Exercise-induced pulmonary hemorrhage

Abstract

Exercise-induced pulmonary hemorrhage (EIPH) is characterizedby the presence of blood in the tracheobronchial airways after exercise. Most breeds used for strenuous exercise are affected. The prevalence of EIPH, irrespective of geographical location, has been reported to vary from 30% in Standardbred racehorses to 70% in Thoroughbred horses used for racing, jumping, eventing, steeplechase and polo. In addition to endoscopic confirmation, pulmonary hemorrhage can be recognized by identification of hemosiderophages (macrophages containing intracytoplasmic hemosiderin) in aspirates of tracheobronchial secretions. Detailed examinations of lungs from horses with a confirmed history of EIPH have identified certain consistent morphologic features that provide strong circumstantial evidence for bronchial arterial bleeding. Evidence of pulmonary hemorrhage is characteristically seen in the dorsocaudal regions of the caudal lung lobes. Stained a light brown-bronze color these regions are symmetrically distributed and in the inflated lung have a fine reticular pattern. The subpleural bronchial arteries are more prominent and appear enlarged and more tortuous in stained regions of the lung. Subgross examination of transverse slices of the caudal lung suggest that the hemorrhage occurs primarily in the dorsal bronchopulmonary segments with the dorsobasal bronchopulmonary segment being most severely involved. Affected regions have gross evidence of small airway disease with increased bronchial arterial supply around these airways and within the parenchyma. On microscopy, affected parenchymal regions have extensive interstitial fibrosis. Large accumulations of hemosiderophages are located within airspaces, terminal airways and within the increased connective tissue around airspaces and airways. Microangiographs of lung sections perfused with latex and barium sulfate revealed marked proliferation of the bronchial arterial circulation in lung regions with evidence of pulmonary hemorrhage. The expanded vascular network appeared to be focused on diseased small airways.