Thus, limbic MR/GR disequilibrium may contribute to the impaired outcome of depressive patients after MI and possibly explain the lack of anti-depressive treatment benefit.

Vagus nerve afferent stimulation: Projection into the brain, reflexive physiological, perceptual, and behavioral responses, and clinical relevance

The afferent vagus nerves project to diverse neural networks within the brainstem and forebrain, based on neuroanatomical, neurophysiological, and functional (fMRI) brain imaging evidence. In response to afferent vagal stimulation, multiple homeostatic visceral reflexes are elicited. Physiological stimuli and both invasive and non-invasive electrical stimulation that activate the afferent vagus elicit perceptual and behavioral responses that are of physiological and clinical significance. In the present review, we address these multiple roles of the afferent vagus under normal and pathological conditions, based on both animal and human evidence.

Duration at high altitude influences the onset of arrhythmogenesis during apnea

PURPOSE

Autonomic control of the heart is balanced by sympathetic and parasympathetic inputs. Excitation of both sympathetic and parasympathetic systems occurs concurrently during certain perturbations such as hypoxia, which stimulate carotid chemoreflex to drive ventilation. It is well established that the chemoreflex becomes sensitized throughout hypoxic exposure; however, whether progressive sensitization alters cardiac autonomic activity remains unknown. We sought to determine the duration of hypoxic exposure at high altitude necessary to unmask cardiac arrhythmias during instances of voluntary apnea.

METHODS

Measurements of steady-state chemoreflex drive (SS-CD), continuous electrocardiogram (ECG) and SpO₂ (pulse oximetry) were collected in 22 participants on 1 day at low altitude (1045 m) and over eight consecutive days at high-altitude (3800 m). SS-CD was quantified as ventilation (L/min) over stimulus index (P_ETCO₂/SpO₂).

RESULTS

Bradycardia during apnea was greater at high altitude compared to low altitude for all days (p < 0.001). Cardiac arrhythmias occurred during apnea each day but became most prevalent (> 50%) following Day 5 at high altitude. Changes in saturation during apnea and apnea duration did not affect the magnitude of bradycardia during apnea (ANCOVA; saturation, p = 0.15 and apnea duration, p = 0.988). Interestingly, the magnitude of bradycardia was correlated with the incidence of arrhythmia per day (r = 0.8; p = 0.004).

CONCLUSION

Our findings suggest that persistent hypoxia gradually increases vagal tone with time, indicated by augmented bradycardia during apnea and progressively increased the incidence of arrhythmia at high altitude.

Turn it off and on again: characteristics and control of torpor

Torpor is a hypothermic, hypoactive, hypometabolic state entered into by a wide range of animals in response to environmental challenge. This review summarises the current understanding of torpor. We start by describing the characteristics of the wide-ranging physiological adaptations associated with torpor. Next follows a discussion of thermoregulation, control of food intake and energy expenditure, and the interactions of sleep and thermoregulation, with particular emphasis on how those processes pertain to torpor. We move on to take a critical view of the evidence for the systems that control torpor entry, including both the efferent circulating factors that signal the need for torpor, and the central processes that orchestrate it. Finally, we consider how the putative circuits responsible for torpor induction integrate with the established understanding of thermoregulation under non-torpid conditions and highlight important areas of uncertainty for future studies.

The nervous system: Orchestra conductor in cancer, regeneration, inflammation and immunity

Although the role of nerves in stimulating cellular growth and dissemination has long been described in tissue regeneration studies, until recently a similar trophic role of nerves in disease was not well recognized. However, recent studies in oncology have demonstrated that the growth and dissemination of cancers also requires the infiltration of nerves in the tumor microenvironment. Nerves generate various neurosignaling pathways, which orchestrate cancer initiation, progression, and metastases. Similarly, nerves are increasingly implicated for their regulatory functions in immunity and inflammation. This orchestrator role of nerves in cellular and molecular interactions during regeneration, cancer, immunity, and inflammation offers new possibilities for targeting or enhancing neurosignaling in human health and diseases.

Utilizing multimodal imaging to visualize potential mechanism for sudden death in epilepsy

Sudden death in epilepsy or SUDEP is a fatal condition that accounts for more than 4000 deaths each year. Limited clinical and preclinical data on sudden death suggest critical contributions from autonomic, cardiac, and respiratory pathways. A potential mechanism for such sudden and severe cardiorespiratory dysregulation may be linked to acid reflux-induced laryngospasm. Here, we expand on our previous investigations and utilize a novel multimodal approach to provide visual evidence of acid reflux-initiated cardiorespiratory distress and subsequent sudden death in seizing rats. We used systemic kainic acid to acutely induce seizure activity in Long Evans rats, under urethane anesthesia. We recorded electroencephalography (EEG), electrocardiography (ECG), chest plethysmography, and esophageal pH signals through a multimodal recording platform, during simultaneous fast MRI scans of the rat stomach and esophagus. MRI images, in correlation with electrophysiology data were used to identify seizure progression, stomach acid movement up the esophagus, cardiorespiratory changes, and sudden death. In all cases of sudden death, esophageal pH recordings alongside MRI images visualized stomach acid movement up the esophagus. Severe cardiac (ST segment elevation), respiratory (intermittent apnea) and brain activity (EEG narrowing due to hypoxia) changes were observed only after acid reached larynx, which strongly suggested onset of laryngospasm following acid reflux. The complementary information coming from electrophysiology and fast MRI scans provided insight into the mechanism of esophageal reflux, laryngospasm, obstructive apnea, and subsequent sudden death in seizing animals. The results carry clinical significance as it outlines a potential mechanism that may be relevant to SUDEP in humans.

Syncope, Epilepsy and Ictal Asystole: A Case Series and Narrative Review

IMPORTANCE

Syncope is a common presentation to emergency departments, and cardiac and neurological aetiologies are the predominant causes. Ictal asystole is a rare cardio-neural phenomenon seen in epilepsy syndromes whereby a seizure causes asystole (≥3 s) leading to syncope.

OBSERVATIONS

We present three cases of ictal asystole, together with a narrative review of the literature to assess the prevalence of the condition and review the pathophysiology, diagnosis and management. Our review of the literature has shown that ictal asystole is an unlikely contributor to sudden unexplained death with epilepsy (SUDEP). Pacemaker insertion may limit morbidity from trauma related to syncopal episodes but does not impact mortality.

CONCLUSIONS AND RELEVANCE

Patients with ictal asystole should be diagnosed with concurrent electroencephalogram-electrocardiograph (EEG-ECG) monitoring, have their anti-epileptic drugs optimised and be considered for epilepsy surgery if feasible. The use of longer term ECG monitoring may be used as a diagnostic aid if ictal asystole is suspected. If there are ongoing syncopal episodes with associated ictal asystole ≥6 seconds, particularly despite medical therapy, a permanent pacemaker may be considered to reduce morbidity. Current guidelines should be updated to reflect the increasing knowledge of this condition.

Cardiorespiratory complications of digestive endoscopy not related to sedation

Although digestive endoscopy is considered to be a safe procedure, both the growing complexity of the techniques and the underlying diseases of patients increase the risk of adverse events during the procedure. Cardiorespiratory events are the most frequent complications, and can occur in patients with or without sedation, although they appear more often when the patient is sedated. The body's physiological response to stress is what causes these adverse events, which are generally mild and transient, although they can be serious. They are more frequent in patients with cardiopulmonary diseases, which logically increase risk. The autonomic nervous system, through its sympathetic and parasympathetic branches, is primarily responsible for these alterations. Patients with asthma or chronic obstructive pulmonary disease have a higher risk of hypoxemia, bronchospasm, and arrhythmia during the endoscopic procedure. Patients with arrhythmia and ischemic heart disease have a higher risk of myocardial ischemia and heart rhythm disturbances. The risk of adverse events during the procedure can be reduced by reviewing the patient's medical history along with a basic clinical examination before endoscopy. A brief interrogation about symptom control can also help the safety of endoscopy.

The Oculocardiac Reflex: A Review

BACKGROUND

A typical oculocardiac reflex (OCR) is a moderate trigemino-vagal bradycardia elicited by tension on an extraocular muscle (EOM) during strabismus surgery; however, many other orbital stimuli can elicit cardiac slowing including retinopathy of prematurity examination.

METHODS

World literature related to trigeminovagal and oculocardiac reflex covering over 15,000 patients including 51 randomized clinical trials and case reports are analyzed and reviewed. Under an ongoing observational trial in Alaska, anesthetic, patient and surgical influences on routine strabismus surgery using prospective, uniform EOM tension are compared seeking sufficient sample size to characterize this individually widely variable cardiac response.

RESULTS

With adequate sample size, and emphasizing clinical studies controlling type of EOM, muscle tension amount and duration, anticholinergic and opioid medications, the following augment OCR; rapid-acting opioids and dexmedetomidine while OCR is reduced in older patients, the right eye, less EOM tension, deeper inhaled agents, hypocarbia, anticholinergic medications and orbital block. In re-operations, the former are relatively poor predictors of subsequent OCR.

CONCLUSION

Profound bradycardia can occur in almost 10% of strabismus surgery cases without anticholinergic preventive measures, but reliable prediction of OCR remains elusive. With foreknowledge and careful anesthetic monitoring of the patient before EOM manipulation, residual adverse sequelae from OCR are fortunately very rare. Despite well over a century of experience, the teleology for this occasionally dramatic cardiac response to eye surgery is still not known.

A Decerebrate Preparation of the Rattlesnake, Crotalus durissus, Provides an Experimental Model for Study of Autonomic Modulation of the Cardiovascular System in Reptiles

AbstractThe South American rattlesnake, Crotalus durissus, has been successfully used as an experimental model to study control of the cardiovascular system in squamate reptiles. Recent technical advances, including equipment miniaturization, have lessened the impact of instrumentation on in vivo recordings, and an increased range of anesthetic drugs has improved recording conditions for in situ preparations. Nevertheless, any animal-based experimental approach has to manage limitations regarding the avoidance of pain and stress the stability of the preparation and duration of experiments and the potentially overriding effects of anesthesia. To address such aspects, we tested a new experimental preparation, the decerebrate rattlesnake, in a study of the autonomic control of cardiovascular responses following the removal of general anesthesia. The preparation exhibited complex cardiovascular adjustments to deal with acute increases in venous return (caused by tail lifting), to compensate for blood flow reduction in the cephalic region (caused by head lifting), for body temperature control (triggered by an external heating source), and in response to stimulation of chemoreceptors (triggered by intravenous injection of NaCN). The decerebrate preparation retained extensive functional integrity of autonomic centers, and it was suitable for monitoring diverse cardiac and vascular variables. Furthermore, reanesthetizing the preparation markedly blunted cardiovascular performance. Isoflurane limited the maintenance of recovered cardiovascular variables in the prepared animal and reduced or abolished the observed cardiovascular reflexes. This preparation enables the recording of multiple concomitant cardiovascular variables for the study of mechanistic questions regarding the central integration of autonomic reflex responses in the absence of anesthesia.

Heightened respiratory-parasympathetic coupling to airways in the spontaneously hypertensive rat

KEY POINTS

Carotid body (CB) chemoreceptors are hyperactive in hypertension, and their acute activation produces bronchoconstriction. We show that the respiratory-modulated bronchiolar tone, pulmonary parasympathetic efferent activity, and the firing frequency and synaptic excitation of bronchoconstrictor motoneurones in the nucleus ambiguus were all enhanced in spontaneous hypertensive (SH) rats. In SH rats, CB denervation reduced the respiratory-related parasympathetic-mediated bronchoconstrictor tone to levels seen in normotensive rats. Chemoreflex evoked bronchoconstrictor tone was heightened in SH versus normotensive rats. The intrinsic electrophysiological properties and morphology of bronchoconstrictor motoneurones were similar across rat strains. The heightened respiratory modulation of parasympathetic-mediated bronchoconstrictor tone to the airways in SH rats is caused by afferent drive from the CBs.

ABSTRACT

Much research has described heightened sympathetic activity in hypertension and diminished parasympathetic tone, especially to the heart. The carotid body (CB) chemoreceptors exhibit hyperreflexia and are hyperactive, providing excitatory drive to sympathetic networks in hypertension. Given that acute CB activation produces reflex evoked bronchoconstriction via activation of parasympathetic vagal efferents, we hypothesised that the parasympathetic bronchoconstrictor activity is enhanced in spontaneously hypertensive (SH) rats and that this is dependent on CB inputs. In situ preparations of Wistar and SH rats were used in which bronchiolar tone, the pulmonary branch of the vagus (pVN) and phrenic nerves were recorded simultaneously; whole cell patch clamp recordings of bronchoconstrictor vagal motoneurones were also made from the nucleus ambiguus. Bronchiolar tone, pVN and bronchoconstrictor motoneurones were respiratory modulated and this modulation was enhanced in SH rats. These differences were all eliminated after CB denervation. Stimulation of the CBs increased the phrenic frequency that caused a summation of the respiratory-related increases in pVN, resulting in the development of bronchoconstrictor tone. This tone was exaggerated in SH rats. The enhanced respiratory-parasympathetic coupling to airways in SH rats was not due to differences in the intrinsic electrophysiological properties of bronchoconstrictor motoneurones but reflected heightened pre-inspiratory- and inspiratory-related synaptic drive. In summary, in SH rats the phasic respiratory modulation of parasympathetic tone to the airways is elevated and the greater development of this bronchoconstrictor tone is caused by the heightened afferent drive originating from the CBs. Thus, targeting the CBs may prove effective for increasing lower airway patency.

Intraocular Pressure Reactivity to Social Stressors

Abstract. A field study was carried out in an optometry clinic, aimed at assessing the role of perceived control and aversiveness of non-contact tonometry in intraocular pressure (IOP) reactivity to psychosocial stressors, and analyzing the covariation with cardiovascular and affective reactivity. Forty-four customers volunteered to participate in the study. Perceived control (self-efficacy and threat) was assessed at the onset. IOP, systolic and diastolic blood pressure, heart rate, affect, and aversiveness of the IOP measurement procedure were assessed throughout five phases with a mean duration for each phase of 9 min: arrival, optometry, baseline, stressor task (speech in public task), and recovery. The results suggest that IOP decreases over time and the stressor task induced a remarkable reactivity in all the physiological variables assessed. The interaction between self-efficacy and threat partially explains individual variability in IOP: a high threat combined with a high self-efficacy yielded higher reactivity in IOP or increased tonic values throughout the phases. The aversiveness of the measurement procedure did not affect IOP. Intraocular Pressure (IOP) is reactive to social stressors and perceived control partially explains individual variability. Cardiovascular and IOP reactivity are parallel phenomena but do not share a common regulatory mechanism.

Approach-Avoidance Decisions Under Threat: The Role of Autonomic Psychophysiological States

Acutely challenging or threatening situations frequently require approach-avoidance decisions. Acute threat triggers fast autonomic changes that prepare the body to freeze, fight or flee. However, such autonomic changes may also influence subsequent instrumental approach-avoidance decisions. Since defensive bodily states are often not considered in value-based decision-making models, it remains unclear how they influence the decision-making process. Here, we aim to bridge this gap by discussing the existing literature on the potential role of threat-induced bodily states on decision making and provide a new neurocomputational framework explaining how these effects can facilitate or bias approach-avoid decisions under threat. Theoretical accounts have stated that threat-induced parasympathetic activity is involved in information gathering and decision making. Parasympathetic dominance over sympathetic activity is particularly seen during threat-anticipatory freezing, an evolutionarily conserved response to threat demonstrated across species and characterized by immobility and bradycardia. Although this state of freezing has been linked to altered information processing and action preparation, a full theoretical treatment of the interactions with value-based decision making has not yet been achieved. Our neural framework, which we term the Threat State/Value Integration (TSI) Model, will illustrate how threat-induced bodily states may impact valuation of competing incentives at three stages of the decision-making process, namely at threat evaluation, integration of rewards and threats, and action initiation. Additionally, because altered parasympathetic activity and decision biases have been shown in anxious populations, we will end with discussing how biases in this system can lead to characteristic patterns of avoidance seen in anxiety-related disorders, motivating future pre-clinical and clinical research.

Ictal activation of oxygen-conserving reflexes as a mechanism for sudden death in epilepsy

OBJECTIVE

To test the hypothesis that death with physiological parallels to human cases of sudden unexpected death in epilepsy (SUDEP) can be induced in seizing rats by ictal activation of oxygen-conserving reflexes (OCRs).

METHODS

Urethane-anesthetized female Long-Evans rats were implanted with electrodes for electrocardiography (ECG), electrocorticography (ECoG), and respiratory thermocouple; venous and arterial cannulas; and a laryngoscope guide and cannula or nasal cannula for activation of the laryngeal chemoreflex (LCR) or mammalian diving reflex (MDR), respectively. Kainic acid injection, either systemic or into the ventral hippocampus, induced prolonged acute seizures.

RESULTS

Reflex challenges during seizures caused sudden death in 18 of 20 rats-all MDR rats (10) and all but two LCR rats (8) failed to recover from ictal activation of OCRs and died within minutes of the reflexes. By comparison, 4 of 4 control (ie, nonseizing) rats recovered from 64 induced diving reflexes (16 per rat), and 4 of 4 controls recovered from 64 induced chemoreflexes (16 per rat). Multiple measures were consistent with reports of human SUDEP. Terminal central apnea preceded terminal asystole in all cases. Heart and respiratory rate fluctuations that paralleled those seen in human SUDEP occurred during OCR-induced sudden death, and mean arterial pressure (MAP) was predictive of death, showing a 17 or 15 mm Hg drop (MDR and LCR, respectively) in the 20 s window centered on the time of brain death. OCR activation was never fatal in nonseizing rats.

SIGNIFICANCE

These results present a method of inducing sudden death in two seizure models that show pathophysiology consistent with that observed in human cases of SUDEP. This proposed mechanism directly informs previous findings by our group and others in the field; provides a repeatable, inducible animal model for the study of sudden death; and offers a potential explanation for observations made in cases of human SUDEP.

Individual Differences in Cross-System Physiological Activity at Rest and in Response to Acute Social Stress

OBJECTIVE

Individual differences in long-term cardiovascular disease risk are related to physiological responses to psychological stress. However, little is known about specific physiological response profiles in young adults that may set the stage for long-term increased cardiovascular disease risk. We investigated individual differences in profiles of resting cardiovascular physiology and stress reactivity, combining parasympathetic, sympathetic, and hemodynamic measures.

METHODS

Participants (n = 744, 71% women, mean [standard deviation] age = 20.1 [2.4] years) underwent the Trier Social Stress Test, while blood pressure (systolic blood pressure, diastolic blood pressure), electrocardiograms (interbeat interval), and impedance cardiograms (preejection period, left ventricular ejection time) were recorded. Respiratory sinus arrhythmia was derived from the combination of the electrocardiogram and the impedance cardiogram. A three-step latent profile analysis (LPA) was performed on resting and reactivity values to derive clusters of individual physiological profiles. We also explored demographic and health behavioral correlates of the observed latent clusters.

RESULTS

For resting physiology, LPA revealed five different resting physiology profiles, which were related to sex, usual physical activity levels, and body mass index. Five cardiovascular stress reactivity profiles were identified: a reciprocal/moderate stress response (Cr1; 29%), and clusters characterized by high blood pressure reactivity (Cr2: 22%), high vagal withdrawal (Cr3; 22%), autonomic coactivation (parasympathetic nervous system and sympathetic nervous system; Cr4; 13%), and overall high reactivity (Cr5; 12%). Men were more likely to belong to the high reactivity (Cr5) cluster, whereas women were more likely to have autonomic coactivation (Cr4).

CONCLUSIONS

We identified five cardiovascular physiological reactivity profiles, with individuals displaying generalized hyperreactivity, predominant vagal withdrawal, autonomic coactivation, or blood pressure-specific hyperreactivity. Longitudinal studies are needed to determine whether these profiles are useful in early detection of individuals at high risk for cardiovascular disease.

Short-term hypoxia does not promote arrhythmia during voluntary apnea

The presence of bradycardic arrhythmias during volitional apnea at altitude may be caused by chemoreflex activation/sensitization. We investigated whether bradyarrhythmic episodes became prevalent in apnea following short‐term hypoxia exposure. Electrocardiograms (ECG; lead II) were collected from 22 low‐altitude residents (F = 12; age=25 ± 5 years) at 671 m. Participants were exposed to normobaric hypoxia (Spo₂ ~79 ± 3%) over a 5‐h period. ECG rhythms were assessed during both free‐breathing and maximal volitional end‐expiratory and end‐inspiratory apnea at baseline during normoxia and hypoxia exposure (20 min [AHX]; 5 h [HX5]). Free‐breathing HR became elevated at AHX (78 ± 10 bpm; p < 0.0001) and HX5 (80 ± 12 bpm; p < 0.0001) compared to normoxia (68 ± 10 bpm), whereas apnea caused significant bradycardia at AHX (nadir end‐expiratory −17 ± 14 bpm; p < 0.001) and HX5 (nadir end‐expiratory −19 ± 15 bpm; p < 0.001), but not during normoxia (nadir end‐expiratory −4 ± 13 bpm), with no difference in bradycardia responses between apneas at AHX and HX5. Conduction abnormalities were noted in five participants during normoxia (Premature Ventricular Contraction, Sinus Pause, Junctional Rhythm, Atrial Foci), which remained unchanged during apnea at AHX and HX5 (Premature Ventricular Contraction, Premature Atrial Contraction, Sinus Pause). End‐inspiratory apneas were overall longer across conditions (normoxia p < 0.05; AHX p < 0.01; HX5 p < 0.001), with comparable HR responses to end‐expiratory and fewer occurrences of arrhythmia. While short‐term hypoxia is sufficient to elicit bradycardia during apnea, the occurrence of arrhythmias in response to apnea was not affected. These findings indicate that previously observed bradyarrhythmic events in untrained individuals at altitude only become prevalent following chronic hypoxia specificlly.

Callous-unemotional traits and fearlessness: A cardiovascular psychophysiological perspective in two adolescent samples using virtual reality

There has been a longstanding debate about the link between callous-unemotional traits and fearlessness. However, biological evidence for a relationship in adolescents is lacking. Using two adolescent samples, we measured emotional reactivity and cardiac measures of sympathetic (pre-ejection period) and parasympathetic (respiratory sinus arrhythmia) reactivity during 3D TV and virtual reality fear induction. Study 1 included 62 community adolescents from a stratified sample. Study 2 included 60 adolescents from Emotional and Behavioral Difficulties schools. Results were consistent across both studies. Adolescents with high callous-unemotional traits showed coactivation of the sympathetic and parasympathetic nervous system. Consistent with these results, youths with callous-unemotional traits self-reported that they felt more in control after the fear induction. Thus, in both samples, youth with callous-unemotional traits displayed a physiological and emotional profile suggesting they maintained control during fear induction. Therefore, it is proposed here that a shift in thinking of youth with callous-unemotional traits as fearless to youth with callous-unemotional traits are better able to manage fearful situations, may be more appropriate.