Biomedical subjects
Publications and source records attributed to J A Rysavy.
Ablation of the kidney was attempted in 12 dogs by injecting 10-30 ml of heated (100 degrees C) contrast medium (Hypaque-60, diatrizoate meglumine) into the renal artery. Complete renal ablation without collateralization was demonstrated. Hot contrast medium is an effective embolic agent, and its use is associated with few of the drawbacks of presently used techniques.
To prevent platelet aggregation following percutaneous transluminal angioplasty (PTA), cyclooxygenase inhibitors such as acetylsalicylic acid (ASA) and indomethacin are recommended. However, ASA blocks both the proaggregating effects of thromboxane (TXA2) and the antiaggregating and vasodilating effects of prostacyclin (PGI2). The authors measured the contractile response of dilated canine carotid arteries in situ and in vitro using an isometric force transducer. Following PTA, contraction of the arterial wall was significantly reduced (p less than 0.01). By blocking cyclooxygenase with indomethacin (3 micrograms/ml), contraction was greatly improved (p less than 0.001). These results suggest that PTA may result in marked release of prostacyclin by the damaged arterial wall, which could account for the decreased responsiveness of the artery to exogenous norepinephrine.
The feasibility of endovascular diathermic vessel occlusion (EDVO) is demonstrated in canines. The technique was standardized by measuring current flow through a monopolar intravascular electrode. Between 150 and 350 mA were applied to a spider-shaped intravascular electrode producing venous occlusion without perivascular damage. With further refinements in instrumentation, EDVO holds promise as a quick, safe method of therapeutic vascular occlusion that may eventually be applied clinically for spermatic vein occlusion.
Diatrizoate (76%) contrast agent heated to 100 degrees C was injected into the veins of dogs and one human volunteer for the nonsurgical occlusion of the vessels. Follow-up venograms and histologic examinations, at intervals varying from one day to four weeks later, revealed thrombosis of the injected veins in all animals. Thrombosis occurred one to five days after injection of contrast agent. The authors conclude that hot contrast medium is a safe and convenient agent for inducing thrombosis. It is much easier to use than mechanical devices, tissue glues, and plastics, which involve complex procedures and specialized equipment. In contrast to other sclerosing agents, hot contrast agent is rapidly converted into a nonsclerosing agent by cooling. The new technique allows a more controlled thermal injury to the vascular wall and is under fluoroscopic control.
The abdominal aortas in eight dogs were successfully occluded with a combination of stainless steel coils and compressed Ivalon (polyvinyl alcohol). There was no evidence of recanalization up to six months later. This combination is useful for the embolization of large arteries and arteriovenous fistulas.
A new technique for embolization with compressed Ivalon plugs is described. Fourteen arteries--six renal, three splenic, two pulmonary, one left gastric, and two abdominal aortas--were occluded in six dogs. In one case of renal artery embolization, three plugs were used, and in one case of abdominal aorta embolization, two were needed for total occlusion. In all other cases only one plug was used. Total occlusion was angiographically demonstrated up to five months following embolization in all but one case. In this case, recanalization was thought to have occurred because of overcompression of the Ivalon plug.
During wedge hepatic venography, mechanical injection should be accomplished at the lowest possible rate in order to avoid hemorrhagic infarction. Small amounts of contrast material should be administered. Hepatic angiography may result in an area of tumor blush at the site of a previous wedge injection.
Small nylon brushes with a stainless steel core have been found safe and effective for transcatheter arterial occlusion. Studies performed in 14 dogs demonstrate the brushes result in rapid occlusion of the renal artery. Follow-up studies for periods up to ten months document the safety and permanence of the occlusion. The animal studies reported herein suggest that these devices can be safely used in humans in cases where large artery occlusion is desired.
Splenoportography, a useful preoperative diagnostic procedure in patients with portal hypertension, has been largely discontinued because of the risk of hemorrhage. We have used both Ivalon and Gelfoam in particle and plug form to plug the needle tract after splenoportography. Initial studies were conducted on six dogs. Plugging of the needle tract by injection of suspensions of small Gelfoam or Ivalon particles resulted in intravasation of these particles into the splenic vein. This was demonstrated by radioactive tagging of particles and the direct collection of splenic blood during the intrasplenic injection. Plugging of the splenic needle tract with compressed Gelfoam caused immediate, complete cessation of bleeding in fully heparinized animals. Because of these experimental results, five humans with decreased platelet counts and severe portal hypertension underwent successful splenoportography without significant hemorrhage. At surgery, successful plugging of the needle tract by Gelfoam was confirmed.
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