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Abstract and Introduction
Abstract
Aims The purpose of this study was to evaluate the effectiveness, feasibility, and safety of a 4-week high-intensity inspiratory muscle training (hi-IMT) in patients with chronic heart failure (CHF).
Methods and results A double-blind randomized clinical trial was carried out in 22 patients with CHF. Participants were assigned to the hi-IMT or sham-IMT group. The trainer device was a prototype of the Orygen-Dual Valve®. The training workloads were adjusted weekly at the inspiratory pressure which allowed the performance of 10 consecutive maximal repetitions (10RM). Main outcomes were strength and endurance of the respiratory muscles assessed by maximal respiratory pressures (PImax and PEmax) and a 10RM manoeuvre, respectively. Twenty-one patients presented impairment in respiratory muscle strength and endurance. Patients in the hi-IMT group showed a significant improvement in both strength and endurance: inspiratory muscle strength in the intervention group increased 57.2% compared with 25.9% in the control group (P = 0.001). The percentage change in endurance was 72.7% for the hi-IMT group compared with 18.2% in the sham-IMT group (P < 0.001). No adverse effects occurred during the intervention.
Conclusion A 4-week hi-IMT with the use of the Orygen-Dual Valve® is shown to be an effective, feasible, and safe tool to improve weakness and fatigue of the inspiratory muscles. The key point of this study is to discuss immediate practical implications in terms of respiratory muscle dysfunction postulated as a potential prognostic factor and as an additional therapeutic target.
Introduction
The current guidelines of the European Cardiology Society and the American College of Cardiology FoundationAmerican Heart Association recommend exercise training as an adjunctive approach to improve clinical status in stable adult patients with current or prior symptoms of heart failure and reduced LVEF.
Chronic heart failure (CHF) is known to alter the structure and/or function of muscles. Strength and endurance are the two main functional properties of both respiratory and peripheral muscles. When the strength and/or endurance is reduced, this is called muscle dysfunction. Strength mainly depends on muscle mass, and endurance is related to its aerobic properties. Muscle weakness is a relatively stable condition related to the loss of muscle strength which requires long-term therapeutic measures (training and/or nutritional interventions). In contrast, muscle fatigue is a temporary dysfunction related to endurance.
Respiratory muscles (RespMs) are the contractile elements that establish airflow between the lungs and the ambient air. A wide variety of studies have focused on RespM abnormalities in CHF patients. The impairment of RespM strength in CHF is related to the severity of the disease. Furthermore, reduced strength and endurance of RespMs are currently recognized as additional factors involved in limited exercise response and health-related quality of life (HRQOL), as well as poor prognosis. Furthermore, inspiratory muscle training (IMT) has been shown to result in improvements in inspiratory strength, functional capacity, ventilatory response to exercise, and HRQOL of patients with CHF and RespM weakness.
Despite the variety of studies, the optimal training scheme is still to be defined. The specifications of the loads to be imposed during training is the main factor determining the outcome. Thus, high-intensity and not too frequent stimuli will bring about an increase in the strength derived from improving fibre and muscle size. In contrast, moderate repetitive efforts result in increased muscle strength, by enlarging the elements involved in aerobic muscle activity. Previous clinical trials supported the effectiveness of low to moderate intensity IMT (maximum 38 cmH2O) alone and in combination with aerobic exercise. To date, only one randomized study has demonstrated that the addition of high-intensity IMT (hi-IMT) to aerobic exercise resulted in incremental benefits in muscle weakness, cardiopulmonary function, and HRQOL. The same authors also reported effects on dyspnoea, functional status, immune response (plasma cytokines, C-reactive protein, and apoptosis mediators), autonomic activity, endothelial vasodilator function, and NT-proBNP levels in case–control studies.
Our research group has demonstrated the good functional results of a 4-week supervised high-intensity respiratory training in patients with COPD. This intervention makes the rehabilitation programme more efficient than usual training as it requires fewer resources in terms of time and staff, and allows patients to acquire skills for further training outside the hospital.
On the basis of these considerations, the primary endpoint of this study was to evaluate the effectiveness, feasibility, and safety of a 4-week hi-IMT in CHF patients and, secondly, to discuss immediate practical implications in terms of RespM dysfunction postulated as a potential prognostic factor and as an additional therapeutic target.
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