Doppler evaluation of renal resistivity index in healthy conscious horses and donkeys

Abstract

The renal resistive index (RRI) is used as a measurement of downstream resistance in arteries. The aim of this study was to assess the RRI of the arcuate arteries by pulsed-wave Doppler ultrasonography in healthy conscious horses and donkeys, and to verify any differences related to age, breed, bodyweight (BW) or body condition (BCS). Thirty-three healthy conscious horses and nine donkeys had their systolic and diastolic flow velocities at the level of the arcuate arteries estimated by pulsed-wave Doppler ultrasound, and the RRI was calculated. The relationship of RRI with age, breed (Trotters vs. other breeds), bodyweight (BW), and body condition score (BCS) were evaluated. PW Doppler evaluation of RRI was successfully applied in most of the horses, but to date not in the donkeys. In horses, median RRI values for the right kidney (0.58±0.006) were statistically higher than for the left (0.51±0.006). For the donkeys the values were comparable. There was no significant difference in RRI between horses younger or older than 15 years, and between breeds in horses. No correlation with age, BW or BCS was found in either horses or donkeys.

Fig 1. Doppler ultrasound image showing an intrarenal arterial Doppler spectrum of the kidney in a healthy conscious horse.

The color Doppler superimposed on the B-mode image was used to identify an arcuate artery, and the PW Doppler sample volume was placed at the intraluminal level (left side of the image). Normal intrarenal Doppler flow velocity waveforms corresponding to four consecutive cardiac cycles (right side of the image).