Functional anatomy of bronchial veins

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Abstract

The amount of bronchial arterial blood that drains into the systemic venous system is not known. Therefore, in this study we further delineated the functional anatomy of the bronchial venous system in six adult, anesthetized, and mechanically ventilated sheep. Through a left thoracotomy, the left azygos vein was dissected and the insertion of the bronchial vein into the azygos vein was identified. A pouch was created by ligating the azygos vein on either side of the insertion of the bronchial vein. A catheter was inserted into this pouch for the measurement of bronchial venous occlusion pressure and bronchial venous blood flow. An ultrasonic flow probe was placed around the common bronchial branch of the bronchoesophageal artery to monitor the bronchial arterial blood flow. Catheters were also placed into the carotid artery and the pulmonary artery. The mean bronchial blood flow was 20.6±4.2 ml min−1 (mean±SEM) and, of this, only about 13% of the blood flow drained into the azygos vein. The mean systemic artery pressure was 72.4±4.1 mmHg whereas the mean bronchial venous occlusion pressure was 38.1±2.1 mmHg. The mean values for blood gas analysis were as follows: bronchial venous blood pH=7.54±0.02, PCO2=35±2.6, PO2=95±5.7mmHg; systemic venous blood—pH=7.43±0.02, PCO2=48±3.2, PO2=42±2.0mmHg; systemic arterial blood—pH=7.51±0.03, PCO2=39±2.1, PO2=169±9.8mmHg. We conclude that the major portion of the bronchial arterial blood flow normally drains into the pulmonary circulation and only about 13% drains into the bronchial venous system. In addition, the oxygen content of the bronchial venous blood is similar to that in the systemic arterial blood.

Introduction

The bronchial circulatory system forms a dense vascular plexus in the airway wall to supply blood and nutrients to the airways [1]. The bronchial vascular plexus is supplied blood by the bronchial arteries. The anatomy of these bronchial arteries has been well described [1], [2], [3], [4], [5], [6]. It has been assumed that the major portion of bronchial arterial blood drains into the pulmonary circulation through the bronchopulmonary anastomoses and only the blood that supplies the extrapulmonary airways is drained into the systemic venous system. Although the anatomy of bronchopulmonary anastomoses as the route for drainage of bronchial arterial blood into the pulmonary circulation has been described [1], the anatomy of the bronchial veins that drain bronchial arterial blood into the systemic venous system has not been well studied. These bronchial veins may have an important role. For example, Paré et al. [7] found that systemic venous hypertension augments airway edema and postulated that this could be due to obstruction of bronchial veins that drain into the systemic venous system resulting in fluid filtration into the extravascular compartment. It is also possible that drugs that are delivered into the body through the tracheaobronchial tree, such as inhaled bronchodilators, get absorbed into the bronchial vascular plexus, and are then transported to the bronchial smooth muscles by the bronchial blood flow. If this were the case, after giving a drug by inhalation, its rate of absorption from the bronchial tree could be studied by measuring the concentration of that drug in the bronchial venous blood. Hence, knowledge of bronchial venous anatomy could have important implications. This research project was undertaken to delineate the anatomy of the bronchial venous drainage.

Section snippets

Surgical preparation

Six adult sheep of mixed breed were fasted for 24 h and then sedated with xylazine (0.25 mg/kg) about 30 min prior to surgery. Following induction of anesthesia with intravenous injection of 8–10 ml of 5% pentobarbital sodium, the sheep were intubated and connected to an anesthesia machine (Ohmeda Anesthesia System Excel 210, Madison, Wisconsin). Anesthesia was maintained with 2–2.5% isoflurane. A gastric tube was passed through the esophagus into the stomach to continuously drain the rumen. The

Results

In all six sheep, we were able to identify only one bronchial vein which drained blood into the left azygos vein at the level of aortic arch. This vein drained blood from the trachea, covering the region around the main tracheal bifurcation, and proximal extrapulmonary bronchi (Fig. 2). In order to confirm that this bronchial vein indeed drained blood that was supplied by the common bronchial branch of the bronchoesophageal artery, in all six sheep we infused 5% dextrose into this artery

Discussion

The major portion of the bronchial arterial blood drains into the pulmonary circulation through the bronchopulmonary anastomoses. It has been postulated that only a small portion of the bronchial arterial blood drains into the systemic venous system, however, the actual amount of blood that drains via this route has not been studied. In the present study we were able to find only a single bronchial vein. By demonstrating that the glucose concentration in the bronchial venous blood dramatically

Acknowledgments

The study was supported by the Department of Veterans Affairs, John Butler Lung Foundation, and the Mountain State Medical Research Institute.

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