Respiration VII Flashcards
During inspiration, what happens to the diaphragm, the chest wall, the lungs, and the pleural space pressure?
The diaphragm contracts, the chest wall is pulled open, and this creates a more negative pleural pressure that causes expansion of the lungs.
How does the alveolar pressure compare to atmospheric pressure during inspiration? How does this affect air flow?
When the lungs get pulled open, the alveolus gets larger and the pressure inside decreases. The alveolar pressure is now lower than atmospheric pressure. This pressure gradient causes air to flow from outside to inside the alveolus.
How does the alveolar pressure compare to atmospheric pressure during expiration? How does this affect air flow?
During expiration, the brain tells the muscles to stop contraction. They relax and ribcage recoils downwards, which increases the pleural pressure (becomes less negative). This will allow the lungs to recoil down. This will increase the alveolar pressure above atmospheric pressure. Air will therefore flow outwards.
What is the formula for air flow during respiration?
Flow = (Palv - Patm)/R
Is the flow of air coming into the lungs positive or negative? And for air leaving the lungs?
The air going in is a negative flow and the air going out is a positive flow (because of the formula).
Describe how the following vary over the course of inspiration:
a) Intrapleural pressure
b) Lung volume
c) Alveolar pressure
d) Air flow
a) As inspiration proceeds, the lungs fill with air, increasing the tidal volume. The increase gradually drops off as the pressure gradient between atmopsheric and alveolar air decreases.
b) Intrapleural pressure decreases as the thoracic cage moves out.
c) Alveolar pressure decreases initially due to the increase in volume of the lungs, then increases again as they fill with air.
d) Air flow is negative as it flows into the alveoli and comes back up as they fill and the pressure gradient decreases.
Describe how the following vary over the course of expiration:
a) Intrapleural pressure
b) Lung volume
c) Alveolar pressure
d) Air flow
a) Intrapleural pressure climbs back up as the thoracic cage comes back down.
b) Lung volume drops as air leaves the lungs due to the compression of air in the alveoli.
c) Alveolar pressure decreases due to the drop in intrapleural pressure, as the lungs can recoil and the volume of the alveoli decreases.
d) Air flow is positive and climbs up, peaks, and comes back down to zero as the lungs empty.
At the end of inspiration, how does Palv compare to Patm?
They are equal to one another (there is no pressure gradient), which is why air flow stops.
At the end of expiration, what is the value of air flow, Palv, and Ppl?
Air flow is 0, Palv is 0, and Ppl is back to its resting pressure of -5 cm H2O.
Changes in pleural pressure during inspiration and expiration depend on what two factors?
- Contractions of the respiratory muscles
- Airway resistance
How does airway resistance affect the pleural pressure change during inspiration?
During inspiration, the real intrapleural pressure is lower than the theoretical one to counteract airway resistance. The opposite is true of expiration.
How does airway resistance affect the pleural pressure change during expiration?
The real intrapleural pressure is higher (less negative) and greater in magnitude than the theoretical intrapleural pressure in order to counteract airway resistance.
What is the formula for the resistance of the airways to gas flow?
Raw = (Palv - Pao) / Flow
How does airway diameter affect resistance?
A large diameter airway can carry a large flow for a given pressure difference and so has a smaller resistance than a small diameter airway
How does asthma affect respiration?
In asthma, airway resistance increases because it causes the constriction of smooth msucle, which prevents the movement of air. Sometimes, there can be mucous that further decreases the lumen of the airway as well.
Describe the graph showing the flow-volume curve of air for varying levels of respiration effort.
The ascending portion varies depending on the level of effort put in, but the descending portion is independent of effort because of the compression of the airways by intrathoracic pressure.
Explain why the descending portion of the flow-volume curve is always the same no matter the respiration effort.
During forced expiration, the pressure in the pleural space goes positive and is greater than the pressure in the airways. This creates a negative transmural pressure in airways. So, the airways collapse. This means that no matter how hard you try, you can’t breathe out air any faster.
True or false? Pleural pressure is always negative. Explain.
False. It is always negative EXCEPT during forced expiration, where it goes as positive as +30 because of the effort of the expiratory muscles.
Compare the pressure of the pleural space, alveoli, and transmural pressure during:
a) Pre-inspiration
b) During inspiration
c) End of inspiration
d) Forced expiration
a) Before inspiration, Paw = 0, Ppl = -5 cm H2o
b) During inspiration, Ppl = -7 cm, Paw = -2
c) At the end of inspiration, Paw = 0 and Ppl = -8. Intramural pressure = +8
d) During forced expiration, Ppl = +30, Plv = +38, transmural pressure = -11. This causes the airways to close.
Describe the lung volume-flow curve for normal individuals (incl. highs and lows)
Range: volume of 2.5 - 7, peaks high at around 7 and falls sharply.
Describe the lung volume-flow curve for individuals with restrictive diseases (incl. highs and lows). Explain why it looks this way.
A subject with a disease like pulmonary fibrosis, which is a restrictive disease, causes stiff alveoli, making it harder to inflate the lungs (recall). If a subject with fibrosis breathes in to max capacity, the compliance of the lungs is low so the total lung capacity is low. Then, if they breathe out as hard as they can, the maximum flow is low compared to a normal subject. This is because the max flow is low, so there’s less driving pressure.
Give an example of a restrictive pulmonary disease and how it affects the lungs.
Pulmonary fibrosis. It causes stiff alveoli, making it harder to inflate the lungs.
For the same lung volume how does expiratory flow compare between normal individuals and individuals with a restrictive lung disease?
For the same lung volume, the subject with fibrosis has a higher flow than a normal subject. This is because their lungs naturally want to collapse, meaning that air will leave faster.
Describe the lung volume-flow curve for individuals with obstructive diseases (incl. highs and lows). Explain why it looks this way.
Here, the lungs are very compliant. The total lung volume is extremely high compared to normal subjects. When they are asked to breathe out as hard as they can, the increase in flow is very slow as a function of the expired flow and the maximum flow is low compared to the normal subject. Because these lungs have no recoil, it is much harder to breathe out. When they breathe out to their residual volume, there is much more left over than in normal subject.
Also note the little scoop on the emphysema patient curve.
