Abstract: A filter for rezeroing an in-vivo pressure sensor is disclosed. The filter operates in a signal mode and a rezero mode. In the signal mode, the filter is a low pass filter which filters out noise. In the rezero mode, the filter is a low pass filter which filters out the dynamic components of an in-vivo pressure signal caused by the rezeroing of the pressure sensor. The filter is switchable between the signal and rezero modes. The filter is implemented by means of an active two pole RC filter with a Butterworth response. A circuit is provided to shorten the time in which the filter reaches its final response characteristic. Also disclosed is a method for processing an output from an in vivo pressure transducer, the output signal comprising noise, a mean pressure signal and a dynamic pressure signal.

Abstract: A catheter introducer assembly is disclosed. The catheter introducer assembly is made UP of a housing having a needle attached to it. A guidewire is slidably located within the lumen of the needle. A catheter assembly is mounted over the needle. Within the housing is a plunger and secured to the plunger is a retainer for releasably retaining the guidewire within the needle lumen. Axial movement of the plunger causes axial movement of the guidewire. The retainer releasably retains the guidewire. Also disclosed is a method of introducing a catheter into a blood vessel. The method involves the steps of piercing the blood vessel with a sharp needle having a catheter mounted axially on it; sliding a guidewire through the lumen of the needle so that the guidewire protrudes from the distal end of the needle and into the vessel; sliding the catheter over the guidewire and into the vessel; withdrawing the needle from the catheter; and retaining the guidewire within the catheter after withdrawal of the needle.