Rodent Model for High Altitude and Ebullism Exposure Studies.

Introduction: Ebullism is the pathophysiological process that occurs as a result of exposures to extremely low ambient pressures, traditionally below 47 mmHg (<0.9 psi, ∼63,000 ft/19,202 m equivalent). However, this field of research has made minimal progress since the 1940s-1960s, when the physiology of high altitude/space operations was being explored. This lack of progress is in part because it is thought of as invariably lethal and also because it requires unique facilities to simulate these environments. As a result, no standardized time/pressure profiles or animal models have been established.

Methods: A rodent animal model (N = 20) was exposed to rapid depressurization as low as 0.3 mmHg for up to 2 min; controls were placed in the chamber but not exposed to a pressure change. Autopsies were performed to characterize the pathophysiology of ebullism at extreme altitudes.

Results: A three-tiered pressure approach was developed that allows for varying degrees of exposure (pressure and time). Although previous studies focused on exposures above or below the Armstrong Line (∼63 kft), we noted significant thermal impacts due to exceeding the water triple point (∼120 kft).

Discussion: This initial study highlights the different pathophysiological regimes that exist beyond Armstrong's line and subdivides ebullism exposures into two different classes, which can be operationally associated with cabin vs. suit depressurization events. These are now presented as Type A Complex Ebullism and Type B Simple Ebullism. The former is characterized by a combination of barotrauma, hypoxia, ebullism, and decompression sickness, while the latter presents as only ebullism. Garbino A, Nusbaum D, Goughnour S, Dalal S, Carminati M-VG, Clark J. Rodent model for high altitude and ebullism exposure studies. Aerosp Med Hum Perform. 2025; 96(3):198-205.