Implantable valve advances blood access

DN Staff

March 6, 2000

4 Min Read
Implantable valve advances blood access

Tewksbury, MA--End stage renal disease or kidney failure entails massive medical, social, and economic costs. Developed nations account for greater than 850,000 hemodialysis patients who require repeated and reliable vascular access to cleanse their bloodstreams. The number is expected to grow 8% annually through 2005. Today 300,000 Americans have their blood cleansed several times a week at a cost of $60,000 to $63,000 per patient per year, of which an average of $18,000 funds the creation and maintenance of blood-access systems that, in large part, are full of complications.

For example, the "gold standard" of blood access in the U.S., called a fistula, is essentially an enlarged vein created by surgically shunting a major arm artery to a large vein. Fistulae take three to four months to mature before large dialysis needles may be inserted, have an average useful life of only 3-5 years, are prone to infection, stenosis (vessel constriction), additional cardiac load, and other complications such as bleeding from the needle sites after dialysis, and an unsightly appearance.

The two other options for blood access have even more drawbacks. The most common, synthetic grafts, are similar to fistulae except they are made from expanded polytetrafluoroethylene. Relatively easy to implant, grafts can be used within a few weeks. Unfortunately, they are more prone to infection and clotting than fistulae, more costly to maintain, and last only about half as long. The easiest form of blood access, the catheter, is recommended for short-term use only because it has the highest rates of infection and clotting. Now there's a whole new class of vascular access that resolves blood-access complications by using an implantable valve and a cannula. Developed by Vasca Inc., the LifeSite(R) Hemodialysis Access System is as easy-to-use as a catheter, yet has far fewer complications.

Initial design criteria for the LifeSite, says Director of Engineering James Brugger, called for using a standard dialysis fistula needle to keep cost low, and to achieve high blood-flow rate through a durable valve. With the goal of developing a small, implantable valve mechanism that uses a 14-gauge, sharp fistula needle to achieve blood flow rates of 400 ml/min, the most difficult part, explains Brugger, was breaking free of previously held assumptions regarding vascular access ports. The novel concept of elastically deforming a steel needle to achieve the seal provided the needed breakthrough. Large bore dialysis needles, he explains, have a rather thin wall thickness, that makes sealing the needle in a tapered seat quite easy, especially with a little twist while pushing.

In order to work, the valve must open and remain open while the needle is inserted. Engineers developed a plunger mechanism that moves in the direction of the needle to open a pinch clamp on a silicon tube. The pinch valve is normally held in the closed position with springs while the patient is out and about. To open the valve, ball bearings in the plunger are displaced as the needle enters, engaging a chamfered recess in the housing.

The biggest engineering challenge was packaging everything into a small, sealed, implantable enclosure that was as low in profile as possible. Brugger explains that using a standard sharp fistula needle created a real challenge. The seal had to be higher than the 0.25-inch long bevel on the fistula needle, yet the tip could not protrude into the flow path at the right angle turn in the valve's flow path. "We simply can't rely on the user to orient the needle in any particular direction, so we have to accommodate for that uncertainty without adding weight. We did that by using smaller bearings, and machining valve components to the limit in terms of material thickness."

Additional details...Contact James Brugger, Vasca Inc., 3 Highwood Dr., Tewksbury, MA 01876; Tel: (978) 863-4403; Fax: (978) 863-4401; E-mail: [email protected].

James Brugger

Responsible for the design and development of the LifeSite(R) Access System, James Brugger was hired as Director of Engineering in 1996 as Vasca Inc.'s second employee. His creativity has been key to the company's development of products and technologies. Previously during his career at COBE Laboratories Inc. and Gambro Healthcare, Mr. Brugger advanced from R&D Engineer to the position of Manager of Disposables Development. He has 26 patents for innovations in blood handling disposables, dialysis equipment, and vascular access, and is an expert in the dynamics of extracorporeal blood handling. Mr. Brugger recently took the position of Vice President of Disposables Engineering at NxSTAGE Medical Inc., a company spun off from Vasca Inc. to develop renal replacement therapy equipment.

Sign up for the Design News Daily newsletter.

You May Also Like