What Is Aerospace Medicine?

Aerospace medicine is the study of the effects of external environmental factors (low pressure, hypoxia, cosmic radiation, etc.) and flight factors (overweight, weightlessness, etc.) on human physiological functions when flying in the atmosphere and outer space. Medical discipline of protective measures.

Aerospace Medicine

Aerospace medicine is the study of external environmental factors (low pressure, hypoxia, cosmic radiation, etc.) and flight factors (

For more than a century from 1770 to the 19th century, scientists from various countries conducted a large number of balloon-borne human and animal experiments. At that time, people did not realize that the high-altitude environment would cause harm to the human body and did not take corresponding protective measures. As a result, human frostbite, ear pain, and loss of consciousness occurred in the ascent.

The research scope of aerospace medicine is very wide. Low-pressure hypoxia is one of the important environmental factors in aerospace. There is a layer of atmosphere around the earth. The fixed components of the atmosphere are mainly nitrogen, oxygen, carbon dioxide, and so on. Atmospheric pressure on the ground plane The weight of the atmospheric column per square centimeter is 1.033 kg, which is equal to the same height of 760 mm of mercury at the same base area. This pressure value is set as the standard pressure. Atmospheric pressure decreases with altitude. When the external pressure decreases to 266.89mm Hg (8000 meters above the sky), people will suffer decompression injury.

When the external environmental pressure is reduced, the gas in the body tissues and body fluids (mainly nitrogen with high solubility in blood and tissue fluids) will be released in the blood vessels to form air bubbles. The air bubbles formed inside the blood vessels become air plugs to block the blood vessels, while compressing local tissues outside the blood vessels.

Air bubbles in the blood vessels circulate to the lungs to cause pulmonary vascular embolism, secondary to pulmonary circulation disorders; air bubbles in the outer thorax of the lungs can cause pneumothorax; air embolisms in the blood vessels of the heart can cause circulation disorders. Air bubbles compress local tissues in the joints of the extremities, especially the knee and shoulder joints, and cause severe pain. This phenomenon is called "flexing limb pain"; the rapid change in air pressure caused by the rapid rise and fall of an aircraft can cause moderate Ear pain is called aviation otitis media.

When a military aircraft is flying, the pressure changes rapidly and violently, and experienced pilots with normal eustachian tube functions can perform ventilation in a timely manner, and middle ear injuries generally do not occur. So when selecting a pilot, pay attention to ear function. Passenger aircraft are generally not subject to sudden pressure changes, so passengers rarely experience middle ear pressure injury.

Changes in air pressure in aviation can also cause occupants' toothache, which is called aviation toothache, and is more common in military pilots. It is characterized by diseased teeth as the center, and spreads around the ears or jaws. Civil aviation passenger aircraft s air pressure changes slowly, and passengers do not experience aviation toothache. Dental caries secondary tooth pulp damage is often the main cause of toothache. The pressure decreases, the residual gas in the pulp cavity expands, compresses blood vessels, and causes toothache. Dentin hypersensitivity, periodontitis, and periodontitis may also cause aviation toothache.

When the external pressure decreases, the absolute partial pressure of oxygen in the air also decreases correspondingly, causing a high altitude anoxia in the flight crew. At a height of 3,000 meters, people will have mild hypoxia, moderate hypoxia can occur at 4,600 meters, and severe hypoxia can occur at altitudes above 6,100 meters. The brain and sensory organs are very sensitive to hypoxia. Hypoxia directly affects the occupant's coordinated actions and intelligent functions (memory, understanding, judgment). Severe hypoxia can cause disturbance of consciousness and lead to serious flight accidents.

Modern airplanes do not fly above 7,000 meters kilometers, and generally still use open cockpits. The higher-performance aircraft uses a sealed pressurized cockpit, which can effectively protect the flight crew from harmful factors such as low-pressure anoxia, low temperature, and high-speed airflow at high altitude. The pressurized cockpit is mainly composed of a cockpit structure and an environmental control system that can withstand a certain pressure difference and has a good sealing performance. The pressurized cockpit can be divided into two types: ventilated and regenerative.

When the aircraft rises and falls, it will produce overweight, and the spacecraft will lose weight when flying in space, both of which will affect the physiological functions of the human body. Aerospace vehicles fly fast, have high maneuverability, and generate powerful overweights (also known as acceleration and overload).

When gravity acts on the human body from head to toe, it is said to be overweight; on the other hand, when gravity moves from foot to head, it is said to be overweight. When being overweight, the blood is transferred from the upper body to the lower body by the force of inertia, causing head and upper body ischemia, visual impairment, and syncope may occur in severe cases. Training and wearing anti-wear can improve overweight endurance.

When the spacecraft launches and returns, it also generates a long time of acceleration, deceleration and overweight, and the overweight value can reach about 8G. The high G value is overweight, and it is difficult for a person to adapt to a sitting position, so the astronauts usually adopt a supine position, which has a slight impact on the human body. People can tolerate lateral overweight of 8G value for more than ten minutes. This type of lateral overweight experienced in aerospace can be tolerated by most people.

Various accelerations in flight are a kind of stimulation to the vestibular organs of the human body, and generally do not cause adverse reactions within a suitable range. When the acceleration stimulation is frequent, severe and prolonged, exceeding the threshold of the vestibular organs, it can cause a motor disease response. Motion sickness includes seasickness, motion sickness, motion sickness, and aerospace sickness. The main symptoms are dizziness, nausea, vomiting, cold sweats, and pale complexion. The etiology is closely related to vestibular organs, and people with deaf and mute vestibular organs who have lost their vestibular function generally do not develop motion sickness. During military flight, the crew is often sickened. Civil aviation passenger planes fly smoothly and the cockpit is comfortable. Generally, no more than 6% of passengers suffer from airsickness.

Weightlessness is a special physical factor in space flight. The structural characteristics of the human body ensure that it resists and adapts to gravity. Manned spaceflight practice has proven that weightlessness has a great impact on the physiological function of the human body, but it is not as severe as originally thought. After living and working continuously for 365 days under the condition of weightlessness, after returning to the earth for a short rest, people can fully recover their health without irreversible physiological changes.

Changes in cardiovascular function. The body loses hydrostatic pressure during weightlessness, and blood and other body fluids don't flow down to the body as usual under gravity. In contrast, blood from the lower body returned to the chest and head, the astronaut's face was swollen, his head was swollen, and his neck varicose veins moved upwards. The sensory body of the human body feels that the body fluid increases, the body reduces the body fluid through the body fluid regulation system, and the body fluid transfers and reflects polyuria, which results in the excretion of water and salt from the urine and the decrease of blood volume; symptoms of reduced cardiovascular function, such as reduced cardiac output, standing Reduced stamina, etc., did not adapt to gravity for a short time after returning to the ground.

With the prolongation of spaceflight, cardiovascular function can reach a new balance at a new level, and heart rate, blood pressure, and exercise endurance return to the levels before flight. Weight loss causes a decrease in blood volume and a decrease in the amount of red blood cells and hemoglobin, which gradually returns to normal with the extension of space time.

During weightlessness, symptoms of motion sickness, such as dizziness, nausea, abdominal discomfort, and posture reversal, are known as aerospace disease, also known as aerospace adaptation syndrome. The incidence rate is about 1/3 to 1/2 of the total number of astronauts. Onset of weight loss in the early stage of aerospace can cause illness for one week, and after one week of weightlessness, the vestibular function can adapt to weightlessness. Some people think that the organs that feel gravity will transmit abnormal signals into the brain during weightlessness, forming signal conflicts such as vestibules, vision, and movement, causing disturbances in the interaction of various analyzers, leading to space sports disease. Space sports disease has not been completely prevented so far, and anti-movement medicines can be taken when it develops.

Bone salt metabolism disorders. Weightlessness will cause the body's bone mineral salts to be metabolized, the calcium and phosphorus excreted by the urine will increase, and the calcium output will be about six grams per month. Weight-bearing calcaneus, femur, and other bone salts are lost, while upper limb flexion and ulna are lighter. The reason for decalcification is that the stimulation of skeletal muscle is weakened or disappeared due to the proper load of vertical load, the blood supply is reduced, the bone cell nutrition changes, the osteoclast function is enhanced, the osteoblast function is weakened, and the decomposition process is greater than the synthesis process. The loss of bone salt causes osteoporosis and it lasts a long time.

Muscle changes caused by weightlessness are mainly manifested in weakening or even atrophy of muscle groups that resist gravity. The reason is that anti-gravity muscles do not need to work, and atrophic atrophy occurs. It is generally believed that a person living under weightlessness for six months will not experience irreversible changes in physiological functions.

Cosmic radiation mainly refers to the flow of high-energy charged particles from all aspects of the Milky Way, consisting of protons, photons, and electrons; followed by a large number of high-energy charged particles released when the sun flare occurs, most of which are protons, followed by "particles; third The species is the rays of the earth's radiation zone. The charged particles are captured by the geomagnetic field near the earth's space, forming a wide range of high-intensity radiation zones, called the earth's radiation zone. Radiation particles act on human cells to cause the ionization effect of atoms.

Cosmic radiation is shielded by the earth s atmosphere, and the dose reached the ground is very small. People have lived on the ground for thirty years. The average natural dose received is only 4.35 to 5.5 rem (dose equivalent unit), so aircraft flying at low altitudes will not be affected. Damage from cosmic radiation.

Manned spaceflight has always attached great importance to the harm of cosmic radiation to astronauts, and various space dosimeters are carried on the spacecraft and the crew to observe the possible harm of cosmic radiation to the human body. Observations show that most of the radiation doses received by US-Soviet astronauts in spaceflight have not reached levels that cause harm, but a small number of astronauts received relatively large doses of radiation.

The amount of dose received during space flight is related to the orbit of navigation, and the dose received when the orbit is high is higher than when the orbit is low. In manned spaceflight, special attention should also be paid to the harm of heavy particles to people. The metal bulkheads of manned spacecraft have anti-radiation effects, but there are certain limits. Radiation damage from solar flares during aerospace should be avoided as much as possible.

The food supply of aircraft occupants should be nutritious. Avoid gas-producing and cellulose-rich foods before flying, and prevent fasting or oversatisfying. Astronaut's food is not only nutritious and suitable for taste, it is important that it be eaten under aerospace conditions. During the space flight, everything in the cabin, including food, is in a state of weightlessness. It can float freely. Meat pastes and jam-like semi-solid foods in the aerospace food can be packed in toothpaste-like aluminum tubes. When you squeeze the aluminum tube, you can pass hard plastic. The tube enters the mouth. This type of food is convenient and safe, but it is not suitable for taste and is now used less often. Bread, snacks, meat pieces, chicken pieces, etc. can be made into bite-size pieces, and the surface is coated with an edible film to prevent food from being broken and chipped.

Canned food is the most popular food currently used in aerospace foods. The internal foods have a certain viscosity and will not float when they are eaten. They have the same characteristics as ground foods. The early aerospace foods were relatively simple. They were just some tube-shaped and compressed lumps of toothpaste. Now there are more than 70 varieties of aerospace foods. There is also an electric stove in the spacecraft to heat food.

For people who have been living in the circadian cycle on the earth's surface for a long time, the psychological and physiological functions gradually form the balance of the human body's internal environment, and some functions have synchronous changes similar to the circadian rhythm. After the day and night cycle of the external environment changes, people cannot adapt in the short term, and some physiological and functional disorders will occur.

Large jet airliners can fly across a time zone in one hour. Travel by jet airliner, flying east or west at high speed for 10 hours. After arriving at the destination, the two places are compared, that is, 10 hours in advance or postponed. Passengers can't adapt to the new time right away, and they may have difficulty adapting temporarily, causing symptoms such as sleep disturbance and fatigue. At the same time, their work efficiency is reduced, and sports performance is not satisfactory. Therefore, passengers with important tasks (such as participating in international conferences and major international sports competitions) should strive to achieve adaptation before and after flight.

Pre-flight adaptation means that if you fly east, you will go to bed early and get up early every day a few days before the flight in order to adapt to the environment's circadian rhythm as early as possible. After-flight adaptation refers to arriving at your destination ahead of time and taking a break of 1-2 days to adapt to the new environment.

A manned spacecraft orbits the earth once a week. Astronauts can see a sunset, a sunrise, and a day and night cycle of more than a dozen sunsets and sunrises within 24 hours a day. The day and night cycle in space is variable. The length of time depends on the orbit of the manned spacecraft flying around the earth. The height of the orbit is long and the day and night cycle is long. The low orbit is short of the day and night cycle.

The orbit of a manned spacecraft is generally low-Earth orbit. It orbits around the ground for about 90 minutes, and there are 16 diurnal changes in 24 hours. Astronauts have long been accustomed to the diurnal cycle on the earth. They are not accustomed to such short-term diurnal changes. They may experience poor sleep, easy to wake up, fatigue, and reduced work efficiency. Aerospace medical workers arrange the astronaut's work and rest system on a 24-hour day-night cycle, which is basically synchronized with the Earth's day-night cycle.