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Metabolic gas kinetics depend upon the level of exercise performed
Author(s) -
Witte Klaus K.A.,
Thackray Simon D.R.,
Lindsay Kenneth A.,
Cleland John G.F.,
Clark Andrew L.
Publication year - 2005
Publication title -
european journal of heart failure
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.149
H-Index - 133
eISSN - 1879-0844
pISSN - 1388-9842
DOI - 10.1016/j.ejheart.2005.05.005
Subject(s) - medicine , respiratory minute volume , carbon dioxide , steady state (chemistry) , kinetics , heart failure , heart rate , respiratory exchange ratio , anaerobic exercise , oxygen , cardiology , zoology , respiratory system , chemistry , physical therapy , blood pressure , biology , physics , organic chemistry , quantum mechanics
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 CO 2 output were correlated to the workload and the percentage of peak performed during the steady state tests. Results: Patients had lower peak oxygen uptake () 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 ( CO 2 ) from peak exercise was significantly greater in the patients than the controls and correlated with peak ( 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 correlated with T for recovery of o 2 ( 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 CO 2 ) and T offset ( r =0.49; p <0.0001 for O 2 and r =0.42; p <0.0005 for CO 2 ) 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.