Forced Vital capacity (FVC)

Total amount of air that can be blown out after a maximal deep breath, as fast as you can.

Note this amount in volume time graph.
Best of 3 attempts is taken.
The normal range is 80-120% predicted.

Forced Expired Volume in One second (FEV1)

The amount of air that can be blown in the first second in the FVC maneuvere. Note this amount in volume time graph..
	The normal range for FEV1 is 80-120% predicted

FEV1/FVC

FEV1 volume devided by FVC expressed as percent.

I am going to create some confusion. There are two ways of judjing the normal range.

• Observed percent less than 75% is indicative of obstruction.
• The children and old people were not included in the original normal data to develop the nomogram. Military recruits were the "normal" subjects. As you get older the elastic recoil dicreases and a value less than 75% is normally seen. Hence percent predicted is used as an alternate method. In general we don't like to use percent of percent. Anyway if you are going to use % pred, the normal range is compact between 90-100.

FEF25-75

Forced expiratory flow rate between 25 to 75% of FVC.

This used to be called maximal mid expiratory flow rate.
We are looking at the flow rate of the mid portion of FVC. Note this in the volume time graph.

The normal range is 75-125%.
This measure is thoght to represent early evidence for obsruction.

Peak expiratory flow rate. Note the location of PEFR in the flow volume loop. This graph represents flow rate against lung volume. Peak flow occurs early during forced expiration. Normal range is 80-100%.

Forced expiratory time(FET) Note the time taken to complete FVC in the volume time graph. Normal is less than 5 seconds. Prolonged FET would suggest airway obstruction.

PIFR Note the peak inspiratory flow in the flow volume loop graph. Note the difference in configuration of inspiratory and expiratory limbs of flow volume loop.

FIVC This measure is obtained while performing flow volume loop. I don't use this value much in interpretaion because we never take enough time to seriously measure inspiratory values.

 

 

 

 

 

 

Maximal voluntary ventilation (MVV) This is the amount of air that can be moved in and out as fast as you can in one minute. We ask the patient to breath as deep and as fast as possible for 10 seconds and express it for a minute. We take the best of 3 meaurements. Usually the first will be lower, the second and third effort will be similar. Lot of coaxing has to be done to encourage the patient to do the best. Click to see how it is performed (not yet).

 

 

 

 

 

 

Flow Volume Loop

Configuration of expiratory limb: Exponential drop in rate of flow Inspiratory limb: Flow rates remain same with a sudden drop off. Peak Expiratory flow Peak Inspiratory flow Patterns

 

 

 

 

 

 

 

 

 

FEV1Forced expiratory volume in one second FEF25-75 Maximal mid expiratory flow rate FET Time in seconds to complete FVC Patterns

 

TV IC ERV SVC

 

 

 

 

 

 

 

 

 

 

Maximal Voluntary Ventilation

Note: Rate Volume