When it is desired to purge air from the catheter, a liquid, such as sterile saline or a saline solution embodying a radiopaque material, may be injected by means of a syringe coupled to the luer fitting of the proximal hub 15 and that purging liquid will flow through the lumen 13 of the catheter forcing air ahead of it and ultimately through the inflation ports 18 to expand the balloon 20.