Abstract 5888: The Oxygen Uptake Efficiency Slope is Reduced in Older Patients with Heart Failure and a Normal Ejection Fraction
The oxygen uptake efficiency slope (OUES), an index of aerobic exercise performance, reflects pulmonary, cardiovascular and skeletal muscle function. The OUES is reduced in patients with systolic heart failure (HF) and demonstrates potential prognostic value in this patient population. We have previously shown that exercise capacity is reduced in HF patients with a normal ejection fraction (NEF), the dominant form of HF in older persons, and to a similar degree as age-matched HF patients with systolic dysfunction. This study tested the hypothesis that the OUES would be decreased in elderly patients with HF-NEF. A total of 146 subjects (mean age: 72 ± 6 years, 59% women) participated in the study. Fifty-nine subjects were diagnosed with systolic HF (EF: 31 ± 10%), 59 with HF-NEF (EF: 60 ± 7%) and 28 were healthy age-matched controls. All subjects underwent cardiopulmonary exercise testing on a lower extremity ergometer using an incremental staged protocol. The OUES was calculated by the following equation: VO2 = a log10VE + b; where a = slope and units = L/min. The minute ventilation/carbon dioxide production (VE/VCO2) slope, peak oxygen consumption (VO2) and peak respiratory exchange ratio (RER) were also determined. Mean peak RER was >1.10 for all groups. One-way ANOVA revealed peak VO2 (systolic HF: 13.6 ±3.3 vs. HF-NEF: 13.0 ± 2.8 vs. controls: 20.2 ± 4.0 mlO2·kg−1·min−1) was significantly lower in both HF groups compared to controls (p<0.001). The VE/VCO2 slope (systolic HF: 38.9 ± 8.3 vs. HF-NEF: 34.6 ± 6.7 vs. controls: 33.3 ± 5.3) was, however, only significantly higher in patients with systolic HF compared to both HF-NEF and control groups (p=0.001). Like peak VO2, the OUES (systolic HF: 1.23 ± 0.41 vs. HF-NEF: 1.22 ± 0.30 vs. controls: 1.51 ± 0.49) was significantly lower in both HF groups compared to controls (p=0.003). Compared to age-matched healthy controls, the OUES is reduced in older HF-NEF patients and to a similar degree as those with systolic HF. This pattern is similar to that of peak VO2 but different from the VE/VCO2 slope, which is not as elevated in HF-NEF as in systolic HF. Thus, as in systolic HF, the OUES may provide independent clinically useful information in older patients with HF-NEF.