AP II Unit 3 Flashcards
During a fowler test you measure about 125 cc of pure oxygen before nitrogen shows up. The nitrogen plateau is reached after another 200 cc. What is the anatomical dead space volume?
225 CC
During the flow volume loop, when does effort dependence no longer apply?
During expiration as you approach FRC; at this point enough small airways have collapsed and alveoli are smaller, which means that increased effort will not increase expiratory flow rate as the narrow airways have become rate-limiting and switch from effort dependence to effort independence
If healthy, what is the maximal inspiratory and expiratory flow rate?
Both are 10 L/min
Do the numbers on the x-axis of the flow volume loop matter?
No, they are arbitrary. What matters is the distance between them.
How would you measure VC on a flow volume loop?
It’s the difference between RV (point on the right) and TLC (point on the left)
What indicates effort on the flow volume loop?
The loop with the greatest curve = the greatest effort, the loop with the smallest curve = the least effort.
The flow volume loop shown in lecture has one flaw, what is it?
The time axis is not adequately shown. Based on that graph, it looks like all the loops end at the same point in time, which we know is not correct. If you have 5 L in the lung, and expire at either 10 L/s or 1L/s, it’s obvious 10 L/s would empty faster than 1. You have to infer this detail from the graph.
What part of the flow volume loop is symmetrical? Which is not?
Inspiration = symmetrical
Expiration = asymmetrical
Why is expiration not symmetrical on the flow volume loop when expiring from TLC?
At TLC, the alveoli are wide open and the airways are wide open = very fast flow rate. As you expire, volumes decrease and airways begin to collapse increasing resistance and rate-limiting how fast we can expire
What are the factors that dictate flow rate of the flow volume loop?
Diameter of the airway, elastic recoil and traction
What kind of flow would you expect with little recoil and little traction?
High chance of airway collapse and increased resistance = slower flow rate
What kind of flow rate would you expect with lots of recoil and traction?
Assuming the alveoli/airways are open = faster flow rate
In an expiratory flow function curve, which curve should mimic the normal curve? Which one does not?
Restrictive looks similar to a normal one, obstructive has a distinctive shark fin appear
Why is expiratory flow rate slower in obstructive disease?
The lungs fill up more but have less elastic recoil, and as you apply PIP, airways can collapse limiting the expiratory flow rate
Why is expiratory flow rate slower in restrictive disease?
The lungs do have more elastic recoil, but they don’t fill up as much, meaning the alveoli are less full which means the airway is narrower and therefore more likely to collapse with increasing PIP
Why is the prolonged expiration bad in obstructive lung disease?
It takes so long to expire, that by the time you need to start inspiration, you haven’t fully expired
When would effort independence start in obstructive lung disease?
It would begin much earlier in obstructive, well before you get close to FRC
Relying solely on recoil pressure to exhale is what kind of breathing?
Passive expiration
When is there no risk of airway collapse?
As long as the internal pressure is higher than PIP
During maximal expiration, there is massive + pressure outside the airways. Why do airways superior to the small airways not collapse despite the fact the pressure inside them is significantly lower than the PIP?
They have cartilage that reinforces them to withstand the extra + pressure
What are the 3 factors that slow expiratory rate during maximal expiration?
Loss of alveolar springs that create recoil, loss of lung volume and loss of small airway traction
In general, what lung pathology is more common to encouter?
Obstructive
In general, is fast or slow expiration indicative of disease?
Slow
What is the formula for resistance in series? Conductance?
Rtotal = R1 + R2
1 / Ctotal = (1 / C1) + (1 / C2)