Blood flow, substrate utilization and heat generation in tissues drained by the azygos vein in man

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Abstract
The present study was undertaken to examine the blood flow, heat generation and substrate utilization in tissues drained by the azygos vein in healthy subjects. Catheters were inserted percutaneously into the azygos vein and the pulmonary artery in 10 healthy male subjects in the basal, post-absorptive state. Blood flow in the azygos vein was measured by thermodilution technique, blood temperature was recorded in both the azygos vein and the pulmonary artery and blood samples for the determination of oxygen content and substrate concentrations were collected from both vessels repeatedly at timed intervals. Free fatty acid (FFA) exchange was evaluated following the intravenous infusion of 14-C labelled oleic acid. The average azygos vein blood flow was 94 +/- 10 ml/min. The coefficient of variation for the flow determination was 3.6%. The blood temperature in the azygos vein was consistently higher than that in the pulmonary artery, indicating an average calculated net heat production in the tissues of 0.5 W. The oxygen uptake to the tissues drained by the azygos vein amounted to 6 +/- 1 ml/min. Significant amounts of glucose, FFA and ketone bodies were taken up in the azygos area, while both glycerol and FFA were released. The FFA uptake could, if oxidized, account for about half of the oxygen uptake. In conclusion, the findings indicate that, in the basal state, the tissues drained by the azygos vein utilize both glucose and FFA. Heat is generated within the area but the rate of generation is low and can largely be explained by the oxidative metabolism. The findings do not support an important role for brown adipose tissue metabolism in the interscapular region in man.