Differential contributions of cardiac, coronary and pulmonary artery vagal mechanoreceptors to reflex control of the circulation

The interactive effects of posture and biological sex on the control of muscle sympathetic nerve activity during rhythmic handgrip exercise

Body posture and biological sex exhibit independent effects on the sympathetic neural responses to dynamic exercise. However, the neural mechanisms (e.g., baroreflex) by which posture impacts sympathetic outflow during rhythmic muscular contractions, and whether biological sex affects posture-mediated changes in efferent sympathetic nerve traffic during exercise, remain unknown. Thus, we tested the hypotheses that increases in muscle sympathetic nerve activity (MSNA) would be greater during upright compared with supine rhythmic handgrip (RHG) exercise, and that females would demonstrate smaller increases in MSNA during upright RHG exercise than males. Twenty young (30 [6] yr; means [SD]) individuals (9 males, 11 females) underwent 6 min of supine and upright (head-up tilt 45°) RHG exercise at 40% maximal voluntary contraction with continuous measurements of MSNA (microneurography), blood pressure (photoplethysmography), and heart rate (electrocardiogram). In the pooled group, absolute MSNA burst frequency (P < 0.001), amplitude (P = 0.009), and total MSNA (P < 0.001) were higher during upright compared with supine RHG exercise. However, body posture did not impact the peak change in MSNA during RHG exercise (range: P = 0.063-0.495). Spontaneous sympathetic baroreflex gain decreased from rest to RHG exercise (P = 0.006) and was not impacted by posture (P = 0.347). During upright RHG exercise, males demonstrated larger increases in MSNA burst amplitude (P = 0.002) and total MSNA (P = 0.001) compared with females, which coincided with greater reductions in sympathetic baroreflex gain among males (P = 0.004). Collectively, these data indicate that acute attenuation of baroreflex-mediated sympathoinhibition permits increases in MSNA during RHG exercise and that males exhibit a greater reserve for efferent sympathetic neural recruitment during orthostasis than females.NEW & NOTEWORTHY The impact of posture and sex on cardiovascular control during rhythmic handgrip (RHG) exercise is unknown. We show that increases in muscle sympathetic nerve activity (MSNA) during RHG are partly mediated by a reduction in sympathetic baroreflex gain. In addition, males demonstrate larger increases in total MSNA during upright RHG than females. These data indicate that the baroreflex partly mediates increases in MSNA during RHG and that males have a greater sympathetic vasoconstrictor reserve than females.

Unusual Presentation of De Winter's Sign Due to Bezold-Jarisch Reflex in a Patient With Severe Aortic Valve Stenosis

The de Winter electrocardiogram (ECG) pattern, marked by upsloping ST depression in leads V2-V6, ST elevation in lead aVR, and tall symmetric T waves, typically indicates left anterior descending artery (LAD) occlusion. Traditionally linked to LAD occlusion, it is rare in severe aortic stenosis and the Bezold-Jarisch reflex (BJR). We report an 83-year-old man with severe aortic stenosis who developed hypotension due to bleeding and exhibited the de Winter ECG pattern. This case highlights how severe aortic stenosis and BJR can lead to significant hemodynamic instability and ischemic ECG changes, resolving after hemodynamic stabilization.

High-Degree Atrioventricular Block and Torsades De Pointes in Severe Aortic Stenosis Treated With Transcatheter Aortic Valve Replacement

Severe aortic stenosis (AS) significantly elevates cardiovascular risk, predisposing patients to high-degree atrioventricular (AV) block and life-threatening tachyarrhythmias, including torsades de pointes (TdP). This case report presents a patient with severe AS who developed high-degree AV block and, subsequently, TdP, highlighting the interplay between bradycardia and mechanisms that trigger ventricular tachycardias. The case underscores the importance of identifying and managing these risk factors to improve patient outcomes.

Interoceptive signals from the heart and coronary circulation in health and disease

This review considers interoceptive signalling from the heart and coronary circulation. Vagal and cardiac sympathetic afferent sensory nerve endings are distributed throughout the atria, ventricles (mainly left), and coronary artery. A small proportion of cardiac receptors attached to thick myelinated vagal afferents are tonically active during the cardiac cycle. Dependent upon location, these mechanoreceptors detect fluctuations in atrial volume and coronary arterial perfusion. Atrial volume and coronary arterial signals contribute to beat-to-beat feedback control and physiological homeostasis. Most cardiac receptors are attached to thinly myelinated or nonmyelinated C fibres, many of which are unresponsive to the cardiac cycle. Of these, there are many chemically sensitive cardiac receptors which are activated during myocardial stress by locally released endogenous substances. In contrast, some tonically inactive receptors become activated by irregular ventricular wall mechanics or by distortion of the ischaemic myocardium. Furthermore, some are excited both by chemical mediators of ischaemia and wall abnormalities. Reflex responses arising from cardiac receptors attached to thinly myelinated or nonmyelinated are complex. Impulses that project centrally through vagal afferents elicit sympathoinhibition and hypotension, whereas impulses travelling in cardiac sympathetic afferents and spinal pathways elicit sympathoexcitation and hypertension. Two opposing cardiac reflexes may provide a mechanism for fine-tuning a composite haemodynamic response during myocardial stress. Sympathetic afferents provide the primary pathway for transmission of cardiac nociception to the central nervous system. However, activation of sympathetic afferents may increase susceptibility to life-threatening arrhythmias. Notably, the cardiac sympathetic afferent reflex predominates in pathophysiological states including hypertension and heart failure.

Short communication: Baroreflex function in embryonic emus (Dromiceius novaehollandiae)

The baroreflex involves cardiovascular homeostatic mechanisms that buffer the system against acute deviations in arterial blood pressure. It is comprised of the cardiac limb which involves adjustments in heart rate and the peripheral limb which involves adjustments in vascular resistance. This negative feedback loop mechanism has been investigated in numerous species of adult vertebrates, however our understanding of the maturation and functional importance of the reflex in developing animals remains poorly understood. In egglaying species, our knowledge of this mechanism is limited to the domestic chicken embryo and the embryonic alligator. While each of these species possess a cardiac baroreflex prior to hatching, they differ in the timing when it becomes functional, with the embryonic chicken possessing the reflex at 90% of incubation, while the alligator possesses the reflex at 70% of incubation. In an effort to determine if bird species might share similar patterns of active baroreflex function, we studied embryonic emus (Dromiceius novaehollandiae). However, we hypothesized that emus would possess a pattern of baroreflex function similar to that of the American alligator given the emu embryo possesses functional vagal tone at 70% of incubation, possibly indicating a more mature collection of cardiovascular control mechanism than those found in embryonic chickens. Our findings illustrate that emu embryos possess a hypotensive baroreflex at 90% of incubation. Therefore, our data fail to support our original hypothesis. While only two species of birds have been studied in this context, it could indicate that baroreflex function is not essential for cardiovascular homeostasis in birds for the majority of in ovo development.

PIEZO Ion Channels in Cardiovascular Functions and Diseases

The cardiovascular system provides blood supply throughout the body and as such is perpetually applying mechanical forces to cells and tissues. Thus, this system is primed with mechanosensory structures that respond and adapt to changes in mechanical stimuli. Since their discovery in 2010, PIEZO ion channels have dominated the field of mechanobiology. These have been proposed as the long-sought-after mechanosensitive excitatory channels involved in touch and proprioception in mammals. However, more and more pieces of evidence point to the importance of PIEZO channels in cardiovascular activities and disease development. PIEZO channel-related cardiac functions include transducing hemodynamic forces in endothelial and vascular cells, red blood cell homeostasis, platelet aggregation, and arterial blood pressure regulation, among others. PIEZO channels contribute to pathological conditions including cardiac hypertrophy and pulmonary hypertension and congenital syndromes such as generalized lymphatic dysplasia and xerocytosis. In this review, we highlight recent advances in understanding the role of PIEZO channels in cardiovascular functions and diseases. Achievements in this quickly expanding field should open a new road for efficient control of PIEZO-related diseases in cardiovascular functions.

Impact of homeostatic body hydration status, evaluated by hemodynamic measures, on different pain sensitization paths to a chronic pain syndrome

Contrasting findings on the mechanisms of chronic pain and hypertension development render the current conventional evidence of a negative relationship between blood pressure (BP) and pain severity insufficient for developing personalized treatments. In this interdisciplinary study, patients with fibromyalgia (FM) exhibiting clinically normal or elevated BP, alongside healthy participants were assessed. Different pain sensitization responses were evaluated using a dynamic 'slowly repeated evoked pain' (SREP) measure, as well as static pain pressure threshold and tolerance measures. Cardiovascular responses to clino-orthostatic (lying-standing) challenges were also examined as acute re- and de-hydration events, challenging cardiovascular and cerebrovascular homeostasis. These challenges involve compensating effects from various cardiac preload or afterload mechanisms associated with different homeostatic body hydration statuses. Additionally, hair cortisol concentration was considered as a factor with an impact on chronic hydration statuses. Pain windup (SREP) and lower pain threshold in FM patients were found to be related to BP rise during clinostatic (lying) rehydration or orthostatic (standing) dehydration events, respectively. These events were determined by acute systemic vasoconstriction (i.e., cardiac afterload response) overcompensating for clinostatic or orthostatic cardiac preload under-responses (low cardiac output or stroke volume). Lower pain tolerance was associated with tonic blood pressure reduction, determined by permanent hypovolemia (low stroke volume) decompensated by permanent systemic vasodilation. In conclusion, the body hydration status profiles assessed by (re)activity of systemic vascular resistance and effective blood volume-related measures can help predict the risk and intensity of different pain sensitization components in chronic pain syndrome, facilitating a more personalized management approach.

Aortic stiffness contributes to greater pressor responses during static hand grip exercise in healthy young and middle-aged normotensive men

Central arterial stiffness can influence exercise blood pressure (BP) by increasing the rise in arterial pressure per unit increase in aortic inflow. Whether central arterial stiffness influences the pressor response to isometric handgrip exercise (HG) and post-exercise muscle ischemia (PEMI), two common laboratory tests to study sympathetic control of BP, is unknown. We studied 46 healthy non-hypertensive males (23 young and 23 middle-aged) during HG (which increases in cardiac output [Q̇c]) and isolated metaboreflex activation PEMI (no change or decreases in Q̇c). Aortic stiffness (aortic pulse wave velocity [aPWV]; applanation tonometry via SphygmoCor) was measured during supine rest and was correlated to the pressor responses to HG and PEMI. BP (photoplethysmography) and muscle sympathetic nerve activity (MSNA) were continuously recorded at rest, during HG to fatigue (35 % maximal voluntary contraction) and 2-min of PEMI. aPWV was higher in middle-aged compared to young males (7.1 ± 0.9 vs 5.4 ± 0.7 m/s, P < 0.001). Middle-aged males also exhibited greater increases in systolic pressure (∆30 ± 11 vs 10 ± 8 mmHg) and MSNA (∆2313 ± 2006 vs 1387 ± 1482 %/min) compared to young males during HG (both, P < 0.03); with no difference in the Q̇c response (P = 0.090). Responses to PEMI were not different between groups. Sympathetic transduction during these stressors (MSNA-diastolic pressure slope) was not different between groups (P > 0.341). Middle-aged males displayed a greater increase in SBP per unit change of Q̇c during HG (∆SBP/∆Q̇c; 21 ± 18 vs 6 ± 10 mmHg/L/min, P = 0.004), with a strong and moderate relationship between the change in systolic (r = 0.53, P < 0.001) and diastolic pressure (r = 0.34, P = 0.023) and resting aPWV, respectively; with no correlation during PEMI. Central arterial stiffness can modulate pressor responses during stimuli associated with increases in cardiac output and sympathoexcitation in healthy males.

A case of recurring perioperative circulatory arrest: mind the autonomic nervous system

We report the case of an elderly woman who developed recurring episodes of unexplained cardiocirculatory arrest. The index event appeared during surgery to fix a fracture of the ankle and consisted of bradypnea, hypotension and asystole, coherent with a Bezold-Jarisch-like cardioprotective reflex. Classical signs of acute myocardial infarction were absent. Yet, occlusion of the right coronary artery (RCA) was observed and successfully revascularized, whereupon circulatory arrests vanished. We discuss several differential diagnoses. Unexplainable circulatory failure, with sinus bradycardia and arterial hypotension, despite lack of ECG signs of ischemia or significant troponin levels, suggest the action of cardioprotective reflexes of the autonomic nervous system. Coronary artery disease is a common source. Attention to cardioprotective reflexes should be taken in the case of unexplained cardiac arrest without overt reasons. We recommend performing coronary angiography to exclude significant coronary stenosis.