Abnormal End-Tidal PO₂ and PCO₂ at the Anaerobic Threshold Correlate Well With Impaired Exercise Gas Exchange in Patients With Left Ventricular Dysfunction

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Background: The aim of the present study was to compare the end-tidal O₂ pressure (PETO₂) to end-tidal CO₂ pressure (PETCO₂) in cardiac patients during rest and during 2 states of exercise: at anaerobic threshold (AT) and at peak. The purpose was to see which metabolic state, PETO₂ or PETCO₂, best correlated with exercise limitation. Methods and Results: Thirty-eight patients with left ventricular (LV) ejection fraction <40% underwent cardiopulmonary exercise testing (CPX). PETO₂ and PETCO₂ were measured during CPX, along with peak O₂ uptake (VO₂), AT, slope of the increase in ventilation (VE) relative to the increase in CO₂ output (VCO₂) (VE vs. VCO₂ slope), and the ratio of the increase in VO₂ to the increase in work rate (ΔVO₂/ΔWR). Both PETO₂ and PETCO₂ measured at AT were best correlated with peakVO₂, AT, ΔVO₂/ΔWR and VE vs. VCO₂ slope. PETO₂ at AT correlated with reduced peak VO₂ (r=-0.60), reduced AT (r=-0.52), reduced ΔVO₂/ΔWR (r=-0.55) and increased VE vs. VCO₂ slope (r=0.74). PETCO₂ at AT correlated with reduced peak VO₂ (r=0.67), reduced AT (r=0.61), reduced ΔVO₂/ΔWR (r=0.58) and increased VE vs. VCO₂ slope (r=-0.80). Conclusions: PETCO₂ and PETO₂ at AT correlated with peak VO₂, AT and ΔVO₂/ΔWR, but best correlated with increased VE vs. VCO₂ slope. PETO₂ and PETCO₂ at AT can be used as a prime index of impaired cardiopulmonary function during exercise in patients with LV failure.