Respiration is the process of oxygenation and carbon dioxide expulsion, the movement of air through the lungs as pressure changes. This process is essential for sustaining life, and proper breathing promotes physiological and psychological health.
In order for humans to live and function, it is essential to supply oxygen to cells and expel carbon dioxide from the body as a result of metabolism, a process known as respiration. The movement of air from the outside of the body to the lungs is called inhalation, and the movement of air from the lungs to the outside of the body is called exhalation. However, this flow of air is closely related to the pressure difference between the lungs and the atmosphere.
To understand this, we first need to look at the components of the respiratory system that are involved in the movement of air. Air enters through the nose and mouth, passes through the trachea and bronchi, and finally enters the alveoli. After traveling through the trachea and bronchi, the air is warmed to body temperature, moistened by the addition of water vapor, and filtered of foreign particles. This keeps the air from damaging the alveoli. Alveoli are air sacs attached to the end of the bronchi in the lungs like grape clusters, where gas exchange takes place. Through the thin walls of the alveoli, oxygen enters the blood, and carbon dioxide moves from the blood to the alveoli and out of the body.
The lungs, which consist of bronchi and alveoli, are located within the rib cage, surrounded by a pleural cavity. The rib cage is made up of bones, including the ribs, and muscles, including the intercostal muscles, which protect the lungs and are completely separated from the abdomen by the diaphragm. The pleural cavity is a completely closed pocket formed by two pleura, which are thin layers of cells, and the space between them is filled with pleural fluid. Since the inner pleura is attached to the lungs and the outer pleura is attached to the rib cage wall, the pleural fluid is what eventually keeps the lungs and rib cage wall together. By analogy, two thin sheets of glass held together by water cannot be easily separated due to the cohesion of water.
So, how does the flow of air occur during the breathing process? It is related to Boyle’s law, which states that an increase in the volume of a container decreases the pressure of a gas, while a decrease in the volume of a container increases the pressure of a gas. The pressure of gas in the alveoli is called alveolar pressure, and the pressure of air outside the body is called atmospheric pressure. In general, air flows from higher to lower pressure, so air enters or leaves the lungs when alveolar pressure is less or more than atmospheric pressure. In other words, the volume of the lungs changes during inspiration and expiration, and this change changes the alveolar pressure according to Boyle’s law, which causes air to flow in and out of the lungs.
Meanwhile, the volume change of the lungs is caused by elastic recoil, transpulmonary pressure, and intrapleural pressure. First, the elastic recoil and transpulmonary pressure of the lungs act in opposite directions. Elastic recoil is a force that tries to return to its original shape in response to a deforming force, and the lungs have an elastic recoil that tries to deflate like a balloon. At the end of inspiration and the beginning of exhalation, the alveolar pressure is equal to atmospheric pressure, so there is no air movement. However, the lungs are always filled with air, so there is also a transpulmonary pressure that tries to expand the lungs. At this point, the elastic recoil of the lungs and the transpulmonary pressure are equal in magnitude but opposite in direction, so the lungs maintain a constant volume in the absence of air flow. The transpulmonary pressure is the alveolar pressure minus the intrapleural pressure, so if the intrapleural pressure changes, the transpulmonary pressure will also change, causing a difference between the elastic recoil of the lungs and the transpulmonary pressure, which changes the volume of the lungs.
Intrapleural pressure is the pressure of the pleural fluid in the pleural cavity and always varies in the range of subatmospheric pressure. The rib cage wall, which is in close contact with the outer pleura, has a tendency to move away from the body in the opposite direction of the force exerted by atmospheric pressure, which is called the elastic recoil of the rib cage wall. The elastic recoil of the rib cage is therefore opposite to the elastic recoil of the lungs, which are pressed against the inner pleura. As a result, the lungs and the rib cage wall are slightly separated from each other, and the intrapleural pressure remains subatmospheric. If the volume of the pleural cavity changes due to muscle movement, the intrapleural pressure changes.
Based on the above, the process of inspiration and exhalation is as follows. Inspiration begins with the diaphragm contracting and moving downward, and the rib cage expanding as the intercostal muscles move the ribs upward and outward. This causes the rib cage wall to move a little further away from the surface of the lungs, increasing the volume of the pleural cavity and causing the intrapleural pressure to be a little lower than it would be without air flow. This increases transpulmonary pressure, and this force is greater than the elastic recoil of the lungs, causing them to expand further. As a result, alveolar pressure decreases relative to atmospheric pressure, so the difference in pressure forces air into the alveoli, and the total amount of air entering the lungs continues to increase as the lung volume increases. However, because the alveoli can only stretch so far and are connected to the outside world, the decreasing alveolar pressure reaches a low point about halfway through inspiration and then begins to increase again. After that, the alveolar pressure equals atmospheric pressure, so there is no airflow at the end of inspiration and the lung volume is maximized. Exhalation follows the same sequence as inspiration, except that the diaphragm changes and the ribs move in the opposite direction, beginning with the rib cage contracting. The volume of the lungs then changes due to changes in intrapleural pressure and transpulmonary pressure, which causes air to escape from the alveoli through the airways and into the atmosphere.
This process is essential to keep us alive. Breathing allows oxygen to enter the body and carbon dioxide to leave, allowing us to generate energy and perform various physiological functions. Furthermore, breathing is also closely related to psychological stability. Deep, regular breathing helps to reduce stress and calm the mind. This is why breathing is an important component of activities such as meditation and yoga.
The importance of breathing is even more pronounced when you exercise. During exercise, your breathing becomes more active because you need more oxygen than usual and you have to expel more carbon dioxide. If you learn to breathe properly, you”ll be able to perform better and feel less fatigued. Conversely, poor breathing can lead to a lack of oxygen in the body and a buildup of carbon dioxide, which can adversely affect your health.
Therefore, we should always be aware of the importance of breathing and strive to learn how to breathe correctly. This will improve both our physiological and psychological health. Breathing is an automatic process that we do without even realizing it, but it is a vital life force. We should never forget the importance of breathing and continue to pay attention to it so that it can make a positive difference in our lives.
