Segmented polyurethane: a new elastomer for biomedical applications.

A segmented polyurethane elastomer, originally developed for elastic thread, is now being used for molded prostheses. Performance of this material when used for components of a heart-assist system warrants a thorough investigation of its effectiveness in a variety of biomedical devices.

Mixing studies during intracarotid artery infusions in an in vitro model.

Sporadic instances of retinal damage and of focal brain toxicity have been observed following intracarotid artery infusions of chemotherapeutic agents (such as BCNU and cis-platinum) for the treatment of glioblastomas. The episodic nature of these toxicities is consistent with the possibility that the drug solutions were streaming from the catheter tip and, therefore, were not well mixed or not uniformly distributed in all branches distal to the catheter tip location. To test this hypothesis, an in vitro system was fabricated which included a transparent model of the human carotid artery and its major branches. These were furnished with pulsatile flow of a blood simulant. Dye solutions infused at several infusion rates through various types of catheters in both supraophthalmic and infraophthalmic positions were monitored and recorded on videotape and photographic film. The effluent streams from distal branches of the model were collected, and the relative concentrations of dye in each branch were determined spectrophotometrically. The results indicate that infusate streaming occurs at low infusion rates. In some cases, the concentration in a given branch can be at least five times the expected concentration. Similar occurrences of streaming in vivo could cause focal toxicity. Methods to improve mixing should be used during intra-arterial administration of drugs; these include increasing the infusion rates and improving catheter tip design.

A miniature toposcopic catheter suitable for small diameter tortuous blood vessels.

A miniature catheter suitable for clinical use based on the principle of the continuously everting tube has been developed and tested extensively in dogs. The 1-mm-dia flexible tube can advance up a narrow tortuous blood vessel 30 cm beyond the tip of the conventional catheter to which it is attached. A slippery hydromer coating combined with a U-shaped cross section enables the tube eversion to be accomplished at an acceptable operating pressure. The new system will provide access to previously inaccessible regions of the body, and has the potential for clinical use in embolizing selected vessels, providing highly localized chemotherapy, and sampling body fluids. The catheter can advance both with and against the blood flow in arteries and veins, and is awaiting clinical trials.

The toposcopic catheter: a design for maneuvering through tortuous vessels.

The toposcopic catheter is an everting tube that advances within a vessel without moving over the endothelium. It easily passed through simulated tortuous vessels which other catheters could not negotiate and was also successful in the external carotid, vertebral, hepatic, renal and coronary arteries in dogs. The catheter advances to its full length (30 cm) or until wedged in small peripheral arteries.

Surface and bulk characteristics of a polyether urethane for artificial hearts.

A segmented polyether urethane was used as the blood contacting surface in a series of 10 heart assist devices implanted in calves for periods up to 35 weeks. At termination, each was examined to correlate blood compatibility and device performance with surface properties, chemical purity, physical stability and affinity for lipid absorption.

Jet-directed catheter for interventional radiology.

A new catheter of dual lumen construction, suitable for clinical use, is capable of navigating acute vessel branches by selective retrojet fluid thrusts issuing from cowlings built into its distal sidewalls. Conventional radiopaque liquids can be used both to drive the system and to fluoroscopically locate its position relative to the vascular network. In vitro studies have shown the catheter to traverse straight vessels and negotiate difficult lateral turns over short radii in the process of entering progressively smaller branches. In vivo studies have verified these capabilities and suggest a means for embolizing tumors and arteriovenous malformations located at otherwise inaccessible regions. For arterial infusion of drugs to treat tumors, the turbulent jet action is utilized to enhance mixing within the blood stream to overcome the streaming phenomenon common to other catheters. The result is better distribution of the agent and increased opportunity for the drug to reach more of the tumor. The catheter system is undergoing clinical trials.

Glioblastoma: catheter techniques for isolated chemotherapy perfusion.

Techniques have been developed for isolated perfusion of chemotherapeutic agents in patients with glioblastoma. Three catheters that facilitate crossing the carotid siphon have been developed; two are based on an everting or toposcopic principle, and one uses microjets for deflectability and improved mixing. Blood from the ipsilateral jugular vein is aspirated at high volumes (300 ml/min) for extracorporeal circulation through an adsorption column (for recovery of carmustine) or dialysers (for recovery of cisplatin). Preliminary experience in 10 patients suggests that high doses of chemotherapeutic agent can be administered using these catheters, with reduced retinal and systemic toxicity.