Normal Doppler velocimetry of renal vasculature in Persian cats

Renal diseases are common in older cats. Decreased renal blood flow may be the first sign of dysfunction and can be evaluated by Doppler ultrasound. But previous studies suggest that the resistive index (RI) has a low sensitivity for detecting renal disease. Doppler waveforms of renal and intrarenal arteries demonstrate decreased blood flow before there are any changes in the RI. The purpose of this study was to evaluate the normal Doppler flowmetrics parameters of renal arteries (RAs), interlobar arteries (IAs) and abdominal aorta (AO) in adult healthy, Persian cats. Twenty-five Persian cats (13 females and 12 males with mean age of 30 months and an age range 12-60 months) with normal clinical examinations and biochemical tests and normal systemic blood pressure were given B-mode ultrasonographies in order to exclude all nephropathies, including polycystic kidney disease. All measurements were performed on both kidneys. Both kidneys (n = 50) were examined by color mapping of the renal vasculature. Pulsed Doppler was used to examine both RAs, the IAs at cranial, middle and caudal sites, and the AO. The RI was calculated for all of the vessels. Early systolic acceleration (ESA) of RA and IA was obtained with Doppler spectral analysis. Furthermore, the ratio indices between RA/AO, and IA/RA velocities were calculated. The mean values of peak systolic velocity (PSV) and the diameter for AO were 53.17 ± 13.46 cm/s and 0.38 ± 0.08 cm, respectively. The mean RA diameter for all 50 kidneys was 0.15 ± 0.02 cm. Considering the velocimetric values in both RAs, the mean PSV and RI that were obtained were 41.17 ± 9.40 cm/s and 0.54 ± 0.07. The RA had a mean ESA of 1.12 ± 1.14 m/s2 and the calculated upper limit of the reference value was 3.40 m/s2. The mean renal-aortic ratio was 0.828 ± 0.296. The IA showed PSV and RI values of 32.16 ± 9.33 cm/s and 0.52 ± 0.06, respectively. The mean ESA of all IAs was 0.73 ± 0.61 m/s2. The calculated upper limit of the reference value was 2.0 m/s2. The mean renal-interlobar artery ratio was 1.45 ± 0.57. The RI values obtained in this study were similar to values reported in the literature. Some conditions that lead to a decrease in compliance and to an increase in vascular resistance can affect the Doppler spectral waveforms without changes in RI. To our knowledge, there are no studies that were directed toward to the normal ESA values of the renal vasculature in Persian cats. This study introduced a new ratio between the PSV of the RA and the IA. This index was developed based on the well-known effects of Doppler on the detection of stenosis, regardless of the cause. Further studies are necessary to verify the hemodynamic behavior of this index under pathological conditions in cats as well as the effect of aging, nephropathies and systemic pressure on Doppler velocimetric parameters.