Reasons for performing study: Arterial calcification is found frequently in the pulmonary artery of racehorses, but the aetiology is unknown. Calcification might be associated with increased wall stress due to arterial geometry (shape) and exercise-induced hypertension.
Hypothesis: High wall stress levels are found in the regions associated with calcified lesion formation, exacerbated as transluminal pressure increases to levels associated with exercise.
Methods: The pulmonary arteries of 5 horses, unaffected by calcification, were dissected and pressurised to resting and exercising physiological transluminal pressures and scanned with MRI. Arterial geometries were reconstructed to form 3D computer models and finite element analyses performed. Wall stress levels were measured in 4 regions of interest: the arterial trunk and bifurcation, the wall ipsilateral and contralateral to the bifurcation. Measurements were made for arterial transluminal pressures of 25, 50 and 100 mmHg.
Results: High wall stress levels were consistently found at the pulmonary artery bifurcation and wall ipsilateral to the bifurcation, where calcified lesions typically form. Lower wall stress levels were found along the trunk and the wall contralateral to the bifurcation where lesions are less frequently found. Wall stress levels increased 5-fold over a 4-fold increase in pressure. The wall stress levels ranged 10 kPa in the wall of the branch contralateral to the bifurcation at 25 mmHg to 400 kPa in the bifurcation at 100 mmHg.
Conclusions: Wall stress from arterial geometry and increased pulmonary artery transluminal pressure are factors that may be associated with calcification of the equine pulmonary artery.
Potential relevance: Arterial calcification may increase the risk of arterial wall failure in racing horses.