The summary is:

There are only four possibilities:
normal or obstructive, restrictive, or mixed defects.
Normal values represent a
range for the individual’s age, sex, height, and race. Greater than 80% of
predicted is a simple cutoff point for normal.
An FEV₁ <80%>1/FVC
can be used to distinguish the two. Mixed values include
reductions in both FEV1 and FVC.




Normal: FVC, FEV1 and FER all >80% of predicted (ALL NORMAL)
Restrictive: FVC<80%,>80% OR <80%>70%.
Obstructive: FVC>80%, FEV1<80% rel="File-List" href="file:///C:%5CDOCUME%7E1%5COwner%5CLOCALS%7E1%5CTemp%5Cmsohtml1%5C01%5Cclip_filelist.xml">There are only four possibilities:
normal or obstructive, restrictive, or mixed defects. Normal values represent a
range for the individual’s age, sex, height, and race. Greater than 80% of
predicted is a simple cutoff point for normal. an FEV₁ <80%>1/FVC
can be used to distinguish the two. Mixed values include
reductions in both FEV1 and FVC.

Answers the following two questions:
1. Are the lungs normal or is there restrictive disease or airway obstruction?
2. If there is airway obstruction, will it respond to bronchodilators?

Uses the following two measurements because all a spirometer can do is measure the volume blown in and the time that takes!
1. FEV1
2. FVC (aka FEV6)
...and from this you then get the ratio of FEV1/FVC, aka the FER.

Normal values are:
1. You should be able to blow 70-75% of the total volume you can blow, within the first second
2.


So, the way that you interpret is:
1. Start with the FVC.
There is only one condition that increases FVC - acromegaly. So, FVC will always either be normal or reduced.
If it is low then the patient has restrictive lung disease or severe obstructive disease, and you will expect that the patient will also have a low FEV1. You can skip over to the third step - the ratio.
If the ratio is >85%, they have restriction or a ventilatory defect.
If the ratio is <70% src="file:///C:/DOCUME%7E1/Owner/LOCALS%7E1/Temp/moz-screenshot-1.png" alt="">
3. If they have obstructive lung disease, then you check to see whether it is reversible with a bronchodilator test. Reversibility is defined as absolument improvement of 200mls or a 12% improvement in FEV1.

A summary table is:


Other things you might see:
PEF= peak flow

The science behind it:



Pearls:
1. A reduced FVC is a hallmark of cardiac failure because the lung parenchyma is infiltrated with fluid.

2. Like everything else, the FER drops with age.

3.

Obstructive

Narrowed
airways decrease the volume of air that can be forcibly exhaled in the first
second (FEV1). Note that the FVC is only achieved after a long exhalation. The
Fev1/FVC ratio is markedly reduced. Expiration is prolonged with a slow rise in
the curve and the plateau is not reached for as long as 15 seconds (in
emphysema).

Restrictive

Both FEV1 and
FVC are reduced. As the airways are open and unblocked expiration is rapid and
completed within 2-3 seconds. The FEV1/FVC ration is normal or increased. A
high or normal proportion is exhaled in the first second, resulting in a rapid
rise in the curve but with long volumes reduced compared with predicted levels.

Mixed

Expiration is
prolonged with a slow rise to plateau levels. The vital capacity is likely to
be significantly reduced compared with an obstructive defect. Mixed patterns,
if less severe, can be difficult to differentiate from obstructive patterns.

4. An average 40yo man will have an FEV1 of 4L and an average 50yo man will have an FEV1 of 3L. A patient with severe COAD will have an FEV1<1L and one with moderate COAD 1-1.5L.

5. A flow-volume curve is of use because it picks up poor effort. A normal curve will look like the sail of a boat - it rises to a peak and then descenfs at 45 degrees until the FVC is reached at teh bottom righ-hand corner.
So, the other patterns that occur are:
-bowl shaped pattern of obstruction:- flow will reach a peak within 2/10ths of a second just as it does in healthy people and will then scoop/droop downwards so that subsequent flow is depressed until it reaches the FVC.
In severe COAD it looks like a rat's tail.

- the RINO pattern is restriction and no obstruction (due to a multitude of diseases that restrict lung volumes):- the pattern resembles a missile as there is a sharp peak and then a steeper decline than normal because there is not much air to expel.

6. For the PEF, 10L/s= 600L/min.

7. A pitfall to be aware of is when people blow out for only a few seconds but have a scooped out curve. Because of this inadequate effort, their FVC will be low and therefore their FER high, masking their airways disease.

8. If there is both a decrease in FVC but no decrease in FER then this is RINO.
If there is a decrease in both then there are two posibilities:
i) moderate airways disease leading to an increased amount of air left in the lungs at expiration and therefore a decreased FVC.
ii) they have COAD or asthma and a superimposed restrictive disorder
You tell the difference by ordering a DLCO, CXR and TLC from a hospital based laboratory

9. Causes of a low FVC:
- lung inc. COAD
- pleural cavity
- chest wall
- diaphragm/respiratory muscles