A sheath for repetitive insertion of high-fidelity micromanometer-tipped catheters

Implantation of micromanometer-tipped catheters into dogs and other animals for invasive high-fidelity blood pressure measurement is expensive and impractical. We have devised an implantable sheath that allows insertion of the transducer each time the animal is to be studied. This eliminates animal-inflicted damage and the need for multiple transducers if several animals are to be instrumented concurrently. The sheath is coextruded from hard and soft forms of polyurethane to form a soft, flexible, thrombus-resistant tubing with a hard thin inner lining having a low coefficient of friction. This allows chronic implantation of the sheath into the heart and major vessels with minimal trauma, yet enables a transducer to be advanced through a sheath only slightly larger than the transducer itself without the frictional resistance common to other soft tubing. The sheath can be tapered for ease of implantation into vessels or curved to the appropriate angle for implantation into the heart. Our polyurethane sheath is a versatile, convenient, and inexpensive alternative to chronic instrumentation with transducers for high-fidelity pressure measurement.