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Further increase in oxygen uptake during early active recovery following maximal exercise in chronic heart failure
H Daida1, T G Allison, B D Johnson
1Division of Cardiovascular Diseases and Internal Medicine, Mayo Clinic, Rochester, Minn 55905, USA.
Study Objective:
Some patients with chronic heart failure manifest a further increase in oxygen uptake (VO2) after maximal exercise whereas others do not. The purpose of this study was to determine the characteristics of chronic heart failure patients with further increase in VO2 in early active recovery following maximal exercise.
Design:
Retrospective analysis of clinical and exercise testing characteristics in patients with or without a further increase in VO2 during early active recovery.
Patients:
One hundred forty-two patients with a history of congestive heart failure and left ventricular ejection fraction of 45%, or less who performed a symptom-limited graded treadmill exercise test.
Measurements And Results:
Expired gases were monitored breath by breath from rest throughout exercise and during 1 min of active recovery. Patients were defined as having a further increase in VO2 if the average VO2 during the initial 30 s of active recovery was greater than or equal to VO2 during the final 30 s of graded exercise and the instantaneous VO2 (from the breath-by-breath plot) at 30 s of active recovery was greater than or equal to the instantaneous VO2 at peak exercise. Thirty patients (21%) showed a further increase in VO2 following peak exercise (group 1), and 112 had decreased VO2 at 30 s after peak exercise (group 2). In group 1, treadmill time was significantly shorter, peak VO2 was significantly lower (16.6 +/- 3.6 vs 21.6 +/- 6.4 mL/kg/min), and peak ventilatory equivalent for carbon dioxide (VE/VCO2) was significantly higher than those in group 2. There was no difference in etiology of heart failure or functional class and medication status.
Conclusion:
A further increase in VO2 during early active recovery was associated with poorer exercise tolerance, lower peak VO2, and higher peak VE/VCO2 in chronic heart failure patients. This sign may be a new functional variable for assessment of chronic heart failure. Further investigations are warranted to clarify the mechanisms and clinical implications of this phenomenon.