Static Lung Volumes

Static Lung Volumes: Lung volumes measure during periods [blank_start]without[blank_end] air flow. Functional Residual Volume (FRC) Volume of gas in lungs at [blank_start]end expiratory[blank_end] level Typical: 2400 mL [blank_start]Decreased[blank_end] with restrictive disease [blank_start]Increased[blank_end] with obstructive disease (air trapping) FRC = ERV + [blank_start]RV[blank_end] FRC = [blank_start]TLC[blank_end] - IC Residual Volume (RV) Volume of gas in lungs after maximal [blank_start]expiration[blank_end]. TYpical: 1200 mL [blank_start]Decreased[blank_end] with restrictive disease [blank_start]Increased[blank_end] with obstructive disease RV = [blank_start]FRC[blank_end] - ERV RV = TLC - [blank_start]RV[blank_end] Total Lung Capacity (TLC) Volume of gas in the lungs following maximal [blank_start]inspiration[blank_end]. Typical: 6000 mL [blank_start]Decreased[blank_end] with restrictive disease [blank_start]Increased[blank_end] with obstructive disease TLC = IRV + [blank_start]VT[blank_end] + ERV + RV TLC = IC + [blank_start]FRC[blank_end] TLC = VC + [blank_start]RV[blank_end]

Increased Lung Volumes: [blank_start]Obstructive[blank_end] disease with [blank_start]air[blank_end] trapping Decreased Volumes: [blank_start]Restrictive[blank_end] diseases

Methods of Measuring Static Volumes He [blank_start]Dilution[blank_end] [blank_start]N2[blank_end] Washout Body [blank_start]Plethysmography[blank_end] [blank_start]Radiological[blank_end] Estimation

He Dilution Uses He in closed system to measure [blank_start]FRC[blank_end] Pt rebreathes known concentration of He ([blank_start]10[blank_end]%) mixed with Room air for up to [blank_start]7[blank_end] minutes. He is distributed throughout lungs until [blank_start]equilibrium[blank_end] is establish between [blank_start]lungs[blank_end] and spirometer. Switch-in should occur at end [blank_start]expiration[blank_end]. Initial and final [blank_start]He[blank_end] concentration are measured and FRC is [blank_start]calculated[blank_end]. EOT when He concentration changes by <.[blank_start]02[blank_end]% in [blank_start]30[blank_end] sec. Add small amounts of [blank_start]O2[blank_end] to replace O2 that is consumed. Measures FRC, ERV. [blank_start]TLC[blank_end] is calculated: RV + VC = TLC Requires a [blank_start]CO2[blank_end] absorber Deadspace is subtracted, add volume to correct for He absorbed in blood.

He Dilution QA Baseline should be flat and % He reading [blank_start]stable[blank_end] prior to switch-in Consistent baseline should be maintained by adding [blank_start]O2[blank_end] to the system Pattern of breathing with [blank_start]increased[blank_end] rate/depth means the [blank_start]CO2[blank_end] absorber needs replaced. EOT occurs when He concentration changes by <.[blank_start]02[blank_end]% in [blank_start]30[blank_end] seconds. Failure to achieve [blank_start]equilibrium[blank_end] indicates a leak. Wait [blank_start]10[blank_end]-[blank_start]15[blank_end] minutes in between tests Report the [blank_start]mean[blank_end] of [blank_start]3[blank_end] acceptable tests.

N2 Washout Measures [blank_start]FRC[blank_end] by replacing N2 in lungs with O2. Pt rebreathes [blank_start]100[blank_end]% O2 for up to 7 minutes or until N2 < [blank_start]1[blank_end]%. Final value of expired N2 = .[blank_start]01[blank_end] Normal lungs will washout in [blank_start]3[blank_end] minutes or less, obstructed pts may not washout completely. Switch in occurs at [blank_start]end expiration[blank_end]. Exhaled gases are collected and final %[blank_start]N2[blank_end] is used to calculated FRC Open circuit method, rapid analyzer gives breath by breath analyzation. Analyzer failure will spike [blank_start]O2[blank_end] but then go back to normal.

N2 Washout QA Normal lungs washout in <3 minutes EOT occurs when N2% changes < [blank_start]1.5[blank_end]% over 3 breaths. Allow [blank_start]15[blank_end] minutes in between tests Report [blank_start]mean[blank_end] of [blank_start]2[blank_end] acceptable tests that are within [blank_start]10[blank_end]% of each other. Zero the N2 analyzer with [blank_start]100[blank_end]% O2.

Body Plethysmogaph Measures: FRC, Vtg (same as [blank_start]FRC[blank_end]), TLC, RV/TLC, Raw. Pt breathes normally for several breaths, then at end exp the shutter closes and pt [blank_start]pants[blank_end]. No [blank_start]airflow[blank_end] is present. Pmouth = [blank_start]Palveolar[blank_end] (plotted [blank_start]vertically[blank_end]) 2nd transducer measure Pbox Pbox = [blank_start]Vtg[blank_end] (plotted [blank_start]horizontally[blank_end]) [blank_start]Boyle's[blank_end] law is used to calculate Vtg: P1V1 - P2V2 Measures trapped gases not in communication with [blank_start]airways[blank_end] Angle of P-V loop should be [blank_start]45[blank_end] degrees. Flattened loop displaced downward = [blank_start]restrictive[blank_end] disease

Body Plethysmograph QA Pmouth transducer: with water or Hg [blank_start]barometer[blank_end] [blank_start]Pbox[blank_end] transducer: with sinewave pump Flow Transducer: [blank_start]Rotameter[blank_end] QC is done using an [blank_start]isothermal[blank_end] lung model to validate the volume measuring ability. Should be within [blank_start]5[blank_end]% of actual volume.

Radiological Estimation of TLC CXR are taken at TLC both [blank_start]laterally[blank_end] and P-A Standard points are marked on image and measurements made and geometric [blank_start]formulas[blank_end] are used to calculate static lung volumes Useful in pts unable to perform [blank_start]tests[blank_end].

Body Plethysmography QA A [blank_start]closed[blank_end] Pmouth/Pbox loop indicates patient panted correctly Open loops indicates compression of gas in [blank_start]oropharynx[blank_end], a [blank_start]leak[blank_end], or patient is panting too [blank_start]fast[blank_end] Minimum of 3 acceptable panting maneuvers should be obtained and [blank_start]Vtg[blank_end] within [blank_start]5[blank_end]% of each other. Gentle pants at end expiration at frequencies of [blank_start].5[blank_end] - [blank_start]1.0[blank_end] Hz

Body Plethysmograph Based on [blank_start]Boyle’s[blank_end] law that pressure and volume vary [blank_start]inversely[blank_end] if the [blank_start]temperature[blank_end] is constant. Measures: Thoracic Gas Volume ([blank_start]Vtg[blank_end]) which equals the [blank_start]FRC[blank_end] and [blank_start]Raw[blank_end] Incorporates a [blank_start]shutter[blank_end] which eliminates [blank_start]pressure[blank_end] changes brought about by [blank_start]airflow[blank_end] or airway resistance Calibration: Pmouth with Hg or water [blank_start]barometer[blank_end] Flows: verified w/[blank_start]rotameter[blank_end] P[blank_start]box[blank_end]: Calibrated with a sine wave pump. More accurately measures FRC in [blank_start]obstructive[blank_end] disease Disadvantages: Pt physical limitations, claustrophobia, unacceptable panting. The Vent in the box allows [blank_start]heat[blank_end] to escape.