Aerobic interval training improves oxygen uptake efficiency by enhancing cerebral and muscular hemodynamics in patients with heart failure

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Abstract

Background

Abnormal ventilatory/hemodynamic responses to exercise contribute to functional impairment in patients with heart failure (HF). This study investigates how interval and continuous exercise regimens influence functional capacity by modulating ventilatory efficiency and hemodynamic function in HF patients.

Methods

Forty-five HF patients were randomized to perform either aerobic interval training (AIT; 3-minute intervals at 40% and 80% VO2peak) or moderate continuous training (MCT; sustained 60% VO2peak) for 30 min/day, 3 days/week for 12 weeks, or to a control group that received general healthcare (GHC). A noninvasive bio-reactance device was adopted to measure cardiac hemodynamics, whereas a near-infrared spectroscopy was employed to assess perfusion/O2 extraction in frontal cerebral lobe (∆[THb]FC / ∆[HHb]FC) and vastus lateralis (∆[THb]VL / ∆[HHb]VL), respectively.

Results

Following the 12-week intervention, the AIT group exhibited higher oxygen uptake efficiency slope (OUES) and lower VE-VCO2 slope than the MCT and GHC groups. Furthermore, AIT, but not MCT, boosted cardiac output (CO) and increased ∆[THb]FC, ∆[THb]VL, and ∆[HHb]VL during exercise. In multivariate analyses, CO was the dominant predictor of VO2peak. ∆[THb]FC and ∆[THb]VL, which modulated the correlation between CO and OUES, were significantly correlated with OUES. Simultaneously, ∆[THb]VL was the only factor significantly associated with VE-VCO2 slope. Additionally, AIT reduced plasma brain natriuretic peptide, myeloperoxidase, and interleukin-6 levels and increased the Short Form-36 physical/mental component scores and decreased the Minnesota Living with Heart Failure questionnaire score.

Conclusions

AIT effectively improves oxygen uptake efficiency by enhancing cerebral/muscular hemodynamics and suppresses oxidative stress/inflammation associated with cardiac dysfunction, and also promotes generic/disease-specific qualities of life in patients with HF.

Introduction

Heart failure (HF) is a major cardiovascular syndrome with increasing incidence and prevalence [1]. This chronic cardiac condition oftentimes accelerates deconditioning and the consequent vicious cycle of numerous associated disorders [2]. Moreover, HF patients on optimal cardiovascular pharmacologic therapy frequently remain burdened by dyspnea and exercise intolerance [3]. Abnormal cerebral and muscular hemodynamic responses to exercise may contribute to impaired functional capacity in HF patients [4]. Recent investigations have suggested that depressed cardiac output (CO) and heightened ventilatory responses to exercise in patients with advanced HF reduced cerebral perfusion/oxygenation and considerably limited exercise performance [4], [5], [6]. Although cardiac rehabilitation is a valuable non-pharmacologic intervention for improving aerobic fitness and overall health status in patients with HF [1], controversy persists regarding the type and degree of exercise that optimally promotes beneficial adaptations in central and peripheral hemodynamics.

Aerobic interval training (AIT) is a more effective modality for improving aerobic fitness than traditional moderate continuous training (MCT) in patients with coronary artery disease or left ventricular dysfunction [7], [8], [9]. Furthermore, the AIT regimen has been demonstrated to rescue impaired contractility, attenuate hypertrophy, and reduce expression of atrial natriuretic peptide of cardiac myocytes in animal model of post-infarction HF [10], [11], [12]. However, few studies have investigated whether AIT influences peripheral (such as cerebral and skeletal muscular tissues) hemodynamics by modulating ventilatory efficiency and the distribution of blood flow from the heart [11], [12]. Moreover, the relationship between changes in tissue perfusion/oxygenation and exercise performance caused by AIT has not yet been established.

This investigation thus attempts to clarify how interval and continuous exercise regimens influence central and peripheral hemodynamic responses to exercise in patients with HF. We hypothesize that AIT influences functional capacity by modulating ventilatory efficiency and cardiac-cerebral-muscular hemodynamic responses to exercise in patients with HF. We also anticipate that AIT improves efficiency in ventilation–perfusion matching during exercise more than does MCT.

Section snippets

Subjects

This study enrolled 45 patients diagnosed with HF from the Department of Cardiology, Chang Gung Memorial Hospital. HF was diagnosed if the patients had (i) a left ventricular ejection fraction (LVEF) ≤ 40% and belonged to New York Heart Association functional classes II to III despite receiving optimal treatment for at least 12 months according to American Heart Association/American College of Cardiology guidelines, or (ii) LVEF > 40% with episodes of acute pulmonary edema after excluding other

Physical fitness and ventilatory efficiency

The three groups did not differ significantly in anthropometric and clinical parameters or functional capacity at the start of the study (Table 1). Following 12 weeks of interventions, the AIT group displayed increased work-rate, VE, VO2 and VCO2 at the ventilation threshold and peak exercise performance (P < 0.05), but no significant changes in physical fitness occurred in either the MCT or GHC groups (Table 2). Moreover, the AIT regimen exhibited significantly elevated OUES (Fig. 1A, P < 0.05) and

Discussion

This investigation clearly demonstrates that the AIT regimen significantly improves the aerobic fitness of HF patients by increasing their ventilatory efficiency and cardiac-cerebral-muscular hemodynamic responses to exercise. However, MCT for 12 weeks did not influence the values of the ventilatory and hemodynamic responses to exercise, and only maintained the ability to perform ventilation–perfusion matching during exercise as a pre-interventional status. Notably, AIT effectively (i) elevates

Conclusions

The AIT regimen designed in this study can enhance central and peripheral hemodynamic responses to exercise, apparently by increasing heart pumping efficiency and the delivery/utilization of O2 to exercising skeletal muscles or cerebral tissues. Furthermore, the improvement of ventilatory efficiency by AIT may contribute to beneficial adaptations in central and peripheral hemodynamics, which effects are accompanied by the better global and disease-specific QoL in patients with HF. However, the

Source of funding

This work was supported by the National Science Council of Taiwan (grant number NSC 96-2314-B-182-001), Chang Gung Medical Research Program (grant number CMRPG 280241) and the Healthy Aging Research Center, Chang Gung University (grant number EMRPD1A0841).

Acknowledgments

The authors would like to thank the volunteers for their enthusiastic participation in the present study. The authors of this manuscript have certified that they comply with the Principles of Ethical Publishing in the International Journal of Cardiology.

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