Air Is A Type of Fluid

When most people hear the word “fluid,” they usually think of liquid. However, gasses, like air, are also fluids. Fluids take on the shape of their containers. Fluids generally do not resist deformation when even the smallest stress is applied, or they resist it only slightly. We call this slight resistance viscosity. Fluids also have the ability to flow. Just as a liquid flows and fills a container, air will expand to fill the available volume of its container. Both liquids and gasses display these unique fluid properties, even though they differ greatly in density.

Air is very light, but it has mass and is affected by the attraction of gravity. Therefore, like any other substance, it has weight, and because of its weight, it has force. Since air is a fluid substance, this force is exerted equally in all directions. Its effect on bodies within the air is called pressure. Under standard conditions at sea level, the average pressure exerted by the weight of the atmosphere is approximately 14.70 pounds per square inch (psi) of surface, or 1,013.2 millibars (mb). The thickness of the atmosphere is limited; therefore, the higher the altitude, the less air there is above. For this reason, the weight of the atmosphere at 18,000 feet is one-half what it is at sea level.

Air Is Comprised of Many Gasses

Air is all around us, but we can’t see it. So what is air, exactly? It’s a mixture of different gases. The air in Earth’s atmosphere is made up of approximately 78 percent nitrogen and 21 percent oxygen. Air also has small amounts of other gases, too, such as carbon dioxide, neon, and hydrogen.

People need to breathe, and so do lots of other animals—and plants! Breathing is part of a process called respiration. During respiration, a living thing takes in oxygen from the air and gives out carbon dioxide. This process gives animals and plants the energy to eat, grow, and live life!

When it’s a hot, muggy summer day, you’ve probably heard the word “humid.” But what does that mean, exactly? Relative humidity is the amount of water that the air can hold before it rains. Humidity is usually measured in percentages, so the highest level of relative humidity—right before it rains—is 100%. Humidity in the air is measured with an instrument called a psychrometer.

Air seems light, but there is a lot of it pushing down on Earth’s surface. This is called air pressure. You experience high air pressure at sea level because the whole atmosphere is pushing down on you. When you’re on top of a mountain, there is less air pushing on you and the pressure is low. That change in pressure can cause your ears to pop when you’re taking off in an airplane or driving up a hill.

Expired Air Isn’t Just Carbon Dioxide

The inhaled air is about 21% oxygen, the typical atmospheric concentration. When you inhale and the air reaches your lungs, some oxygen will be removed into the bloodstream and a large quantity of carbon dioxide will be added into the gas mix in your airways.

The typical composition of exhaled air is about 16% oxygen, a loss of about 5% volume, which is then occupied by carbon dioxide, thus making the composition 79% nitrogen, 16% oxygen, 5% carbon dioxide and trace gases, in comparison to inhaled air which is roughly 79% nitrogen and 21% oxygen with carbon dioxide only in trace amounts together with other trace components.

How Supplemental Oxygen Therapy Helps The Patient

Given that the atmosphere has about 21% oxygen and 78% nitrogen and humans actually don’t use all the oxygen in the environment (considering that expired air has 16% oxygen), increasing the amount of oxygen concentration of a single breath will increase the amount of oxygen inspired. The oxygen replaces the nitrogen in the air. Whatever is causing the patient to have problems breathing, simply adding more oxygen will decrease the patient’s work of breathing. Further, increasing oxygenation will decrease the patient’s transition from respiratory distress to respiratory compromise. Shock (hypoperfusion) by it’s very nature affects cellular respiration. Administering oxygen to patient in shock (hypotension) will increase cellular respiration and decrease the side effects of shock.