Why does exercise induced pulmonary haemorrhage occur?

Exercise-induced pulmonary haemorrhage in the horse: results of a detailed clinical, post mortem and imaging study. I. Clinical profile of horses

Detailed physical and clinical examinations were performed on 26 Thoroughbred racehorses which were used subsequently in a series of studies to investigate the contribution of the pulmonary and bronchial arterial circulations to the pathophysiology of exercise-induced pulmonary haemorrhage (EIPH). Twenty-five of the horses had been retired from race training in Hong Kong during the 1984-85 season, all but four raced that season; one horse had been retired the previous season. The average number of races for the group that season was 4.1 +/- 2 with an average distance of 1502 +/- 216 metres, mean racing speed 15.5 +/- 0.5 metres/sec. Time from last race to necropsy was 177 +/- 155 days, range 12 to 572 days. All but one horse had a known history of either EIPH or epistaxis. Time from last recorded incident of expistaxis (17 horses) to necropsy was 156 +/- 141 days, range 12 to 513 days, with a longer interval since last recorded endoscopic observation of EIPH. Focal abnormal lung sounds were detected in the dorsocaudal lungfields on auscultation during rebreathing in three horses and six had tracheobronchial cytology consistent with previous episodes of pulmonary haemorrhage (haemosiderophages). No other characteristics which might have allowed separation of this group of horses from other Thoroughbred horses recently in race training were identified.