Doppler evaluation of testicular artery blood flow: effect of dogs’ size and age

Doppler evaluation of testicular artery blood flow is used in humans to assess reproductive function and testicular pathology. In the studies where canine testicular blood flow was characterized (1, 2), dogs were clinically healthy and not older than 8 years. Most of canine testicular disorders, however, are related to advancing age and often their diagnosis must be formulated in presence of comorbidities. A comprehensive description of testicular artery blood flow in a clinical population is missing in literature. The aims of the study were to describe, in a hospital population of dogs without ultrasonographic evidence of testicular lesions, the testicular artery blood flow, and to evaluate the effect of dogs’ age and size on the blood flow parameters. Methods: Fifty-two dogs presented between 2015 and 2017 at the University of Pisa Veterinary Teaching Hospital were evaluated. All dogs were triaged to green category and no drug that could alter systemic pressure or testicular function was administered. The peak systolic velocity (PSV), end-diastolic velocity (EDV), pulsatility index (PI) and resistive index (RI) within the distal supra-testicular artery were measured with a 5–13 MHz linear array transducer. Blood flow parameters of right and left testes were compared by Wilcoxon matched pairs sum test, while age groups (adult: 25-84 months, old: >84 months) and size groups (small: < 15kg, medium: 16-40 kg) were compared by Mann Withney test. Values are shown as median and interquartile range (IQR). Differences were considered statistically significant when P<0.05. Results: Doppler measurements were not statistically different between the right and left testes, thus the mean between the two was used for the analyses. Median values (IQR) of PSV, EDV, PI or RI in this population were 15.82 cm/s (4.82), 6.86 cm/s (2.62), 0.92 (0.43), 0.56 (0.15), respectively. The waveforms of the testicular artery showed a monophasic blood flow pattern characteristic of a low resistance vessel. Age did not affect significantly PSV, EDV, PI or RI. EDV showed higher values in medium sized dogs [7.7 cm/s (1.60) vs 5.5 cm/s (1.49); P< 0.05] and a tendency was seen in smaller compared to larger dogs for a higher PI [1.04 (0.48) vs 0.82 (0.32); P=0.09] and RI [0.60 (0.14) vs 0.55 (0.15); P= 0.06]. These results confirm what previously described for adult dogs (2). In bulls, the testicular artery is longer in heavier animals and this leads to an increased blood flow. Differences in testicular Doppler velocity parameters might be explained by different lengths of the testicular artery (3). In conclusion, dog size affected testicular blood flow in a hospital population, while age group, adult or older dogs, had no effect.