Abnormal end-tidal PO 2 and PCO 2 at the anaerobic threshold correlate well with impaired exercise gas exchange in patients with left ventricular dysfunction

Abstract

Background: The aim of the present study was to compare the end-tidal O 2 pressure (PETO 2) to end-tidal CO 2 pressure (PETCO 2) 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, PETO 2 or PETCO 2, best correlated with exercise limitation. Methods and Results: Thirty-eight patients with left ventricular (LV) ejection fraction <40% underwent cardiopulmonary exercise testing (CPX). PETO 2 and PETCO 2 were measured during CPX, along with peak O 2 uptake (VO 2), AT, slope of the increase in ventilation (VE) relative to the increase in CO 2 output (VCO 2) (VE vs. VCO 2 slope), and the ratio of the increase in VO 2 to the increase in work rate (ΔVO 2/ΔWR). Both PETO 2 and PETCO 2 measured at AT were best correlated with peakVO 2, AT, ΔVO 2/ΔWR and VE vs. VCO 2 slope. PETO2 at AT correlated with reduced peak VO 2 (r=-0.60), reduced AT (r=-0.52), reduced ΔVO 2/ΔWR (r=-0.55) and increased VE vs. VCO 2 slope (r=0.74). PETCO 2 at AT correlated with reduced peak VO 2 (r=0.67), reduced AT (r=0.61), reduced ΔVO 2/ΔWR (r=0.58) and increased VE vs. VCO 2 slope (r=-0.80). Conclusions: PETCO 2 and PETO 2 at AT correlated with peak VO 2, AT and ΔVO 2/ΔWR, but best correlated with increased VE vs. VCO 2 slope. PETO 2 and PETCO 2 at AT can be used as a prime index of impaired cardiopulmonary function during exercise in patients with LV failure.