Diffusion Studies (Mod 5) Flashcards
What laws could influence diffusion?
- Ficks law
- Grahams law
- Henrys law
What could be limitations on oxygen diffusion?
Abnormal increase in diffusion path due to:
- Fibrosis
- Interstital edema
- Alveolar fluid
- Interstitial fibrosis
- and things that disrupt the diffusion surface area (emphysema)
What is diffusion?
Net movement of molecules; From high to low concentrations; From high to low pressures
- Diffusion gradient
- Diffusion across alveolar capillary membrane
(O2 and CO2) - Contnues until equilbrium is reached
How is diffusion capacity measured?
SIngled breath CO diffusion test (DLCO)
- slide 14 add
DLCO normal values
- slide 14 add
DLCO equation?
- slide 14 add
What does CO Diffusion capacity standardization depend on?
Capacity to exchange depends on structural and functional properties of the lung
What structural properties of the lungs affect CO Diffusion capacity standardization?
Lung gas volume
- path length for diffusion
- Thickness and area of the A/C membrane
- Effects of airway closure
- Amount of blood in capillaries supplying ventilated alveoli
What properties properties of the lungs affect CO Diffusion capacity standardization?
Absolute levels of ventilation and perfusion
- distribution of ventilation and perfusion, relative to one another (V/Q?)
- Compsition of alveolar gas
- Diffusion characteristics of the A/C membrane
- Concentration and binding components of hemoglobin
- Partial pressure of gas in the blood coming back to the lungs
What is the biggest limitation to CO diffusion?
The A/C membrane itself
Why is CO used for Diffusion capacity standardization?
What is CO transfer dependant on for Diffusion capacity standardization?
Indications for DLCO testing
To quantify impairment or diagnose the following parenchyma lung diseases:
- insert info from slide 20
Clinical use of DLCO?
Assessment of gas diffusion across the a/c membrane
- add slide 19 crap
Why is DLCO used before radiation therapy like chemo?
Radiation therapies stiffen up the lungs.
- also helps to check if there is any damage from the radiation therapy itself
What factors could affect DLCO testing?
- what factors could increase the DLCO value?
What factors could affect DLCO testing?
- what factors could decrease the DLCO value?
Mueller maneuver vs Valsalva maneuver?
Both involve a closed glottis; both could scew the results of a DLCO test
- Take a breath in against the glottis while closed (increase DLCO)
- Take a breath out against a closed glottis
Absolute contraindications for DLCO testing?
Carbon monoxide toxicity
- Dangerous levels of desaturation w/o supplemental oxygen
- Cut off is if they drop below 85% on room air
Relative contraindications for DLCO testing?
- Mental confusion or muscular in coordination (or inability to perform/fatigue)
- Inadequate lip seal on mouth piece
- Large meal or vigorous exercise immediately prior to the test
- Smoking within 1 hours of the test
Hazards/complications of DLCO testing?
Single breath technique requires a breath hold at TLC
- interruption of supplemental oxygen, resulting in desaturations
- Transmission of infection
How do vasalva or muller maneuvers affect cardiac output
They alter venous return to the heart and pulmonary capillary blood volume
- how?
Add slides 29-34
How much time should there be between DLCO tests?
4 mins between tests
- allows gas to eliminated from the lungs
- longer times should be considered for COPD pts (10mins)
- Subject remain seated
- Deep inspirations in this period could encourage test gas elimination
Ask again about washout volumes tomorrow for DLCO
don’t need to know calculations for slides 39-40; just understand where they come from
I believe these slides identify where the tracer gasses go, so it doesn’t mean it’s necessarily for DLCO testing, could be for helium as well (slide 40)
Acceptable test criteria for DLCO testing?
Proper quality controlled equipment
- inspired volume of >85% of largest VC in < 4 secs
- Stable calculated breath hold for 10 (+/-) 2 secs
- Expiration in <4s and sample collection time <3 secs
Reporting DLCO
Report the average of test results
- 2 acceptable tests required ; they should be within 2 ml of CO/min/mmHg of each other or within 10% of the highest value
- DLCO should be adjusted for Hb, COhb, PiO2
What is the limit of DLCO tests that should be conducted?
No more than 4 tests (slides say 5, keep this in mind tho)
DLCO grading system?
slide 43
VA vs Va?
- VA = Alveolar volume
- Va = Arterial volume
