Static Lung Volumes

Static Lung Volumes: Lung volumes measure during periods air flow.

Functional Residual Volume (FRC)
Volume of gas in lungs at level
Typical: 2400 mL
with restrictive disease
with obstructive disease (air trapping)
FRC = ERV +
FRC = - IC

Residual Volume (RV)
Volume of gas in lungs after maximal .
TYpical: 1200 mL
with restrictive disease
with obstructive disease
RV = - ERV
RV = TLC -
Total Lung Capacity (TLC)
Volume of gas in the lungs following maximal .

Typical: 6000 mL
with restrictive disease
with obstructive disease
TLC = IRV + + ERV + RV
TLC = IC +
TLC = VC +

Increased Lung Volumes: disease with trapping

Decreased Volumes: diseases

Methods of Measuring Static Volumes
He
Washout
Body
Estimation

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

He Dilution QA

Baseline should be flat and % He reading prior to switch-in
Consistent baseline should be maintained by adding to the system
Pattern of breathing with rate/depth means the absorber needs replaced.
EOT occurs when He concentration changes by <.% in seconds.
Failure to achieve indicates a leak.
Wait - minutes in between tests
Report the of acceptable tests.

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

N2 Washout QA
Normal lungs washout in <3 minutes
EOT occurs when N2% changes < % over 3 breaths.
Allow minutes in between tests
Report of acceptable tests that are within % of each other.
Zero the N2 analyzer with % O2.

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

Body Plethysmograph QA
Pmouth transducer: with water or Hg
transducer: with sinewave pump
Flow Transducer:
QC is done using an lung model to validate the volume measuring ability.
Should be within % of actual volume.

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

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

Body Plethysmograph
Based on law that pressure and volume vary if the is constant.
Measures: Thoracic Gas Volume () which equals the and
Incorporates a which eliminates changes brought about by or airway resistance

Calibration:
Pmouth with Hg or water
Flows: verified w/
P: Calibrated with a sine wave pump.

More accurately measures FRC in disease
Disadvantages: Pt physical limitations, claustrophobia, unacceptable panting.

The Vent in the box allows to escape.