Lesson 1, Topic 1
In Progress

Gas Exchange


It is a colorless, odorless, and tasteless gas. The air we breathe contains approximately 21% oxygen. We need oxygen to parameterise food and to manufacture energy for cellular function. The body consumes oxygen, produces heat and other forms of energy. The air we exhale contains about 16% oxygen.

Blood carries oxygen in two different ways: dissolved in plasma and chemically bound to hemoglobin . Due to its great ability to attach to hemoglobin under normal pressure and temperature conditions, there is a small amount of dissolved oxygen in plasma (2 to 3%). Much of the oxygen is therefore combined with hemoglobin.

According to the law of the diffusion of gases , these move by simple diffusion from the areas of higher partial pressure to the areas of lower partial pressure. Thus, haemoglobin gives oxygen to tissues because the partial pressure of oxygen in tissues is lower than the partial pressure of oxygen in the blood.


The air we breathe contains on average about 0.033% carbon dioxide. Carbon dioxide is a residual product of our metabolism and is transported in the blood, a small part dissolved in plasma, another attached to hemoglobin or proteins. The air we exhale contains about 4% carbon dioxide.

The process of spreading this gas is the same, but now in the opposite direction. Hemoglobin gives carbon dioxide into the pulmonary alveolos, because the partial pressure of carbon dioxide inside the alveole is lower than the partial pressure of carbon dioxide in the blood.

The production of carbon dioxide is continuous and the greater the more effort is exerted during diving. Its release during expiration should be the subject of the greatest attention.

The efforts made by the diver (fast swimming, swimming against the current), together with the resistance offered by the regulator (especially if it is poorly tuned), plus the decrease in air fluidity with increased depth and the anxiety of the diver initiated when entering an element that is not usual, translate into a higher production of carbon dioxide. If it is not properly eliminated in the expiratory cycle, this gas can lead to serious situations of which we will talk ahead.

In this situation, the respiratory act becomes a reflected act, unlike what happens on the surface, in which the expiratory phase is passive. The diver must exhale deeply to eliminate as much CO2 as possible produced. In addition, you should avoid all useless efforts and keep your equipment in optimal operating conditions.


It is one of the inert gases present in atmospheric air that do not participate in any metabolic function, and represents approximately 78% of the air we breathe. Since our body does not use nitrogen, the amount that enters the body through the wall of the pulmonary alveolo is the same amount that comes out and the air that expires also contains 78% nitrogen.

This gas if not disposed properly, can cause serious problems, of which we will talk in Module 13 – Tables and Computers.