Efficacy of an Inspiratory Muscle Training Protocol With Resistive Airflow Loading on Exercise Capacity, Respiratory Muscle Strength and Quality of Life in Individuals With Heart Failure: a Randomized Clinical Trial

Heart failure (HF) is a complex clinical syndrome characterized by the inability of the cardiovascular system to deliver sufficient blood flow and oxygen to meet the metabolic demands of peripheral tissues. It affects more than 64 million people worldwide and remains one of the leading causes of hospitalization, disability, and mortality among adults. Despite advances in pharmacological and device-based therapies, many patients continue to experience symptoms such as dyspnea, fatigue, exercise intolerance, and impaired quality of life. These symptoms are major determinants of disease burden and frequently persist despite optimal medical management.

Although heart failure has traditionally been considered a disorder primarily involving cardiac dysfunction, increasing evidence indicates that peripheral and respiratory impairments substantially contribute to functional limitations. Among these, inspiratory muscle weakness has emerged as an important and potentially modifiable factor. Reduced inspiratory muscle strength is common in patients with both heart failure with reduced ejection fraction (HFrEF) and heart failure with preserved ejection fraction (HFpEF) and has been associated with reduced exercise capacity, increased dyspnea, impaired ventilatory efficiency, autonomic dysfunction, and poorer clinical outcomes.

The pathophysiological consequences of inspiratory muscle weakness extend beyond the respiratory system. During exercise, fatigued respiratory muscles activate the respiratory muscle metaboreflex through stimulation of group III and IV afferent fibers. This reflex increases sympathetic nervous system activity and promotes peripheral vasoconstriction, particularly in locomotor muscles. As a consequence, blood flow is redistributed from exercising skeletal muscles toward the respiratory muscles, accelerating peripheral fatigue and limiting exercise tolerance. This mechanism contributes to the reduced functional capacity commonly observed in patients with heart failure.

Several studies have demonstrated that inspiratory muscle training (IMT) can improve inspiratory muscle strength and endurance, reduce dyspnea, enhance exercise performance, improve ventilatory efficiency, and increase quality of life. Additional evidence suggests that IMT may positively influence autonomic regulation, muscle oxygenation, endothelial function, and cardiovascular health. Consequently, inspiratory muscle training has become an increasingly important adjunctive therapy within cardiovascular rehabilitation programs.

Despite these promising findings, important questions remain unanswered. First, the optimal inspiratory muscle training modality for patients with heart failure has not been established. Most previous studies have employed inspiratory pressure-threshold devices. These devices require patients to generate a predetermined inspiratory pressure before airflow occurs, resulting in resistance that may not be maintained uniformly throughout the inspiratory maneuver. Consequently, the amount of inspiratory work performed during each breath may be limited.