Skeletal muscle failure in heart failure

Skeletal muscle atrophy in heart failure with diabetes: from molecular mechanisms to clinical evidence

Two highly prevalent and growing global diseases impacted by skeletal muscle atrophy are chronic heart failure (HF) and type 2 diabetes mellitus (DM). The presence of either condition increases the likelihood of developing the other, with recent studies revealing a large and relatively poorly characterized clinical population of patients with coexistent HF and DM (HFDM). HFDM results in worse symptoms and poorer clinical outcomes compared with DM or HF alone, and cardiovascular-focused disease-modifying agents have proven less effective in HFDM indicating a key role of the periphery. This review combines current clinical knowledge and basic biological mechanisms to address the critical emergence of skeletal muscle atrophy in patients with HFDM as a key driver of symptoms. We discuss how the degree of skeletal muscle wasting in patients with HFDM is likely underpinned by a variety of mechanisms that include mitochondrial dysfunction, insulin resistance, inflammation, and lipotoxicity. Given many atrophic triggers (e.g. ubiquitin proteasome/autophagy/calpain activity and supressed IGF1-Akt-mTORC1 signalling) are linked to increased production of reactive oxygen species, we speculate that a higher pro-oxidative state in HFDM could be a unifying mechanism that promotes accelerated fibre atrophy. Overall, our proposal is that patients with HFDM represent a unique clinical population, prompting a review of treatment strategies including further focus on elucidating potential mechanisms and therapeutic targets of muscle atrophy in these distinct patients.

Reactive Oxygen Species/Nitric Oxide Mediated Inter-Organ Communication in Skeletal Muscle Wasting Diseases

SIGNIFICANCE

Cachexia is defined as a complex metabolic syndrome that is associated with underlying illness and a loss of muscle with or without loss of fat mass. This disease is associated with a high incidence with chronic diseases such as heart failure, cancer, chronic obstructive pulmonary disease (COPD), and acquired immunodeficiency syndrome (AIDS), among others. Since there is currently no effective treatment available, cachectic patients have a poor prognosis. Elucidation of the underlying mechanisms is, therefore, an important medical task. Recent Advances: There is accumulating evidence that the diseased organs such as heart, lung, kidney, or cancer tissue secrete soluble factors, including Angiotensin II, myostatin (growth differentiation factor 8 [GDF8]), GDF11, tumor growth factor beta (TGFβ), which act on skeletal muscle. There, they induce a set of genes called atrogenes, which, among others, induce the ubiquitin-proteasome system, leading to protein degradation. Moreover, elevated reactive oxygen species (ROS) levels due to modulation of NADPH oxidases (Nox) and mitochondrial function contribute to disease progression, which is characterized by loss of muscle mass, exercise resistance, and frailty.

CRITICAL ISSUES

Although substantial progress was achieved to elucidate the pathophysiology of cachexia, effectice therapeutic strategies are urgently needed.

FUTURE DIRECTIONS

With the identification of key components of the aberrant inter-organ communication leading to cachexia, studies in mice and men to inhibit ROS formation, induction of anti-oxidative superoxide dismutases, and upregulation of muscular nitric oxide (NO) formation either by pharmacological tools or by exercise are promising approaches to reduce the extent of skeletal muscle wasting. Antioxid. Redox Signal. 26, 700-717.

Supervised exercise training versus usual care in ambulatory patients with left ventricular assist devices: A systematic review

Implantation of left ventricular assist devices (LVAD) has increased because of improved safety profile and limited availability of heart transplantation. Although supervised exercise training (ET) programs are known to improve exercise capacity and quality of life (QoL) in heart failure (HF) patients, similar data is inconclusive in LVAD patients. Thus, we performed a systematic review on studies that incorporated supervised ET and measured peak oxygen uptake in LVAD patients. A total of 150 patients in exercise and 55 patients in control groups were included from 8 studies selected from our predefined criteria. Our systematic review suggests supervised ET has an inconsistent effect on exercise capacity and QoL when compared to control groups undergoing usual care. A quantitative sub-analysis was performed with 4 studies that provided enough data to compare peak oxygen uptake and QoL at baseline and at follow-up. After at least 6 weeks of training, LVAD patients undergoing supervised ET demonstrated significant improvement in exercise capacity (standardized mean difference [SMD] = 0.735, 95% Confidence Interval-[CI], 0.31-1.15 units of the standard deviation, P = 0.001) and QoL scores (SMD = 1.58, 95% CI 0.97-2.20 units of the standard deviation, P <0.001) when compared to the usual care group, with no serious adverse events with exercise. These results suggest that supervised ET is safe and can improve patient outcomes in LVAD patients when compared to the usual care.

Effects of cardiac resynchronization therapy on muscle sympathetic nerve activity

INTRODUCTION

Muscle sympathetic nerve activity (MSNA) is an independent prognostic marker in patients with heart failure (HF). Therefore, its relevance to the treatment of HF patients is unquestionable.

OBJECTIVES

In this study, we investigated the effects of cardiac resynchronization therapy (CRT) on MSNA response at rest and during exercise in patients with advanced HF.

METHODS

We assessed 11 HF patients (51 ± 3.4 years; New York Heart Association class III-IV; left ventricular ejection fraction 27.8 ± 2.2%; optimal medical therapy) submitted to CRT. Evaluations were made prior to and 3 months after CRT. MSNA was performed at rest and during moderate static exercise (handgrip). Peak oxygen consumption (VO2 ) was evaluated by means of cardiopulmonary exercise test. HF patients with advanced NYHA class without CRT and healthy individuals were also studied.

RESULTS

CRT reduced MSNA at rest (48.9 ± 11.1 bursts/min vs 33.7 ± 15.3 bursts/min, P < 0.05) and during handgrip exercise (MSNA 62.3 ± 13.1 bursts/min vs 46.9 ± 14.3 bursts/min, P < 0.05). Among HF patients submitted to CRT, the peak VO2 increased (12.9 ± 2.8 mL/kg/min vs 16.5 ± 3.9 mL/kg/min, P < 0.05) and an inverse correlation between peak VO2 and resting MSNA (r = -0.74, P = 0.01) was observed.

CONCLUSIONS

In patients with advanced HF and severe systolic dysfunction: (1) a significant reduction of MSNA (at rest and during handgrip) occurred after CRT, and this behavior was significantly superior to HF patients receiving only medical therapy; (2) MSNA reduction after CRT had an inverse correlation with O2 consumption outcomes.

The role of glucose in self-control: another look at the evidence and an alternative conceptualization

The strength model suggests that self-control relies on a limited resource. One candidate for this resource is glucose. Counter to the proposals of the glucose hypothesis, this study argues that the resource issue is one of allocation, not of limited supply. It addresses the argument from three perspectives: the evolution of mental processes at the species level, the adaptation of these same processes at the individual level, and the physiology of glucose transport. It is argued here that the brain has both sufficient resources and resource delivery mechanisms with which to support self-control but that these resources are allocated in accordance with personal priorities. As an alternative to the limited resource model, the current study proposes a resource-allocation model of self-control and presents several testable hypotheses.

Electrical Stimulation of Skeletal Muscles An Alternative to Aerobic Exercise Training in Patients With Chronic Heart Failure?

The aim of this study was to investigate whether electrical stimulation of skeletal muscles could represent a rehabilitation alternative for patients with chronic heart failure (CHF). Thirty patients with CHF and NYHA class II-III were randomly assigned to a rehabilitation program using either electrical stimulation of skeletal muscles or bicycle training. Patients in the first group (n = 15) had 8 weeks of home-based low-frequency electrical stimulation (LFES) applied simultaneously to the quadriceps and calf muscles of both legs (1 h/day for 7 days/week); patients in the second group (n = 15) underwent 8 weeks of 40 minute aerobic exercise (3 times a week). After the 8-week period significant increases in several functional parameters were observed in both groups: maximal VO2 uptake (LFES group: from 17.5 +/- 4.4 mL/kg/min to 18.3 +/- 4.2 mL/kg/min, P < 0.05; bicycle group: from 18.1 +/- 3.9 mL/kg/min to 19.3 +/- 4.1 mL/kg/min, P < 0.01), maximal workload (LFES group: from 84.3 +/- 15.2 W to 95.9 +/- 9.8 W, P < 0.05; bicycle group: from 91.2 +/- 13.4 W to 112.9 +/- 10.8 W, P < 0.01), distance walked in 6 minutes (LFES group: from 398 +/- 105 m to 435 +/- 112 m, P < 0.05; bicycle group: from 425 +/- 118 m to 483 +/- 120 m, P < 0.03), and exercise duration (LFES group: from 488 +/- 45 seconds to 568 +/- 120 seconds, P < 0.05; bicycle group: from 510 +/- 90 seconds to 611 +/- 112 seconds, P < 0.03). These results demonstrate that an improvement of exercise capacities can be achieved either by classical exercise training or by home-based electrical stimulation. LFES should be considered as a valuable alternative to classical exercise training in patients with CHF.

The role of exercise training in patients with chronic heart failure

The National Institute for Clinical Excellence (NICE) has recommended that exercise training be offered to patients with chronic heart failure (CHF). This recommendation is supported by research-based evidence from a variety of studies over the past 10 years. Initially, the studies were concerned primarily with the safety and effectiveness of exercise in these high-risk patients, but more recent studies have begun to investigate the most appropriate methods of exercise for this patient population. This article presents a systematic review of the literature relating to exercise training and CHE. It then attempts to identify, in light of the evidence, the most effective programme of exercise, including type, duration and degree of exercise. Finally, it discusses practical application and implementation of the research findings into everyday health care, including issues such as staff development and training, assessment, exercise and prescription for individual patients, and evaluation of the service.

Glycogen and glycogen phosphorylase associated with sarcoplasmic reticulum: effects of fatiguing activity

The purpose of the present study was to investigate the effects of fatiguing muscular activity on glycogen, glycogen phosphorylase (GP), and Ca(2+) uptake associated with the sarcoplasmic reticulum (SR). Tetanic contractions (100 ms, 75 Hz) of the gastrocnemius and plantaris muscles, elicited once per second for 15 min, significantly reduced force to 26.5 +/- 4.0% and whole muscle glycogen to 23% of rested levels. SR glycogen levels were 415.4 +/- 76.6 and 20.4 +/- 2.1 microg/mg SR protein in rested and fatigued samples, respectively. The optical density of GP from SDS-PAGE was reduced to 21% of control, whereas pyridoxal 5'-phosphate concentration, a quantitative indicator of GP content, was significantly reduced to 3% of control. GP activity after exercise, in the direction of glycogen breakdown, was reduced to 4% of control. Maximum SR Ca(2+) uptake rate was also significantly reduced to 81% of control. These data demonstrate that glycogen and GP associated with skeletal muscle SR are reduced after fatiguing activity.

R403Q and L908V mutant beta-cardiac myosin from patients with familial hypertrophic cardiomyopathy exhibit enhanced mechanical performance at the single molecule level

Familial hypertrophic cardiomyopathy (FHC) is a disease of the sarcomere. In the beta-myosin heavy chain gene, which codes for the mechanical enzyme myosin, greater than 40 point mutations have been found that are causal for this disease. We have studied the effect of two mutations, the R403Q and L908V, on myosin molecular mechanics. In the in vitro motility assay, the mutant myosins produced a 30% greater velocity of actin filament movement (v(actin)). At the single molecule level, v(actin) approximately d/t(on), where d is the myosin unitary step displacement and t(on) is the step duration. Laser trap studies were performed at 10 microM MgATP to estimate d and t(on) for the normal and mutant myosin molecules. The increase in v(actin) can be explained by a significant decrease in the average t(on)'s in both the R403Q and L908V mutants (approximately 30 ms) compared to controls (approximately 40 ms), while d was not different for all myosins tested (approximately 7 nm). Thus the mutations affect the kinetics of the cross-bridge cycle without any effect on myosin's inherent motion and force generating capacity. Based on these studies, the primary signal for the hypertrophic response appears to be an apparent gain in function of the individual mutant myosin molecules.

Apoptosis and changes in contractile protein pattern in the skeletal muscle in heart failure

Chronic heart failure is characterized as a clinical disorder by exercise intolerance. There are two factors that are independently responsible for the reduced exercise capacity: (a) a shift from myosin heavy chain 1 (MHC1) to MHC2a and MHC2b and (b) muscle atrophy. We have demonstrated, both in experimental models of heart failure and in man, that the more severe the heart failure, the greater the magnitude of skeletal muscle apoptosis. In the monocrotaline treated rat, that develops a severe right-sided heart failure, the increased number of apoptotic nuclei was paralleled by increasing levels of circulating TNFalpha. In agreement with some recent observations showing that sphingolipids can mediate programmed cell death, we found that in animals with heart failure and high number of apoptotic nuclei, circulating levels of sphingosine were significantly increased. In a study conducted in patients with heart failure we found a correlation between exercise capacity limitation and skeletal myocytes apoptosis. There was also a correlation between degree of muscle atrophy and magnitude of apoptosis. The shift in MHCs, although with a different mechanism, is also responsible for the reduced exercise capacity in these patients. In fact there is a strong correlation between indices of severity of CHF and MHC composition. Muscle fatigue, appears earlier in patients that have a greater skeletal muscle expression of 'fast' MHCs. We have also demonstrated that MHCs shift and apoptosis can be prevented by using angiotensin II converting enzyme inhibitors and angiotensin II receptor blockers.

Skeletal muscle disorders in heart failure

Heart failure is associated with reduction of exercise capacity that cannot be solely ascribed to reduced maximal oxygen uptake (VdotO2max). Therefore, research has focused on changes in skeletal muscle morphology, metabolism and function. Factors that can cause such changes in skeletal muscle comprise inactivity, malnutrition, constant or repeated episodes of inadequate oxygen delivery and prolonged exposure to altered neurohumoural stimuli. Most of these factors are not specific for the heart failure condition. On the other hand, heart failure is more than one clinical condition. Congestive heart failure (CHF) develops gradually as a result of deteriorating contractility of the viable myocardium, myocardial failure. Is it possible that development of this contractile deficit in the myocardium is paralleled by a corresponding contractile deficit of the skeletal muscles? This question cannot be answered today. Both patient studies and experimental studies support that there is a switch to a faster muscle phenotype and energy metabolism balance is more anaerobic. The muscle atrophy seen in many patients is not so evident in experimental studies. Few investigators have studied contractile function. Both fast twitch and slow twitch muscles seem to become slower, not faster as might be expected, and this is possibly linked to slower intracellular Ca2+ cycling. The neurohumoural stimuli that can cause this change are not known, but recently it has been reported that several cytokines are increased in CHF patients. Thus, the changes seen in skeletal muscles during CHF are partly secondary to inactivity, but the possibility remains that the contractility is altered because of intracellular changes of Ca2+ metabolism that are also seen in the myocardium.

Predictors of early post-cardiac transplant exercise capacity

BACKGROUND

This study was conducted to identify which pre- and perioperative clinical parameters were predictive of predischarge submaximal exercise capacity and early postdischarge maximal exercise capacity in cardiac transplant recipients.

METHODS

We studied 24 patients (mean age = 46; 25% African American) who underwent cardiac transplantation followed by an early (immediately posttransplant) postoperative exercise training program. The patients' submaximal exercise capacity was measured at hospital discharge (25 days posttransplant) using the 6-minute distance walk test. Maximal cardiopulmonary exercise testing was done within 4 months of hospital discharge (68 days) to measure peak exercise oxygen consumption (VO2) and to estimate peak exercise capacity as measured by metabolic equivalents (METs). Six clinical variables were assessed for their relationship with predischarge submaximal exercise capacity and 10 clinical variables were evaluated for their relationship with early posttransplant maximal exercise capacity.

RESULTS

Predischarge submaximal exercise capacity was correlated with postdischarge estimated METs (r = 0.43; P = 0.04). No predictors of predischarge submaximal exercise capacity were identified. Predictors of estimated peak exercise METs following discharge were younger age, longer time since resolution of rejection, and shorter postoperative hospitalization. Younger age was the only predictor of peak VO2.

CONCLUSION

Postoperative physical training may improve exercise capacity early after transplantation and minimize effects of preoperative clinical factors that could negatively affect exercise capacity. Interpretation of these results, however, is limited by the small sample and absence of a nonexercising control group. Older recipients, those with a longer length of hospital stay, and shorter duration of time since resolution of rejection may be at risk of reduced early postoperative maximal exercise capacity. Identification of these predictors is important to maximize early reconditioning efforts and plan outpatient rehabilitation.

A controlled trial of exercise rehabilitation after heart transplantation

BACKGROUND

In patients who have received a cardiac transplant, the denervated donor heart responds abnormally to exercise and exercise tolerance is reduced. The role of physical exercise in the treatment of patients who have undergone cardiac transplantation has not been determined. We assessed the effects of training on the capacity for exercise early after cardiac transplantation.

METHODS

Twenty-seven patients who were discharged within two weeks after receiving a heart transplant were randomly assigned to participate in a six-month structured cardiac-rehabilitation program (exercise group, 14 patients) or to undergo unstructured therapy at home (control group, 13 patients). Each patient in the exercise group underwent an individualized program of muscular-strength and aerobic training under the guidance of a physical therapist, whereas control patients received no formal exercise training. Cardiopulmonary stress testing was performed at base line (within one month after heart transplantation) and six months later.

RESULTS

As compared with the control group, the exercise group had significantly greater increases in peak oxygen consumption (mean increase, 4.4 ml per kilogram of body weight per minute [49 percent] vs. 1.9 ml per kilogram per minute [18 percent]; P=0.01) and workload (mean increase, 35 W [59 percent] vs. 12 W [18 percent]; P=0.01) and a greater reduction in the ventilatory equivalent for carbon dioxide (mean decrease, 13 [20 percent] vs. 6 [11 percent]; P=0.02). The mean dose of prednisone, the number of patients taking antihypertensive medications, the average number of episodes of rejection and of infection during the study period, and weight gain did not differ significantly between the groups.

CONCLUSIONS

When initiated early after cardiac transplantation, exercise training increases the capacity for physical work.

Skeletal muscle function and its relation to exercise tolerance in chronic heart failure

OBJECTIVES

This study sought to define the relation between muscle function and bulk in chronic heart failure (HF) and to explore the association between muscle function and bulk and exercise capacity.

BACKGROUND

Skeletal muscle abnormalities have been postulated as determinants of exercise capacity in chronic HF. Previously, muscle function in chronic HF has been evaluated in relatively small numbers of patients and with variable results, with little account being taken of the effects of muscle wasting.

METHODS

One hundred male patients with chronic HF and 31 healthy male control subjects were studied. They were matched for age (59.0 +/- 1.0 vs. 58.7 +/- 1.7 years [mean +/- SEM]) and body mass index (26.6 +/- 0.4 vs. 26.3 +/- 0.7 kg/m2). We assessed maximal treadmill oxygen consumption (VO2), quadriceps maximal isometric strength, fatigue (20-min protocol, expressed in baseline maximal strength) and computed tomographic cross-sectional area (CSA) at midthigh.

RESULTS

Peak VO2 was lower in patients (18.0 +/- 0.6 vs. 33.3 +/- 1.4 ml/min per kg, p < 0.0001), although both groups achieved a similar respiratory exchange ratio at peak exercise (1.15 +/- 0.01 vs. 1.19 +/- 0.03, p = 0.13). Quadriceps (582 vs. 652 cm2, p < 0.05) and total leg muscle CSA (1,153 vs. 1,304 cm2, p < 0.005) were lower in patients with chronic HF. Patients were weaker than control subjects (357 +/- 12 vs. 434 +/- 18 N, p < 0.005) and also exhibited greater fatigue at 20 min (79.1% vs. 92.1% of baseline value, p < 0.0001). After correcting strength for quadriceps CSA, significant differences persisted (5.9 +/- 0.2 vs. 7.0 +/- 0.3 N/cm2, p < 0.005), indicating reduced strength per unit muscle. In patients, but not control subjects, muscle CSA significantly correlated with peak absolute VO2 (R = 0.66, p < 0.0001) and is an independent predictor of peak absolute VO2.

CONCLUSIONS

Patients with chronic HF have reduced quadriceps maximal isometric strength. This weakness occurs as a result of both quantitative and qualitative abnormalities of the muscle. With increasing exercise limitation there is increasing muscle weakness. This progressive weakness occurs predominantly as a result of loss of quadriceps bulk. In patients, this muscular atrophy becomes a major determinant of exercise capacity.

Exercise limitation in chronic heart failure: central role of the periphery

The symptoms of chronic heart failure (CHF) are predominantly shortness of breath and fatigue during exercise and reduced exercise capacity. Disturbances of central hemodynamic function are no longer considered to be the major determinants of exercise capacity. The two symptoms of fatigue and breathlessness are often considered in isolation. A pulmonary abnormality is usually considered to be the cause of abnormal ventilation, and increased dead space ventilation has come to be accepted as a major cause of the increased ventilation relative to carbon dioxide production seen in CHF. Rather than decreased skeletal muscle perfusion, an intrinsic muscle abnormality is considered to be responsible for fatigue. Another abnormality seen in CHF is persistent sympathetic nervous system activation, which is difficult to explain on the basis of baroreflex activation. There is increasing evidence for the importance of skeletal muscle ergoreceptors or metaboreceptors in CHF. These receptors are sensitive to work performed, and activation results in increased ventilation and sympathetic activation. The ergoreflex appears to be greatly enhanced in CHF. We put forward the "muscle hypothesis" as an explanation for many of the pathophysiologic events in CHF. Impaired skeletal muscle function results in ergoreflex activation. In turn, this causes increased ventilation, thus linking the symptoms of breathlessness and fatigue. Furthermore, ergoreflex stimulation may be responsible for persistent sympathetic activation.

Specific changes in skeletal muscle myosin heavy chain composition in cardiac failure: differences compared with disuse atrophy as assessed on microbiopsies by high resolution electrophoresis

OBJECTIVE

In congestive heart failure (CHF) the skeletal muscle of the lower limbs develops a myopathy with atrophy and shift from the slow type to the fast type fibres. The aim was to test the hypothesis that this myopathy is specific and not simply related to detraining, by comparing patients with different degrees of CHF with patients with severe muscle atrophy due to disuse.

DESIGN

Case-control study involving 50-150 micrograms needle biopsies of the gastrocnemius muscle. By an electrophoretic micromethod, the three isoforms of myosin heavy chains (MHC) were separated.

PATIENTS

Five patients restricted to bed for more than one year because of stroke with disuse atrophy and normal ventricular function, and 19 with CHF were studied. There were seven age matched controls.

MAIN OUTCOME MEASURES

The percentage of MHC1 (slow isoform), MHC2a (fast oxidative), and MHC2b (fast glycolytic) was determined by densitometric scan and correlated with indices of severity of cardiac failure.

RESULTS

Ejection fraction was 42.5 (SD 15.2)% in CHF, 59.5 (1.0)% in disuse atrophy and 60.3 (1.4)% in controls (P < 0.001 v both). The degree of muscle atrophy as calculated by the body mass index/gastrocnemius cross sectional area, showed a profound degree of atrophy in patients with muscle disuse [0.94 (0.39)]. This was worse than in the controls [4.27 (0.16), P < 0.0005] and the CHF patients [2.60 (1.10), P < 0.005]. Atrophy in CHF patients was also greater than in controls (P < 0.005). MHC1 was lower in CHF than in disuse atrophy [51.83 (15.04) v 84.5 (17.04), P < 0.01] while MHC2b was higher [23.5 (7.4) v 7.25 (7.92), P < 0.001]. There was a similar trend for MHC2a [24.83 (15.01) v 8.25 (9.12), P < 0.05]. Within the CHF group there was a positive correlation between NYHA class and MHC2a (r = 0.47, P < 0.05) and MHC2b (r = 0.55, P < 0.01) and a negative correlation between NYHA class and MHC1 (r = -0.74, P < 0.001). Similarly, significant correlations were found for ejection fraction, diuretic consumption score, exercise test tolerance, and degree of muscle atrophy.

CONCLUSIONS

The CHF myopathy appears to be specific and not related to detraining. The magnitude of MCH redistribution correlates with the severity of the disease. The electrophoretic micromethod used is very sensitive and reproducible. Biopsies are so well tolerated that can be repeated frequently, allowing thorough follow up.

Explaining fatigue in congestive heart failure

Fatigue is a prominent symptom in patients with chronic heart failure, limiting physical activity and impairing quality of life. Although the underlying mechanisms are not clearly identified, alterations associated with peripheral adaptation in heart failure appear to play an important role, including a variably impaired peripheral perfusion during exercise, reduced oxidative capacity of skeletal muscle, impaired muscle strength, and possibly reflex mechanisms associated with alterations in the metabolism of skeletal muscle. Exercise training can, in part, reverse these peripheral alterations, improve exercise capacity, and alleviate fatigue.

Perfusion/ventilation mismatch during exercise in chronic heart failure: an investigation of circulatory determinants

BACKGROUND

The ventilatory cost of carbon dioxide (CO2) elimination on exercise (VE/VCO2) is increased in chronic heart failure (CHF). This reflects increased physiological dead space ventilation secondary to mismatching between perfusion and ventilation during exercise. The objectives of this study were to investigate the relation of this increased VE/VCO2 slope to the syndrome of CHF or to limitation of the exercise related increase of pulmonary blood flow, or both.

PATIENTS AND METHODS

Maximal treadmill exercise tests with respiratory gas analysis were performed in 45 patients with CHF (defined as resting left ventricular ejection fraction < 40% on radionuclide scan); 15 normal controls; 23 patients with coronary artery disease and normal resting left ventricular function; and 13 pacemaker dependent patients (six with and seven without CHF) directly comparing exercise responses in rate responsive and fixed rate mode.

RESULTS

Patients with CHF had a steeper VE/VCO2 slope than normal controls: this was related inversely to peak VO2 below 20 mol/min/kg. In patients with coronary artery disease in whom peak VO2 (at respiratory exchange ratio > 1) was as limited as in the patients with CHF but resting left ventricular function was normal, the VE/VCO2 slope was normal. In pacemaker dependent patients fixed rate pacing resulted in lower exercise capacity and peak VO2 than rate responsive pacing; the VE/VCO2 slope was normal in patients without CHF but steeper than normal in patients with CHF; the VE/VCO2 slope was steeper during fixed rate than during rate responsive pacing in these patients with CHF.

CONCLUSIONS

These findings suggest that the perfusion/ventilation mismatch during exercise in CHF is related to the chronic consequences of the syndrome and not directly to limitation of exercise related pulmonary flow. Only when the syndrome of CHF is present can matching between perfusion and ventilation be acutely influenced by changes in pulmonary flow.

Intrinsic alterations of diaphragm muscle in experimental cardiomyopathy

Diaphragmatic function was investigated in the cardiomyopathic Syrian hamster (CSH) from the dilated Bio 53:58 strain, after long-term therapy with the angiotensin-converting enzyme inhibitor perindopril. Twenty-two 1-month old CSHs were treated during a 5-month period by either oral gavage with perindopril (1 mg/kg/day) (n = 11) or placebo (n = 11). Control hamsters from the F1B strain received placebo (n = 7). Mechanical properties were studied in isolated diaphragm strips electrically stimulated in both twitch and tetanic conditions. Compared with F1B control hamsters, peak active tension and positive (+dP/dtmax) and negative (-dP/dtmax) peaks of isometric tension derivative were significantly depressed in placebo treated CSHs. Compared with placebo-treated CSHs, peak active tension was significantly higher in perindopril-treated CSHs in both twitch (25 +/- 4 vs 16 +/- 1 mN/mm2; p < 0.01) and tetanus modes (56 +/- 4 vs 38 +/- 2 mN/mm2; p < 0.01). Moreover, +dP/dtmax and -dP/dtmax were improved significantly in twitch (p < 0.01 and p < 0.01, respectively) and tetanus modes (p < 0.05 and p < 0.01, respectively). We conclude that, in the CSH, long-term therapy with the angiotensin-converting enzyme inhibitor perindopril helped to preserve the diaphragmatic function.

Effect of angiotensin-converting enzyme inhibitors on the peripheral circulation in heart failure

In patients with chronic heart failure, the increase in blood flow to working muscle is attenuated and oxygen consumption is lower for any given workload of exercise, compared with normal subjects. This impaired metabolic vasodilation during exercise cannot be restored with short-term administration of angiotensin-converting enzyme (ACE) inhibitors. However, long-term ACE inhibition increases blood flow to skeletal muscle, and this increase is closely correlated with improvement in systemic oxygen consumption. The delayed effect of ACE inhibitors may be related to an interference with the vascular tissue renin-angiotensin system and remodeling of the vascular wall. In addition, endothelial-dependent dilation in response to acetylcholine is blunted in the forearm of patients with chronic heart failure, indicating an impaired endothelial function in this setting. There is experimental evidence that long-term ACE inhibition improves endothelial dysfunction; thus, one might speculate that the beneficial long-term effect of ACE inhibitors on peripheral flow may be, in part, related to its ability to restore normal endothelial function. Vasodilators such as hydralazine that improve blood flow to working muscle after acute administration do not increase skeletal muscle oxygen consumption, indicating that oxygen utilization is not improved. Ultrastructural analysis of skeletal muscle revealed that intrinsic alterations of skeletal muscle exist in patients with chronic heart failure; that is, the oxidative capacity of skeletal muscle is impaired in severe heart failure and contributes to the reduced exercise capacity.(ABSTRACT TRUNCATED AT 250 WORDS)