There is no doubt that the human body is genetically adapted to be as close to sea level as possible. Even life in the highlands is uncomfortable for those who were not born there. What is it about? Well, for the purposes of two factors: atmospheric pressure and oxygen partial pressure.

A column of air above our heads

Pressure is a physical quantity that is defined as the derivative of a force with respect to an area, or as a force acting perpendicular to a unit area. At sea level, our heads can support the weight of a column of air more than thirty kilometers high, which is equivalent to a pressure of 1 atmosphere (1.01325 bar or 101,325 pascals).

And why do we not notice this heaviness from above? Well, simply because our body internally also registers the atmosphere of pressure. As Sir Isaac Newton postulated, “two forces of the same magnitude acting in opposite directions balance each other.” However, as we climb higher, the pressure we maintain becomes less and does not match the internal pressure. And from here there are certain physiological changes. We can get an idea of ​​what it means to rise from the ground an average of ten kilometers for a long time.

suffocated neurons

But this is not the only phenomenon that affects us. There is another very important variable to consider: the pressure of oxygen, the gas our cells need to live. Measured in millimeters of mercury (mm Hg), it should be between 75 and 100 mm Hg. Art. (or 10.5 to 13.5 kilopascals). When its concentration in the blood decreases, so-called hypoxemia occurs.

If this indicator falls below 60 mm Hg. Art., hypoxia occurs, which disrupts the normal functioning of cells. Considering that neurons are the cells that endure hypoxic conditions the worst, it is understandable that when we are faced with situations of low oxygen concentration, neurological symptoms appear. If severe hypoxia lasts more than four minutes, neurons begin to die.

This explains why, before flying, we are advised to quickly put on a mask in an emergency in order to breathe in oxygen if there is a depressurization in the cabin and thereby prevent us from quickly losing consciousness. And for this reason, fighter pilots who have to endure sudden changes in altitude always wear an oxygen mask.

Ringing in the ears, headaches and dizziness

If we spend a long time at high altitude, as is usually the case on long flights, there may be discomfort associated with changes in atmospheric pressure and oxygen pressure.

Among the most common manifestations, ringing in the ears with hearing impairment, the so-called tinnitus, stands out. The eardrum, the flexible membrane that protects the outside of the ear, is very sensitive to changes in pressure. Although the aircraft compensates for this by building up internal pressure (cabin pressurization), they sometimes occur very quickly. If this change is prolonged, dizziness and nausea may occur, since the ear is also a balance organ.

Oxygenation of the passenger compartment and cockpit is extremely important because the higher the altitude, the lower the oxygen pressure. If this is not done correctly, there is a risk that we will be tormented by headaches (headaches), which can develop into dizziness if the situation is not reversed.

vulnerable passengers

Taking into account all of the above, it can be understood that some people do not want to make long flights. So, in patients with respiratory pathologies, such as chronic obstructive pulmonary disease (COPD) and asthma, breathing difficulties may occur due to a decrease in the partial pressure of oxygen in the cabin.

It can also be dangerous to board an aircraft for people suffering from serious cardiovascular diseases such as recent myocardial and cerebral infarction, arrhythmias and severe hypertension. In these cases, the problem is the possibility of hypoxia of the heart muscle, since it will be compensated by an increase in its heart rate and respiratory rate.

For pregnant women, long-haul flights carry more risk as the pregnancy progresses. 36 weeks is generally considered the limit for any type of flight, or 32 in the case of multiple pregnancies. Exposure to pressure can provoke childbirth or exacerbate pathologies in a pregnant woman. This would be completely undesirable for women with a history of abortion, severe anemia, hypertension, or poorly controlled diabetes.

In any case, air travel is a safe, efficient, fast and 100% recommended way to travel. Aviation technology, with its pressurization systems, allows passengers to barely notice the described discomfort. Knowing the symptoms allows us, if they appear, to know what to do.

José Miguel Robles Romero, PhD, Professor in the Department of Nursing, University of Huelva

This article was originally published on The Conversation. Read the original.

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