Investigation of the performance of two types of the doppler catheter in vitro

There is considerable interest in the use of Doppler catheters for measuring coronary flow reserve in humans. Two types are currently available, these being models having side-mounted or tip-mounted transducers. The performance of these catheters was carefully observed in Silastic tubing perfused with blood by a roller pump. Each catheter was used with two types of positioning wire: a rigid wire and a standard J-tip guidewire. Linear regressions of velocity vs. flow rate were performed. Both catheters performed well with the rigid wire (r greater than or equal to 0.992). When used with the J-tip, the end-mounted catheter suffered decreased performance because of positioning difficulties, while the side-mounted catheter performance was within 6% of the ideal. Measurements made with the side-mounted catheter at low flow rates underestimated the expected response for forward flow. Because of the ease of positioning, the side-mounted catheter is judged to be more useful in measuring flow ratios.