The concentration of oxygen, lactate and glucose in the central veins, right heart, and pulmonary artery: a study in patients with pulmonary hypertension

INTRODUCTION: Decreases in oxygen saturation (SO(2)) and lactate concentration [Lac] from superior vena cava (SVC) to pulmonary artery have been reported. These gradients (ΔSO(2 )and Δ[Lac]) are probably created by diluting SVC blood with blood of lower SO(2 )and [Lac]. We tested the hypothesis that ΔSO(2 )and Δ[Lac] result from mixing SVC and inferior vena cava (IVC) blood streams. METHODS: This was a prospective, sequential, observational study of hemodynamically stable individuals with pulmonary artery hypertension (n = 9) who were about to undergo right heart catheterization. Catheters were advanced under fluoroscopic guidance into the IVC, SVC, right atrium, right ventricle, and pulmonary artery. Samples were obtained at each site and analyzed for SO(2), [Lac], and glucose concentration ([Glu]). Analysis of variance with Tukey HSD test was used to compare metabolite concentrations at each site. RESULTS: There were no differences in SO(2 )or [Lac] between IVC and SVC, both being greater than their respective pulmonary artery measurements (P < 0.01 for SO(2 )and P < 0.05 for [Lac]). SO(2 )and [Lac] in right atrium, right ventricle, and pulmonary artery were similar. ΔSO(2 )was 4.4 ± 1.4% (mean ± standard deviation) and Δ[Lac] was 0.16 ± 0.11 mmol/l (both > 0; P < 0.001). Δ[Glu] was -0.19 ± 0.31 mmol/l, which was not significantly different from zero, with SVC [Glu] being less than IVC [Glu]. CONCLUSION: Mixing of SVC with IVC blood does not account for the development of ΔSO(2 )and Δ[Lac] in hemodynamically stable individuals with pulmonary artery hypertension. An alternate mechanism is mixing with coronary sinus blood, implying that ΔSO(2 )and Δ[Lac] may reflect changes in coronary sinus SO(2 )and [Lac] in this patient population.