test 5 Flashcards
(44 cards)
Pleural pressure during inspiration
Expansion of chest cavity results in further decrease in pressure (-7.5 cmH2O)
Decrease in pressure associated with increased lung volume (500 mls)
Pleural pressure during expiration
Recoil of chest cavity returns pressure back to resting level
Increase in pressure associated with decreased lung volume (500 mls)
Alveolar Pressure
Pressure of the air inside the alveoli
At the start of inspiration, all parts of the respiratory tree are equal to what
- equals atmospheric pressure
atmospheric pressure = 0 cmH2O
IN order to move air into alveoli, pressure must what
pressure in alveoli MUST be lower than atmospheric pressure, i.e. alveolar pressure MUST be negative
what increases the pressure in the alveoli
-gas coming in
Alveolar Pressure during inspiration
Expansion of chest cavity results in decrease in plural pressure which causes alveolar pressure to drop
Alveolar pressure drops to -1cmH2O which draws 500 mls of air into the alveoli
Takes 2 seconds to inspire the 500 mls of air
Alveolar Pressure during expiration
Recoil of chest cavity returns pleural pressure back to resting level and alveolar pressure increases to +1 cmH2O pushing 500 mls of air out of the alveoli
Takes 2 to 3 seconds to expire the 500 mls of air
-it’s a passsive
What determines how quickly the pleural pressure changes?
- how much change in volume in thoracic cage
2. Compliance of the Lungs: the more compliant = the easier to move the lungs
What determines how quickly the alveolar pressure changes?
- Gradient
- resistance
- compliance of the lungs
what is Transpulmonary Pressure
Difference between alveolar pressure and pleural pressure
-Pressure difference between inside of alveoli and outer surface of lungs
Measure of elastic forces in lungs that tend to collapse lungs (recoil pressure)
Increase in transpulmonary pressure indicates
The forces trying to
collapse the lungs have increased
When are the forces that are trying to collapse the lung the largest? (largest traspulmonary pressure)
- during inspiration
- this is why we can exhale without using a lot of force
Lung Compliance
Compliance – how much the lungs will expand for each unit increase in transpulmonary pressure
-Allows time for equilibrium of gas flow
Normal – 200 mls of air for each 1 cmH2O increase in transpulmonary pressure
At any given pleural pressure a person can move more gas during
- expiration
- because natural lung tendencies is to collapse
- inspiration you are working against the elastic forces
slope of the compliance curve for inspiration vs expiration
Shape of curve determined by elastic forces of the lungs
-compliance during both inspiration and expiration starts low and becomes higher (easier to move the air)
A change in pleural pressure (changes transpulmonary pressure) which changes the volume of air that moves into or out of the alveoli
-if compliance goes down you have to do more work to inflate the lungs (pulmonary problems)
Elastic forces of lung tissue
Stretch of elastin & collagen fibers – stretch as lungs fill
Approximately 1/3 of total elastic forces
-the more you stretch it, the more difficult it becomes to stretch
Elastic forces caused by surface tension of fluid lining inside wall of alveoli (air-fluid interface)
Approximately 2/3 of total elastic forces
Becomes a problem if surfactant is not present in alveolar fluid
-it would be a lot easier to breath if we didn’t have that layer of water on the inside of the alveoli
Air – water interface
Water molecules at the surface form very strong attraction – actually cause the water surface to contract
Alveoli – filled with air but inner surface covered with thin layer of water
Layer of water in contact with air trying to contract which tends to cause the alveoli to contract and try to collapse
This tends to aide expiration but works against inspiration
Surfactant
Reduces surface tension of water
Secreted by special epithelial cells called “type II alveolar epithelial cells” (10% of alveolar surface area)
Contains several phospholipids
-Do not dissolve uniformly in water
-Spread over water surface reducing surface tension 8% to 50%
natural force at work trying to collapse each and every alveoli
- 4 cm H2O
collapsing pressure equation
Collapsing Pressure = (2 x Surface tension) / (Radius of alveolus)
an increase in collapsing pressure
- more difficult to move gas into the lung
