Correct occlusive bladder width for indirect blood pressure measurement in horses.

The influence of occlusive bladder width on blood pressure, measured indirectly using a doppler ultrasound technique at the middle coccygeal artery, was studied in 6 anesthetized horses. The relationship was investigated on tails with and without hair, and the optimum bladder width (BW)/tail girth (TG) ratio was determined for systolic pressure (SP) and diastolic pressure (DP), with the data grouped as unclipped tails (TT-1), clipped tails (TT-2), and both unclipped and clipped tails collectively (TTB). The optimum BW/TG ratios for SP and DP were 0.296 and 0.866 for TT-1, 0.376 and 1.156 for TT-2, and 0.339 and 0.983 for TTB, respectively. Despite the differences in optimal BW/TG ratios between TT-1 and TT-2, their regression equations were not significantly (P less than 0.05) different and therefore, data could be considered as TTB. The regression equations for TTB showed that a BW/TG ratio of 0.482 underestimated SP and overestimated DP by approximately 8.8%. In mature Thoroughbreds (mean TG 21.5 cm), this value corresponded to a BW of 10.4 cm. Blood pressure measured directly in the greater metatarsal artery was significantly different from that measured directly in the middle coccygeal artery in individual horses, but when averaged over all horses, there was no significant difference between the 2 sites.