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
