Pathogenesis, risk factors and impact of EIPH

Introduction

Important advances in the understanding of exercise-induced pulmonary haemorrhage (EIPH) have been made over the last 30 years; however, much still remains unknown about the condition in equine athletes. This session will summarise current knowledge on the pathophysiological mechanism of EIPH, risk factors for EIPH and epistaxis and the impact of the condition on equine performance and welfare.

Pathogenesis

Currently, the accepted pathophysiological mechanism of EIPH is stress failure of the pulmonary capillaries, due to excessive transmural pressure created by very high intra-capillary pressure (predominantly due to high blood pressure) and low intraalveolar pressure (generated by negative intra pleural pressures associated with inspiration) produced during exercise. This theory is supported by evidence of very high pulmonary arterial, venous and capillary pressures in exercising horses, and ultrastructural evidence (albeit in a limited number of horses) of disruption of endothelial and alveolar epithelial wall layers with accumulation of red blood cells within the alveolar wall interstitium and alveolar space after strenuous exercise [1,2]. Bleeding from the bronchial circulation during exercise has been suggested based upon histological evidence of bronchial angiogenesis in horses that have experienced previous episodes of EIPH; however, the contribution of the bronchial circulation to EIPH has not been determined. […]