Inspiratory Muscle Weakness in Diastolic Dysfunction

Skeletal muscle abnormalities in heart failure with preserved ejection fraction

Almost half of all heart failure (HF) disease burden is due to HF with preserved ejection fraction (HFpEF). The primary symptom in patients with HFpEF, even when well compensated, is severe exercise intolerance and is associated with their reduced quality of life. Recently, studies showed that HFpEF patients have multiple skeletal muscle (SM) abnormalities, and these are associated with decreased exercise intolerance. The SM abnormalities are likely intrinsic to the HFpEF syndrome, not a secondary consequence of an epiphenomenon. These abnormalities are decreased muscle mass, reduced type I (oxidative) muscle fibers, and reduced type I-to-type II fiber ratio as well as a reduced capillary-to-fiber ratio, abnormal fat infiltration into the thigh SM, increased levels of atrophy genes and proteins, reduction in mitochondrial content, and rapid depletion of high-energy phosphate during exercise with markedly delayed repletion of high-energy phosphate during recovery in mitochondria. In addition, patients with HFpEF have impaired nitric oxide bioavailability, particularly in the microvasculature. These SM abnormalities may be responsible for impaired diffusive oxygen transport and/or impaired SM oxygen extraction. To date, exercise training (ET) and caloric restriction are some of the interventions shown to improve outcomes in HFpEF patients. Improvements in exercise tolerance following aerobic ET are largely mediated through peripheral SM adaptations with minimal change in central hemodynamics and highlight the importance of targeting SM to improve exercise intolerance in HFpEF. Focusing on the abnormalities mentioned above may improve the clinical condition of patients with HFpEF.

Inspiratory and leg muscle blood flows during inspiratory muscle metaboreflex activation in heart failure with preserved ejection fraction

The purpose of this study was to determine the cardiovascular consequences elicited by activation of the inspiratory muscle metaboreflex in patients with heart failure with preserved ejection fraction (HFpEF) and controls. Patients with HFpEF (n = 15; 69 ± 10 yr; 33 ± 4 kg/m2) and controls (n = 14; 70 ± 8 yr; 28 ± 4 kg/m2) performed an inspiratory loading trial at 60% maximal inspiratory pressure (PIMAX) until task failure. Mean arterial pressure (MAP) was measured continuously. Near-infrared spectroscopy and bolus injections of indocyanine green dye were used to determine the percent change in blood flow index (%ΔBFI) from baseline to the final minute of inspiratory loading in the vastus lateralis and sternocleidomastoid muscles. Vascular resistance index (VRI) was calculated. Time to task failure was shorter in HFpEF than in controls (339 ± 197 s vs. 626 ± 403 s; P = 0.02). Compared with controls, patients with HFpEF had a greater increase from baseline in MAP (16 ± 7 vs. 10 ± 6 mmHg) and vastus lateralis VRI (76 ± 45 vs. 32 ± 19%) as well as a greater decrease in vastus lateralis %ΔBFI (-32 ± 14 vs. -17 ± 9%) (all, P < 0.05). Sternocleidomastoid %ΔBFI normalized to absolute inspiratory pressure was higher in HFpEF compared with controls (8.0 ± 5.0 vs. 4.0 ± 1.9% per cmH2O·s; P = 0.03). These data indicate that patients with HFpEF exhibit exaggerated cardiovascular responses with inspiratory muscle metaboreflex activation compared with controls.NEW & NOTEWORTHY Respiratory muscle dysfunction is thought to contribute to exercise intolerance in heart failure with preserved ejection fraction (HFpEF); however, the underlying mechanisms are unknown. In the present study, patients with HFpEF had greater increases in leg muscle vascular resistance index and greater decreases in leg muscle blood flow index compared with controls during inspiratory resistive breathing (to activate the metaboreflex). Furthermore, respiratory muscle blood flow index responses normalized to pressure generation during inspiratory resistive breathing were exaggerated in HFpEF compared with controls.

Abnormal skeletal muscle blood flow, contractile mechanics and fibre morphology in a rat model of obese-HFpEF

KEY POINTS

Heart failure is characterised by limb and respiratory muscle impairments that limit functional capacity and quality of life. However, compared with heart failure with reduced ejection fraction (HFrEF), skeletal muscle alterations induced by heart failure with preserved ejection fraction (HFpEF) remain poorly explored. Here we report that obese-HFpEF induces multiple skeletal muscle alterations in the rat hindlimb, including impaired muscle mechanics related to shortening velocity, fibre atrophy, capillary loss, and an impaired blood flow response to contractions that implies a perfusive oxygen delivery limitation. We also demonstrate that obese-HFpEF is characterised by diaphragmatic alterations similar to those caused by denervation - atrophy in Type IIb/IIx (fast/glycolytic) fibres and hypertrophy in Type I (slow/oxidative) fibres. These findings extend current knowledge in HFpEF skeletal muscle physiology, potentially underlying exercise intolerance, which may facilitate future therapeutic approaches.

ABSTRACT

Peripheral skeletal muscle and vascular alterations induced by heart failure with preserved ejection fraction (HFpEF) remain poorly identified, with limited therapeutic targets. This study used a cardiometabolic obese-HFpEF rat model to comprehensively phenotype skeletal muscle mechanics, blood flow, microvasculature and fibre atrophy. Lean (n = 8) and obese-HFpEF (n = 8) ZSF1 rats were compared. Skeletal muscles (soleus and diaphragm) were assessed for in vitro contractility (isometric and isotonic properties) alongside indices of fibre-type cross-sectional area, myosin isoform, and capillarity, and estimated muscle PO₂ . In situ extensor digitorum longus (EDL) contractility and femoral blood flow were assessed. HFpEF soleus demonstrated lower absolute maximal force by 22%, fibre atrophy by 24%, a fibre-type shift from I to IIa, and a 17% lower capillary-to-fibre ratio despite increased capillary density (all P < 0.05) with preserved muscle PO₂ (P = 0.115) and isometric specific force (P > 0.05). Soleus isotonic properties (shortening velocity and power) were impaired by up to 17 and 22%, respectively (P < 0.05), while the magnitude of the exercise hyperaemia was attenuated by 73% (P = 0.012) in line with higher muscle fatigue by 26% (P = 0.079). Diaphragm alterations (P < 0.05) included Type IIx fibre atrophy despite Type I/IIa fibre hypertrophy, with increased indices of capillarity alongside preserved contractile properties during isometric, isotonic, and cyclical contractions. In conclusion, obese-HFpEF rats demonstrated blunted skeletal muscle blood flow during contractions in parallel to microvascular structural remodelling, fibre atrophy, and isotonic contractile dysfunction in the locomotor muscles. In contrast, diaphragm phenotype remained well preserved. This study identifies numerous muscle-specific impairments that could exacerbate exercise intolerance in obese-HFpEF.

Alterations of the respiratory system in heart failure

The review discusses mechanisms for the development of the pathology of the respiratory system in patients with CHF, such as various types of periodic respiration, pulmonary hypertension due to the pathology of the left chambers of the heart, and remodeling of the respiratory musculature. The role of chemo- and baroreceptors of the carotid zone, as well as the hyperactivation of the respiratory muscle metaboreflex in the development of the pathology of the respiratory system, and the mediated exacerbation of CHF are discussed.

Exercise Training Reveals Inflexibility of the Diaphragm in an Animal Model of Patients With Obesity-Driven Heart Failure With a Preserved Ejection Fraction

BACKGROUND

Respiratory muscle weakness contributes to exercise intolerance in patients with heart failure with a preserved ejection fraction (HFpEF)-a condition characterized by multiple comorbidities with few proven treatments. We aimed, therefore, to provide novel insight into the underlying diaphragmatic alterations that occur in HFpEF by using an obese cardiometabolic rat model and further assessed whether exercise training performed only after the development of overt HFpEF could reverse impairments.

METHODS AND RESULTS

Obese ZSF1 rats (n=12) were compared with their lean controls (n=8) at 20 weeks, with 3 additional groups of obese ZSF1 rats compared at 28 weeks following 8 weeks of either sedentary behavior (n=13), high-intensity interval training (n=11), or moderate-continuous training (n=11). Obese rats developed an obvious HFpEF phenotype at 20 and 28 weeks. In the diaphragm at 20 weeks, HFpEF induced a shift towards an oxidative phenotype and a fiber hypertrophy paralleled by a lower protein expression in MuRF1 and MuRF2, yet mitochondrial and contractile functional impairments were observed. At 28 weeks, neither the exercise training regimen of high-intensity interval training or moderate-continuous training reversed any of the diaphragm alterations induced by HFpEF.

CONCLUSIONS

This study, using a well-characterized rat model of HFpEF underpinned by multiple comorbidities and exercise intolerance (ie, one that closely resembles the patient phenotype), provides evidence that diaphragm alterations and dysfunction induced in overt HFpEF are not reversed following 8 weeks of aerobic exercise training. As such, whether alternative therapeutic interventions are required to treat respiratory muscle weakness in HFpEF warrants further investigation.

High-intensity interval training prevents oxidant-mediated diaphragm muscle weakness in hypertensive mice

Hypertension is a key risk factor for heart failure, with the latter characterized by diaphragm muscle weakness that is mediated in part by increased oxidative stress. In the present study, we used a deoxycorticosterone acetate (DOCA)-salt mouse model to determine whether hypertension could independently induce diaphragm dysfunction and further investigated the effects of high-intensity interval training (HIIT). Sham-treated (n = 11), DOCA-salt-treated (n = 11), and DOCA-salt+HIIT-treated (n = 15) mice were studied over 4 wk. Diaphragm contractile function, protein expression, enzyme activity, and fiber cross-sectional area and type were subsequently determined. Elevated blood pressure confirmed hypertension in DOCA-salt mice independent of HIIT (P < 0.05). Diaphragm forces were impaired by ∼15-20% in DOCA-salt vs. sham-treated mice (P < 0.05), but this effect was prevented after HIIT. Myosin heavy chain (MyHC) protein expression tended to decrease (∼30%; P = 0.06) in DOCA-salt vs. sham- and DOCA-salt+HIIT mice, whereas oxidative stress increased (P < 0.05). Enzyme activity of NADPH oxidase was higher, but superoxide dismutase was lower, with MyHC oxidation elevated by ∼50%. HIIT further prevented direct oxidant-mediated diaphragm contractile dysfunction (P < 0.05) after a 30 min exposure to H₂O-₂ (1 mM). Our data suggest that hypertension induces diaphragm contractile dysfunction via an oxidant-mediated mechanism that is prevented by HIIT.-Bowen, T. S., Eisenkolb, S., Drobner, J., Fischer, T., Werner, S., Linke, A., Mangner, N., Schuler, G., Adams, V. High-intensity interval training prevents oxidant-mediated diaphragm muscle weakness in hypertensive mice.

The presence and impact of diastolic dysfunction on physical function and body composition in hemodialysis patients

BACKGROUND

Cardiovascular (CV) diseases are the main cause of death in maintenance hemodialysis (MHD) patients. Muscle wasting and physical function decline are common in MHD patients, and significantly impair their quality of life. These can result from abnormalities in cardiac function, which can be further worsened by physical deconditioning. Left ventricular diastolic function parameters were recently shown to be a better predictor of exercise capacity than systolic measures in patients with CV complications. But little is known about the relationship between cardiac function and physical function in MHD patients.

METHODS

In 82 MHD patients, left ventricular systolic dysfunction (LVSD) was assessed by ejection fraction and fractional shortening with echocardiography, and left ventricular diastolic dysfunction (LVDD) was assessed by pulse wave and tissue Doppler indices. Physical function was assessed by gait speed, performance on a shuttle walk test, and leg muscle strength. Dual-emission X-ray absorptiometry (DXA) was used to measure whole body lean mass (WBLM).

RESULTS

The prevalence of LVDD and LVSD was 48.8 and 12.2%, respectively. Gait speed, shuttle walk time, leg strength, and WBLM% were significantly higher in the group without LVDD than with LVDD (p < 0.05 for all). However, there was no significant difference in any measure of physical function or body composition between patients with and without LVSD.

CONCLUSION

These data suggest that LVDD is more closely related to physical function and body composition than LVSD in MHD patients, and hence that LVDD may be an important therapeutic target.

Inspiratory Muscle Weakness is Associated With Exercise Intolerance in Patients With Heart Failure With Preserved Ejection Fraction: A Preliminary Study

BACKGROUND

The relationship between inspiratory muscle weakness (IMW) and exercise intolerance in patients with heart failure with preserved ejection fraction (HFpEF) remains unestablished.

METHODS AND RESULTS

The present study enrolled 40 patients with HFpEF (EF ≥45%). IMW was defined as maximum inspiratory pressure <70% normal predicted values. The function of the diaphragm was assessed by means of ultrasound measurement of muscle thickening of the diaphragm. IMW was prevalent in 27.5% of patients. Patients with IMW had significantly lower vital capacity relative to normal predicted values (%VC), lower knee extensor muscle strength in relation to body weight (%KEMS), poorer nutritional status as assessed by means of the Geriatric Nutritional Risk Index, and shorter 6-minute walk distance (6MWD) compared with patients without IMW (all P < .05). Impaired diaphragm muscle thickening at end-inspiration (median value < 3.9 mm) was significantly associated with a high prevalence of IMW and reduced 6MWD (all P < .05). Subgroup analysis showed that IMW was accompanied by a further decrease in 6MWD in patients with restrictive pulmonary dysfunction (%VC <80%) or lower-limb muscle weakness (median %KEMS <30%; all P < .05).

CONCLUSIONS

IMW is associated with exercise intolerance in patients with HFpEF.

Breathing exercises and inspiratory muscle training in heart failure

Breathing exercises (BE) and inspiratory muscle training (IMT) have been demonstrated to improve ventilation and ventilation-to-perfusion matching, and to improve exercise, functional performance, and many pathophysiologic manifestations of heart failure (HF). This article provides an extensive review of BE and IMT in patients with HF and identifies several key areas in need of further investigation, including the role of expiratory muscle training, IMT targeted at various locations of inspiration (early, mid, or late inspiration), and alteration of the ratio of inspiratory time to total breath time, all of which have substantial potential to improve many pathophysiologic manifestations of HF.

Causes of exercise intolerance in heart failure with preserved ejection fraction: searching for consensus

Exercise intolerance is one of the cardinal symptoms of heart failure with preserved ejection fraction (HFpEF). We review its mechanistic basis using evidence from exercise studies. One barrier to a consensus understanding of the pathophysiology is heterogeneity of the patient population. Therefore, we pay special attention to varying study definitions of the disease and their possible impact on the causal factors that are implicated. We then discuss the role of exercise testing and its potential to subtype HFpEF in to more homogeneous mechanism-based subclasses.

Cardiac and skeletal myopathy in Fabry disease: a clinicopathologic correlative study

Skeletal muscle disturbances are commonly reported in patients with Fabry disease. Whether they derive from cardiac dysfunction or direct muscle involvement is still unclear. Clinical, noninvasive, and invasive cardiac and muscle studies, including an endomyocardial and muscle biopsy, were obtained in 12 patients (mean age, 42.1 ± 12.6 years; range, 24-58 years) with Fabry disease. In the youngest patients (group A, 4 men aged <35 years), results of cardiac and skeletal noninvasive studies were normal, except for reduced velocities in tissue Doppler imaging. Histologic examination indicated that muscle myocytes were unaffected, whereas muscle vessels showed the presence of mild glycosphingolipid accumulation in endothelial and smooth muscle cells. In the heart, cardiomyocytes and endothelial and smooth muscle cells of intramural cardiac vessels were involved by the disease. The oldest patients (group B, 6 men and 2 women aged >35 years) showed ultrasound muscle disarray and electromyography signs of myopathy, increased left ventricular mass, and normal cardiac function. Histologic examination showed that muscle myocytes contained mild glycosphingolipid accumulation compared with severe engulfment of cardiomyocytes. Moreover, similar infiltration of myocardial and muscle intramural vessels, causing lumen narrowing and fibrofatty tissue replacement, was observed. Direct muscle involvement occurs in patients with Fabry disease. It is milder and delayed compared with that in the heart. The difference in organ function and the need of residual α-galactosidase A activity are the likely causes.

Increased left ventricular stiffness impairs exercise capacity in patients with heart failure symptoms despite normal left ventricular ejection fraction

Aims. Several mechanisms can be involved in the development of exercise intolerance in patients with heart failure despite normal left ventricular ejection fraction (HFNEF) and may include impairment of left ventricular (LV) stiffness. We therefore investigated the influence of LV stiffness, determined by pressure-volume loop analysis obtained by conductance catheterization, on exercise capacity in HFNEF. Methods and Results. 27 HFNEF patients who showed LV diastolic dysfunction in pressure-volume (PV) loop analysis performed symptom-limited cardiopulmonary exercise testing (CPET) and were compared with 12 patients who did not show diastolic dysfunction in PV loop analysis. HFNEF patients revealed a lower peak performance (P = .046), breathing reserve (P = .006), and ventilation equivalent for carbon dioxide production at rest (P = .002). LV stiffness correlated with peak oxygen uptake (r = -0.636, P < .001), peak oxygen uptake at ventilatory threshold (r = -0.500, P = .009), and ventilation equivalent for carbon dioxide production at ventilatory threshold (r = 0.529, P = .005). Conclusions. CPET parameters such as peak oxygen uptake, peak oxygen uptake at ventilatory threshold, and ventilation equivalent for carbon dioxide production at ventilatory threshold correlate with LV stiffness. Increased LV stiffness impairs exercise capacity in HFNEF.

Quality of life, dyspnea and ventricular function in patients with hypertension

AIM

This paper is a report of an investigation of the relationship between health-related quality of life and left ventricular function among patients with hypertension who did not fulfil the criteria for heart failure.

BACKGROUND

Heart failure is a common consequence of hypertension, with Doppler echocardiography being the gold-standard tool to evaluate left ventricular function, mainly hypertension-induced left ventricular damage. Echocardiographic data indicating poorer ventricular function have been related to lower levels of health-related quality of life in patients with systolic and/or diastolic heart failure. However, data are still lacking regarding the correlation between health-related quality of life and left ventricular function and structure in patients with hypertension who do not fulfil the criteria for heart failure.

METHOD

Between September 2005 and February 2007, 98 patients with hypertension without systolic or diastolic heart failure were evaluated. Health-related quality of life was assessed using the Medical Outcomes Study Short Form-36. Left ventricular function was evaluated through Tissue Doppler echocardiography.

RESULTS

Statistically significant but weak correlations (varying from r = -0.22 to 0.35) were observed between some of the Short Form-36 domains and echo data. To consider the potential effect of dyspnoea in this relationship, patients were split according to the presence or absence of the symptom. In the subgroup without dyspnoea, similar patterns of correlation were observed (varying from r = 0.26 to 0.32). In the subgroup with dyspnoea, however, more and stronger correlations were observed between echo data and health-related quality of life domains, varying from r = -0.40 to 0.50.

CONCLUSION

Nurses should be aware of the relevance of evaluating the functional echocardiographic data of patients who not fulfil heart failure criteria, but who experience dyspnoea in order to implement appropriate action plans.

Relationship between exercise capacity and cardiac diastolic function assessed by time-volume curve from 16-frame gated myocardial perfusion SPECT

OBJECTIVE

Echocardiographic studies have suggested an association between diastolic dysfunction and exercise intolerance. The aim of this study was to examine the relationship between exercise capacity and left ventricular (LV) function during stress myocardial scintigraphy, and to investigate whether or not this relationship is caused by ischemia during exercise.

METHODS

The studied patients underwent technetium-99m sestamibi quantitative gated SPECT, including treadmill exercise. Myocardial stress images were acquired 30 min after the first tracer injection (370 MBq) during maximal exercise. Three hours later, the second tracer (740 MBq) was injected, and resting images were acquired 30 min after this injection. The presence of ischemia was determined by tracer accumulation. From the same data source, LV diastolic parameters [first third filling fraction (1/3FF), first third filling rate (1/3FR), peak filling rate (PFR) and time to PFR (TPF)], and systolic parameters [ejection fraction (EF), peak ejection rate (PER), time to PER (TPE) and first third ejection fraction (1/3EF)] were analyzed.

RESULTS

Subjects with exercise inability (<6 METs) were excluded. In 45 patients, diastolic parameters 1/3FF, 1/3FR, PFR and TPF correlated significantly with exercise duration (r = 0.32*, 0.37*, 0.37* and -0.40(#), respectively; *p < 0.05, (#) p < 0.01), but systolic parameters EF, PER, TPE and 1/3EF did not. At rest, 1/3FF, PFR and PER were significantly increased, suggesting functional deterioration during exercise. Even after 3 h, 1/3FR, PFR and TPF still correlated significantly with exercise duration (r = 0.29*, 0.36* and -0.30*, respectively; *p < 0.05). Such findings were observed even when the 10 patients who exhibited ischemia during exercise were excluded (1/3FR: r = 0.34*; PFR: r = 0.37*; TPF: r = -0.36*; *p < 0.05, n = 35).

CONCLUSIONS

Our findings suggested that LV diastolic dysfunction, not systolic dysfunction, is associated with limited exercise capacity independent of the occurrence of ischemia.

Respiratory muscle function and exercise intolerance in heart failure

Inspiratory muscle weakness (IMW) is prevalent in patients with chronic heart failure (CHF) caused by left ventricular systolic dysfunction, which contributes to reduced exercise capacity and the presence of dyspnea during daily activities. Inspiratory muscle strength (estimated by maximal inspiratory pressure) has independent prognostic value in CHF. Overall, the results of trials with inspiratory muscle training (IMT) indicate that this intervention improves exercise capacity and quality of life, particularly in patients with CHF and IMW. Some benefit from IMT may be accounted for by the attenuation of the inspiratory muscle metaboreflex. Moreover, IMT results in improved cardiovascular responses to exercise and to those obtained with standard aerobic training. These findings suggest that routine screening for IMW is advisable in patients with CHF, and specific IMT and/or aerobic training are of practical value in the management of these patients.

Diastolic dysfunction in exercise and its role for exercise capacity

Diastolic dysfunction is frequent in elderly subjects and in patients with left ventricular hypertrophy, vascular disease and diabetes mellitus. Patients with diastolic dysfunction demonstrate a reduced exercise capacity and might suffer from congestive heart failure (CHF). Presence of symptoms of CHF in the setting of a normal systolic function is referred to as heart failure with normal ejection fraction (HFNEF) or, if evidence of an impaired diastolic function is observed, as diastolic heart failure (DHF). Reduced exercise capacity in diastolic dysfunction results from a number of pathophysiological alterations such as slowed myocardial relaxation, reduced myocardial distensibility, elevated filling pressures, and reduced ventricular suction forces. These alterations limit the increase of ventricular diastolic filling and cardiac output during exercise and lead to pulmonary congestion. In healthy subjects, exercise training can enhance diastolic function and exercise capacity and prevent deterioration of diastolic function in the course of aging. In patients with diastolic dysfunction, exercise capacity can be enhanced by exercise training and pharmacological treatment, whereas improvement of diastolic function can only be observed in few patients.

Risk stratification in cardiac amyloidosis: novel approaches

Amyloidosis is a term for diseases with extracellular deposition of insoluble beta-fibrillar proteins in different organs. The heart is primarily involved in more than half of patients with immunoglobulin light-chain amyloidosis or hereditary amyloidosis and associated with poor prognosis. Different traditional diagnostic tools that have been described for risk stratification lack of sufficient sensitivity and specificity for patient survival. Until November 2004 in 50 consecutive patients with light chain amyloidosis and 15 patients with hereditary amyloidosis electrocardiography, echocardiography, Holter monitoring, cardiopulmonary exercise test, lung function testing, tilt-test, and laboratory investigations have been performed at our department. Cardiac amyloidosis was found in 32 patients. Interventricular septum (14.3+/-0.5 mm vs. 12.3+/-0.7 mm, P<0.05), plasma NT-proBNP (7154+/-2122 ng/l vs. 380+/-113 ng/l; P<0.01), cardiac Troponin T (0.105+/-0.030 vs. 0.019+/-0.010 microg/l; P<0.05) were increased in patients with cardiac amyloidosis as compared to patients light chain amyloidosis but no cardiac involvement. Maximal inspiratory (Pimax) and expiratory (Pemax) mouth pressure were decreased with CA compared to controls. Correlation of NT-proBNP and interventricular septum thickness (r=0.53, P=0.029) as well as and Pimax (r=0.72, P<0.01) or Pemax (r=0.69; P<0.01) was noticed. A correlation of grade of arrhythmias in Holter monitoring and syncopes was not observed. Cardiac involvement of amyloid disease carries a poor prognosis and is not well characterized by classic heart failure determinants. Heart transplantation based on novel risk markers including NT-proBNP might be a suitable therapeutic approach for patients with manifest cardiac amyloidosis, but will require alternative patient selection and listing criteria.