Respiratory Mechanics I Flashcards
In what generations of alveolar branches does gas exchange take place?
The last four generations (20-23)
Length and diameter gets smaller as the airways branch
What is the residual volume?
Volume left in the lung at zero pressure
Can’t get all of the air out of the lung
What are the conventions of hydrostatic pressures on the lungs?
They’re very small, so expressed in cm H2O
Expressed relative to barometric pressure, which is always zero
Describe the elastic recoil forces acting on the lung and the functional residual capacity.
Chest wall exerts in the direction of expanding
Lungs exerts in the direction of collapsing
When the two forces are equal and opposite, this is referred to as the functional residual capacity
What two factors make up the lung elastic recoil forces?
Lung tissue elastic recoil - polymer molecules that make up the physical lung, exert a restorative force in response to inflation
Surface tension forces - Water on the surface of the alveoli exert forces to reduce the size of the surface, or collapse the lung
Surface tension is the main contributor to lung recoil*
What is laplace’s law?
P = 2T/r
Pressure is inversely proportional to the radius
How do surface tension forces work in an alveolus?
Water on the surface of the alveolus completely surrounds it. This means that water particles on the air-water surface are being pulled by attractive forces exerted by its neighboring molecules. This results in a net inward force (because of the spherical shape) to tend to collapse the alveolus
What is surfactant and what is its role in the lungs?
Complex mixture of phospholipids and protein secreted by type II alveolar cells
Lowers surface tension by inserting itself between water molecules at the gas-liquid interface
What is the primary muscle of inspiration?
Diaphragm
Intercostal muscles are a much smaller part
Accessory muscles of the shoulder girdle are not involved in quiet breathing, but can be recruited during exerceis, coughing and sneezing, as well as conditions like COPD and emphysema
Describe normal exhalation
Passive process in which the diaphragm relaxes, reducing the volume of the thoracic cage and driving air out of the lungs (due to elastic recoil)
What is forced exhalation?
Active process used during exercise or hyperventilation
Uses abdominal muscles and internal intercostals
What is Boyle’s law?
Pressure of a gas is inversely proportional to volume at constant temperature
What is a Pneumothorax?
Air enters the pleural cavity, leading to partial or total collapse of the lung
Different from atelectasis, where there is no air in the pleural cavity
