Objective and importance: The "tight-fit" hypothesis and subsequent current understanding of acute mountain sickness (AMS) is that individuals with less compliant cerebrospinal fluid systems (smaller ventricles and cerebrospinal fluid spaces) have a greater increase in intracranial pressure (ICP) for a given increase in brain volume as a result of hypoxic cerebral edema. There has only been 1 study of direct (telemetric) ICP measurement at high altitude. This was performed in 1985 on 3 subjects by Brian Cummins up to a maximum height of 16,500 ft (5030 m). The group also investigated the "tight-fit" hypothesis by correlating computed tomographic scans that measured ventricular size (read blindly) with headache score and AMS symptomatology in 10 subjects. Unfortunately, the data were thought to have been destroyed by fire, and, hence, the findings were not published. The data have now been rediscovered, and this article reviews the methodology and findings of this unique piece of work.
Results: The ICP monitoring study demonstrated that ICP remained normal at rest at all altitudes; however, in the single subject with AMS, there was a dramatic increase in ICP even on minimal exertion. The computed tomographic scan analysis of brain compliance demonstrated an inverse correlation between ventricular size and headache score.
Conclusion: This unique research, which is unlikely to ever be repeated, is the only report of direct ICP measurement at high altitude. This and the computed tomographic study provide the first objective evidence supporting the "tight-fit" hypothesis of AMS.