Abstract-Autonomic dysfunction, including baroreceptor attenuation and sympathetic activation, has been reported in patients with myocardial infarction (MI) and has been associated with increased mortality. We tested the hypotheses that exercise training (ET) in post-MI patients would normalize arterial baroreflex sensitivity (BRS) and muscle sympathetic nerve activity (MSNA), and long-term ET would maintain the benefits in BRS and MSNA. Twenty-eight patients after 1 month of uncomplicated MI were randomly assigned to 2 groups, ET (MI-ET) and untrained. A normal control group was also studied. ET consisted of three 60-minute exercise sessions per week for 6 months. We evaluated MSNA (microneurography), blood pressure (automatic oscillometric method), heart rate (ECG), and spectral analysis of RR interval, systolic arterial pressure (SAP), and MSNA. Baroreflex gain of SAP-RR interval and SAP-MSNA were calculated using the ␣-index. At 3 to 5 days and 1 month after MI, MSNA and low-frequency SAP were significantly higher and BRS significantly lower in MI patients when compared with the normal control group. ET significantly decreased MSNA (bursts per 100 heartbeats) and the low-frequency component of SAP and significantly increased the low-frequency component of MSNA and BRS of the RR interval and MSNA. These changes were so marked that the differences between patients with MI and the normal control group were no longer observed after ET. MSNA and BRS in the MI-untrained group did not change from baseline over the same time period. ET normalizes BRS, low-frequency SAP, and MSNA in patients with MI. These improvements in autonomic control are maintained by long-term ET. Key Words: myocardial infarction Ⅲ sympathetic nerve activity Ⅲ exercise training Ⅲ autonomic control Ⅲ baroreflex control P revious studies show that myocardial infarction (MI) is linked to increased sympathetic nervous activity 1,2 and impaired arterial baroreflex sensitivity (BRS). 3 These findings of autonomic dysfunction have been associated with increased mortality in patients after MI. 4 -10 La Rovere et al 7 demonstrated that decreased BRS is associated with cardiac mortality risk. A follow-up of 61 months in uncomplicated post-MI patients with preserved left ventricular function showed that depressed BRS discriminated a subgroup at long-term high risk for cardiovascular mortality. 10 Increased muscle sympathetic nerve activity (MSNA) is an independent predictor of poor prognosis in patients with chronic heart failure, including patients with chronic heart failure after MI. 11 Thus, a therapeutic strategy targeted to the improvement in autonomic control in patients with MI represents an important clinical goal.In patients with cardiovascular disease, studies have shown that physical exercise is an important strategy to improve autonomic function. Exercise training has been shown to decrease MSNA 12 and improve BRS 12-14 in patients with MI. It remains unknown whether the magnitude of change in autonomic control actually normalizes BRS and sy...

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Toschi-Dias E, Trombetta IC, Dias da Silva VJ, Maki-Nunes C, Cepeda FX, Alves MJ, Drager LF, Lorenzi-Filho G, Negrao CE, Rondon MU. Time delay of baroreflex control and oscillatory pattern of sympathetic activity in patients with metabolic syndrome and obstructive sleep apnea. Am J Physiol Heart Circ Physiol 304: H1038-H1044, 2013. First published January 25, 2013; doi:10.1152/ajpheart.00848.2012.-The incidence and strength of muscle sympathetic nerve activity (MSNA) depend on the magnitude (gain) and latency (time delay) of the arterial baroreflex control (ABR). However, the impact of metabolic syndrome (MetS) and obstructive sleep apnea (OSA) on oscillatory pattern of MSNA and time delay of the ABR of sympathetic activity is unknown. We tested the hypothesis that MetS and OSA would impair the oscillatory pattern of MSNA and the time delay of the ABR of sympathetic activity. Forty-three patients with MetS were allocated into two groups according to the presence of OSA (MetS ϩ OSA, n ϭ 21; and MetS Ϫ OSA, n ϭ 22). Twelve aged-paired healthy controls (C) were also studied. OSA (apnea-hypopnea index Ͼ 15 events/h) was diagnosed by polysomnography. We recorded MSNA (microneurography), blood pressure (beat-to-beat basis), and heart rate (EKG). Oscillatory pattern of MSNA was evaluated by autoregressive spectral analysis and the ABR of MSNA (ABR MSNA, sensitivity and time delay) by bivariate autoregressive analysis. Patients with MetS ϩ OSA had decreased oscillatory pattern of MSNA compared with MetS Ϫ OSA (P Ͻ 0.01) and C (P Ͻ 0.001). The sensitivity of the ABR MSNA was lower and the time delay was greater in MetS ϩ OSA compared with MetS Ϫ OSA (P Ͻ 0.001 and P Ͻ 0.01, respectively) and C (P Ͻ 0.001 and P Ͻ 0.001, respectively). Patients with MetS Ϫ OSA showed decreased oscillatory pattern of MSNA compared with C (P Ͻ 0.01). The sensitivity of the ABR MSNA was lower in MetS Ϫ OSA than in C group (P Ͻ 0.001). In conclusion, MetS decreases the oscillatory pattern of MSNA and the magnitude of the ABR MSNA. OSA exacerbates these autonomic dysfunctions and further increases the time delay of the baroreflex response of MSNA. latency of baroreflex control; muscle sympathetic nerve activity variability; heart rate variability SYMPATHETIC NERVE ACTIVITY is increased in patients with metabolic syndrome (MetS) (11,22), which enhances the risk of cardiovascular disease and likely cardiac death (5,20,21). Obstructive sleep apnea (OSA), a frequent comorbidity in patients with MetS (8), is characterized by recurrent episodes of partial or complete upper airway obstruction during sleep, leading to intermittent hypoxemia and frequent arousals from sleep (40). Additionally, OSA exacerbates the muscle sympathetic nerve activity (MSNA) in patients with MetS (12, 37) and impairs arterial baroreflex control (ABR) of heart rate (HR) (12, 37). Grassi et al. (12) demonstrated that ABR of HR was further decreased in patients with MetS and OSA. We confirmed that OSA exacerbates the dysfunction of the ABR of HR in patients with MetS (37).The ...

Sildenafil induces vasodilation and is used for treating erectile dysfunction. Although its influence on resting heart function appears to be minimal, recent studies suggest that sildenafil can increase sympathetic activity. We therefore tested whether sildenafil injected into the central nervous system alters the autonomic control of the cardiovascular system in conscious rats. The effect of sildenafil citrate injected into the lateral cerebral ventricle was evaluated in conscious rats by means of the recording of lumbar sympathetic nerve activity (LSNA), spectral analysis of systolic arterial pressure and heart rate variability, spontaneous baroreflex sensitivity, and baroreflex control of LSNA. Intracerebroventricular (ICV, 100 microg /5 microl) administration of sildenafil caused remarkable tachycardia without significant change in basal arterial pressure and was associated with a conspicuous increase (47 +/- 14%) in LSNA. Spectral analysis demonstrated that systolic arterial pressure oscillations in the low frequency (LF) range were increased (from 6.3 +/- 1.5 to 12.8 +/- 3.8 mmHg(2)), whereas the high frequency (HF) range was not affected by ICV administration of sildenafil. Sildenafil increased pulse interval oscillations at LF and decreased them at HF. The LF-HF ratio increased from 0.04 +/- 0.01 to 0.17 +/- 0.06. Spontaneous baroreflex sensitivity measured by the sequence method and the baroreflex relationship between mean arterial pressure and LSNA were not affected by ICV administration of sildenafil. In conclusion, sildenafil elicited an increase in sympathetic nerve activity that is not baroreflex mediated, suggesting that this drug is able to elicit an autonomic imbalance of central origin. This finding may have implications for understanding the cardiovascular outcomes associated with the clinical use of this drug.

Alterations of the autonomic reflex control of the cardiovascular system have been demonstrated in clinical and animal models of insulin‐dependent diabetes mellitus. Established neuroaxonal dystrophy is considered the neuropathological hallmark of chronic experimental diabetes. However, the afferent arm of the arterial baroreflex, that is, the carotid sinus nerve and the aortic depressor nerve, has received much less attention in studies dealing with this physiopathological model. The attenuation of the pressure response to bilateral carotid occlusion in conscious rats indicates a derangement of the baroreflex, probably involving an alteration of the carotid sinus nerve. There is histological evidence obtained from adult spontaneous insulin‐dependent diabetic rats (strain BB/S) of a carotid sinus nerve with signs of axonal swelling and intramyelinic edema, suggesting diabetic neuropathy. The study of aortic baroreceptor activity in anesthetized rats with short‐ and long‐term streptozotocin diabetes by means of cross‐spectral analysis of baroreceptor activity versus arterial pressure revealed a dysfunction in the afferent arm of the baroreflex even during a short period of diabetes. The morphology of the aortic depressor nerve of streptozotocin‐diabetic rats indicated axonal atrophy by visual analysis remarkably at the distal segments of the nerves. This finding was confirmed by morphometric study of the myelinated fibers. In conclusion, although studies of the arterial baroreceptors related to experimental diabetes are scanty in the literature, there is electrophysiological and histological evidence demonstrating that the carotid sinus and the aortic depressor nerves are abnormal in this experimental model.

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A low resting heart rate (HR) would be of great benefit in cardiovascular diseases. Ivabradine—a novel selective inhibitor of hyperpolarization-activated cyclic nucleotide gated (HCN) channels- has emerged as a promising HR lowering drug. Its effects on the autonomic HR control are little known. This study assessed the effects of chronic treatment with ivabradine on the modulatory, reflex and tonic cardiovascular autonomic control and on the renal sympathetic nerve activity (RSNA). Male Wistar rats were divided in 2 groups, receiving intraperitoneal injections of vehicle (VEH) or ivabradine (IVA) during 7 or 8 consecutive days. Rats were submitted to vessels cannulation to perform arterial blood pressure (AP) and HR recordings in freely moving rats. Time series of resting pulse interval and systolic AP were used to measure cardiovascular variability parameters. We also assessed the baroreflex, chemoreflex and the Bezold-Jarish reflex sensitivities. To better evaluate the effects of ivabradine on the autonomic control of the heart, we performed sympathetic and vagal autonomic blockade. As expected, ivabradine-treated rats showed a lower resting (VEH: 362 ± 16 bpm vs. IVA: 260 ± 14 bpm, p = 0.0005) and intrinsic HR (VEH: 369 ± 9 bpm vs. IVA: 326 ± 11 bpm, p = 0.0146). However, the chronic treatment with ivabradine did not change normalized HR spectral parameters LF (nu) (VEH: 24.2 ± 4.6 vs. IVA: 29.8 ± 6.4; p > 0.05); HF (nu) (VEH: 75.1 ± 3.7 vs. IVA: 69.2 ± 5.8; p > 0.05), any cardiovascular reflexes, neither the tonic autonomic control of the HR (tonic sympathovagal index; VEH: 0.91± 0.02 vs. IVA: 0.88 ± 0.03, p = 0.3494). We performed the AP, HR and RSNA recordings in urethane-anesthetized rats. The chronic treatment with ivabradine reduced the resting HR (VEH: 364 ± 12 bpm vs. IVA: 207 ± 11 bpm, p < 0.0001), without affecting RSNA (VEH: 117 ± 16 vs. IVA: 120 ± 9 spikes/s, p = 0.9100) and mean arterial pressure (VEH: 70 ± 4 vs. IVA: 77 ± 6 mmHg, p = 0.3293). Our results suggest that, in health rats, the long-term treatment with ivabradine directly reduces the HR without changing the RSNA modulation and the reflex and tonic autonomic control of the heart.

The last decade has brought a comprehensive change in our view of cardiac remodeling processes under both physiological and pathological conditions, and cardiac stem cells have become important new players in the general mainframe of cardiac homeostasis. Different types of cardiac stem cells show different capacities for differentiation into the three major cardiac lineages: myocytes, endothelial cells and smooth muscle cells. Physiologically, cardiac stem cells contribute to cardiac homeostasis through continual cellular turnover. Pathologically, these cells exhibit a high level of proliferative activity in an apparent attempt to repair acute cardiac injury, indicating that these cells possess (albeit limited) regenerative potential. In addition to cardiac stem cells, mesenchymal stem cells represent another multipotent cell population in the heart; these cells are located in regions near pericytes and exhibit regenerative, angiogenic, antiapoptotic, and immunosuppressive properties. The discovery of these resident cardiac stem cells was followed by a number of experimental studies in animal models of cardiomyopathies, in which cardiac stem cells were tested as a therapeutic option to overcome the limited transdifferentiating potential of hematopoietic or mesenchymal stem cells derived from bone marrow. The promising results of these studies prompted clinical studies of the role of these cells, which have demonstrated the safety and practicability of cellular therapies for the treatment of heart disease. However, questions remain regarding this new therapeutic approach. Thus, the aim of the present review was to discuss the multitude of different cardiac stem cells that have been identified, their possible functional roles in the cardiac regenerative process, and their potential therapeutic uses in treating cardiac diseases.