HNO-ärztliche Aspekte der Höhenmedizin

Abstract

The World Health Organisation estimates that about 40 million tourists every year climb to high (2,500-5,300 m) and extremely high altitudes (5,300-8,850 m). Thus altitude sickness and other health risks are increasing accordingly and so this fact requires clarification and advice for tourists in order to reduce the risks. That applies to the otolaryngologist, too. The non-traumatic health risks all result from the atmospheric conditions at high altitudes, in particular due to the lower atmospheric pressure. The partial pressure of oxygen (pO2), the temperature and the partial pressure of water vapour decrease continuously with increasing altitude and at the summit of the highest mountain on earth, Mt. Everest, the pO2 is reduced by two-thirds, from 212 to about 70 hPa. The temperature drops on average 6.5 degrees C per 1,000 m and at -20 degrees C 1 m3 of air contains at most just about 1 g of water vapour. The shortage of oxygen above 2500 m cannot be compensated for at once. Respiratory alcalosis, followed by hyperventilation, improves the alveolar loading of red blood cells (RBC) with oxygen, however, it also reduces the ventilatory drive from the central CO2-chemosensors as well from the peripheral O2-chemosensors located in the carotid bodies. Not until the alcalosis has been balanced by a renal secretion of bicarbonate, does the pO2-driven ventilatory stimulus normalize and the relative increase of RBC as a result of altitude diuresis improve and complete the acclimatisation. Up to an altitude of 4,000 m this adaptation takes several days to one week and up to 5,000 m up to 2 weeks. If acclimatisation has not taken place or has been insufficient, acute mountain sickness may develop. It is a harmless disorder, although it noticeably affects people physically and mentally and in some rare cases it might even develop into a life-threatening high-altitude edema in the brain or in the lung. Hematocrit values of up to 58 or even 60% at great altitudes are quite usual. Up to an altitude of 7,500 m the distortion product signals of the otoacustic emissions decrease not only between 1,000 and 1,500 Hz, but also between 3,000 and 4,000 Hz. The reduction of the inner ear signals, however, is reversible and disappears after descent. For the vestibular organ high altitudes do not mean a risk, either. 70% of all infections suffered by trekkers and climbers affect the upper airways. The cold, dry mountain air damages the mucociliary apparatus and thus leads a disposition towards acute recurrences in climbers suffering from chronic inflammations of the tonsils, the paranasal sinuses and the middle ear. In the oxygen-poor air these recurrences do not heal at all, or only very slowly, but also often tend to have a rather more complicated course.