Implantable sensor for intraoperative and postoperative monitoring of blood flow: A preliminary report

We have developed an implantable 20 MHz Doppler flow sensor, to monitor blood flow in patients after operation. During surgery the sensor is wrapped around a blood vessel and secured in place with a releasable tie. No tissue puncturing techniques are required. The lead wires, together with a release cable, are exteriorized through the chest wall. Several days after operation, the tie is externally released, and the sensor is pulled out. Twenty-seven sensors were implanted in 24 dogs for up to 16 days. All were extracted successfully with minimal visible behavioral reaction in the awake dogs and caused no thrombosis or vascular damage. The Doppler velocity signals had excellent linear correlations (r = 0.99) with data from electromagnetic flow sensors and timed blood collections. In addition, the sensors were applied to coronary artery bypass grafts in 31 patients for up to 2 days after operation. High-quality signals were obtained, and intraoperatively recorded signals agreed well with simultaneous electromagnetic flow tracings. All sensors were extracted with minimal discomfort to the awake patients and with no complications. Thus, the implantable flow sensor is a safe, reliable, accurate, and simple method for intraoperative and postoperative monitoring of blood flow in vessels 2.5 to 5 mm in diameter.