Progressive improvement in hemodynamic response to muscle metaboreflex in heart transplant recipients

Exercise capacity, muscle strength and objectively measured physical activity in patients after heart transplantation

Maximal exercise capacity of patients after heart transplantation (HTX) remains limited, affecting their quality of life. Evidence on the evolution of muscle strength and physical activity (PA) post-HTX is lacking, but a prerequisite to tailor cardiac rehabilitation programmes. Forty-five consecutive patients were evaluated every 3 months during the first year post-HTX. Functional exercise capacity (Six minutes walking distance test (6MWD)), peripheral (Quadriceps strength (QF)) and respiratory (Maximal inspiratory strength (MIP)) muscle strength were evaluated. PA (number of steps (PAsteps), active time (PAactive) and sedentary time (PAsed)) was objectively measured. 6MWD, QF, MIP, PAsteps and PAactive significantly improved over time (P < 0.001). No change in PAsed was noticed (P = 0.129). Despite improvements in 6MWD and QF, results remained substantially below those of age-and gender-matched healthy subjects. One year post-HTX, 30% of patients presented with peripheral muscle weakness. Baseline levels of 6MWD and QF were significantly higher in patients with pretransplant LVAD-implantation and this difference was maintained during follow-up. cardiac rehabilitation, combining aerobic exercise training and peripheral muscle strength training, is mandatory in patients post-HTX. Inspiratory muscle training should be implemented when respiratory muscle weakness is present. Programmes improving physical activity and reducing sedentary time post-HTX are essential.

The ergoreflex: how the skeletal muscle modulates ventilation and cardiovascular function in health and disease

The control of ventilation and cardiovascular function during physical activity is partially regulated by the ergoreflex, a cardiorespiratory reflex activated by physical activity. Two components of the ergoreflex have been identified: the mechanoreflex, which is activated early by muscle contraction and tendon stretch, and the metaboreflex, which responds to the accumulation of metabolites in the exercising muscles. Patients with heart failure (HF) often develop a skeletal myopathy with varying degrees of severity, from a subclinical disease to cardiac cachexia. HF‐related myopathy has been associated with increased ergoreflex sensitivity, which is believed to contribute to dyspnoea on effort, fatigue and sympatho‐vagal imbalance, which are hallmarks of HF. Ergoreflex sensitivity increases significantly also in patients with neuromuscular disorders. Exercise training is a valuable therapeutic option for both HF and neuromuscular disorders to blunt ergoreflex sensitivity, restore the sympatho‐vagal balance, and increase tolerance to physical exercise. A deeper knowledge of the mechanisms mediating ergoreflex sensitivity might enable a drug or device modulation of this reflex when patients cannot exercise because of advanced skeletal myopathy.

Combined mental task and metaboreflex impair cerebral oxygenation in patients with type 2 diabetes mellitus

Cardiovascular regulation is altered by type 2 diabetes mellitus (DM2), producing an abnormal response to muscle metaboreflex. During physical exercise, cerebral blood flow is impaired in patients with DM2, and this phenomenon may reduce cerebral oxygenation (COX). We hypothesized that the simultaneous execution of a mental task (MT) and metaboreflex activation would reduce COX in patients with DM2. Thirteen individuals suffering from DM2 (6 women) and 13 normal age-matched controls (CTL, 6 women) participated in this study. They underwent five different tests, each lasting 12 min: postexercise muscle ischemia (PEMI) to activate the metaboreflex, control exercise recovery (CER), PEMI + MT, CER + MT, and MT alone. COX was evaluated using near-infrared spectroscopy with sensors applied to the forehead. Central hemodynamics was assessed using impedance cardiography. We found that when MT was superimposed on the PEMI-induced metaboreflex, patients with DM2 could not increase COX to the same extent reached by the CTL group (101.13% ± 1.08% vs. 104.23% ± 2.51%, P < 0.05). Moreover, patients with DM2 had higher mean blood pressure and systemic vascular resistance as well as lower stroke volume and cardiac output levels compared with the CTL group, throughout our experiments. It was concluded that patients with DM2 had reduced capacity to enhance COX when undertaking an MT during metaboreflex. Results also confirm that patients with DM2 had dysregulated hemodynamics during metaboreflex, with exaggerated blood pressure response and vasoconstriction. This may have implications for these patients' lack of inclination to exercise.

Changes in Resting and Exercise Hemodynamics Early After Heart Transplantation: A Simulation Perspective

Introduction: During heart transplantation (HTx), cardiac denervation is inevitable, thus typically resulting in chronic resting tachycardia and chronotropic incompetence with possible consequences in patient quality of life and clinical outcomes. To this date, knowledge of hemodynamic changes early after HTx is still incomplete. This study aims at providing a model-based description of the complex hemodynamic changes at rest and during exercise in HTx recipients (HTxRs). Materials and Methods: A numerical model of early HTxRs is developed that integrates intrinsic and autonomic heart rate (HR) control into a lumped-parameter cardiovascular system model. Intrinsic HR control is realized by a single-cell sinoatrial (SA) node model. Autonomic HR control is governed by aortic baroreflex and pulmonary stretch reflex and modulates SA node activity through neurotransmitter release. The model is tuned based on published clinical data of 15 studies. Simulations of rest and exercise are performed to study hemodynamic changes associated with HTxRs. Results: Simulations of HTxRs at rest predict a substantially increased HR [93.8 vs. 69.5 beats/min (bpm)] due to vagal denervation while maintaining normal cardiac output (CO) (5.2 vs. 5.6 L/min) through a reduction in stroke volume (SV) (55.4 vs. 82 mL). Simulations of exercise predict markedly reduced peak CO (13 vs. 19.8 L/min) primarily resulting from diminished peak HRs (133.9 vs. 169 bpm) and reduced ventricular contractility. Yet, the model results show that HTxRs can maintain normal CO for low- to medium-intensity exercise by increased SV augmentation through the Frank-Starling mechanism. Conclusion: Relevant hemodynamic changes occur after HTx. Simulations suggest that (1) increased resting HRs solely result from the absence of vagal tone; (2) chronotropic incompetence is the main limiting factor of exercise capacity whereby peripheral factors play a secondary role; and (3) despite the diminished exercise capacity, HTxRs can compensate chronotropic incompetence by a preload-mediated increase in SV augmentation and thus maintain normal CO in low- to medium-intensity exercise.

A brief bout of exercise in hypoxia reduces ventricular filling rate and stroke volume response during muscle metaboreflex activation

Purpose

The hemodynamic consequences of exercise in hypoxia have not been completely investigated. The present investigation aimed at studying the hemodynamic effects of contemporary normobaric hypoxia and metaboreflex activation.

Methods

Eleven physically active, healthy males (age 32.7 ± 7.2 years) completed a cardiopulmonary test on an electromagnetically braked cycle-ergometer to determine their maximum workload (W_max). On separate days, participants performed two randomly assigned exercise sessions (3 minutes pedalling at 30% of W_max): (1) one in normoxia (NORMO), and (2) one in normobaric hypoxia with FiO₂ set to 13.5% (HYPO). After each session, the following protocol was randomly assigned: either (1) post-exercise muscle ischemia (PEMI) to study the metaboreflex, or (2) a control exercise recovery session, i.e., without metaboreflex activation. Hemodynamics were assessed with impedance cardiography.

Results

The main result was that the HYPO session impaired the ventricular filling rate (measured as stroke volume/diastolic time) response during PEMI versus control condition in comparison to the NORMO test (31.33 ± 68.03 vs. 81.52 ± 49.23 ml·s⁻¹,respectively, p = 0.003). This caused a reduction in the stroke volume response (1.45 ± 9.49 vs. 10.68 ± 8.21 ml, p = 0.020). As a consequence, cardiac output response was impaired during the HYPO test.

Conclusions

The present investigation suggests that a brief exercise bout in hypoxia is capable of impairing cardiac filling rate as well as stroke volume during the metaboreflex. These results are in good accordance with recent findings showing that among hemodynamic modulators, ventricular filling is the most sensible variable to hypoxic stimuli.

Effect of Combined Mental Task and Metaboreflex Activation on Hemodynamics and Cerebral Oxygenation in Patients With Metabolic Syndrome

Objective: The hemodynamic response to muscle metaboreflex has been reported to be significantly altered by metabolic syndrome (MS), with exaggerated systemic vascular resistance (SVR) increments and reduced cardiac output (CO) in comparison to healthy controls (CTLs). Moreover, patients with metabolic disorders, such as type 2 diabetes, have proven to have impaired cerebral blood flow in response to exercise. Thus, we hypothesized that contemporary mental task (MT) and metaboreflex would result in reduced cerebral oxygenation (COX) in these patients.

Methods: Thirteen MS patients (five women) and 14 normal age-matched CTLs (six women) were enrolled in this study. All the participants underwent five different tests, each lasting 12 min: post-exercise muscle ischemia (PEMI) to activate the metaboreflex, control exercise recovery (CER), PEMI + MT, CER + MT, and MT alone. Cerebral oxygenation was evaluated using near-infrared spectroscopy with sensors applied to the forehead. Hemodynamics were measured using impedance cardiography.

Results: The main results show that MS patients had higher SVR and lower CO levels compared to the CTL group during metaboreflex activation. Stroke volume and ventricular filling and emptying rates were also significantly reduced. Moreover, when MT was added to PEMI, COX was significantly increased in the CTL group with respect to the baseline (103.46 ± 3.14%), whereas this capacity was reduced in MS patients (102.37 ± 2.46%).

Conclusion: It was concluded that (1) patients with MS showed hemodynamic dysregulation during the metaboreflex, with exaggerated vasoconstriction and that (2) as compared to CTL, MS patients had reduced capacity to enhance COX when an MT superimposed the metaboreflex.

Exercise intolerance and fatigue in chronic heart failure: is there a role for group III/IV afferent feedback?

Exercise intolerance and early fatiguability are hallmark symptoms of chronic heart failure. While the malfunction of the heart is certainly the leading cause of chronic heart failure, the patho-physiological mechanisms of exercise intolerance in these patients are more complex, multifactorial and only partially understood. Some evidence points towards a potential role of an exaggerated afferent feedback from group III/IV muscle afferents in the genesis of these symptoms. Overactivity of feedback from these muscle afferents may cause exercise intolerance with a double action: by inducing cardiovascular dysregulation, by reducing motor output and by facilitating the development of central and peripheral fatigue during exercise. Importantly, physical inactivity appears to affect the progression of the syndrome negatively, while physical training can partially counteract this condition. In the present review, the role played by group III/IV afferent feedback in cardiovascular regulation during exercise and exercise-induced muscle fatigue of healthy people and their potential role in inducing exercise intolerance in chronic heart failure patients will be summarised.

The Effect of Anodal Transcranial Direct Current Stimulation Over Left and Right Temporal Cortex on the Cardiovascular Response: A Comparative Study

Background: Stimulation of the right and left anterior insular cortex, increases and decreases the cardiovascular response respectively, thus indicating the brain’s lateralization of the neural control of circulation. Previous experiments have demonstrated that transcranial direct current stimulation (tDCS) modulates the autonomic cardiovascular control when applied over the temporal cortex. Given the importance of neural control for a normal hemodynamic response, and the potential for the use of tDCS in the treatment of cardiovascular diseases, this study investigated whether tDCS was capable of modulating autonomic regulation.

Methods: Cardiovascular response was monitored during a post-exercise muscle ischemia (PEMI) test, which is well-documented to increase sympathetic drive. A group of 12 healthy participants performed a PEMI test in a control (Control), sham (Sham) and two different experimental sessions where the anodal electrode was applied over the left temporal cortex and right temporal cortex with the cathodal electrode placed over the contralateral supraorbital area. Stimulation lasted 20 min at 2 mA. The hemodynamic profile was measured during a PEMI test. The cardiovascular parameters were continuously measured with a transthoracic bio-impedance device both during the PEMI test and during tDCS.

Results: None of the subjects presented any side effects during or after tDCS stimulation. A consistent cardiovascular response during PEMI test was observed in all conditions. Statistical analysis did not find any significant interaction and any significant main effect of condition on cardiovascular parameters (all ps > 0.316) after tDCS. No statistical differences regarding the hemodynamic responses were found between conditions and time during tDCS stimulation (p > 0.05).

Discussion: This is the first study comparing the cardiovascular response after tDCS stimulation of left and right TC both during exercise and at rest. The results of the current study suggest that anodal tDCS of the left and right TC does not affect functional cardiovascular response during exercise PEMI test and during tDCS. In light of the present and previous findings, the effect of tDCS on the cardiovascular response remains inconclusive.

Hemodynamic abnormalities during muscle metaboreflex activation in patients with type 2 diabetes mellitus

Metaboreflex is a reflex triggered during exercise or postexercise muscle ischemia (PEMI) by metaboreceptor stimulation. Typical features of metaboreflex are increased cardiac output (CO) and blood pressure. Patients suffering from metabolic syndrome display hemodynamic abnormalities, with an exaggerated systemic vascular resistance (SVR) and reduced CO response during PEMI-induced metaboreflex. Whether patients with type 2 diabetes mellitus (DM2) have similar hemodynamic abnormalities is unknown. Here we contrast the hemodynamic response to PEMI in 14 patients suffering from DM2 (age 62.7 ± 8.3 yr) and in 15 age-matched controls (CTLs). All participants underwent a control exercise recovery reference test and a PEMI test to obtain the metaboreflex response. Central hemodynamics were evaluated by unbiased operator-independent impedance cardiography. Although the blood pressure response to PEMI was not significantly different between the groups, we found that the SVR and CO responses were reversed in patients with DM2 as compared with the CTLs (SVR: 392.5 ± 549.6 and -14.8 ± 258.9 dyn·s^-1·cm^-5; CO: -0.25 ± 0.63 and 0.46 ± 0.50 l/m, respectively, in DM2 and in CTL groups, respectively; P < 0.05 for both). Of note, stroke volume (SV) increased during PEMI in the CTL group only. Failure to increase SV and CO was the consequence of reduced venous return, impaired cardiac performance, and augmented afterload in patients with DM2. We conclude that patients with DM2 have an exaggerated vasoconstriction in response to metaboreflex activation not accompanied by a concomitant increase in heart performance. Therefore, in these patients, blood pressure response to the metaboreflex relies more on SVR increases rather than on increases in SV and CO. NEW & NOTEWORTHY The main new finding of the present investigation is that subjects with type 2 diabetes mellitus have an exaggerated vasoconstriction in response to metaboreflex activation. In these patients, blood pressure response to the metaboreflex relies more on systemic vascular resistance than on cardiac output increments.

Blood Flow Restriction Training Reduces Blood Pressure During Exercise Without Affecting Metaboreflex Activity

Objective: Blood flow restriction training (BFRT) has been proposed to induce muscle hypertrophy, but its safety remains controversial as it may increase mean arterial pressure (MAP) due to muscle metaboreflex activation. However, BFR training also causes metabolite accumulation that may desensitize type III and IV nerve endings, which trigger muscle metaboreflex. Then, we hypothesized that a period of BFR training would result in blunted hemodynamic activation during muscle metaboreflex.

Methods: 17 young healthy males aged 18–25 yrs enrolled in this study. Hemodynamic responses during muscle metaboreflex were assessed by means of postexercise muscle ischemia (PEMI) at baseline (T0) and after 1 month (T1) of dynamic BFRT. BFRT consisted of 3-min rhythmic handgrip exercise applied 3 days/week (30 contractions per minute at 30% of maximum voluntary contraction) in the dominant arm. On the first week, the occlusion was set at 75% of resting systolic blood pressure (always obtained after 3 min of resting) and increased 25% every week, until reaching 150% of resting systolic pressure at week four. Hemodynamic measurements were assessed by means of impedance cardiography.

Results: BFRT reduced MAP during handgrip exercise (T1: 96.3 ± 8.3 mmHg vs. T0: 102.0 ± 9.53 mmHg, p = 0.012). However, no significant time effect was detected for MAP during the metaboreflex activation (P > 0.05). Additionally, none of the observed hemodynamic outcomes, including systemic vascular resistance (SVR), showed significant difference between T0 and T1 during the metaboreflex activation (P > 0.05).

Conclusion: BFRT reduced blood pressure during handgrip exercise, thereby suggesting a potential hypotensive effect of this modality of training. However, MAP reduction during handgrip seemed not to be provoked by lowered metaboreflex activity.

The Impact of Cardiovascular Diseases on Cardiovascular Regulation During Exercise in Humans: Studies on Metaboreflex Activation Elicited by the Post-exercise Muscle Ischemia Method

BACKGROUND

Hemodynamics during dynamic exercise is finely regulated by some neural mechanisms. One of these mechanisms is the metabolic part of the exercise pressor reflex, i.e. the muscle metaboreflex. Hemodynamic response during the metaboreflex is characterised by the recruitment of the reserves in cardiac inotropism, pre-load, after-load and chronotropism. If one of these reserves is exhausted, then the cardiovascular response is achieved by recruiting one of the other reserves, thereby indicating a remarkable plasticity of the control of circulation.

CONCLUSION

In this review, the effects of a number of cardiovascular diseases - such as heart failure, heart failure with preserved ejection fraction, hypertension, type 1 and type 2 diabetes mellitus, obesity and metabolic syndrome - on hemodynamics during the metaboreflex are reviewed.

Metaboreflex-mediated hemodynamic abnormalities in individuals with coronary artery disease without overt signs or symptoms of heart failure

This study was devised to investigate the effect of coronary artery disease (CAD) without overt signs of heart failure on the cardiovascular responses to muscle metaboreflex activation. We hypothesized that any CAD-induced preclinical systolic and/or diastolic dysfunction could impair hemodynamic response to the metaboreflex test. Twelve men diagnosed with CAD without any sign or symptoms of heart failure and 11 age-matched healthy control (CTL) subjects participated in the study. Subjects performed a postexercise muscle ischemia (PEMI) test to activate the metaboreflex. They also performed a control exercise recovery test to compare data from the PEMI test. The main results were that the CAD group reached a similar mean arterial blood pressure response as the CTL group during PEMI. However, the mechanism by which this response was achieved was different between groups. In particular, CAD achieved the target mean arterial blood pressure by increasing systemic vascular resistance (+383.8 ± 256.6 vs. +91.2 ± 293.5 dyn·s^-1·cm^-5 for the CAD and CTL groups, respectively), the CTL group by increasing cardiac preload (-0.92 ± 8.53 vs. 5.34 ± 4.29 ml in end-diastolic volume for the CAD and CTL groups, respectively), which led to an enhanced stroke volume and cardiac output. Furthermore, the ventricular filling rate response was higher in the CTL group than in the CAD group during PEMI ( P < 0.05 for all comparisons). This study confirms that diastolic function is pivotal for normal hemodynamics during the metaboreflex. Moreover, it provides evidence that early signs of diastolic impairment attributable to CAD can be detected by the metaboreflex test. NEW & NOTEWORTHY Individuals suffering from coronary artery disease without overt signs of heart failure may show early signs of diastolic dysfunction, which can be detected by the metaboreflex test. During the metaboreflex, these subjects show impaired preload and stroke volume responses and exaggerated vasoconstriction compared with controls.

Hypertension in Patients with Cardiac Transplantation

Hypertension is a common complication among post cardiac transplant recipients affecting more than 95% of patients. Increased blood pressure poses a significant cardiovascular morbidity and mortality in these patients; it should be identified quickly and needs to be managed appropriately. Understanding the pathophysiology and contributing factors to this disease in these complex and unique patients is the key to appropriate treatment selection.

Hemodynamic response to muscle reflex is abnormal in patients with heart failure with preserved ejection fraction

The aim of the present investigation was to assess the role of cardiac diastole on the hemodynamic response to metaboreflex activation. We wanted to determine whether patients with diastolic function impairment showed a different hemodynamic response compared with normal subjects during this reflex. Hemodynamics during activation of the metaboreflex obtained by postexercise muscle ischemia (PEMI) was assessed in 10 patients with diagnosed heart failure with preserved ejection fraction (HFpEF) and in 12 age-matched healthy controls (CTL). Subjects also performed a control exercise-recovery test to compare data from the PEMI test. The main results were that patients with HFpEF achieved a similar mean arterial blood pressure (MAP) response as the CTL group during the PEMI test. However, the mechanism by which this response was achieved was markedly different between the two groups. Patients with HFpEF achieved the target MAP via an increase in systemic vascular resistance (+389.5 ± 402.9 vs. +80 ± 201.9 dynes·s^-1·cm^-5 for HFpEF and CTL groups respectively), whereas MAP response in the CTL group was the result of an increase in cardiac preload (-1.3 ± 5.2 vs. 6.1 ± 10 ml in end-diastolic volume for HFpEF and CTL groups, respectively), which led to a rise in stroke volume and cardiac output. Moreover, early filling peak velocities showed a higher response in the CTL group than in the HFpEF group. This study demonstrates that diastolic function is important for normal hemodynamic adjustment to the metaboreflex. Moreover, it provides evidence that HFpEF causes hemodynamic impairment similar to that observed in systolic heart failure.NEW & NOTEWORTHY This study provides evidence that diastolic function is important for normal hemodynamic responses during the activation of the muscle metaboreflex in humans. Moreover, it demonstrates that diastolic impairment leads to hemodynamic consequences similar to those provoked by systolic heart failure. In both cases the target blood pressure is obtained mainly by means of exaggerated vasoconstriction than by a flow-mediated mechanism.

Effects of Six Months Training on Physical Capacity and Metaboreflex Activity in Patients with Multiple Sclerosis

Patients with multiple sclerosis (MS) have an increased systemic vascular resistance (SVR) response during the metaboreflex. It has been hypothesized that this is the consequence of a sedentary lifestyle secondary to MS. The purpose of this study was to discover whether a 6-month training program could reverse this hemodynamic dysregulation. Patients were randomly assigned to one of the following two groups: the intervention group (MSIT, n = 11), who followed an adapted training program; and the control group (MSCTL, n = 10), who continued with their sedentary lifestyle. Cardiovascular response during the metaboreflex was evaluated using the post-exercise muscle ischemia (PEMI) method and during a control exercise recovery (CER) test. The difference in hemodynamic variables such as stroke volume (SV), cardiac output (CO), and SVR between the PEMI and the CER tests was calculated to assess the metaboreflex response. Moreover, physical capacity was measured during a cardiopulmonary test till exhaustion. All tests were repeated after 3 and 6 months (T3 and T6, respectively) from the beginning of the study. The main result was that the MSIT group substantially improved parameters related to physical capacity (+5.31 ± 5.12 ml·min⁻¹/kg in maximal oxygen uptake at T6) in comparison with the MSCTL group (−0.97 ± 4.89 ml·min⁻¹/kg at T6; group effect: p = 0.0004). However, none of the hemodynamic variables changed in response to the metaboreflex activation. It was concluded that a 6-month period of adapted physical training was unable to reverse the hemodynamic dys-regulation in response to metaboreflex activation in these patients.

Ischemic preconditioning reduces hemodynamic response during metaboreflex activation

Ischemic preconditioning (IP) has been shown to improve exercise performance and to delay fatigue. However, the precise mechanisms through which IP operates remain elusive. It has been hypothesized that IP lowers the sensation of fatigue by reducing the discharge of group III and IV nerve endings, which also regulate hemodynamics during the metaboreflex. We hypothesized that IP reduces the blood pressure response during the metaboreflex. Fourteen healthy males (age between 25 and 48 yr) participated in this study. They underwent the following randomly assigned protocol: postexercise muscle ischemia (PEMI) test, during which the metaboreflex was elicited after dynamic handgrip; control exercise recovery session (CER) test; and PEMI after IP (IP-PEMI) test. IP was obtained by occluding forearm circulation for three cycles of 5 min spaced by 5 min of reperfusion. Hemodynamics were evaluated by echocardiography and impedance cardiography. The main results were that after IP the mean arterial pressure response was reduced compared with the PEMI test (means ± SD +3.37 ± 6.41 vs. +9.16 ± 7.09 mmHg, respectively). This was the consequence of an impaired venous return that impaired the stroke volume during the IP-PEMI more than during the PEMI test (-1.43 ± 15.35 vs. +10.28 ± 10.479 ml, respectively). It was concluded that during the metaboreflex, IP affects hemodynamics mainly because it impairs the capacity to augment venous return and to recruit the cardiac preload reserve. It was hypothesized that this is the consequence of an increased nitric oxide production, which reduces the possibility to constrict venous capacity vessels.

Metaboreflex activity in multiple sclerosis patients

PURPOSE

The muscle metaboreflex activation has been shown essential to reach normal hemodynamic response during exercise. It has been demonstrated that patients with multiple sclerosis (MS) have impaired autonomic functions and cardiovascular regulation during exercise. However, to the best of our knowledge, no previous research to date has studied the metaboreflex in MS patients. The purpose of this study was to investigate the hemodynamic response to metaboreflex activation in patients with MS (n = 43) compared to an age-matched, control group (CTL, n = 21).

METHODS

Cardiovascular response during the metaboreflex was evaluated using the post-exercise muscle ischemia (PEMI) method and during a control exercise recovery (CER) test. The difference in hemodynamics between the PEMI and the CER test was calculated and this procedure allowed for the assessment of the metaboreflex response. Hemodynamics was estimated by impedance cardiography.

RESULTS

The MS group showed a normal mean blood pressure (MBP) response as compared to the CTL group (+6.5 ± 6.9 vs. +8 ± 6.8 mmHg, respectively), but this response was achieved with an increase in systemic vascular resistance, that was higher in the MS with respect to the CTL group (+137.6 ± 300.5 vs. -14.3 ± 240 dyne · s(-1) cm(-5), respectively). This was the main consequence of the MS group's incapacity to raise the stroke volume (-0.65 ± 10.6 vs. +6.2 ± 12.8 ml, respectively).

CONCLUSION

It was concluded that MS patients have an impaired capacity to increase stroke volume (SV) in response to low level metaboreflex, even if they could sustain the MBP response by vasoconstriction. This was probably a consequence of their chronic physical de-conditioning.

Differences in hemodynamic response to metaboreflex activation between obese patients with metabolic syndrome and healthy subjects with obese phenotype

Patients suffering from obesity and metabolic syndrome (OMS) manifest a dysregulation in hemodynamic response during exercise, with an exaggerated systemic vascular increase. However, it is not clear whether this is the consequence of metabolic syndrome per se or whether it is due to concomitant obesity. The aim of the present investigation was to discover whether OMS and noncomplicated obesity resulted in different hemodynamic responses during the metaboreflex. Twelve metabolically healthy but obese subjects (MHO; 7 women), 13 OMS patients (5 women), and 12 normal age-matched controls (CTL; 6 women) took part in this study. All participants underwent a postexercise muscle ischemia protocol to evaluate the metaboreflex activity. Central hemodynamics were evaluated by impedance cardiography. The main result shows an exaggerated increase in systemic vascular resistance from baseline during the metaboreflex in the OMS patients as compared with the other groups (481.6 ± 180.3, −0.52 ± 177.6, and −60.5 ± 58.6 dynes·s−1·cm−5 for the OMS, the MHO, and the CTL groups, respectively; P < 0.05). Moreover, the MHO subjects and the CTL group showed an increase in cardiac output during the metaboreflex (288.7 ± 325.8 and 703.8 ± 276.2 ml/m increase with respect to baseline), whereas this parameter tended to decrease in the OMS group (−350 ± 236.5 ml/m). However, the blood pressure response, which tended to be higher in the OMS patients, was not statistically different between groups. The results of the present investigation suggest that OMS patients have an exaggerated vasoconstriction in response to metaboreflex activation and that this fact is not due to obesity per se.

Neural regulation of cardiovascular response to exercise: role of central command and peripheral afferents

During dynamic exercise, mechanisms controlling the cardiovascular apparatus operate to provide adequate oxygen to fulfill metabolic demand of exercising muscles and to guarantee metabolic end-products washout. Moreover, arterial blood pressure is regulated to maintain adequate perfusion of the vital organs without excessive pressure variations. The autonomic nervous system adjustments are characterized by a parasympathetic withdrawal and a sympathetic activation. In this review, we briefly summarize neural reflexes operating during dynamic exercise. The main focus of the present review will be on the central command, the arterial baroreflex and chemoreflex, and the exercise pressure reflex. The regulation and integration of these reflexes operating during dynamic exercise and their possible role in the pathophysiology of some cardiovascular diseases are also discussed.

Improvement in hemodynamic responses to metaboreflex activation after one year of training in spinal cord injured humans

Spinal cord injured (SCI) individuals show an altered hemodynamic response to metaboreflex activation due to a reduced capacity to vasoconstrict the venous and arterial vessels below the level of the lesion. Exercise training was found to enhance circulating catecholamines and to improve cardiac preload and venous tone in response to exercise in SCI subjects. Therefore, training would result in enhanced diastolic function and capacity to vasoconstrict circulation. The aim of this study was to test the hypothesis that one year of training improves hemodynamic response to metaboreflex activation in these subjects. Nine SCI individuals were enrolled and underwent a metaboreflex activation test at the beginning of the study (T0) and after one year of training (T1). Hemodynamics were assessed by impedance cardiography and echocardiography at both T0 and T1. Results show that there was an increment in cardiac output response due to metaboreflex activity at T1 as compared to T0 (545.4 ± 683.9 mL·min⁻¹ versus 220.5 ± 745.4 mL·min⁻¹, P < 0.05). Moreover, ventricular filling rate response was higher at T1 than at T0. Similarly, end-diastolic volume response was increased after training. We concluded that a period of training can successfully improve hemodynamic response to muscle metaboreflex activation in SCI subjects.

Pathophysiology of human heart failure: importance of skeletal muscle myopathy and reflexes

In the last 20 years there has been mounting evidence that chronic heart failure (CHF) has a complex pathophysiology, which begins with an abnormality of the heart as a 'primum movens', but involves adaptive changes in many body parts, including the cardiovascular, musculoskeletal, renal, neuroendocrine, haemostatic, immune and inflammatory systems. Alterations in skeletal muscle are also of importance in limiting functional capacity in patients with CHF, because reduced physical activity plays some part in the muscle alterations in CHF. On the whole, these abnormalities resemble those induced by physical deconditioning. Moreover, the overactivation of signals originating from skeletal muscle receptors (mechano-metaboreceptors) is an intriguing hypothesis proposed to explain the origin of symptoms and the beneficial effect of exercise training in the CHF syndrome. These reflexes may contribute to sympathetic overactivation, to exercise intolerance and to the progression of CHF syndrome. The so-called metaboreflex has been reported to be hyperactive in CHF and to be responsible for a paradoxical increase in systemic vascular resistance and decrease in cardiac output whenever activated in these patients. This report is a brief summary of the latest news in this area of research.

Effects of acute vasodilation on the hemodynamic response to muscle metaboreflex

The aim of the present study was to test the contribution of stroke volume (SV) in hemodynamic response to muscle metaboreflex activation in healthy individuals. We hypothesized that an acute decrease in cardiac afterload and preload due to the administration of a vasodilating agent could reduce postexercise muscle ischemia (PEMI)-induced SV response. Ten healthy males (age 33.6 ± 1.3 yr) were enrolled and randomly assigned to the following study protocol: 1) PEMI session, 2) control exercise recovery (CER) session, 3) PEMI after sublingual administration of 5 mg of isosorbide dinitrate (ISDN), and 4) CER after ISDN. Central hemodynamics were evaluated by means of impedance cardiography. The main findings were a blunted SV response during metaboreflex following acute arterial and venous vasodilation, associated with a reduction in cardiac diastolic time and filling, and a decrement of systemic vascular resistance. These hemodynamic changes restrain blood pressure response during metaboreflex activation. Our results indicate that hemodynamic response to metaboreflex activation is a highly integrated phenomenon encompassing complex interplay between heart rate, cardiac performance, preload, and afterload and that impairment of one or more of these parameters leads to altered hemodynamic response to metaboreflex.