Spirometry
Spirometry (meaning the measuring of breath) is most common of pulmonary function tests(PFTs), measuring lung function, specifically the measurement of th amount (volume) and /or speed (flow) of air that can be inhaled and exhaled. Spirometry is an important tool used for generating pneumatochographs which are helpful in assessing contribution such as asthama, pulmonary fibrosis, cyclic fibrosis, and COPD
| Terminology /Measurement | Calculation | Description/Definitions |
|---|---|---|
| Total lung capacity(TLC) | =IRV+Vt+ ERV+RV | The volume of air contained in the lung at the end of maximal inspiration.The total volume of the lung(i.e.:the volume of air in the lungs after maximum inspiration). |
| Vitalcapacity (VC) | =IRV+Vt+ ERV | The amount of air that can be forced out of the lungs after a maximal inspiration. Emphasis on completeness of expiration. The maximum volume of air that can be volumatary moved in and out of the respiratory system. |
| Forced vital capacity(FVC) | measured | The amount of air that can be maximally forced out of the lungs after a maximal inspiration. Emphasis on speed. |
| Tidal volume(Vt) | measured | The amount of air breathed in or out during normal respiration. The volume of air an individual is normally breathing in and out. |
| Residual volume(RV) | measured | The amount of air left in the lungs after a maximal exhalation. The amount of air that is always in the lungs and can never be expired (I.e. the amount of air that stays in the lungs after maximum expiration.) |
| Expiratory reserve volume(ERV) | measured | The amount of additional air that can be pushed out after the end expiratory level of normal breathing. (At the end of a normal breath, the lungs contain the residual volume plus the expiratory reserve volume, or around 2.4 liters. If one then goes on and exhales as much as possible, only the residual volume of 1.2 liters remains.) |
| Functional residual capacity(FRC) | =ERV+RV | The amount of air left in the lungs after a tidal breath out. The amount of air that stays in the lungs during normal breathing. |
| Inspiratory reserve volume(IRV) | measured IRV=VC(TV+ERV) | The additional air that can be inhaled after a normal tidal breath in. The maximum volume of air that can be inspired in addition to the tidal volume. |
| Inspiratory capacity(IC) | =TV+IRV | The maximal volume that can be inspired following a normal expiration. |
| Anatomical dead space | measured | The volume of the conducting airways. Measured with fowler method. |
| Physiologic dead volume | The anatomical dead space plus the alveolar dead space |
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