Minute ventilation/carbon dioxide production in chronic heart failure

Piergiuseppe Agostoni, Susanna Sciomer, Pietro Palermo, Mauro Contini, Beatrice Pezzuto, Stefania Farina, Alessandra Magini, Fabiana De Martino, Damiano Magrì, Stefania Paolillo, Gaia Cattadori, Carlo Vignati, Massimo Mapelli, Anna Apostolo, Elisabetta Salvioni

In chronic heart failure, minute ventilation (VE) for a given carbon dioxide production (VCO2) 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 VE versus VCO2 relationship, analysed either as ratio or as slope, enables us to evaluate the causes and entity of the VE/perfusion mismatch. Moreover, the VE axis intercept, i.e. when VCO2 is extrapolated to 0, embeds information on exercise-induced dead space changes, while the analysis of end-tidal and arterial CO2 pressures provides knowledge about reflex activities. The VE versus VCO2 relationship has a relevant prognostic power either alone or, better, when included within prognostic scores. The VE versus VCO2 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 VE versus VCO2 slope as percentage of the predicted value, due to age and gender interferences. Relevant attention is needed in VE versus VCO2 analysis in the presence of heart failure comorbidities. Finally, VE versus VCO2 abnormalities are relevant targets for treatment in heart failure.