Values of the slope of VE vs VCO₂ relationship, VE_Yint, RR_Yint and volume of dead space in heart failure patients (upper panel) and healthy subjects (lower panel) with 0 mL, 250 mL and 500 mL of additional dead space.

<p>Data are presented as means ± SD; <b>RR_Yint</b> = respiratory rate calculated as Y intercept of RR vs VCO₂ relationship; <b>VCO₂</b> = carbon dioxide production; <b>VD_Yint</b> = dead space volume calculated as VE_Yint/RR_Yint; <b>VD_meas</b> = dead space volume measured by P_aCO₂ in heart failure patients and estimated by P_ETCO₂ in healthy subjects; <b>VE</b> = ventilation; <b>VE_Yint</b> = ventilation at VCO₂ = 0, calculated as Y intercept of VE vs VCO₂ relationship.</p>†<p>p<0.001 versus +250 mL;</p>§<p>p<0.001 versus +500 mL;</p>*<p>p<0.01 versus +500 mL;</p>&<p>p<0.05 versus +250 mL;</p>$<p>p<0.05 versus +500 mL;</p>©<p>p<0.01 versus +250 mL.