Hemodynamic Changes Attending Anqiocardioqraphy

Hypertonicity is an outstanding characteristic of the contrast solutions used for radiographic visualization of the cardiovascular system. The osmolarity of a number of these agents ranges from 1,300 to over 2,300 milliosmols per liter, values severalfold greater than that of blood serum (6, 23). In previous studies, important hemodynamic changes have been shown to result from intracardiac injection of these hypertonic materials for angiocardiography. A fall in systemic arterial pressure was consistently observed fifteen to thirty seconds after injection of contrast substance, and elevation of the cardiac output was documented as early as one minute after injection (8, 14, 17, 24). Hypervolemia and systemic vasodilatation were proposed as mechanisms underlying these alterations in blood pressure and flow (8). Although the osmotic properties of radiocontrast agents are thought to be of primary importance in causing the hemodynamic changes which occur, little information is available about the actual magnitude and time course of blood osmolality immediately after angiocardiography. Further, the means by which peripheral vasodilatation is produced by these materials has not been studied, although a direct action of contrast medium upon vascular smooth muscle has been suggested (8). Finally, the temporal relationships between the concentration of contrast medium and the hemodynamic changes have not been completely described. Our experiments were designed to study the osmolality of arterial blood during the first circulation of a contrast agent and to evaluate the mechanisms responsible for the decrease in systemic arterial pressure and the rise in cardiac output that occur with angiocardiography. Methods Twenty-two dogs were lightly anesthetized with sodium pentobarbital (25 mg/kg); their weights varied from 14 to 25 kg. The left ventricle was catheterized with a No. 7F retrograde catheter from the right superficial femoral artery. The left femoral artery was cannulated with a 15 cm length of polyethylene tubing with an inside diameter of 0.11 cm; this catheter sampled arterial blood for a Colson densitometer at a rate of 24.7 ml/min. when dye dilution curves were done. A No. 7F catheter was inserted into each femoral vein, and both were advanced into the inferior vena cava. One was used for injections of indocyanine green and the other for administration of various drugs. The left brachial artery was cannulated with a 15 cm length of polyethylene tubing for measurement of systemic arterial pressure with a Statham P-23D strain gauge. Recordings were made by a direct-writing oscillograph. In a large number of clinical angiocardiograms in our laboratory 80 per cent sodium iothalamate3 (6, 12, 16) was used as the contrast agent in an average dose for each injection of 0.5 ml/kg. This agent and dose per injection were employed in this study. All animals received multiple injections; the average total dose per animal was 1.6 ml/kg per experiment. Sodium iothalamate (SIO) has an osmolarity of 2264 mOsm/L (6).