Pulmonary Gas Distribution Flashcards
What does a single breath N2 elimination test (SB N2) measure?
- evenness of distribution of inspired gases
- closing volume/closing capacity
What does phase I of closing volume/closing capacity represent?
deadspace (100% O2, no N2)
What does phase II of closing volume/closing capacity represent?
combination of deadspace and alveolar gases (N2 gases begin to increase)
What does phase III of closing volume/closing capacity represent?
alveolar gas
How is the evenness of gas distribution in phase III shown on the closing volume/closing capacity?
- mid-portion of the test is flat
- poor distribution slants up more
What is phase IV of the closing volume/closing capacity?
- shows a sudden rise in the N2%
- called the closing volume (airway closure)
- airway closure of dependent regions
- reason compression of lower airways
What is the closing capacity?
the adding of the closing volume to the RV
What other tests measure the distribution of gases?
ventilation scans
How is the closing volume affected with obstructive disease?
- closing volume is elevated
- slow of phase III is increased
What does DLCO stand for?
carbon monoxide diffusion capacity
What does DLCO measure?
- all the factors that affect the diffusion of a gas across the A-C membrane
- measured in ml/min/mmHg
What is normal DLCO?
25 mL/min/mmHg
What factors affect DLCO?
- Hb, Hct
- body position
- breath holding time
- lung volume
- smoking
What does an increase in eosinophils cause?
increase in inflammation
What does decreased DLCO occur in?
- pulmonary fibrosis
- sarcoidosis
- ARDS
- edema
What does increased DLCO occur in?
- exercise
- asthma
- obesity
- polycythemia
- intralveolar hemorrhage, L to R intracardiac shunts
In corrected alveolar volume, a pure reduction in DLCO can represent ___
small lungs
Why should you compare decreased DLCO to alveolar volume?
to evaluate alveolar-capillary membrane abnormalities
What are the first three patient performance standards (ATS)?
- all patients should be carefully instructed on the procedure
- the therapist should demonstrate the procedure to the patient
- a minimum of three (3) acceptable procedures should be recorded
What are the last four patient performance standards (ATS)?
- no false starts
- test should not differ by more than 5%
- “best test” should be determined and recorded
- “best test” = highest FVC and FEV1
What are the measurement principles?
- specificity
- sensitivity
- validity
- reliability
What does specificity mean?
how we known it is valid. ratio of true negative results to the patient’s results
What does sensitivity mean?
ratio of true positive results to the patient’s results
What are the steps of infection control?
- standard precautions
- clean mouthpiece, tubing
- low resistance bacteria filter
- handwashing
- do not have to routinely clean interior
