title: Metabolic gas kinetics depend upon the level of exercise performed.
abstract: 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 O2 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 O2 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 (O2) and carbon dioxide (CO(2)) from peak exercise was significantly greater in the patients than the controls 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 O2 were increased in patients for each of the steady state tests and peak V(O2) correlated with T for recovery of O2 (r=0.44; p<0.05 from 15%, r=0.35; p= or <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 O2 and r=0.23; p<0.05 for CO2) and T(offset) (r=0.49; p<0.0001 for O2 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.
authors.affiliation: Department of Academic Cardiology, Castle Hill Hospital, Castle Road, Cottingham, Hull HU16 5JQ, United Kingdom. klauswitte@hotmail.com
authors.forename: Klaus K A
authors.initials: KK
authors.lastname: Witte
authors.forename: Simon D R
authors.initials: SD
authors.lastname: Thackray
authors.forename: Kenneth A
authors.initials: KA
authors.lastname: Lindsay
authors.forename: John G F
authors.initials: JG
authors.lastname: Cleland
authors.forename: Andrew L
authors.initials: AL
authors.lastname: Clark
mesh_terms: D001784:Blood Gas Analysis; D002248:Carbon Monoxide / Q000097:blood / Q000378:metabolism*; D016022:Case-Control Studies; D005080:Exercise Test; D017079:Exercise Tolerance / Q000502:physiology*; D005260:Female; D006333:Heart Failure / Q000175:diagnosis*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000097:blood*; D010101:Oxygen Consumption / Q000502:physiology; D005082:Physical Exertion / Q000502:physiology; D011336:Probability; D011659:Pulmonary Gas Exchange; D012016:Reference Values; D018570:Risk Assessment; D012720:Severity of Illness Index
chemical_list: D002248:Carbon Monoxide; D010100:Oxygen