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Decompression strain during long-duration, high-altitude exposures

Effects of intermittent excursions to moderate altitude and inspired fractions of oxygen

Time: Fri 2021-09-17 10.00

Location:, Huddinge, Sweden (English)

Subject area: Technology and Health

Doctoral student: Rickard Ånell , Omgivningsfysiologi, Centrum för flyg- och rymdfysiologi, SAPC, KTH

Opponent: Associate Professor Ole Hyldegaard,

Supervisor: Professor Ola Eiken, Omgivningsfysiologi, Centrum för flyg- och rymdfysiologi, SAPC; Doktor Mikael Gennser, Omgivningsfysiologi, Centrum för flyg- och rymdfysiologi, SAPC; Doktor Mikael Grönkvist, Omgivningsfysiologi, Centrum för flyg- och rymdfysiologi, SAPC

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Today´s tactical demands and new technical solutions in fighter aircraft entail longer exposure periods at higher altitudes than before. A low cabin pressure protects pilots from pulmonary barotrauma in case of a sudden loss of cabin pressure, however it can also generate a supersaturation of nitrogen (N2) in the tissues, increasing the risks of bubble formation and decompression sickness (DCS). To be able to perform long-duration missions at high altitude, in-air refuelling is required, often performed at lower cabin altitudes between 15000-20000 ft. Therefore, the aim of the thesis was to explore different mechanisms that could affect decompressive strain during long and intermittent high altitude-exposures. In our experiments, upon which this thesis is based, we examined how ambient pressure and different breathing gas-mixtures affected the N2 washout and presence of venous gas emboli (VGE) as markers of decompressive strain, in particular during long-duration exposures. The thesis is based on four different studies and a short communication. The first two studies measured N2-washout during normoxic exposures. In studies I- IV, VGE were measured during normoxic or hyperoxic conditions with different ambient pressures. The results show that a high enough pressure increase compressed the existing bubbles and decreased the number of VGE before returning to high altitude. Hyperoxia alone did not protect subjects from VGE formation and DCS, whereas a combination of an early recompression during high-altitude exposures while breathing 100% O2 decreased VGE, probably by changing the bubble content from N2 to O2, making the bubbles unstable, probably reducing the risk for DCS returning to high altitude.