MR44

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MR43 | MR45 | MCQ-Respiratory | Finals Black Bank

Contents

Question

MR44 ANZCA version [2003-Aug] Q148, [2004-Aug] Q89, [2005-Apr] Q85, [Mar06] Q82, [Jul06] Q70, [Mar10]

Correct statements regarding expiratory-inspiratory flow-volume loops
include all of the following EXCEPT 

A. in obstructive disease the expiratory curve has a scooped out or concave appearance 
B. in restrictive disease expiratory flows are usually decreased in relation to lung volume 
C. in restrictive disease the expiratory curve has a convex appearance 
D. the expiratory curve is largely effort independent 
E. the inspiratory curve is effort dependent


B. taken directly from examinationi anaestheisa book quote"The shape of the flow-volume loop in restrictive disease will demonstrate reduction of both total lung capacity and residual volume. Expiratory flows may be increased relative to lung volume. A steepness in the curve may reflect an increase in mid-expiratory flows caused by increased elastic recoil, and the curve typically has a convex appearance" - minkel777


B is the incorrect answer. In restrictive pattern, both volume and flow is decreased however volume decreases more than flow......spooky

Worked answer

MR44 ANZCA version [2003-Aug] Q148, [2004-Aug] Q89, [2005-Apr] Q85, [Mar06] Q82, [Jul06] Q70 Correct statements regarding expiratory-inspiratory flow-volume loops include all of the following EXCEPT

  • A. in obstructive disease the expiratory curve has a scooped out or concave appearance - true
  • B. in restrictive disease expiratory flows are usually decreased in relation to lung volume - some people are saying this is incorrect: Expiratory flows are decreased, as are lung volumes... this seems to be true to me. It would also make sense because in restrictive disease, the compliance of the lungs is decreased, so exp flow (a passive process) would be decreased more so than the actual lung volumes.
  • C. in restrictive disease the expiratory curve has a convex appearance - this sounds the most incorrect to me: the shape of the curve is similar to a normal flow-volume loop, just with a smaller magnitude
  • D. the expiratory curve is largely effort independent - true
  • E. the inspiratory curve is effort dependent - true


minkel777 = B is asnwer to choose. "While obstructive lung disease is characterized by a concave slope of the passive expiratory FV loop, restrictive lung disease often results in convex loop patterns" "A normal, non-pathological F/V loop will descend in a straight or a convex line from top (PEF) to bottom (FVC)."

Comments

WARNING - This is a severely flawed MCQ.
The options all relate to a flow-volume loop for a MAXIMUM forced expiration 
BUT - the question stem does NOT state this so it cannot be answered. 

As long as the expiration remains within the maximum flow-volume envelope, then a wide variety
of different 'actual' shapes can be obtained during sub-maximal expirations (as shown in West). 
As this is an "all except" MCQ, the author thinks that 4 options are true and only one is not. 

The amazing thing about this MCQ is that this is the Aug03 version, and it has been used
again in Jul04 & Apr05. This means the MCQ was rated very highly in its discrimination index, which 
of course is interesting seeing that it is wrongly worded. The examiners (and obviously the candidates) 
have treated the MCQ as though it does say MAXIMUM forced expiratory curve. The wording was
unaltered in the now released Sep04 paper (MCQ-89 on that paper).

If it had been fixed up, then:
*A is correct - this is the "standard" description of a curve in such patients
*B is wrong (If the flow rate is related to lung volume the flow rate is often HIGHER than normal)
*C is problematic as the descending part of the expiratory curve is often drawn with a slightly
convex appearance but usually without any discussion or explanation
*D is "sort of correct" providing you assume that they really mean to refer to the descending part of
the expiratory curve - this is the bit that is usually stated to be "effort-independent" due to 
dynamic airway compression. Presumably, they have used "largely" to indicate this so that this can be
considered 'correct'
*E is correct because airway compression does not occur. During inspiration, there is a distending
pressure on the airway (so decreased airway resistance) and, to a certain extent, increased effort
is rewarded with increased flow. 
So it seems to be option "B" that they intend to be correct.

I agree B is wrong. Restrictive lung disease maintain flow rates, it just decreases in volume, FEV1 is maintained, a major difference between obstructive and restrictive lung disease.--Drpeace 21:00, 23 May 2012 (CDT)

Sorry Drpeace and etc but you need to revise respi physiology. See pulmonary-function-fig4_large.jpg And spirometry_for_airway_diseases1318425801858.jpg 1. FEV1 is REDUCED, not maintained, in restrictive lung disease. The FEV1/FVC ratio is maintained or even increased. 2. Flow rate is definitely reduced in restrictive lung disease - see spirometry loop. I also picture a normal lung as a balloon and fibrosed lung as a basketball - to deflate them, the basketball definitely has reduced flow because it is much stiffer. Together with reduced lung volume, it makes answers B the correct answer.

References

[SpirXpert http://www.spirxpert.com/welcome.htm] All you ever wanted to know about spirometry.--Chris 23:08, 13 Jul 2007 (EDT)

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