Both tidal volume and respiratory rate are closely regulated when oxygen demand increases. There are two types of work conducted during respiration: flow-resistive and elastic work. Flow-resistive work refers to the work of the alveoli and tissues in the lung, whereas elastic work refers to the work of the intercostal muscles, chest wall, and diaphragm.
When the respiratory rate is increased, the flow-resistive work of the airways is increased and the elastic work of the muscles is decreased. When the respiratory rate is decreased, the flow-resistive work is decreased and the elastic work is increased.
Surfactant is a complex mixture of phospholipids and lipoproteins that works to reduce the surface tension that exists between the alveoli tissue and the air found within the alveoli. By lowering the surface tension of the alveolar fluid, it reduces the tendency of alveoli to collapse. Surfactant works like a detergent to reduce the surface tension, allowing for easier inflation of the airways.
When a balloon is first inflated, it takes a large amount of effort to stretch the plastic and start to inflate the balloon.
If a little bit of detergent were applied to the interior of the balloon, then the amount of effort or work needed to begin to inflate the balloon would decrease; it would become much easier. This same principle applies to the airways. A small amount of surfactant on the airway tissues reduces the effort or work needed to inflate those airways and is also important for preventing collapse of small alveoli relative to large alveoli. Sometimes, in babies that are born prematurely, there is lack of surfactant production; as a result, they suffer from respiratory distress syndrome and require more effort to inflate the lungs.
In pulmonary diseases, the rate of gas exchange into and out of the lungs is reduced. Two main causes of decreased gas exchange are compliance how elastic the lung is and resistance how much obstruction exists in the airways. A change in either can dramatically alter breathing and the ability to take in oxygen and release carbon dioxide.
Examples of restrictive diseases are respiratory distress syndrome and pulmonary fibrosis. In both diseases, the airways are less compliant and stiff or fibrotic, resulting in a decrease in compliance because the lung tissue cannot bend and move.
In these types of restrictive diseases, the intrapleural pressure is more positive and the airways collapse upon exhalation, which traps air in the lungs. Forced or functional vital capacity FVC , which is the amount of air that can be forcibly exhaled after taking the deepest breath possible, is much lower than in normal patients; the time it takes to exhale most of the air is greatly prolonged.
A patient suffering from these diseases cannot exhale the normal amount of air. Obstructive diseases and conditions include emphysema, asthma, and pulmonary edema. In emphysema, which mostly arises from smoking tobacco, the walls of the alveoli are destroyed, decreasing the surface area for gas exchange.
The overall compliance of the lungs is increased, because as the alveolar walls are damaged, lung elastic recoil decreases due to a loss of elastic fibers; more air is trapped in the lungs at the end of exhalation.
Asthma is a disease in which inflammation is triggered by environmental factors, obstructing the airways. The obstruction may be due to edema, smooth muscle spasms in the walls of the bronchioles, increased mucus secretion, damage to the epithelia of the airways, or a combination of these events.
Those with asthma or edema experience increased occlusion from increased inflammation of the airways. This tends to block the airways, preventing the proper movement of gases. Those with obstructive diseases have large volumes of air trapped after exhalation. They breathe at a very high lung volume to compensate for the lack of airway recruitment.
The pulmonary circulation pressure is very low compared to that of the systemic circulation; it is also independent of cardiac output. Recruitment is the process of opening airways that normally remain closed when cardiac output increases. As cardiac output increases, the number of capillaries and arteries that are perfused filled with blood increases. These capillaries and arteries are not always in use, but are ready if needed. However, at times, there is a mismatch between the amount of air ventilation, V and the amount of blood perfusion, Q in the lungs.
Dead space is characterized by regions of broken down or blocked lung tissue. Dead spaces can severely impact breathing due to the reduction in surface area available for gas diffusion. As a result, the amount of oxygen in the blood decreases, whereas the carbon dioxide level increases.
Anatomical dead space, or anatomical shunt, arises from an anatomical failure, while physiological dead space, or physiological shunt, arises from a functional impairment of the lung or arteries. An example of an anatomical shunt is the effect of gravity on the lungs. The lung is particularly susceptible to changes in the magnitude and direction of gravitational forces. When someone is standing or sitting upright, the pleural pressure gradient leads to increased ventilation further down in the lung.
As a result, the intrapleural pressure is more negative at the base of the lung than at the top; more air fills the bottom of the lung than the top. Likewise, it takes less energy to pump blood to the bottom of the lung than to the top when in a prone position lying down.
Perfusion of the lung is not uniform while standing or sitting. This is a result of hydrostatic forces combined with the effect of airway pressure. An anatomical shunt develops because the ventilation of the airways does not match the perfusion of the arteries surrounding those airways.
As a result, the rate of gas exchange is reduced. Note that this does not occur when lying down because in this position, gravity does not preferentially pull the bottom of the lung down.
When a healthy individual stands up quickly after lying down for a while, both ventilation and perfusion increase. A physiological shunt can develop if there is infection or edema in the lung that obstructs an area.
The lung has the capability to compensate for mismatches in ventilation and perfusion. Davis AT Collection. Davis PT Collection. Murtagh Collection. About Search. Enable Autosuggest. You have successfully created a MyAccess Profile for alertsuccessName. Home Books Pulmonary Physiology, 8e. Previous Chapter.
Next Chapter. AMA Citation Chapter 6. In: Levitzky MG. Levitzky M. Michael G. Pulmonary Physiology, 8e. McGraw Hill; Accessed November 11, APA Citation Chapter 6.
Levitzky MG. McGraw Hill. MLA Citation "Chapter 6. Download citation file: RIS Zotero. Reference Manager. It is the process of air flowing into the lungs during inspiration inhalation and out of the lungs during expiration exhalation.
Air flows because of pressure differences between the atmosphere and the gases inside the lungs. Air, like other gases, flows from a region with higher pressure to a region with lower pressure.
Muscular breathing movements and recoil of elastic tissues create the changes in pressure that result in ventilation. Pulmonary ventilation involves three different pressures:. Atmospheric pressure is the pressure of the air outside the body.
0コメント