A Pig Model of High Altitude Pulmonary Edema

Abstract

High altitude pulmonary edema (HAPE) affects unacclimatized individuals ascending rapidly to high altitude. The pathogenesis of HAPE is not fully elucidated, and many investigative techniques that could provide valuable information are not suitable for use in humans; thus, an animal model is desirable. Rabbits, sheep, dogs, and ferrets have been shown not to consistently develop HAPE, and studies in rats are limited by the animal's small size and inconsistent response. Pigs develop a marked pulmonary vasoconstrictive response to hypoxia, and preliminary studies of HAPE in pigs have been promising. To determine the suitability of pigs as an animal model of HAPE, we exposed six subadult (20 to 25 kg) pigs to normobaric hypoxia (10% oxygen) for 48 hr. One week before, and immediately after exposure to hypoxia, under anesthesia, arterial blood gases were obtained and bronchoalveolar lavage (BAL) and chest x-ray were performed. Hypoxia increased alveolar-arterial pressure difference for oxygen from 22 ± 9 to 38 ± 5 torr, p < 0.01) and red cell (from 12.3 ± 5.9 to 27.4 ± 5.3 cells × 10⁵/mL^-1, p < 0.001) and white cell (from 1.59 ± 0.90 to 7.88 ± 3.36 cells × 10⁵/mL^-1, p < 0.05) concentrations in BAL in all animals. Total BAL protein concentration increased by 64% and fractional albumin by 38% (both p < 0.05) posthypoxia. One animal had evidence of pulmonary edema on X ray. Some pigs develop findings consistent with early HAPE when exposed to normobaric hypoxia. Increasing the duration of hypoxic exposure or exercising the animals in hypoxia may better model the disease process observed in humans with clinically significant HAPE.