13- FEV1- FVC

KYJ13- FEV1/FVC Ratio

In "knowing your jargon" we look at the common jargon terms that our colleagues throw around. Today it is the respiratory diagnostic term FEV1:FVC.  These diagnostics are performed as a respiratory function study using a technique called Spirometry.  Nurses often have to record Spirometry, but don't always feel confident with the result interpretation, so let's have a crack at explaining some.

Take a breath in.  Breathe in.   Now take in a big breath and exhale as fast as you can and as much as you can through open mouth.

If you played along, what you just did was blow your FVC.
Forced Vital Capacity (FVC) is the total volume of air that you can exhale after taking in a big breath, then forcibly empty your lungs.  Your normal FVC varies with Age, height and sex.  Everyone's chest is different in dimension.
Example: a 45 year old woman 170cm has a FVC of 4 litres.

The other half of the ratio is the FEV1.  This stands for "Forced Expiratory Volume in 1second".  FEV1 is a function of how fast you can exhale all your air .  In a normally healthy lung, more than 80% of your breath should be able to be expelled in the first 1 second.

In restrictive lung diseases (asthma, bronchitis, emphysema, Ca) the ability to vent off breath fast is limited.
A diagnosis of COPD is made based on a FEV1 that is less than 70% of predicted FVC.

In these gas trapping disease states, alveolar destruction, narrowed bronchioles, and mucous production cause the passage of air to be restricted, thus slower in its ability to vent off.

An FEV1 measures the actual volume of gas inside that first 1 second, and for the exams of the 45 yo woman of 170cm that should have a FVC of 4 litres, her FEV1 should be at least 3.2 litres

FEV1/FVC ratio
Mathematically , 3.2/4 is 0.8 or 80%.

A similar quick test is the PEFR (Peak Expiratory Flow Rate) or simply, "peak flow".

Similar to FEV1 where a forceful exhalation volume is measured over one second. The peak flow looks at speed of your breath as litres per minute (L/min).

When you forcibly exhale the fastest flow of air is recorded judged on a set of predicted norms.  In the example we've used, you would predict a 45 yo 170cm woman could blow around 430-450 L/min.

Now that's a lot of wind!!

Like FEV1 a lower than predicted PEFR suggests acute worsening of exhalation ability.  It is useful to monitor asthma, especially in children who may use a peak flow meter daily as part of their written asthma plans.

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And... Breathe easy!!