Respiratory L2: Respiratory Mechanics Flashcards
Both lungs are surrounded by a closed chamber. What is this called?
“pleural sac” or intrapleural space.
- Has fluid inside
How do we breathe? Humans are ________+ve/-ve breathers.
- –ve type breathers- don’t actively push air into lungs
- Create lower than atmospheric pressure in lungs
What is the parietal pleura?
surrounds ribcage and diaphragm
What is the visceral pleura?
surrounds both lungs
Alveolar surface tension is responsible for the __________ gradient and the _______________ pressure.
transmural pressure; at rest lower-than-atmospheric intrapleural
The _____________ prevents the lungs from collapsing. If the intrapleural pressure is allowed to equalise with the atmospheric pressure, visceral and parietal pleurae separate and the lung collapses resulting in a ______.
transmural pressure gradient; pneumothorax
Lower than atmospheric pressure in pleural cavity due to lungs wanting to _______ (expand/collapse) (alveoli surface tension= driving force for lung recoil) –> pulls visceral pleural _____ (inwards/outwards) –> ________ (increased/decreased) intra-pleural space –> ____ (increase/decrease) pressure –> pulls parietal pleural _______ (inwards/outwards) –> pulls ribs/ribcage _____ (inwards/outwards) (bent in)
collapse; inwards; increased; decreased; inwards; inwards
All stops when ___________ = __________. Lower than atmospheric pressure in intrapleural space
lungs wanting to collapse; ribs wanting to spring out
A decrease in pulmonary surfactant molecule results in a decrease of _________.
Intra-pleural pressure (pulls in more)
What causes a collapsed lung? 6 steps.
- Injury to parietal pleural
- lower than atmospheric pressure begins to equalise to atmospheric pressure
- nothing holds lungs from collapsing
- alveoli collapse
- rib cage springs out
- collapse lung
When a lung is collapsed, what is different about the space between the parietal and visceral pleura?
In a normal healthy lung = no “space” (only called that)
In a collapsed lung = renal space between the parietal and visceral lung
What are the 7 steps of inspiration in quiet breathing?
- Lowering the diaphragm (connect to parietal)
- pulls parietal pleural
- decreased intrapleural pressure
- pulls visceral pleural apart
- intra-alveolar pressure falls below atmospheric pressure
- air flows into lungs
- inflates lungs
What are the 6 steps of expiration in quiet breathing?
- Relaxation of the diaphragm
- exhalation (passive)
- intrapleural pressure returns to the normal lower than atmospheric pressure.
- recoil of the lung
- lower than atmospheric intra-alveolar pressure
- air moves out of the lungs.
How does forced expiration in quiet breathing occur? What muscles are responsible?
- Intercostals and abdominal muscles are used
- push diaphragm upwards (pressure in intra-pleural space)
- push alveoli
- flatten rib cage
- forced expiration
What are 2 things that airflow rate is dependent on?
- pressure gradient
- airway resistance
What is airway resistance dependent on?
Due to friction along the wall of the airways
Depends mostly on the diameter of the airway.
Increased pressure in the airways = ____ (increased/decreased) airflow
Increased
Air molecules flow ___ (towards/against) vessel walls. This _____ (increases/decreases) the friction and the airflow rate ______(speeds up/slows down).
against; increases; slows down
Smaller vessels have ____ (more/less) air molecules
More
Larger vessels have ____ (more/less) air molecules
Less
What is the meaning of resistance/conductance?
Airflow rate- how quickly airflow conducts air
What is the flow dependent on in a rigid tube? For example, if the pressure changes the diameter of the conduit.
In a rigid tube, flow is dependent on the pressure difference between each end and the diameter of the tube.
What is the flow dependent on in a compliant tube/wall? For example, if the pressure changes the diameter of the conduit
In a tube with compliant walls, flow is also dependent on absolute pressure because pressure between lumen and outside will change the cross section area (diameter) of the conduit.
What is the meaning of compliance/elastance?
- Elastance- Not elastic – opposite
- Compliance- very easily deformed
- Eg. table
- Low compliance
- High elastance
The thickness of airway walls _____ (does/doesn’t) have an impact on compliance and elastance. Smaller airways have ______ (thicker/thinner) walls and are more ______ (compliant/elastant).
Does; thinner; compliant
How does someone increase ventilation in inspiration? What are the 6 steps?
- contraction of the diaphragm and external intercostal
- muscles expand the thoracic cavity
- Increase intrapleural space (pull visceral pleural inwards and parietal pleural out)
- decreased intrapleural pressure
- decreased intra-alveolar pressure (compared to higher atmospheric pressure)
- air flows into lungs (from higher atmospheric pressure to lower alveolar)
- inflates lungs
How does someone increase ventilation in expiration? How does that occur? Be specific with the 2 muscles and the steps.
Internal intercostal muscles:
- contraction of the internal intercostal muscles
- flattens the ribcage
Abdominal muscles:
- contraction of the abdominal muscles
- pushes the diaphragm upwards
- increased intrapleural pressure + together with the recoil of the lung
- increased intra-alveolar pressure
- air moves out of the lungs
What is dynamic airway closure?
When frictional losses cause the airway pressure to fall below the surrounding elevated intrapleural pressure, the small non-rigid airways are compressed closed, blocking further expiration and trapping air within the alveoli.
What is residual volume?
The amount of air left in the alveoli after dynamic airway closure
What are 3 forces keeping the alveoli open?
- Transmural pressure gradient
- Pulmonary surfactant
- Alveolar interdependence
What are 2 forces promoting alveolar collapse?
- Elasticity of stretched pulmonary connective tissue
- Alveolar surface tension
Prematurely born babies often present with Respiratory Distress Syndrome due to insufficient ___________.
pulmonary surfactant production
What are 4 things that pulmonary surfactant deficiency leads to?
POSSIBLE EXAM QUESTION
- increased alveolar surface tension = increased recoil of the lung
- increased transmural pressure gradient and decreased intrapleural pressure
- late small airway closure with decreased residual volume
- increased recoil of the lung and decreased compliance of the lung = increased breathing effort
What are the 3 treatment methods for pulmonary surfactant deficiency?
POSSIBLE EXAM QUESTION
- Artificial surfactant moelcules
- Mechanical ventilation (+ve)
- Actively push +ve air into lungs
- Can have damage on fragile baby
- Iron lung
- Whole chest gets sealed –> machine sucks air out –> decrease pressure around (more gentle)
- Immobile during procedure
How does forced expiration occur? What are the 8 steps?
- Inflate lungs to max.
- Increase extra recoil of lungs
- Use abdominal muscles to do forced expiration
- Increased intra-pleural pressure- pressure starts to decay (airway resistance)
- Increase alveoli pressure
- Increased pressure gradient between alveoli and atmosphere
- Air flows out faster from small to large airway
- Out
How do we stop expiration? What are the 4 steps?
- Increased pressure starts to compress small airways
- Become more compliant (usually elastant)
- Close airway
- Stop breathing out
What is the different between passive and forced expiration?
(a) Passive- no use of muscles (recoil of lungs and pressure change)
(b) Forced- uses abdominal muscles
How does forced expiration occur during exercise? What are the steps? How does it vary to normal voluntary forced expiration?
- Less increased intrapleural pressure
- Still some gradient between alveoli and atomosphere
- Breathe out
- But never reach dynamic airway closure
How does injury or disease (eg. decreased diameter of airways) affect expiration? What are the 6 steps?
- Small airways are even smaller due to decreased diameter
- Increased air resistance
- Close processes of the airway occur faster
- Lose pressure faster (eg. exhale less air than normal)
- Air trapping
- Early dynamic airway closure
How does injury or disease (eg. decreased recoil of lungs) affect expiration? What are the steps?
- Decreased recoil of lungs
- Increased transmural pressure gradient (not as low as normal)
- Lungs don’t recoil/shrink back as much
- Increased intra-pleural pressure
- Muscle force
- Early dynamic airway closure
Between parietal and visceral pleura is a closed chamber (______ space). Usually very close together so isn’t a “space”
potential
What can you physically see in a patient with a collapsed lung? Why?
Can see ribs protruding
- Lungs wanting to collapse = ribs want to spring out
- Usually should be equal and stop
What is the transmural pressure gradient across the lung wall?
Intra-alveolar pressure — intrapleural pressure
What is the transmural pressure gradient across the thoracic wall?
Atmospheric pressure — intrapleural pressure
During inspiration, intra-alveolar pressure is _____ than atmospheric pressure.
less
During expiration, intra-alveolar pressure is ______than
atmospheric pressure.
greater
At the end of both inspiration and expiration, intra-alveolar pressure is ________to atmospheric pressure because the alveoli are in direct communication with the atmosphere, and air continues to flow down its pressure gradient until the two pressures equilibrate.
equal
Throughout the respiratory cycle, intrapleural pressure is ______than intra-alveolar pressure. Thus, a ________ gradient always exists, and the lung is always stretched to some degree, even during expiration.
less; transmural pressure
How does alveolar surface tension (and pulmonary surfactant molecules) cause the normal lower than atmospheric intrapleural pressure?
- Alveolar surface tension causes
- Decrease in alveolar volume
- Increase in intrapleural volume
- Decrease in intrapleural pressure
How does alveolar surface tension (and deficency of pulmonary surfactant molecules) cause the normal lower than atmospheric intrapleural pressure?
- Pulmonary surfactant molecules (prevent collapse of alveoli) deficiency
- Even more increase in alveolar surface tension
- Even more decrease in alveolar volume
- Pulls visceral pleural inwards
- Even more increase in intrapleural space
- Even more decrease in inreapleural pressure
THUS, aa deficiency in pumonary surfactant molecule = even more decrease in intrapleural pressure
