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Lung volumes & deadspace

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Physiology 3120
Tom Stavraky

Human Physiology Wednesday, February 3, 2010 “Respiratory III” Lung Volumes & Deadspace • Measure volumes by spirometry  Hook person up to tube  Every turn person inhales, bell moves down and pen moves up; vice-versa for exhalation • Volume definitions (using spirometry as basis)  Tidal volume: volume inhaled with each breath; usually around 500mL  Vital capacity: volume of air that can be forcibly exhaled after maximal inspiration  Residual volume: volume of air remaining in the lungs after maximal expiration  Cannot be measured with a spirometer (only measures movement of pen in response to ventilation)  Functional residual capacity: volume of air remaining in lungs after normal expiration  Inspiratory reserve volume: volume of air that can be forcibly inhaled following normal inspiration; becomes smaller as you exercise  Total lung capacity: volume of air in the lungs at the end of a maximal inspiration  Minute volume/pulmonary ventilation: volume inhaled per minute; calculated by TV x frequency of respiration  Forced expiratory volume-1 second (FEV-1sec): fraction of vital capacity expired in one second  About 80% in 1 sec normally  In asthmatic, this may decrease (<60%); airways are constricted  Maximum voluntary ventilation (MVV); a.k.a. maximal breathing capacity: volume that can be moved into and out of the lung in one minute by voluntary effort (about 125-170L per minute) • TLC, RV, and FRC cannot be measured using spirometry, but can use the helium dilution method  Doesn’t diffuse into blood, so doesn’t cross blood-gas barrier (stays in the lung)  By opening up valve, helium distributes itself in the lungs  Using the concentration/volume relationship, we can calculate these values • Deadspace  Airways don’t participate in gas exchange; referred to as anatomic deadspace; physiological deadspace is the volume of air entering the lung that
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