Physiological interpretation of almost loss of consciousness

Background: The phenomenon of almost loss of consciousness (A-LOC) is although known to the aviation fraternity since the 1980s, it is not well researched. Very few studies have attempted to elaborate the characteristics of A-LOC. The present study is a retrospective analysis which has endeavored to address the lacunae in literature. Materials and Methods: A retrospective analysis of the G training data in high-performance human centrifuge for a time span of 4 years (2009–2013) was carried out. Results: A total of 71 A-LOC incidents were reported and were analyzed for better understanding of A-LOC. On the basis of findings such as nystagmus, maintenance of postural tone, convulsions, amnesia, and dreams during A-LOC, neurophysiology of A-LOC has been hypothesized. Conclusion: The presence of nystagmus and maintenance of body posture suggest intact vestibulo-ocular reflex and sensory-motor tract, respectively. Non-recollection of dreams, amnesia suggests breach in memory and/ or information processing for higher functions. The mechanism of A-LOC in toto can be explained by regional differences in blood flow and vulnerability of cerebral centers to ischemic hypoxia. Convulsions in A-LOC could be attributed to hyperexcitability of nerve fibers due to hypoxia.