Comparing methods for prescribing exercise for individuals with chronic heart failure

This study examined the accuracy of current recommended guidelines for prescribing exercise intensity using the methods of percentage of heart rate reserve (%HRR), percentage of VO₂ peak (%VO₂peak) and percentage of VO₂ reserve (%VO₂R) in a clinical population of chronic heart failure (CHF) patients. The precision of prescription of exercise intensity for 45 patients with stable CHF (39:6 M:F, 65±9 yrs (mean±SD)) was investigated. VO₂peak testing is relatively common among patients with cardiac disease, but the assessment of VO₂rest is not common practice and the accepted standard value of 3.5 mL/kg/min is assumed in the application of %VO2R (%VO₂R_3.5). In this study, VO₂rest was recorded for 3 min prior to the start of a symptom-limited exercise test on a cycle ergometer. Target exercise intensities were calculated using the VO₂ corresponding to 50 or 80 %HRR, VO₂peak and VO₂R. The VO₂ values were then converted into prescribed speeds on a treadmill in km/hr at 1 %grade using ACSM’s metabolic equation for walking. Target intensities and prescribed treadmill speeds were also calculated with the %VO₂R method using the mean VO₂rest value of participants (3.9 mL/kg/min) (%VO₂R_3.9). This was then compared to the exercise intensities and prescribed treadmill speeds using patient’s measured VO₂rest. Error in prescription correlates the difference between %VO₂R_3.5 and %VO₂R_3.9 compared to %VO₂R with measured VO₂rest. Prescription of exercise intensity through the %HRR method is imprecise for patients on medications that blunt the HR response to exercise. %VO₂R method offers a significant improvement in exercise prescription compared to %VO₂peak. However, a disparity of 10 % still exists in the %VO₂R method using the standard 3.5 mL/kg/min for VO₂rest in the %VO₂R equation. The mean measured VO₂rest in the 45 CHF patients was 11 % higher (3.9±0.8 mL/kg/min) than the standard value provided by ACSM. Applying the mean measured VO₂rest value of 3.9 mL/kg/min rather than the standard assumed value of 3.5 mL/kg/min proved to be closer to the prescribed intensity determined by the actual measured resting VO₂. These results suggest that the %HRR method should not be used to prescribe exercise intensity for CHF patients. Instead, VO₂ should be used to prescribe exercise intensity and be expressed as %VO₂R with measured variables (VO₂rest and VO₂peak).

Reliability of isokinetic strength and aerobic power testing for patients with chronic heart failure

PURPOSE: The objective of this study was to assess the reliability of testing skeletal muscle strength and peak aerobic power in a clinical population of patients with chronic heart failure (CHF).

METHODS: Thirty-three patients with CHF (New York Heart Association (NYHA) Functional Class 2.3 ± 0.5; left ventricular ejection fraction 27% ± 7%; age 65 ± 9 years; 28:5 male-female ratio) underwent two identical series of tests (T1 and T2), 1 week apart, for strength and endurance of the muscle groups responsible for knee extension/flexion and elbow extension/flexion. The patients also underwent two graded exercise tests on a bicycle ergometer to measure peak oxygen consumption (VO_2peak). Three months later, 18 of the patients underwent a third test (T3) for each of the measures. Means were compared using MANOVA with repeated measures for strength and endurance, and ANOVA with repeated measures for VO_2peak.

RESULTS: Combining data for all four movement patterns, the expression of strength increased from T1 to T2 by 12% ± 25% (P < .001; intraclass correlation coefficient [ICC] = 0.89). Correspondingly, endurance increased by 13% ± 23% (P = .004; ICC = 0.87). Peak oxygen consumption was not significantly different (16.2 ± 0.8 and 16.1 ± 0.8 mL·kg^-1·min^-1 for T1 and T2, respectively;P = .686; ICC = 0.91). There were no significant differences between T2 and T3 for strength (2% ± 17%;P = .736; ICC = 0.92) or muscle endurance (-1% ± 15%;P = .812; ICC = 0.96), but VO_2peak decreased from 16.7 ± 1.2 to 14.9 ± 0.9 mL·kg^-1·min^-1 (-10% ± 18%;P = .021; ICC = 0.89).

CONCLUSIONS: These data suggest that in a population of patients with CHF, a familiarization trial for skeletal muscle strength testing is necessary. Although familiarization is not required for assessing oxygen consumption as a single measurement, VO_2peak declined markedly in the 3-month period for which these patients were followed. Internal consistency within patients was high for the second and third strength trials and the first and second tests of VO_2peak.

Moderate-intensity resistance exercise training in patients with chronic heart failure improves strength, endurance, heart rate variability, and forearm blood flow

Thirty-nine CHF patients (New York Heart Association Functional Class = 2.3±0.5; left ventricular ejection fraction 28%±7%; age 65±11 years; 33:6 male:female) underwent 2 identical series of tests, 1 week apart, for strength and endurance of the knee and elbow extensors and flexors, VO_2peak, HRV, FBF at rest, and FBF activated by forearm exercise or limb ischemia. Patients were then randomized to 3 months of resistance training (EX, n = 19), consisting of mainly isokinetic (hydraulic) ergometry, interspersed with rest intervals, or continuance with usual care (CON, n = 20), after which they underwent repeat endpoint testing. Combining all 4 movement patterns, strength increased for EX by 21±30% (mean±SD, P<.01) after training, whereas endurance improved 21±21% (P<.01). Corresponding data for CON remained almost unchanged (strength P<.005, endurance P<.003 EX versus CON). VO_2peak improved in EX by 11±15% (P<.01), whereas it decreased by 10±18% (P<.05) in CON (P<.001 EX versus CON). The ratio of low-frequency to high-frequency spectral power fell after resistance training in EX by 44±53% (P<.01), but was unchanged in CON (P<.05 EX versus CON). FBF increased at rest by 20±32% (P<.01), and when stimulated by submaximal exercise (24±32%, P<.01) or limb ischemia (26±45%, P<.01) in EX, but not in CON (P<.01 EX versus CON).

Exercise and Sports Science Australia position statement on exercise training and chronic heart failure

Chronic heart failure (CHF) is a complex syndrome characterised by progressive decline in left ventricular function, low exercise tolerance and raised mortality and morbidity. Regular exercise participation has been shown to be a safe and effective treatment modality in the majority of CHF patients, partially reversing some of the maladaptations evident in myocardial and skeletal muscle function, and resulting in improvements in physical fitness and quality of life, and perhaps reduced mortality. The volume and intensity of exercise that is recommended depends on the syndrome severity, however in most patients it should consist of a combination of low-to-moderate intensity aerobic (endurance) exercise on most days of the week and individually prescribed low-to-moderate intensity resistance (strength) training at least twice per week. Additionally, all patients should be closely monitored prior to and during exercise for contraindications by an appropriately trained health professional. The purpose of this statement is to inform and guide exercise practitioners and health professionals in the safe and effective prescription and supervision of exercise for patients with CHF.

Circuit resistance training in chronic heart failure improves skeletal muscle mitochondrial ATP production rate—A randomized controlled trial

Background : We aimed to determine the role of skeletal muscle mitochondrial ATP production rate (MAPR) in relation to exercise tolerance after resistance training (RT) in chronic heart failure (CHF).

Methods and Results : Thirteen CHF patients (New York Heart Association functional class 2.3 ± 0.5; Left ventricular ejection fraction 26 ± 8%; age 70 ± 8 years) underwent testing for peak total body oxygen consumption (VO_2peak), and resting vastus lateralis muscle biopsy. Patients were then randomly allocated to 11 weeks of RT (n = 7), or continuance of usual care (C; n = 6), after which testing was repeated. Muscle samples were analyzed for MAPR, metabolic enzyme activity, and capillary density. VO_2peak and MAPR in the presence of the pyruvate and malate (P+M) substrate combination, representing carbohydrate metabolism, increased in RT (P < .05) and decreased in C (P < .05), with a significant difference between groups (VO_2peak, P = .005; MAPR, P = .03). There was a strong correlation between the change in MAPR and the change in peak total body oxygen consumption (VO_2peak) over the study (r = 0.875; P < .0001), the change in MAPR accounting for 70% of the change in VO_2peak.

Conclusions : These findings suggest that mitochondrial ATP production is a major determinant of aerobic capacity in CHF patients and can be favorably altered by muscle strengthening exercise.

Respiratory muscle dysfunction and training in chronic heart failure

A characteristic feature of chronic heart failure (CHF) is reduced exercise tolerance. Several factors contributing to this have been identified, including alterations in central haemodynamics, skeletal muscle oxygen utilisation and respiratory muscle dysfunction. This review focuses on abnormalities identified in respiratory muscle structure and function in CHF and recent evidence for the benefit of selective inspiratory muscle training in CHF. Included in this review are findings from original investigations, with a specific focus on recent published data.

A haptic training environment for the heart myoblast cell injection procedure

The heart muscle of a cardiac arrest victim continues to accumulate damage throughout its lifetime. This reduces the heart's ability to pump sufficient oxygen and nutrient blood to meet the body's needs. Medical researchers have shown that direct injection of pre-harvested skeletal myoblast cells into the heart can restore some muscle function [1]. This operative procedure usually necessitates the surgeon to open a patient's chest. The open chest procedure is usually a lengthy process and often extends the recovery time of the patient. Alternatively, a high accuracy surgical aid robotic system can be used to assist the thoracoscopic surgery [2][3]. While the robotic surgical method aids faster patient recovery, a less experienced surgeon can potentially cause damage to surrounding tissue.

This paper presents a study into the development of a virtual haptically-enabled heart myoblast injection simulation environment, which can be used to train new surgeons to get hands on experience with the process. The paper also discusses the development of a generic constraint motion technique for needle insertion. Experiments on human performance measures and efficacy, while interacting with haptic feedback training models, are also presented. The experiment involved 10 operators, with each person repeating the needle insertion and injection 10 times. A notable improvement in the task execution time with the number of repetitions was observed. Operators improved their time by up to 300% compared to their first training attempt for a static heart scenario. Under a dynamic heart motion, operator's performance was slightly lower, with the successful rate of completing the experiment reduced from 84% to 75%.

Growth restriction before and after birth increases kinase signaling pathways in the adult rat heart

To investigate the mechanisms for the previously reported development of adult cardiac hypertrophy in male rats following growth restriction, the levels of oxidative stress and activation of signaling kinases were measured in the left ventricle (LV) of adult rat offspring. In experiment one, bilateral uterine vessel ligation to induce uteroplacental insufficiency and growth restriction in the offspring (Restricted) or sham surgery was performed during pregnancy. Litters from sham mothers had litter size either reduced (Reduced Litter), which also restricted postnatal growth, or were left unaltered (Control). In males, Reduced Litter offspring had increased LV phosphorylation of AMPKa, p38 MAPK and Akt compared with Restricted and Controls (P,0.05). In females, both Restricted and Reduced Litter adult offspring had increased LV phosphorylation of p38 MAPK and Akt, however, only Restricted offspring had increased phosphorylation of AMPKa (P,0.05). In addition, only Restricted male offspring displayed LV oxidative stress (P,0.05). Experiment two investigated in mothers exposed to uteroplacental insufficiency or sham surgery the effects of cross-fostering offspring at birth, and therefore the effects of the postnatal lactational environment. Surprisingly, the cross-fostering itself resulted in increased LV phosphorylation of AMPKa and Akt in females and increased phosphorylation of Akt in males compared with Control non-cross-fostered offspring (P,0.05). In conclusion, kinase signaling in the adult LV can be programmed by uteroplacental insufficiency induced growth restriction in a gender-specific manner. In addition, the heart of adult rats is also sensitive to programming following the postnatal intervention of cross-fostering alone as well as by postnatal growth restriction.