Diffusion Studies (Mod 5)

Question 1

What laws could influence diffusion?

Answer 1

• Ficks law
• Grahams law
• Henrys law

Question 2

What could be limitations on oxygen diffusion?

Answer 2

Abnormal increase in diffusion path due to:

• Fibrosis
• Interstital edema
• Alveolar fluid
• Interstitial fibrosis
• and things that disrupt the diffusion surface area (emphysema)

Question 3

What is diffusion?

Answer 3

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

Question 4

How is diffusion capacity measured?

Answer 4

SIngled breath CO diffusion test (DLCO)

• slide 14 add

Question 5

DLCO normal values

Answer 5

• slide 14 add

Question 6

DLCO equation?

Answer 6

• slide 14 add

Question 7

What does CO Diffusion capacity standardization depend on?

Answer 7

Capacity to exchange depends on structural and functional properties of the lung

Question 8

What structural properties of the lungs affect CO Diffusion capacity standardization?

Answer 8

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

Question 9

What properties properties of the lungs affect CO Diffusion capacity standardization?

Answer 9

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

Question 10

What is the biggest limitation to CO diffusion?

Answer 10

The A/C membrane itself

Question 11

Why is CO used for Diffusion capacity standardization?

Question 12

What is CO transfer dependant on for Diffusion capacity standardization?

Question 13

Indications for DLCO testing

Answer 13

To quantify impairment or diagnose the following parenchyma lung diseases:

• insert info from slide 20

Question 14

Clinical use of DLCO?

Answer 14

Assessment of gas diffusion across the a/c membrane

• add slide 19 crap

Question 15

Why is DLCO used before radiation therapy like chemo?

Answer 15

Radiation therapies stiffen up the lungs.

• also helps to check if there is any damage from the radiation therapy itself

Question 16

What factors could affect DLCO testing?

• what factors could increase the DLCO value?

Question 17

What factors could affect DLCO testing?

• what factors could decrease the DLCO value?

Question 18

Mueller maneuver vs Valsalva maneuver?

Answer 18

Both involve a closed glottis; both could scew the results of a DLCO test

1. Take a breath in against the glottis while closed (increase DLCO)
2. Take a breath out against a closed glottis

Question 19

Absolute contraindications for DLCO testing?

Answer 19

Carbon monoxide toxicity

• Dangerous levels of desaturation w/o supplemental oxygen
• Cut off is if they drop below 85% on room air

Question 20

Relative contraindications for DLCO testing?

Answer 20

• 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

Question 21

Hazards/complications of DLCO testing?

Answer 21

Single breath technique requires a breath hold at TLC

• interruption of supplemental oxygen, resulting in desaturations
• Transmission of infection

Question 22

How do vasalva or muller maneuvers affect cardiac output

Answer 22

They alter venous return to the heart and pulmonary capillary blood volume

• how?

Question 23

Add slides 29-34

Question 24

How much time should there be between DLCO tests?

Answer 24

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

Question 25

Ask again about washout volumes tomorrow for DLCO

Question 26

don’t need to know calculations for slides 39-40; just understand where they come from

Answer 26

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)

Question 27

Acceptable test criteria for DLCO testing?

Answer 27

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

Question 28

Reporting DLCO

Answer 28

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

Question 29

What is the limit of DLCO tests that should be conducted?

Answer 29

No more than 4 tests (slides say 5, keep this in mind tho)

Question 30

DLCO grading system?

Answer 30

slide 43

Question 31

VA vs Va?

Answer 31

• VA = Alveolar volume
• Va = Arterial volume