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BACKGROUND
The total amount of air that the subject inhales and exhales depends on the condition of the lungs of the subject. There are many respiratory volumes namely tidal volume, inspiratory reserve volume, expiratory reserve volume and residual volume. These respiratory volumes can be combined in specific ways to obtain respiratory capacities namely vital capacity, functional residual capacity, inspiratory capacity and lastly the total lung capacity.
Tidal volume (VT) is the total amount of air that is inspired or expired during normal breathing when the subject is at rest. This is around 500 ml of air per breath. The vital capacity (VC) is the total amount of air that is exchanged with the atmosphere. This is the sum total of tidal volume, inspiratory reserve volume and expiratory reserve volume.1
The aim of the study is to determine the tidal volume and vital capacity.
The measurements of respiratory volumes and respiratory capacities are collectively called as pulmonary function tests. Spirometry measures the volume and speed of airflow moving in and out of the lungs using standard equipment called as spirometer.
Source: Wikipedia
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REQUIREMENTS
Subjects: Human
Apparatus: Spirometer
Disposable sterile mouth piece
Alcohol swabs
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PROCEDURE
The subject sits straight and comfortably in a chair next to the spirometer. The disposable sterile mouth piece is attached and made sure the needle is positioned at “0”. The spirometer has to be held at the base of the equipment. The subject’s nostrils have to be pinched so as to prevent the escape of air through the nasal airway while blowing through the spirometer. The mouthpiece is placed between lips loosely, through the corner of the mouth and the subject is asked to breathe normally to establish a normal breathing pattern. To complete this procedure, it takes around 15 minutes.
Measurement of tidal volume
The subject exhales into the spirometer for the next 5 successive breaths. The reading on the spirometer has to be recorded for a total of the 5 breaths and divide it by 5 to calculate the average volume. This value is the average Tidal Volume in ml.2
Measurement of vital capacity
The subject inhales as deeply as possible and then without a pause exhales all the air into the spirometer. Care should be taken by the subject while exhaling as the air should not escape from the corner of the sterile mouthpiece. The lungs should be empty after exhalation. The value on the spirometer is recorded. Wait for 15-30 seconds to repeat this process again the second time. Wait again for 15-30 seconds to repeat this process for the third time. The largest volume exhaled noted on the spirometer among the three attempts is the Vital Capacity in ml. The spirometer is disinfected using an alcohol swab.2
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CONCLUSION
Spirometry is a method of assessing the lung functions by measuring the total volume of air expelled from the lungs of the subject after a maximal inhalation. This helps in diagnosis of lung diseases namely obstructive and restrictive lung diseases.
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REFERENCES
- www.indiana.edu-Lab#11: Respiratory physiology
- https;//www.nsd.org
