Complex sentence: High altitude cerebral edema (or HACE) is a severe and sometimes fatal form of altitude sickness that results from capillary fluid leakage due to the effects of hypoxia on the mitochondria-rich endothelial cells of the blood--brain barrier.
Split into simpler sentences: High altitude cerebral edema (or HACE) is a severe and sometimes fatal form of altitude sickness. Results from capillary fluid leakage due to the effects of hypoxia on the mitochondria-rich endothelial cells of the blood--brain barrier.