Metabolic gas kinetics depend upon the level of exercise perfonned

Background: The kinetics of oxygen and carbon dioxide at the onset of and recovery from exercise are slowed in patients with chronic heart failure (CHF). The aim of the present study was to establish whether the kinetics of O-2 are influenced by the work rate. Methods: Thirteen CHF patients and 12 control subjects underwent bicycle-based peak exercise testing with metabolic gas exchange analysis. Each subject then exercised at 15%, 25% and 50% of the maximal workload achieved until reaching steady state. Time constants for onset (T-onset) and offset (T-offset) for O-2 uptake and CO2 Output were Correlated to the workload and the percentage of peak V-O2, performed during the steady state tests. Results: Patients had lower peak oxygen uptake (pV(O2)) and the relation between ventilation and carbon dioxide output was steeper in patients than controls. T-offset for both oxygen (O-2) and carbon dioxide (CO2) from peak exercise was significantly greater in the patients than the than controls. T-offset, kcontrols and correlated with peak V-O2 (r=0.56,p < 0.005 and r=0.58, p < 0.005). T-onset and T-offset for O-2 were increased in patients for each of the steady state tests and peak V-O2, correlated with T for recovery Of 02 (r=0.44; p < 0.05 from 15%, r=0.35; p=< 0.05 from 25%, and r=0.54;p < 0.01 from 50%). There was a correlation between the T-onset (r=0.42; p < 0.0005 for O-2 and r=0.23;p < 0.05 for CO2) and T-offset (r=0.49; p < 0.0001 for O-2 and r=0.42; p < 0.0005 for CO2) and oxygen uptake as a percentage of peak exercise. Conclusions: This study demonstrates that the time constants of onset and offset for oxygen are dependent upon the degree of exertion performed relative to the individual's peak capacity. (c) 2005 European Society of Cardiology. Published by Elsevier B.V. All rights reserved.