Analysis of oxygen mask-induced soft tissue and nasal bone problems in F-16 pilots

In the present dissertation we investigated the effect of in-flight oxygen masks on the noses of Royal Netherlands Air Force (RNLAF) F-16 pilots. We explained the use of an in-flight oxygen mask by RNLAF F-16 pilots, and presented the medical complaints associated with its usage and related to the nose. The pathophysiology and prevention of similar symptoms observed in athletes were discussed to help explain the pathophysiology of the oxygen mask-induced symptoms. In a review of the literature the pathophysiology of the adaptive response of the nasal bone to the exerted contact pressure and friction by the oxygen mask was discussed. The adaptive response of the nasal bone consists of forming new bone. Via mechanotransduction a biochemical response is mounted by the nasal bone. Intermittent dynamic mechanical loading with recovery periods generates a much stronger bone formation response than one continuous loading period. An analysis of the fit of the oxygen mask demonstrated that a suboptimal fit of the oxygen mask was regarded as a potential contributing factor to inflicting the symptoms of the nose. A 3D analysis of the fit of the oxygen mask allowed us to evaluate how closely the oxygen mask fit the face. As the main finding we observed that there was space for movement in the nasal area. In-flight displacement may result in exertion of excessive pressure and friction on the nose. The findings of a cross-sectional questionnaire among the RNLAF F-16 pilots and a prospective post-flight pain score study were presented. It allowed us to make an inventory of the symptoms and revealed which conditions worsened and lessened the symptoms according to the pilots. We objectified the latter findings by prospectively collecting pain scores after each flight for several months in a row both in The Netherlands and in operational theater. The conditions that were reported to worsen the symptoms correlated to certain types of missions that received high pain scores. In a pilot it was evaluated how much pressure the oxygen mask exerted during static conditions. The pressure was measured on the nose and chin when the oxygen mask and the helmet were donned. The baseline exerted pressure was compared to the exerted pressure while the pilot made protocolized head movements. In a subsequent study, the effect of dynamic conditions on the exerted contact pressure on the nose were obtained in the human centrifuge. The pressure changes on the nose were higher than on the chin. Another main finding was that shear stress and friction were present: during the acceleration phase the mask moved. This chapter demonstrated that pressure and friction are exerted chronically. To conclude, the main conclusions of the thesis and strategies for future preventive measures were discussed