Abstract
Background:
Systemic hypertension in dogs requires timely diagnosis to prevent target organ damage. While ultrasonographic assessment of the aorta-to-caudal vena cava (Ao/CVC) ratio has been proposed as a non-invasive indicator of elevated blood pressure, no studies have explored whether computed tomography (CT) can serve the same purpose. CT offers objective vascular measurements and may overcome some limitations of ultrasonography.

Aim:
This study aimed to determine whether CT-derived vascular ratios, specifically the Ao/CVC and a novel aorta-to-first lumbar vertebra (Ao/L1) ratio, differ between hypertensive and normotensive dogs. Additional analyses examined the influence of anesthetic status and measurement site on these ratios.

Methods:
In this retrospective study, 32 dogs that underwent same-day CT and Doppler blood pressure measurements were classified as hypertensive (systolic BP >140 mmHg) or normotensive. At three anatomical locations, the abdominal aortic diameter was evaluated relative to the caudal vena cava and L1 vertebral body. Statistical comparisons were performed to assess group differences and potential confounding factors.

Results:
Neither the Ao/CVC nor Ao/L1 ratio differed significantly between hypertensive and normotensive dogs (p = 0.393 and p = 0.229, respectively). However, the Ao/CVC ratio was significantly lower in anesthetized dogs (p = 0.03), while the Ao/L1 ratio remained unaffected. No significant differences in ratio values were observed between measurement sites. These findings suggest systemic hypertension does not induce measurable enlargement of the abdominal aorta, which is detectable by CT.

Conclusion:
This is the first study to evaluate CT-derived vascular indices as potential markers of systemic hypertension in dogs. The absence of significant differences suggests that aortic diameter may not reflect blood pressure status reliably and that previous ultrasonographic findings may reflect venous variability or methodological artifacts rather than actual arterial changes. The Ao/L1 ratio may offer a stable, CT-specific metric for future vascular assessments. Prospective studies with direct modality comparisons are warranted.

Key words: Aorta to caudal vena cava ratio; Aorta to first lumbar vertebra ratio; Blood pressure; Canine; CT.