LUNG VOLUMES
www.propofology.com
Dr. David Lyness
@Gas_Craic
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RV increases with age to a max of approximately 3L. FRC also increases.
IC & VC decrease with age.
Only FRC, RV and TLC cannot be measured with spirometry (use a plethysmograph).
Only FRC, RV and TLC cannot be measured with spirometry (use a plethysmograph).
To know RV and FRC you need to know TLC!
All measurements are at body temp and pressure saturated.
All measurements are at body temp and pressure saturated.
When anaesthetised lungs = end tidal expiration volume - this is why
filling FRC with 02 vital for pre oxygenation.
Plethysmograph = patient is placed inside a sealed chamber with a single mouthpiece. At the end of normal expiration, the mouthpiece is closed. The patient is then asked to make an inspiratory effort. As the patient tries to inhale, the lungs expand, decreasing pressure within the lungs and increasing lung volume. This, in turn, increases the pressure within the box since it is a closed system and the volume of the box compartment has decreased to accommodate the new volume of the subject.
You can see airflow resistance using a plethysmograph.
Boyle's Law is used to calculate the unknown volume within the lungs - pressure of a given mass of an ideal gas is inversely proportional to its volume at a constant temperature. You can see pressure changes in the box and those calculate volume.
The pressure change is representative of the WHOLE lungs and will give you total lung capacity...
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