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Ultrasonographic technique for the abdominal aorta
caudal abdominal aorta (AAo) may be imaged through the left lateral, right lateral or ventral abdominal windows. The transducer is positioned just ventral to the lumbar transverse processes, for the left or right lateral window, and the AAo can be imaged in dorsal longitudinal and transverse planes. In the left longitudinal plane, the AAo appears as an anechoic, pulsatile tubular structure along the dorsal midline immediately ventral to the vertebral bodies. Mobile echoes may be visible within the vessel lumen. The walls are thin, smooth, echogenic structures that run nearly parallel to each other. The AAo is adjacent to the caudal vena cava (CVC), both running parallel to each other. Cranial to the renal vessels, the AAo and CVC diverge, with the CVC deviating in a cranioventral direction. The AAo is located in the near field while the CVC is in the far-field. The aortic wall is slightly thicker than that of the CVC. The diameter of the AAo frequently appears to be larger than that of the CVC, probably because the diameter of the CVC is foreshortened. When mild transducer pressure is applied to the abdominal wall, there is a uniform narrowing of the tubular lumen of the vessels that is more pronounced in the CVC. The AAo can be followed caudally to its external iliac arterial branches, as it narrows in diameter. It may also be followed cranially to the aortic hiatus at the level of the 13th thoracic or 1st lumbar vertebra. However, interference from ribs and gastrointestinal gas makes visualization of the AAo cranial to the renal arteries difficult, especially in deep-chested dogs. Imaging from the ventral abdominal window in a sagittal plane with the transducer placed medial to the right kidney may give a better view of the cranial AAo. In the transverse plane, the AAo is a round or oval anechoic structure. Compression by transducer pressure causes the vessel to adopt a more oval or elliptical shape, especially in the CVC. When imaged from the right lateral abdominal window, The AAo is located in the far-field, while the CVC is in the near field. The visceral branches of the AAo that can be readily visualized by B-mode ultrasonography include the coeliac artery, cranial mesenteric artery, left renal artery, right renal artery, and caudal mesenteric artery.
Doppler patterns of the normal abdominal aortic flow
The aortic blood flow is towards the transducer when the transducer is angled cranially in a longitudinal imaging plane. The AAo has a typical plug flow velocity profile with a typical high resistance pattern. The velocity distribution or gradient is narrow. The waveform has a high, sharp systolic peak with a large, clear spectral window. Mild turbulence occurs during late systole (deceleration slope). There is a retrograde early diastolic flow, followed by a low forward late diastolic flow. If there is a longer pause between two ventricular contractions, additional waves with lower velocities occur. In humans, the waveform changes slightly from proximal to distal AAo. Caudal to the renal arteries, the flow reversal in early diastole and reduction in late diastole of the aortic velocity occur to a greater degree due to the high resistance to blood flow through the muscles of the hind limbs.
Chapter 1. General introduction
Chapter 2. Literature review
Chapter 3. Influence of normovolemic anemia on Doppler characteristics of the abdominal aorta and splanchnic vessels in Beagles
Chapter 4. Doppler ultrasonographic changes in the canine kidney during normovolaemic anemia
Chapter 5. Influence of normovolaemic anemia on Doppler-derived blood velocity ratios of abdominal splanchnic vessels in clinically normal dogs
Chapter 6. Comparison of effects of uncomplicated canine babesiosis and canine normovolemic anemia on abdominal splanchnic Doppler characteristics – A preliminary investigation
Chapter 7. General discussion
Chapter 8. Summary
Appendix A. A canine normovolaemic acute anemia model
Appendix B. Selection of uncomplicated canine babesiosis cases
