 Furthermore, the magnitude of exercise-induced pulmonary arterial, capillary and venous hypertension is reportedly similar in horses either with or without EIPH.This theory is based on the fact that, during galloping, the absence of any bone attachment of the forelegs to the spine in the horse causes the shoulder to compress the cranial rib cage.The compression of the chest initiates a pressure wave of compression and expansion which spreads outwards.