Prolonged Kinetics of Recovery of Oxygen Consumption After Maximal Graded Exercise in Patients With Chronic Heart Failure

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Abstract
Background Patients with chronic heart failure (CHF) often complain of prolonged dyspnea after exercise. The determinants of oxygen consumption after exercise in these patients are unknown. We hypothesized that the kinetics of oxygen consumption recovery after graded exercise was prolonged in parallel with the recovery of muscle energy stores, was not affected by the exercise level, and could be used to assess the circulatory response to exercise. Methods and Results Seventy-two patients with CHF in Weber’s class A (n=28), B (n=21), and C/D (n=23) and 13 healthy subjects performed maximal upright bicycle exercise with breath-by-breath respiratory gas analysis. Kinetics of recovery of ventilation (V̇e), oxygen consumption (V̇o2), and CO2 production (V̇co2) after exercise were characterized by T1/2, the time to reach 50% of the peak value. T1/2 V̇o2 (seconds) increased with the severity of CHF (97±17 for CHF A [P<.05 versus CHF B, P<.05 versus CHF C/D], 119±22 for CHF B [P<.05 versus control subjects, P<.05 versus CHF A, and P<.05 versus CHF C/D], 155±55 for CHF C/D [P<.05 versus control subjects, P<.05 versus CHF A, and P<.05 versus CHF B] compared with 77±17 for control subjects). T1/2 V̇co2 and T1/2 V̇e also increased similarly with the worsening of CHF. T1/2 V̇o2 was correlated negatively with peak V̇o2 (r=.65) and was reproducible (r=.96). To study the relation between T1/2 V̇o2 and the duration of exercise, 10 healthy subjects and 22 patients underwent a second graded test at 75% and/or 50% of peak workload. T1/2 V̇o2 was minimally shortened, at only 50% of peak workload (P=.02). Finally, 19 patients underwent 31P nuclear magnetic resonance spectroscopy of the anterior compartment of the leg during exercise; the half-time of recovery of the ratio of inorganic phosphate to creatine phosphate (T1/2 Pi/PCr), reflecting the level of involvement of oxidative metabolism in the restoration of energetic metabolites after exercise, was linearly correlated with the half-time of V̇o2 recovery (r=.70, P<.01). Conclusions Postexercise T1/2 V̇o2 increases when CHF worsens, perhaps in part a result of slower kinetics of recovery of muscle energy stores. The time course of oxygen consumption recovery may represent a simple new criterion for measuring the impairment of the circulatory response to exercise in CHF, even submaximal exercise.

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