Lung Mechanics Flashcards
What is tidal volume
Volume of air moving in and out -
What is ventilation no
The process of inspiration and expiration - the physical action of breathing ad moving air into and out the lung.
Is breathing voluntary?
Rhythmic and involuntary, neurones in resp centre of brain auto generate impulses to inspiration muscles, can be voluntary too
Describe lung mechanics in quiet inspiration
Air is drawn into the airways by active expansion of the thoracic cavity, which in turn expands the lungs. Dropping the intrapullmonary pressure below atmospheric pressure which pulls air into the lungs
Bowles law = inverse relationship between pressure and volume of a gay
Describe lung mechanics in quiet expiration
Air is expelled passively, by replacing the muscles used in insporation -> reduces volume of thoracic cavity -> reduces vol of lungs.expending no energy.elastic recoil. Increases pressure above atmospheric pressure. Air leaves.
What keeps the lungs against the chest wall?
- Lungs have natural elastic recoil - tendency to “want to collapse in”, esp with increased stretch
- Yet lugs are kept against chest wall without physical attachment during inspiration and expiration
- Pleural fluid found between visceral and parietal pleura (in intrapleural ‘space’) forms seal between lung and thoracic wall - makes sure visceral pleura and parietal pleura stuck together - surface tension created by thin film of fluid
so lungs expand with thoracic cavity
What is the resting exploratory level?
State of equilibrium.
- lungs pill in and up
- chest wall pulls out (elastic recoil)
- diaphragm pulls down (passive stretch not active contraction)
- Forces are equal and opposite so balance out (=no movement chest wall)
- tendency to always want to return to this state
How does ventilation disturb the equilibrium
Inspiration - muscles contract to allow east wall and diaphragm to overcome inward pull of lung recoil hence chest starts to expand
- expiration - muscles stop contacting, chest wall & diaphragm no longer overcome inward pull of lung recoil - return to resting expiratory level
How does the inward pull f the ling result in a negative pressure (relative to atm) between pleura
Pressure in intrapleural space is always negative relative to atm pressure due to elastic recoil of lung pulling visceral pleura nears and chest wall pulling parietal pleura outwards
- intrapleural pressure is negative throughout expiration and insporation (becomes more negative up until end of inspiration due to greatest forces trying to separate the 2 layers)
What happens if integrity of pleural seal is broken
Negative pressure in intrapleural space draws air from outside chest wall into space, collapsing lung = pneumothorax. Eg due to stab wound
What is expiratory reserve volume
Air that can be forced out over and above the tidal volume
What are the accessory muscles of inspiration,]
Involved in forced inspiration: SCM, scalene, Serratus anterior, pec major
Accessory muscles of expiration: internal intercostal, abdominal wall msucles
When are inspiration and expiration forced
During exercise but also diseases which affect the lungs and do not allow ai in and out as easily
What is lung compliance
More effort used in stretching the lungs. Stretchiness is known as compliance. The higher the compliance the easier it is to stretch. This is determined by elastic tissue and surface tension of fluid lining alveoli
What does the fluid surrounding the alveoli do
Surface tension of fluid limits expansion of alveoli. Decreases compliance making it difficult for alveolu and therefore lungs to expand.
Surfactant (secreted by type II pneumocytes) counters this - has detergent properties.
Acts to disrupt interaction between fluid molecules on alveolus surface, reducing surface tension
How does surfactant function depend on alveoli size?
Surface tension constantly “wanting to collapse down alveoli”
Larger alveoli -> surfactant molecules spread further apart, less effective at disrupting the urface tension. Surface tension increase as lung expands (hence forced inspiration harder than quiet)
Smaller alveoli -> surfactant molecules closer together when
- more effective at disrupting surface tension of fluid
- reduce surface tension
The force required to expand small alveoli is less than required for large alveoli
How does surfactant prevent small alveoli from collapsing into big alveoli?
Due to surfactant, bigger alveoli have greater surface tension than smaller. Thus pressure snide bigger alveoli stays higher despite it being bigger. Ie pressure does not drop despite increased volume, as the increased pull inwards from surface tension counters this. If pressure remains high in bigger alveoli, keeps pressures equal to smaller alveoli, prevents collapsing of smal into bug
What is law of Laplace
Pressure = 2*surface tension/radius
When is surfactant present in a fest
> 25 weeks. Resp distress syndrome is premature babies - lack o surfactant
Why are tubes small
Large SA for gas exchange.
How does the parallel arrangement of small airways compensate for the increase in individual resistance
Numerous airways run in parallel - compensates for increase in individual resistance. In normal lungs, highest resistance is upper resp tree, lowest in smaller airways. Except when these become compressed during forced expiration - collapses airways without cartilage so even a small decrease in tube size causes a dramatic increase in resistance
Airways resistance to flow adds little to the work of breathing in healthy lungs. Most effort is i overcoming eslastic recoil of lungs
