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(Chest. 2003;124:572-579.)
© 2003 American College of Chest Physicians

Oxygen Cost of Exercise Is Increased in Heart Failure After Accounting for Recovery Costs*

Steven H. Mitchell, MD; Natalie P. Steele, MD; Kenneth M. Leclerc, MD; Mark Sullivan, MD, PhD and Wayne C. Levy, MD

* From the Division of Cardiology (Drs. Mitchell, Steele, Sullivan, and Levy), Department of Medicine, University of Washington School of Medicine, Seattle; and Madigan Army Medical Center (Dr. Leclerc), Tacoma, WA.

Correspondence to: Wayne C. Levy, MD, Division of Cardiology, Box 356422, 1959 NE Pacific St, Seattle, WA 98195; e-mail: levywc{at}u.washington.edu

Study objectives: The oxygen cost during exercise has been reported to be decreased in patients with congestive heart failure (CHF), implying an increased efficiency (lower oxygen uptake [O2] per Watt [O2/W]); however, these studies ignored the oxygen debt that is increased in heart failure.

Subjects: The primary aim of this research was to evaluate the total oxygen cost (work O2/W) during exercise and recovery in patients with heart failure as compared with healthy adults.

Design and patients: We performed a retrospective analysis comparing the exercise O2/W, the recovery O2/W, the work O2/W, and the O2/W relationship above and below the ventilatory threshold (VT) in 11 healthy control subjects and 45 patients with CHF.

Results: The exercise O2/W was decreased by 29% (p < 0.0001) in patients with CHF; however, the recovery O2/W was increased by 167% (p < 0.0001) and the work O2/W was increased by 14% in patients with CHF (p = 0.014). The O2/W slope increased above the VT (+ 27%, p = 0.0017) in both normal subjects and patients with CHF, suggesting a decrease in efficiency above the VT. There was an inverse correlation (r = 0.646, p < 0.0001) between exercise O2/W and recovery O2/W, implying that subjects with a low exercise O2/W were not efficient but rather accumulated a large oxygen debt that was repaid following completion of exercise.

Conclusions: Heart failure is associated with lower exercise O2/W; however, the patient with heart failure is not efficient, but rather accumulating a large oxygen debt (recovery O2/W) that is repaid following exercise. In addition, the work O2/W (including both exercise and recovery) is increased in patients with heart failure in comparison to control subjects, and correlates inversely with the percentage of predicted O2. The large recovery O2/W is likely due to impaired oxygen delivery to exercising muscle during exercise. The increase in the work O2/W is probably due to changes in skeletal muscle fiber type that occur in patients with heart failure (type I to type IIb).

Key Words: congestive heart failure • exercise • oxygen cost • oxygen uptake • recovery kinetics




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