The resistive and elastic work of breathing during exercise in patients with chronic heart failure

Patients with heart failure (HF) display numerous derangements in ventilatory function, which together serve to increase the work of breathing (Wb) during exercise. However, the extent to which the resistive and elastic properties of the respiratory system contribute to the higher Wb in these patients is unknown. We quantified the resistive and elastic Wb in patients with stable HF (n=9; New York Heart Association functional class I-II) and healthy control subjects (n=9) at standardised levels of minute ventilation (V'E) during graded exercise. Dynamic lung compliance was systematically lower for a given level of V'E in HF patients than controls (p<0.05). HF patients displayed slightly higher levels of inspiratory elastic Wb with greater amounts of ventilatory constraint and resistive Wb than control subjects during exercise (p<0.05). Our data indicates that the higher Wb in HF patients is primarily due to a greater resistive, rather than elastic, load to breathing. The greater resistive Wb in these patients probably reflects an increased hysteresivity of the airways and lung tissues. The marginally higher inspiratory elastic Wb observed in HF patients appears related to a combined decrease in the compliances of the lungs and chest wall. The clinical and physiological implications of our findings are discussed.