Diameters of abdominal veins and arteries during nitrate therapy

The effects of 1.6 mg NTG on the diameter of abdominal veins and arteries were investigated by means of ultrasound tomography in 26 and 28 healthy persons respectively. Fourteen patients served as controls in the venous studies and 28 in the arterial measurements. The diameter of the caval vein decreased in anterior-posterior direction within 5 minutes after nitroglycerin administration by about 22% from 14.2 +/- 4.0 mm to 11.1 +/- 3.3 mm (p less than 0.005). In contrast, the portal vein enlarged by about 27% from 10.3 +/- 1.8 mm to 13.1 +/- 2.3 mm, the superior mesenteric vein by about 12% from 8.2 +/- 1.6 to 9.2 +/- 1.4 mm, and the splenic vein by about 23% from 6.6 +/- 2.3 mm to 8.1 +/- 1.8 mm (p less than 0.001). The superior mesenteric artery and the proper hepatic artery dilated by about 12% from 7.8 +/- 0.9 mm to 8.7 +/- 0.9 mm and from 6.5 +/- 1.0 mm to 7.3 +/- 0.7 mm respectively (p less than 0.001). There was no significant change in the diameter of the abdominal aorta, however. The results show that NTG induces a relaxation of the abdominal veins and of the abdominal arteries of the muscular type. They suggest that the splanchnic veins participate essentially in the therapeutically important venous pooling effect of NTG. The reduced peripheral venous return is made sonographically visible by a collapse of the inferior vena cava. Furthermore, the influence on the windkessel function after administration of NTG seems to be mediated not by the aorta itself, but rather by its large muscular-type branches like the mesenteric and hepatic arteries.