Severe Neurological Decompression Sickness in a U-2 Pilot

Abstract

Severe neurological decompression sickness (DCS) has been a rare entity in the U.S. Air Force, including the U-2 community. In over 50 yr of operation, few U-2 pilots reported severe neurological DCS in flight despite the extreme altitudes at which they operate. This article describes a near-fatal case of neurological DCS that occurred during a combat mission. The injury left the pilot with permanent cognitive deficits that correlated with focal lesions present on magnetic resonance imaging of his brain. To our knowledge, the images presented herein are the first to show radiological evidence of brain injury induced by altitude DCS. Though only a single case, the objective and clinical findings in the case pilot are similar to results documented in divers suffering DCS with central nervous system injury and victims of traumatic brain injury. DCS will remain a potentially serious threat to current and future air and space operations.

Altitude Decompression Sickness Incidence Among U-2 Pilots: 1994-2010

“…The reasons are unclear. Interestingly, several neurologic cases described in this study demonstrated signifi cant lesions on brain MRI, an uncommon fi nding ( 6 ). The defi nitive cause(s) for the apparent rise in both quantity and severity of DCS cases among U-2 pilots in recent years has not yet been fully explained.…”

Lower neurocognitive function in U-2 pilots

“…3 At this time, the precise mechanisms of CNS damage due to hypobaria are uncertain. Previously, we hypothesized that CNS damage may be caused by microbubble occlusion of small arterioles, by platelet thrombi produced by accelerated coagulation in the presence of nitrogen microbubbles, 29,30 or by direct tissue damage from microparticles and activation of proinflammatory leukocytes.…”

“…We hypothesized that in the absence of hypobaric exposure, there should be no significant differences in either the burden or distribution of WMH between DOCs and U2Ps. The DOC median WMH volume was 0.013 cm 3 Current cognitive assessment group comparisons. There were no significant differences between U2Ps and AFPs for any of the age-adjusted MAB-II measures after applying the Sidak adjustment (table 1).…”

“…A single U2P (excluded from all analysis) experienced neurocognitive impairment sufficient to preclude further pilot duties, but this was an unusual case not representative of the U-2 population. 3 One pilot included in this study experienced repeated episodes of headache associated with high flight and was therefore restricted to pressurized aircraft with no subsequent clinical symptoms or impairments. In addition, although 2 pilots in this study did voluntarily withdraw from the U-2 program before testing, neither one demonstrated any clinical neurocognitive deficit and both remained on active flying status medically qualified for all USAF aircraft including the U-2 without restriction.…”

“…3 In response to an increased incidence of NDCS in the United States Air Force (USAF), 4,5 research was performed that demonstrated pilots who experienced NDCS had increased volume and number of subcortical T2-weighted white matter hyperintensity (WMH) abnormalities. 6 Follow-up research reported significant elevation of WMH in high-altitude pilots without clinical symptoms of NDCS.…”