Pulmonary Medicine-Spirometry                           ISSN 1930-6741


Author: Ramesh Kaul, MD


Spirometry is a performance test for lung function. Spirometry is done for checking the Forced Expiratory Volume in One second (FEV1).

FEV1 is essentially the maximum volume of air  blown out in one second.

This is compared to the normal standard calculated for the person.

The standards are calculated from age, sex , weight and height of a person from existing tables.

The second part of the test is to make a person blow out as much air out as possible in the cylinder usually in 6 second or more this is called Forced Vital Capacity (FVC).

FVC is essentially the maximum air blown in one breath with no time limit.

Below 80% is considered abnormal and below 50% is considered severe decrease.

The FEVI (Forced Expiratory Volume in 1sec) is compared to the FVC (Forced Vital Capacity) this is the FEVI/FVC RATIO and should be 70% or above for a normal person.

Low ratio FEVI/FVC suggest  obstructive air flow or limited air flow. The obstruction can occur anywhere from upper airway,  vocal cords, throat, to lower airways the wind pipe bronchial tubes or even small bronchioles. It can occur in all or any part of the airway if some one has locked jaws the nostril can cause obstruction. But the test is done from the mouth thus measures total flow.

MVV or minute voluntary ventilation is a rapid breathing maneuver done over 15 seconds and multiplied by four to calculate a performance over one minute.

This is compared to a standard and then the performance reflects a sum of FEV1 and the neuromuscular status of a person. If FEVI is normal low MVV reflects muscle weakness or deconditioning of a person.



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