Cardiac Output Changes During Exercise in Heart Failure Patients: Focus on Mid-Exercise

Abstract Aims Peak exercise oxygen uptake (VO2) and cardiac output (CO) are strong prognostic indexes in heart failure (HF) but unrelated to real-life physical activity, which is associated to submaximal effort. Methods and results We analysed maximal cardiopulmonary exercise test with rest, mid-exercise, and peak exercise non-invasive CO measurements (inert gas rebreathing) of 231 HF patients and 265 healthy volunteers. HF patients were grouped according to exercise capacity (peak VO2 50% and ≥50% pred, Groups 1 and 2). To account for observed differences, data regarding VO2, CO, stroke volume (SV), and artero-venous O2 content difference ΔC(a-v)O2 were adjusted by age, gender, and body mass index. A multiple regression analysis was performed to predict peak VO2 from mid-exercise cardiopulmonary exercise test and CO parameters among HF patients. Rest VO2 was lower in HF compared with healthy subjects; meanwhile, Group 1 patients had the lowest CO and highest ΔC(a-v)O2. At mid-exercise, Group 1 patients achieved a lower VO2, CO, and SV 0.69 (interquartile range 0.57–0.80) L/min; 5.59 (4.83–6.67) L/min; 62 (51–73) mL than Group 2 0.94 (0.83–1.1) L/min; 7.6 (6.56–9.01) L/min; 77 (66–92) mL and healthy subjects 1.15 (0.93–1.30) L/min; 9.33 (8.07–10.81) L/min; 87 (77–102) mL. Rest to mid-exercise SV increase was lower in Group 1 than Group 2 (P = 0.001) and healthy subjects (P 0.001). At mid-exercise, ΔC(a-v)O2 was higher in Group 2 13.6 (11.8–15.4) mL/100 mL vs. healthy patients 11.6 (10.4–13.2) mL/100 mL (P = 0.002) but not different from Group 1 13.6 (12.0–14.9) mL/100 mL. At peak exercise, Group 1 patients achieved a lower VO2, CO, and SV than Group 2 and healthy subjects. ΔC(a-v)O2 was the highest in Group 2. At multivariate analysis, a model comprising mid-exercise VO2, carbon dioxide production (VCO2), CO, haemoglobin, and weight predicted peak VO2, P 0.001. Mid-exercise VO2 and CO, haemoglobin, and weight added statistically significantly to the prediction, P 0.050. Conclusions Mid-exercise VO2 and CO portend peak exercise values and identify severe HF patients. Their evaluation could be clinically useful.