Measurement of lung volumes provides a tool for understanding normal function of the lungs as well as disease states.
| Parameter | Description |
|---|---|
| Tidal Volume | volume of air inspired & expired with each normal breath. Normal TV is approximately 500 ml |
| Inspiratory Reserve Volume | Additional volume that can be inspired above tidal volume. Normal IRV is approximately 3000 ml |
| Expiratory Reserve Volume | Additional volume that can be expired below tidal volume. Normal ERV is approximately 1000 ml |
| Residual Volume | the volume of air remaining in the lungs after forced expiration. Normal R.V is approximately 1200 ml can not be measured with spirometry |
| Functional Residual Capacity | Is R.V+ ERV. Normal FRC is approximately 2200 ml. Is the volume remaining in the lung after normal tidal Volume is expired. |
| Vital Capacity | Is IRV+TV+ ERV. Normal VC is approximately 4600 ml. Is the volume that can be expired after maximal inspiratory effort |
| Total lung Capacity | Is VC+RV. Normal TLC is approximately 5700 ml. Is the maximum volume to which lungs can be expanded with greatest possible efforts. |
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(Ganong)The amount of air that moves into the lungs with each inspiration (or the amount that moves out with each expiration) is called the tidal volume. The air inspired with a maximal inspiratory effort in excess of the tidal volume is the inspiratory reserve volume. The volume expelled by an active expiratory effort after passive expiration is the expiratory reserve volume, and the air left in the lungs after a maximal expiratory effort is the residual volume. Normal values for these lung volumes, and names applied to combinations of them, are shown in .The space in the conducting zone of the airways occupied by gas that does not exchange with blood in the pulmonary vessels is the respiratory dead space. The vital capacity, the largest amount of air that can be expired after a maximal inspiratory effort, is frequently measured clinically as an index of pulmonary function. It gives useful information about the strength of the respiratory muscles and other aspects of pulmonary function. The fraction of the vital capacity expired during the first second of a forced expiration (FEV1, timed vital capacity, gives additional information; the vital capacity may be normal but the FEV1 reduced in diseases such as asthma, in which airway resistance is increased because of bronchial constriction. The amount of air inspired per minute (pulmonary ventilation, respiratory minute volume) is normally about 6 L (500 mL/breath × 12 breaths/min). The maximal voluntary ventilation (MVV), or, as it was formerly called, the maximal breathing capacity, is the largest volume of gas that can be moved into and out of the lungs in 1 minute by voluntary effort. The normal MVV is 125-170 L/min.