Different Determinants of Ventilatory Inefficiency at Different Stages of Reduced Ejection Fraction Chronic Heart Failure Natural History

BackgroundIt is not known whether determinants of ventilation (VE)/volume of exhaled carbon dioxide (VCO2) slope during incremental exercise may differ at different stages of reduced ejection fraction chronic heart failure natural history. Methods and ResultsVE/VCO2 slope was fitted up to lowest VE/VCO2 ratio, that is, a proxy of the VE/perfusion ratio devoid of nonmetabolic stimuli to ventilatory drive. VE/VCO2 slope tertiles were generated from our database (<27.5 [tertile 1], ≥27.5 to <32.0 [tertile 2], and ≥32.0 [tertile 3]), and 147 chronic heart failure patients with repeated tests yielding VE/VCO2 slopes in 2 different tertiles were selected. Determinants of VE/VCO2 slope changes across tertile pairs 1 versus 2, 2 versus 3, and 1 versus 3 were assessed by exploring changes in VE and VCO2 at lowest VE/VCO2 and those in VE/work rate (W) and VCO2/W slope. Resting and peak cardiac output (CO) were calculated as VO2/estimated arteriovenous O2 difference and the CO/W slope analyzed. Notwithstanding a pro...