Exercise-induced pulmonary haemorrhage in the horse: results of a detailed clinical, post mortem and imaging study. IV. Changes in the bronchial circulation demonstrated by C.T. scanning and microradiography.

The purpose of this study was to use radiographic contrast techniques and special imaging methods to identify and high-light bronchial arterial involvement in lung lesions associated with exercise-induced pulmonary haemorrhage (EIPH) in horses. The lungs from four horses with histories of EIPH were prepared for computerised tomographic scanning and microradiography by perfusing the broncho-oesophageal artery with a mixture of red latex and either barium or iodine contrast materials while the pulmonary supply received only blue latex. Computerised tomographic scan slices of the prepared inflated lungs were obtained from the caudal tip of the lung to the hilus. Microradiography of selected lung slices was also performed on a Faxitron. Diffuse areas of increased density, with preferential bronchial arterial supply noted on the computerised tomographic scans were confirmed by microradiography. Dense focal and diffuse plexuses of markedly hypertrophied and highly branched bronchial arterial networks were identified, centred around certain small airways. The vascular supply to these plexuses was recruited predominantly from neighbouring bronchial vessels, and in some cases, from the enlarged vasa vasorum of pulmonary arteries sending anastomoses to the affected areas. The authors conclude that bronchial vascular lesions in EIPH cases are the likely origin of haemorrhage; that small airway disease is the probable initiating stimulus for bronchial vascular proliferation in these lesions; and that the morphology and nature of the neovascular tissue in these lesions provides the conditions leading to haemorrhage in the lungs of horses with EIPH.