Is the elevated slope relating ventilation to carbon dioxide production in chronic heart failure a consequence of slow metabolic gas kinetics?

OBJECTIVE

Patients with heart failure have slow metabolic gas exchange kinetics, which may contribute to the elevated slope of the relationship between ventilation and carbon dioxide production (Ve/Vco(2) slope).

SETTING

A tertiary referral centre for cardiology.

SUBJECTS

Eleven patients with stable chronic heart failure and 11 age-matched controls.

DESIGN

Each subject underwent maximal bicycle-based peak exercise testing with metabolic gas exchange analysis and three further repeated tests at 15%, 25% and 50% of the load achieved at peak exercise. The ventilation and carbon dioxide production from each of these steady-state tests was used to re-calculate the Ve/Vco(2) slope and compared with the Ve/Vco(2) slope derived from the maximal test.

RESULTS

Peak oxygen consumption [mean (S.D.)] was lower in heart failure patients [18.2 (4.0) vs. 31.2 (6.3) ml/kg per min; P<0.001] than in controls. The Ve/Vco(2) slope was steeper in patients than controls [32.7 (8.3) vs. 27.1 (1.6); P<0.05]. There was no difference between the Ve/Vco(2) slope reconstructed from the three steady state tests and resting data and that gained from the maximal test [35.3 (7.8) vs. 25.9 (3.2); P=0.43].

CONCLUSIONS

The elevated slope of the relationship between ventilation and carbon dioxide production is not a consequence of the short stages of a standard incremental exercise test combined with delayed metabolic gas kinetics in heart failure patients.