mountain sickness

the condition that results from unaccustomed exposure to a high altitude (4 500 m or more above sea level). Reduced atmospheric pressure and shortage of oxygen cause deep rapid breathing ( HYPERVENTILATION ), which lowers the concentration of carbon dioxide in the blood ( see ALKALOSIS ). Symptoms include nausea, exhaustion, and anxiety. In severe cases there may be acute shortness of breath due to fluid collecting in the lungs (pulmonary OEDEMA ), which requires treatment by diuretics and return to a lower altitude.