Sunday, March 10, 2013

Changes in volume





Lung Volumes


There are several lung volumes and capacities that are useful to understand respiratory physiology and they are briefly described below.


Tidal Volume

Is the amount of air that moves into the lungs with each inspiration (or the amount that moves out of the lungs with each expiration). 

Inspiratory Reserve Volume (IRV) 

The air inspired with a maximal inspiratory effort in excess of the tidal volume is the.

Expiratory Reserve Volume (ERV) 


The volume expelled by an active expiratory effort after passive expiration. 


Residual Volume



Is volume of air left in the lungs after a maximal expiratory effort. 
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 forced vital capacity (FVC), 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 is referred to as FEV1 (formerly the timed vital capacity). 

The FEV1 to FVC ratio (FEV1/FVC) is a useful tool in the diagnosis of airway disease. The amount of air inspired per minute (pulmonary ventilation, respiratory minute volume) is normally about 6 L (500 mL/ breath x 12 breaths/min). The maximal voluntary ventilation (MVV) is the largest volume of gas that can be moved into and out of the lungs in 1 min by voluntary effort. The normal MVV is 125 to 170 L/min.


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