Inspiratory Muscle Training Improves Intercostal and Forearm Muscle Oxygenation in Patients With Chronic Heart Failure: Evidence of the Origin of the Respiratory Metaboreflex

Background: The impact of inspiratory muscle training (IMT) on respiratory and peripheral muscle oxygenation and perfusion during inspiratory muscle fatigue in patients with chronic heart failure (HF) has not been established. Methods and Results: Twenty-six patients with chronic HF were randomly assigned to either 8 weeks of IMT or a control group. Inspiratory fatigue was induced by means of a progressive inspiratory resistive loading protocol until there was an inability to sustain inspiratory pressure, when the inspiratory muscle metaboreflex should be activated. The main outcomes were intercostal and forearm muscle oxygen saturation and deoxygenation as measured by means of near-infrared spectroscopy (NIRS) and blood lactate levels. Inspiratory muscle strength was increased by 78% (P < .001) after 8 weeks of participation in the IMT group. IMT attenuated the reduction of oxygen saturation in intercostal and forearm muscles and the increase in blood lactate during respiratory fatigue (P < .001 and P < .05, respectively). These changes were different from the control group (P < .01, P < .05, and P < .05, respectively). After 8 weeks, similar increases in oxygen consumption, mean arterial pressure, heart rate, stroke volume, and cardiac output were observed in both groups during respiratory fatigue. Conclusions: This randomized controlled clinical trial demonstrates that IMT attenuates the respiratory muscle oxygen demand-delivery mismatch during respiratory fatigue in patients with chronic HF.