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Resting Lung Volumes An Introduction to Spirometry

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Spirometer Tracing

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Measurement Static lung volumes can be measured using a spirometer creating a paper trace Residual lung volume measurement is difficult because the volume can not be exhaled We will use a method known as nitrogen dilution

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Residual Lung Volume The volume of air left in the lungs after a maximal expiration Small passageways close before all of the air from the alveoli is expelled If the alveoli were to be completely emptied, they would stick together and be very difficult to reopen

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Why measure RV? Basic scientific interest Get an accurate density from hydrostatic weighing Determine whether or not it aids performance in sports (especially of interest are water sports) Determine whether it is anatomical or can change based on training

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Basic Procedure Subject maximally expires to residual volume Subject breathes in and out 100% oxygen from a spirometer (of a known volume) After an equilibrium has been reached the Nitrogen level in the spirometer is measured

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Nitrogen Dilution Technique Nitrogen is metabolically inert (it is neither produced nor consumed by the body) Nitrogen dilution is merely balancing an equation Initial Amount of N 2 = Final Amount N 2

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Components of Initial Amount of N 2 Nitrogen in the Spirometer F N 2 i spirometer x V i spirometer *Spirometer Volumes include the bell volume and the dead space Nitrogen in the Lungs F N 2 i Lung x RV –F N 2 i Lung is the fraction of Nitrogen inspired (79%) –RV is the Residual Volume

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Components of Final Amount of N2 Nitrogen in the connected system of the spirometer and lungs measured during equilibrium F N 2 f x V f –F N 2 f The fraction of nitrogen in the lungs and spirometer at equilibrium A measured variable –V f The sum of the volume of the spirometer (including both the dead space and the bell) and the Residual Volume

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Distribution of Nitrogen in the System

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Calculating RV Using the information on the last three slides RV can be calculated from the three measured variables (initial fraction N 2, final fraction N 2, and initial spirometer volume) The BTPS correction factor must be used to determine the actual volume of gas in the conditions inside the lungs

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Dynamic Lung Volumes Forced Expiratory Volume in 1.0 seconds (FEV 1.0) Forced Expiratory Volume in 3.0 seconds (FEV 3.0) Maximum Voluntary Ventilation (MVV)

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Forced Expiratory Volumes The percent of vital capacity expelled in a set time period Give indications of health problems not of fitness or training FEV 1.0 normal value ~80% of FVC FEV 3.0 normal value ~98% of FVC

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FEV Spirometer Examples

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Maximum Voluntary Ventilation Maximum amount that can be exhaled per unit time Usually measured over 12 seconds Units are in L/min Debatable application to fitness, training status, or athletic performance

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Factors Influencing Lung Volumes Height Gender Age Ethnic Background Disease These factors are used in determining prediction equations for lung volumes

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Standardizing Gas Volumes Gas volumes change as temperature and pressure change These relationships are determined by Charles’ Law and Boyle’s Law

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Water Vapor Pressure The amount of water vapor that can be held in the air increases as temperature increases This increases the pressure measured Therefore when gas volumes are measured the water vapor pressure must be taken into account as part of the pressure change

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Correction Factors The difference in conditions between the lab (where the volume is measured) and inside the body (the volume we are hoping to determine) must be corrected for

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BTPS/STPD Correction The conditions in the lab are called ATPS or ambient temperature pressure and saturation In order for comparison of volumes in different circumstances STPD or the standard temperature and pressure dry is used In order to determine the actual volume of air that the lungs contain, BTPS or body temperature pressure and saturation conditions are used

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