Breathing Efficiency in Systolic Heart Failure: Impact of Hyperventilation and Dead Space

Background Patients with heart failure (HF) often develop pulmonary system abnormalities. Specifically, an abnormal ventilation relative to metabolic demand (V E /VCO 2 , ventilatory efficiency) during exercise has been shown to be an important marker of disease severity and prognosis. The purpose of this investigation was to focus on the factors that underlie the abnormal breathing efficiency in this population. Methods 14 controls (10 male) and 40 (36 male) mod‐severe HF patients, age 52±12 and 56±8 yrs, respectively, performed graded exercise on a cycle ergometer. Gas exchange and blood gas measurements were made during submaximal exercise (~65% peak VO 2 ) and used to quantify the influence of hyperventilation (PaCO 2 ) and dead space ventilation (V D ) on V E /VCO 2 . Results The V E /VCO 2 ratio was lower in controls (30±4) than in HF (45±9, p<0.001) due to a lower PaCO 2 and higher V D /V T that contributed an estimated 29% and 71%, respectively, to the increased V E /VCO 2 (p<0.05). The elevated V D /V T in HF was in turn the result of a tachypneic breathing pattern (lower V T , 877±306 vs 2003±504ml, p<0.01) in the presence of a relatively normal V D (9.6±3.8 vs 11.9±5.7 L/min, p=0.094). Conclusion The abnormal ventilation in relation to metabolic demand in HF during exercise is predominantly due to alterations in breathing pattern, rather than hyperventilation or changes in ventilation/perfusion relationships. HL71478