What is altitude sickness?

Altitude sickness is actually a series of clinical symptoms. When people who have lived in the plains for a long time enter the plateau, especially above 3,000 meters above sea level, this syndrome will appear. What is altitude sickness? According to the severity of the disease, altitude sickness can be divided into three categories: altitude sickness, high-altitude pulmonary edema and high-altitude coma. This is mainly due to the harsh natural environment of the plateau. Furthermore, the most effective way to treat altitude sickness is to transport the patient to the plains. During transportation, attention should be paid to keeping warm and supplementing oxygen supplements to maintain vital signs.

Causes

For those who live in plateaus for a long time, their bodies gradually adapt to the special natural conditions of the plateau. The reason for adaptation is that under the regulation of neurohumoral factors, various functions of the body undergo corresponding changes, especially the respiratory and circulatory systems. In plateau areas, the difference in oxygen partial pressure between the atmosphere and the alveoli decreases with increasing altitude, which directly affects alveolar gas exchange, the rate at which blood carries oxygen, and the release of combined oxygen in tissues, resulting in insufficient oxygen supply to the body and hypoxia. For those who first ascend to the plateau, hypoxia indirectly stimulates the respiratory center through peripheral chemoreceptors (mainly the carotid body), causing an early increase in ventilation, allowing the body to inhale more oxygen to compensate. This process is the human body's adaptation to plateau hypoxia. It takes 1 to 3 months to gradually transition to stable adaptation, which is called plateau acclimatization. Individual adaptation varies greatly. Generally, people can adapt quickly within an altitude of 3,000 meters, but only some people can adapt to altitudes between 4,200 and 5,330 meters, and it takes a long time for them to adapt. Around 5,330 meters is the critical altitude for human adaptation, and it is easy to experience hypoxia reaction. The higher the altitude, the lower the partial pressure of oxygen in the atmosphere, and the more severe the body's hypoxia becomes. The speed of climbing and the intensity of labor can also affect the degree of altitude sickness. In addition, factors such as excessive mental stress, fatigue, infection, malnutrition and low temperature also affect the onset of the disease.

Clinical manifestations

Altitude sickness often occurs when climbing a mountain for the first time, especially in the first few days, which is called an acute reaction. Any altitude sickness that persists for more than 3 months is called a chronic reaction. Abroad, altitude sickness is divided into five syndromes: acute mountain sickness, high-altitude pulmonary edema, high-altitude cerebral edema, high-altitude retinal hemorrhage and chronic mountain sickness. In my country, altitude sickness is divided into two categories: acute altitude sickness and chronic altitude sickness.

1. Acute mountain sickness

(1) Acute altitude sickness: When people enter a plateau above 3,000 meters in a short period of time, or when plateau residents return to the plateau after living in the plains for a period of time, they may experience reactions such as headache, dizziness, palpitations, and shortness of breath. Severe cases may include loss of appetite, nausea, vomiting, insomnia, fatigue, abdominal distension and chest tightness. Examination revealed mild cyanosis of the lips and facial edema.

(2) High altitude pulmonary edema: The incidence rate is about 3%. Based on acute mountain sickness, it occurs when the altitude reaches above 4,000 meters, but it can also occur in fast climbers at 2,500 meters. Therefore, some people develop the disease rapidly 3 to 48 hours after climbing, while others develop the disease as late as 3 to 10 days. Symptoms include headache, chest tightness, cough, dyspnea, inability to lie flat, etc. Some severe cases may have oliguria, cough up large amounts of bloody foamy sputum, and even unconsciousness. Physical signs include cyanosis and decreased breath sounds in both lungs, which are filled with moist rales. X-rays show lighter, flake-like, and fuzzy shadows in both lung fields, which are most obvious near the hilum of the lungs, and the right side is often more severe than the left side.

(3) High-altitude cerebral edema, also known as high-altitude coma or high-altitude encephalopathy. The morbidity is low, but it is more likely to cause death. It occurs in people who quickly enter plateaus above 4,000 meters, with an acute onset, mostly at night. The main cause of the disease is acute hypoxia, which causes spasm and increased permeability of small blood vessels in the brain, resulting in cerebral edema. In addition to the early symptoms of acute altitude sickness, patients also experience increased intracranial pressure, such as severe headache and vomiting. Mental symptoms such as confusion, depression or excitement, and delirium may also occur. Some patients experience convulsions, followed by drowsiness, lethargy, and even coma. The patient's pulse rate increases, breathing becomes extremely irregular, pupils are slow to react to light, and sometimes pathological reflexes, optic disc edema, and hemorrhage occur. The cerebrospinal fluid is normal, but the pressure may be slightly high.

2. Chronic mountain sickness

According to clinical manifestations, it is divided into five types, but the manifestations of each type overlap. Most cases are mixed types with pulmonary hypertension and cardiac changes as the main features.

(1) Chronic altitude sickness: Although some patients have lived in the plateau for a certain period of time, the symptoms of altitude sickness still persist, often with neurasthenia syndrome, and sometimes with arrhythmia or transient fainting.

(2) High altitude heart disease is more common in children. Due to their poor ability to compensate for hypoxia, hypoxia causes pulmonary vascular spasm and sclerosis, which increases pulmonary artery pressure. The right ventricle enlarges due to continued overload, leading to right heart failure. In addition, increased blood pressure and blood viscosity also affect the left ventricle, causing hypertrophy of the entire heart and total heart failure. Hypoxia can also lead to turbid swelling of myocardial cells, focal necrosis and myocardial fiber rupture. Children may experience cyanosis, shortness of breath, edema, paroxysmal cough, night crying, and mental depression; adults may experience symptoms such as palpitations, cough, cyanosis, edema, and physical decline.

(3) High-altitude polycythemia: The higher the altitude and the longer the stay, the more red blood cells there are. An increase in red blood cells causes increased blood viscosity.

(4) High-altitude hypertension: The main clinical manifestation is neurasthenia syndrome, which rarely causes heart and kidney damage. After returning to the lowlands, blood pressure quickly returned to normal.