Exercise training attenuates the pressor response evoked by peripheral chemoreflex in rats with heart failure

Exercise modulates sympathetic and vascular function in chronic kidney disease

BACKGROUNDChronic kidney disease (CKD) is characterized by chronic overactivation of the sympathetic nervous system (SNS), which increases the risk of cardiovascular (CV) disease and mortality. SNS overactivity increases CV risk by multiple mechanisms, including vascular stiffness. We tested the hypothesis that aerobic exercise training would reduce resting SNS activity and vascular stiffness in patients with CKD.METHODSIn this randomized controlled trial, sedentary older adults with CKD underwent 12 weeks of exercise (cycling, n = 32) or stretching (an active control group, n = 26). Exercise and stretching interventions were performed 20-45 minutes/session at 3 days/week and were matched for duration. Primary endpoints include resting muscle sympathetic nerve activity (MSNA) via microneurography, arterial stiffness by central pulse wave velocity (PWV), and aortic wave reflection by augmentation index (AIx).RESULTSThere was a significant group × time interaction in MSNA and AIx with no change in the exercise group but with an increase in the stretching group after 12 weeks. The magnitude of change in MSNA was inversely associated with baseline MSNA in the exercise group. There was no change in PWV in either group over the study period.CONCLUSIONOur data demonstrate that 12 weeks of cycling exercise has beneficial neurovascular effects in patients with CKD. Specifically, exercise training safely and effectively ameliorated the increase in MSNA and AIx observed over time in the control group. This sympathoinhibitory effect of exercise training showed greater magnitude in patients with CKD with higher resting MSNA.TRIAL REGISTRATIONClinicalTrials.gov, NCT02947750.FUNDINGNIH R01HL135183; NIH R61AT10457; NIH NCATS KL2TR002381; and NIH T32 DK00756; NIH F32HL147547; and VA Merit I01CX001065.

Contribution of Peripheral Chemoreceptors to Exercise Intolerance in Heart Failure

Peripheral chemoreceptors (PChRs), because of their strategic localization at the bifurcation of the common carotid artery and along the aortic arch, play an important protective role against hypoxia. Stimulation of PChRs evokes hyperventilation and hypertension to maintain adequate oxygenation of critical organs. A relationship between increased sensitivity of PChRs (hyperreflexia) and exercise intolerance (ExIn) in patients with heart failure (HF) has been previously reported. Moreover, some studies employing an acute blockade of PChRs (e.g., using oxygen or opioids) demonstrated improvement in exercise capacity, suggesting that hypertonicity is also involved in the development of ExIn in HF. Nonetheless, the precise mechanisms linking dysfunctional PChRs to ExIn remain unclear. From the clinical perspective, there are two main factors limiting exercise capacity in HF patients: subjective perception of dyspnoea and muscle fatigue. Both have many determinants that might be influenced by abnormal signalling from PChRs, including: exertional hyperventilation, oscillatory ventilation, ergoreceptor oversensitivity, and augmented sympathetic tone. The latter results in reduced muscle perfusion and altered muscle structure. In this review, we intend to present the milieu of abnormalities tied to malfunctioning PChRs and discuss their role in the complex relationships leading, ultimately, to ExIn.

Respiratory muscle training decreases diaphragm DNA damage in rats with heart failure

Respiratory muscle training (RMT) promotes beneficial effects on respiratory mechanics, heart and lung morphological changes, and hemodynamic variables in rats with heart failure (HF). However, the relation between RMT effects and diaphragm oxidative stress remains unclear. Therefore, the aim of this study was to evaluate the RMT effects on diaphragm DNA damage in HF rats. Wistar rats were allocated into 4 groups: sedentary sham (Sed-Sham, n = 8), trained sham (RMT-Sham, n = 8), sedentary HF (Sed-HF, n = 8), and trained HF (RMT-HF, n = 8). The animals underwent a RMT protocol (30 min/day, 5 days/week for 6 weeks), whereas sedentary animals did not exercise. Groups were compared by a two-way ANOVA and Tukey’s post hoc tests. In rats with HF, RMT promoted reduction in pulmonary congestion (p < 0.0001) and left ventricular end diastolic pressure (p < 0.0001). Moreover, RMT produced a decrease in the diaphragm DNA damage in HF rats. This was demonstrated through the reduction in the percentage of tail DNA (p < 0.0001), tail moment (p < 0.01), and Olive tail moment (p < 0.001). These findings showed that a 6-week RMT protocol in rats with HF promoted an improvement in hemodynamic function and reduces diaphragm DNA damage.

Revisiting the physiological effects of exercise training on autonomic regulation and chemoreflex control in heart failure: does ejection fraction matter?

Heart failure (HF) is a global public health problem that, independent of its etiology [reduced (HFrEF) or preserved ejection fraction (HFpEF)], is characterized by functional impairments of cardiac function, chemoreflex hypersensitivity, baroreflex sensitivity (BRS) impairment, and abnormal autonomic regulation, all of which contribute to increased morbidity and mortality. Exercise training (ExT) has been identified as a nonpharmacological therapy capable of restoring normal autonomic function and improving survival in patients with HFrEF. Improvements in autonomic function after ExT are correlated with restoration of normal peripheral chemoreflex sensitivity and BRS in HFrEF. To date, few studies have addressed the effects of ExT on chemoreflex control, BRS, and cardiac autonomic control in HFpEF; however, there are some studies that have suggested that ExT has a beneficial effect on cardiac autonomic control. The beneficial effects of ExT on cardiac function and autonomic control in HF may have important implications for functional capacity in addition to their obvious importance to survival. Recent studies have suggested that the peripheral chemoreflex may also play an important role in attenuating exercise intolerance in HFrEF patients. The role of the central/peripheral chemoreflex, if any, in mediating exercise intolerance in HFpEF has not been investigated. The present review focuses on recent studies that address primary pathophysiological mechanisms of HF (HFrEF and HFpEF) and the potential avenues by which ExT exerts its beneficial effects.