System Makes Heart Surgery More Tolerable

Engineers from Santa Clara, CA-based CardioVention (http://rbi.ims.ca/3846-559) say they have departed from conventions developed during 50 years of heart-lung machine history, and in doing so are able to dramatically reduce the blood volume and surface area used by such machines. At the same time, they say, they've minimized the potential for dangerous air entrainment into the blood during heart surgeries. "Surgeons can still get the access they need to the heart without causing a huge (physiological) response to the invasiveness of the procedure," notes Ben Brian, VP of R&D for CardioVention.

The technology could be significant for patients undergoing extensive procedures that require surgeons to stop a beating heart and place the body on an "extracorporeal circuit" that circulates blood. Such systems typically draw large volumes of blood from the patient and place it in a venous reservoir, where they add chemicals and run the blood over a large surface area that removes air. But those conventional systems can be very stressful for some patients, making survival more difficult for the sickest of them.

CardioVention's solution is to integrate cardiopulmonary bypass system functions—such as pumping, oxygenation, filtration, and air removal—into a compact unit, which, by virtue of its smaller size, reduces trauma. The first step toward that downsizing is the use of an active air removal system, known as the AirVac. Developed by engineers at CardioVention, the disposable AirVac employs an air sensor and a solenoid valve. When air is sensed, the AirVac momentarily opens the solenoid valve, thus allowing air to be removed through a vacuum line.

With AirVac, the new system is able to eliminate the venous reservoir, the largest and most bio-incompatible part of a conventional cardiopulmonary system. "Instead of having an open reservoir with air and antifoam (chemicals), we've a closed flow path," Brian says. "So we remove air through a much smaller volume, and that allows us to scale back the size of the other devices."

Indeed, the other key component of CardioVention's CORx system is an Integrated Membrane Oxygenator (IOS), which incorporates an air filter, membrane oxygenator (artificial lung), and centrifugal pump in a single, small enclosure. The integrated centrifugal pump in the base of the IOS propels blood through the artificial lung via a vane-type impeller. Using a single-piece ferromagnetic insert molded into thermoplastic polyurethane, the impeller spins on dual ABEC-7 bearings sealed on a stainless steel shaft. As it rotates, the centrifugal pump also helps eliminate entrained air by "pulling Gs," and therefore enabling the air to move upward, toward the AirVac port. Furthermore, the IOS employs a filter designed to recirculate any entrained air up to the air removal chamber.

As a result of the more compact design, the new system exposes the patient's blood to less than 1.2m² of surface area, whereas conventional systems typically range between 12 and 15m². The new system also dramatically reduces the volume of blood that is recirculated from the patient.

CardioVention engineers say that the new design now makes it possible for even the sickest patients to tolerate recirculating blood through a machine while the heart is removed for surgery. "When you take blood outside the body and expose it to more than 10m² of foreign surface area, that's very traumatic," Brian concludes. "Because this system is so much smaller, it makes complete bypass surgery more accessible to even the sickest patients."

Ben Brian holds a Ph.D. in chemical engineering. Previously, he developed oxygenators and biomaterials for Cobe Laboratories Inc. and served as a strategic marketing director for the Ethicon Division of Johnson & Johnson.