Minute ventilation/carbon dioxide production in chronic heart failure.

In chronic heart failure, minute ventilation (') for a given carbon dioxide production (' ) might be abnormally high during exercise due to increased dead space ventilation, lung stiffness, chemo- and metaboreflex sensitivity, early metabolic acidosis and abnormal pulmonary haemodynamics. The ' ' relationship, analysed either as ratio or as slope, enables us to evaluate the causes and entity of the '/perfusion mismatch. Moreover, the ' axis intercept, when ' is extrapolated to 0, embeds information on exercise-induced dead space changes, while the analysis of end-tidal and arterial CO pressures provides knowledge about reflex activities. The ' ' relationship has a relevant prognostic power either alone or, better, when included within prognostic scores. The ' ' slope is reported as an absolute number with a recognised cut-off prognostic value of 35, except for specific diseases such as hypertrophic cardiomyopathy and idiopathic cardiomyopathy, where a lower cut-off has been suggested. However, nowadays, it is more appropriate to report ' ' slope as percentage of the predicted value, due to age and gender interferences. Relevant attention is needed in ' ' analysis in the presence of heart failure comorbidities. Finally, ' ' abnormalities are relevant targets for treatment in heart failure.