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Breathing

• Breathing consists of four stages: alveolar ventilation, diffusion of oxygen and carbon dioxide between alveoli and blood, oxygen and carbon dioxide transport in blood and body fluids, and regulation of ventilation.

Mechanism of Pulmonary Ventilation

• The lungs expand and contract in two ways: by the upward and downward movement of the diaphragm, and by raising and lowering the ribs. Ordinary breathing is mostly done by contraction, and relaxation, of the diaphragm. During heavy breathing other muscles can be used.

The pressure of the covering of the lung and its changes during breathing

• Covering of the lungs is the pressure of the fluid in the small space between the two layers of lung cover, which are; visceral pleura and the parietal pleura or chest wall.
• The pressure is usually negative, and in a normal person at the start of inhalation is -5cmH2O. The lung pressure supplies the suction required to keep the lungs open, even during rest. During normal inhalation, pressure decreases and goes down to about -7.5cmH2O.

Pressure Between Two areas of the Lung Cover

• The difference in pressure between the lung area's pressure and alveolar pressure is known as transpulmonary pressure.

Compliance of the Lungs

• The extent to which the lungs will expand for each unit increase in two pressures between two areas of the pleural space is called pulmonary compliance, also known as lung compliance.
• The characteristic of lung compliance determines the strength of elastic forces in the lungs. These forces are of two, which are: the elastic forces of lung tissue; and the elastic forces created due to the surface tension of the fluid coating the inside walls of the alveoli, and other air spaces of the lungs.
• The amount of pressure required to expand air-filled lungs is about three times the pressure to expand saline-filled lungs. Therefore, tissue elastic forces, which tend to collapse air-filled lungs, constitute only one third of the total elastic power of the lungs, while elastic forces resulting from surface tension make up two thirds.

Surfactant

• Water molecules on the surface of water have a strong attraction when the water forms a surface facing air, with the water always trying to come together. This action tend to collapse the alveoli, inside walls of which are covered with water.
• Secreted by alveolar epithelial cells of type II, surfactant reduces the surface tension.
• Surfactant consist of multiple phospholipids, proteins, and ions. Its main component is the phospholipid dipalmitoylphosphatidylcholine, surfactant apoproteins, and calcium ions.
• Surface tension in the fluid coating the alveoli decreases two to seven fold when surfactant is mixed in the fluid.

Collapse Pressure Caused by Surface Tension

• The collapse of the lungs created by surface tension happens when airways that originate from, or feed into, the alveoli are obstructed, therefore surface tension tends to cause the alveoli to collapse
• The collapse pressure of alveoli is calculated by the formula: Pressure = 2 X Surface Tension / Radius
• The amount of pressure is higher in the alveoli having a smaller size, given newborns do not yet have enough surfactant when they are born. The lack of surfactant causes Neonatal respiratory distress syndrome (hyaline membrane disease), which is lethal if non treated.

Work of Breathing

• Lung expansion, and not contraction of the lungs, is an active process and, therefore, related to the work of breathing.
• Lung expansion has 3 steps; work is required to distend the lungs against elastic forces of the lungs and chest, called capacity work, or resilience work; required to overcome viscosity of the lung and chest wall called fabric resistance work; and to overcome airway resistance during movement of air through the lungs, also known as airways resistance work

Lung Volumes and Capacities

• Spirogram showing volume changes inside the lungs for each phase of breathing. For purposes of this section, air in lung are divided into four capacities and four volumes
• Tidal volume, is volume of air inhaled and exhaled for each normal breath for both the lungs, about 500 milliliters for a male adult
• Inspiratory reserve volume, amount of extra air inhaled beyond tidal volume, in full force, into the lungs (about 3000 milliliters)
• Expiratory Reserve Volume, or VRV, represents the additional volume of air that can be exhaled with maximum effort after a normal exhalation. It typically averages around 1,100 milliliters.
• Residual Volume, is air that remains in the lungs despite forceful exhale (about 1200 milliliters)

Lung Capabilities

• Two or more lung volumes can be considered at same time, they are: inspiratory capacity, capacity of Functional residual, and vital
• Inspiratory Capacity, volume of air that can be inhaled following normal exhalation. It amounts to around 3500 milliliters
• Functional Capacity, is also known as the Functional Residual Capacity. This capacity corresponds to the amount of air that remains in the lungs following a normal exhalation, and it averages approximately 2,300 milliliters in volume.
• Vital Capacity, made up of three, the inspiratory reserve, tidal, and expiratory

Total lung Capacity

• Which is the amount of air until the lungs can expand, which is about 5800 milliliters. Made up VCs
• Residual Volume (RV) and Functional Reserve Capacity (FRC) cant be measured directly (dont empty enough) via indirect method named helium dilution

Anatomic Dead Space & Physiological Dead Space

• Dead space excludes alveoli and adjacent related air to areas anatomic.
• Sometimes alvoli are dead or blood too weak, they also consider part of volume called physicologic The body measures to measure that dead space which results.

Tidal Volume

• Is defined as: Minute Respiratory Volume, is measure of total fresh air that travels via airways (VT X RR), around 6 L/min

• Minute Respiratory Volume Alveoli =Fresh Air(Gas Volume) Alveoli RR = 4.2L L/min

Function Airways

• Function consists of taking into account air pressure inside so it can expel it outside.