SM 150a, 152a, 153a, 154a - Mechanics I-IV Flashcards
What is transthoracic pressure (Ptt)?
[Equation, explanation]
Ptt = PiP - PB
Transthoracic pressure acts to suck the chest wall inward
When is transpulmonary pressure (Ptp) equal in magnitude to PiP?
When the glottis is open, PA = 0
(Ptp = PA - PiP)
[Transpulmonary pressure is the pressure that gives rise to ventilation]
If transrespiratory pressure (Ptr) is positive, where will air flow when the glottis opens?
Out of the alveoli
Ptr = PA - PB
If Ptr is positive, PA is higher than PB, and air will flow down the pressure gradient, out of the alveoli
An alveolus with a smaller radius will experience a stronger/weaker inward force due to surface tension than an alveolus with a larger radius
An alveolus with a smaller radius will experience a stronger inward force due to surface tension than an alveolus with a larger radius
Which airways in the lung are most susceptible to dynamic compression?
Small airways in the basilar parts of the lung
If you are starting from RV (after a really, really big exhalation), which part of the lung recieves more ventilation, the base or the apex?
Why?
The apex
The starting PiP at the apex of the lung is in the beefy part of the volume/PiP curve; slight changes in PiP starting from this point will result in more volume change (better ventilation)
The PiP at the base is higher than zero; these alveoli are collapsed/compressed and are not well ventilated unless PiP becomes a bit more negative
When the lungs are contracted…
Is the recoil force large or small?
How is PiP affected?
When the lungs are contracted (think expiration),
Recoil force is small (imagine a resting rubber band)
PiP is less negative than during inspiration, returns to equillibrium (eq ~ -5 cm/H20)
The chest wall is not expanding and elastic recoil is not as strong; the forces that act to pull the chest wall out and the lungs in during inspiration are not active during expiration
(The chest wall and lungs love each other and when they are able to reunite PiP is happy and less negative :) )
If patient has normal lungs but a chest wall that stiffer than normal, how will FRC change?
How will PiP be affected?
FRC will be larger
PiP will be more negative
(The recoil force of the lung will be larger - It will be more stretched than normal, so it will pull more inward more strongly)
(The chest wall won’t “give” as much to meet the lung)
What is transpulmonary pressure (Ptp)?
[Equation and explanation]
Ptp = PA - PiP
Acts to inflate the lungs
If transrespiratory pressure (Ptr) is negative, where will air flow when the glottis opens?
Into the alveoli
Ptr = PA - PB
If Ptr is negative, PA is lower than PB, and air will flow down the pressure gradient, into the alveoli
Does surfactant act more strongly on small or large alveoli?
Why?
Small alveoli
As the lung contracts, the surface area decreases and surfactant becomes concentrated into a smaller space (basically, the layer of surfactant gets thicker)
This works unless alveoli gets so small (lung size is below FRC) that surfactant phase-changes to a solid; at this point, surface tension is ~0
Which transmural pressure works to suck the chest wall inward?
Transthoracic pressure (Ptt)
What are the conditions of ATPS?
Ambient termperature and pressure, saturated H2O
What is the equation for the partial pressure of a gas, in the gas phase (Pg) in dry air?
Pg = Fg, dry * (PB - PH2O)
- Fg, dry = gas fraction, dry
- PB = barometric pressure
- PH2O = water vapor pressure
What is transrespiratory pressure (Ptr)?
[Equation, explanation]
Ptr = PA - PB
The potential pressure gradient for flow into or out of the alveoli
The difference between PA and PB when the glottis is closed and the respiratory muscles are relaxed
