What does Helium Solution method use to measure FRC
Closed system
Describe the steps in the Helium Solution technique
Pt rebreathes a known concentration 10% of Helium mixed with room air from a spirometer for up to 10 minutes
When should the “switch in” occur during the helium dilution method
End of normal exhalation when only the FRC is left in the lungs
How is the patients FRC calculated using the helium dilution method
Helium analyzer, Wheatstone bridge, thermal conductivity
With helium dilution, when does “end of test” occur
Concentration change <0.02% change over 30 seconds or maximum 10 minute test
Why is it important to keep a consistent baseline during helium dilution
Need oxygen to stabilize volume
What does helium dilution technique directly measure
FRC
What does the helium dilution method utilize and require
A closed system and requires a scrubber
For helium dilution what 2 volumes must be subtracted and why
Small volume of FRC to account for helium absorbed in blood, dead space from breathing valve
What does nitrogen washout measure
FRC
How is nitrogen washout accomplished
100% oxygen until nitrogen concentration is <1.5% for 3 breaths
