Respiratory S3 (Done) Flashcards
What is the function of pleural fluid?
Thin layer of fluid that ensures lungs fill the thoracic cavity during inspiration by ensuring visceral pleura moves with parietal
What is a pneumothorax?
Breach in integrity of the pleural seal
Leads to lung collapse (lung(s) do not expand with thoracic cavity)
Describe the forces exerted by the lung and on the lung at resting expiratory volume
What happens if these forces are disturbed?
Lungs pull in and up
Thoracic cage pulls out
Passive stretch of diaphragm pulls down
Forces are in equilibrium
If Disturbed:
If disturbed (E.g. in inspiration) the lungs and surrounding structures will spring back to resting expiratory volume (equilibrium regained)
What is the difference between and inspiration from resting expiratory volume and quiet expiration?
Quiet Expiration:
Passive process, just stop breathing in
Inspiration from resting expiratory volume:
Active
Via intercostals and diaphragm (major muscle of quiet respiration)
How does forced expiration differ from quiet expiration?
Active not passive
Force exerted by abdominal muscles
Then inspiration back to resting expiratory level is passive
In what scenarios would quiet breathing require additional work?
If diaphragm cannot move into abdomen
- Pregnancy
- Obesity
- Corsets
What is lung complicance?
The stretchiness of the lungs
Volume change per unit pressure change
Therefore higher complience means easier to stretch (lower pressures needed to acheive desired volume)
What are the 3 major factors that affect lung compliance?
Surface tension of surfactant
Elasticity of walls
Detergents
Describe how surface tension affects the lungs
At interface of water and air surface tension arises
Created by attraction of underlying molcules to surface molecules
This force reduces compliance
Describe the involvement of detergents in the lung and how they affect compliance and breathing
Produced by type 2 alveolar cells (surfactant)
At low lung volume detergents lower surface tension
They disrupt interactions between surface molecules
At higher volumes this effect is reduced
Therfore bigger breaths are harder than smaller breaths as lung compliance lowers as volume increases
What is hysteresis and how does it affect respiration?
Hysteresis is a phenomenon wherby there are different energies required to move a system in different directions
Respiration:
Energy put into stretching a film of surfactant is not recovered when the film recoils
This loss is greatest when tibal volume is maximal
Therefore smaller breaths are more energy effiecient
How is hysteresis in the lungs represented?
Graph
Y = Surface tension
X= Surface area
A loop is formed, the area of this loop respresents energy loss
What are bubbles?
A film of fluid surrounding gas (like an alveolus)
There is equilibrium between gas pressure and tension
What is Laplace’s law and what can we take from it?
Pressure in bubble = (2 x Surface tension) / radius
Therefore:
- Bigger bubbles have lower pressure than smaller bubbles
- If a big bubble is connected to a smaller bubble gas will flow from smaller bubble into lower pressure bigger bubble
Describe how Laplace’s law is not an accurate respresentative of lung function
Alveoli form an interconnecting set of bubbles
If Laplace’s law applied, bigger aveoli would ‘eat’ smaller alveoli
However:
As alveoli get bigger surface tension increases (as detergents lose effect)
Therefore raising pressure in bigger bubbles, preventing Alveoli ‘cannabilisation’
Describe the causes and features of respiratory distress syndrome
Causes:
In babies born premature there is too little surfactant
This can also be triggered in adults by trauma
Features:
Lungs are stiff and only few, large alveoli
Small alveoli collapse into bigger ones without surfactant/detergent
What is airway resistance like:
- In individual bronchi
- The entire respiratory tree
Why is this?
Bronchi:
Relatively High
Airway:
Relatively low
Because:
Poiseulle’s law
Smaller tubes have higher flow resistance
Large number of small airways in parallel compensates for increase in resistance (lower resistance)
At each branch resistance decreases
Compare airway resistance in:
- The trachea
- All Small airways (Bronchioles)
Trachea:
Relatively high
All Bronchioles:
Relatively low
How is airway resistance affected by forced expiration?
Lung compressed and hence the small airways are narrowed
This increases resistance to airflow
Air is ‘trapped’ in alveoli
What are the causes of obstructive airway disease?
What are the consequences regarding airway resistance?
Causes:
Narrowed airways from disease (Asthma, Bronchitis)
Consequences:
Airway resistance increases earlier in expiration (due to narrowed airways)
Breathing out can become very difficult (pursed lip breathing)
