Introduction.
Respiration volume refers to the gas volume in the lungs at a particular time during the respiratory cycle. The measurement of lung volumes is very integral to the pulmonary function test. An adult male has about six liters of air as the average total lung capacity. Factors such as gender, ethnicity, body composition, and age tend to make the volumes vary.
Lung Capacity.
Lung capacities can be derived from a summation of various lung volumes
- Tidal Volume- the amount of air inhaled or exhaled during one breathing cycle. Shows the various mechanics of the respiratory muscles and centers and their respective functions. A normal adult’s value is about 10% of the vital capacity.
- Inspiratory Reserve Volume, the amount of air usually kept in reserve that can be forcibly inhaled during deep breathing beyond a tidal inhalation. The normal adult’s value is 1900-3300ml.
- Expiratory reserve volume, it is the amount of air forcibly exhaled beyond a tidal exhalation. In adults, it’s about 1200ml and 700.
- Residue Volume, the remaining amount of air in the lungs after an expiratory reserve volume. It’s about 1200ml in adults.
Lung capacities include:
- Inspiratory capacity, calculated as the sum of tidal volume and inspiratory reserve volume. Essentially it is the volume of air that can be inhaled during a state of rest.
- Total Lung Capacity, derived from a summation of the four lung volumes. It is the maximum volume of air the lungs can accommodate after a maximum inspiration.
- Vital Capacity, calculated by the summation of tidal volume, expiratory reserve volume, and inspiratory reserve volume. It is the total amount of exhaled air after a maximum inhalation. It reflects expiratory and inspiratory muscle strength and the ability to cough and take deep breaths.
- Functional Residue Capacity, calculated from the summation of expiratory reserve and residual volumes. It is the remaining amount of air in the lungs beyond an exhalation.
Lung volume measurement.
Lung volume measurements are necessary for correct physiological diagnosis.The lung volumes can be measured by inspiratory reserve volume, Spirometry-Tidal volume, and Expiratory reserve volume. Measurement of Functional residual capacity, residual volume, and Total lung capacity are through nitrogen washout, body plethysmography, and the helium dilution technique. Body plethysmography employs Boyle’s law. Nitrogen washout technique is based on the removal of nitrogen from the lungs, while a person breathes 100% oxygen through dilution properties of gases.
