MEASUREMENT OF CARDIAC LEFT-VENTRICULAR PRESSURE IN CONSCIOUS RATS USING A FLUID-FILLED CATHETER

A fluid-filled catheter consisting of 100 cm of PE50 polyethylene tubing welded to 7 cm of PE10 polyethylene tubing (PE50/PE10) was constructed for the purpose of measuring the rate of left ventricular pressure development (+ dP/dt) in conscious, freely moving rats. Prior to in vivo experiments, four PE50/PE10 catheters were randomly selected, and their natural frequencies and damping ratios were determined using a square wave impact. The mean (n = 4), natural frequency of these catheters was shown to be 35.0 +/- 5.5 Hz, and the mean damping ratio was 0.83 +/- 0. 10. Natural frequency plotted against increasing PE50 tubing length was shown to have a slope of - 0.44 Hz/cm with a correlation coefficient of 0.99. The effect of the 7-cm PE10 tubing segment on the catheter damping ratio was also demonstrated. One of the four PE50/PE10 type catheters exhibited a damping ratio of 0.74 +/- 0.09. When the 7-cm PE10 tube was removed, the damping ratio was reduced to 0.31 +/-0.04. Left ventricular + dP/dt obtained in conscious rats with a PE50/PE10 catheter (n = 7; 6300 +/- 300 mmHg/sec) was significantly less than the + dP/dt obtained using a 100-cm PE50 catheter (n = 6; 9400 +/- 400 mmHg/sec). The results of this study make it clear that the PE50/PE10 catheter is suitable for the measurement of left ventricular + dP/dt in the conscious rat, and that catheter design has a profound influence on both the catheter natural frequency and damping ratio.