Resting Lung Volumes

Resting Lung Volumes An Introduction to Spirometry

Spirometer Tracing

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

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

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

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

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 N2 = Final Amount N2

Components of Initial Amount of N2 • Nitrogen in the Spirometer FN2ispirometer x Vispirometer *Spirometer Volumes include the bell volume and the dead space • Nitrogen in the Lungs FN2iLung x RV • FN2iLung is the fraction of Nitrogen inspired (79%) • RV is the Residual Volume

Components of Final Amount of N2 • Nitrogen in the connected system of the spirometer and lungs measured during equilibrium FN2f x Vf • FN2f • The fraction of nitrogen in the lungs and spirometer at equilibrium • A measured variable • Vf • The sum of the volume of the spirometer (including both the dead space and the bell) and the Residual Volume

Distribution of Nitrogen in the System

Calculating RV • Using the information on the last three slides RV can be calculated from the three measured variables (initial fraction N2, final fraction N2, and initial spirometer volume) • The BTPS correction factor must be used to determine the actual volume of gas in the conditions inside the lungs

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)

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

FEV Spirometer Examples

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

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

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

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

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

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

Resting Lung Volumes