Lung Testing E: Resp muscle strength, DLCO

Question 1

What is the value of a typical MIP? (Include units)

Answer 1

-60 cm H2O

Question 2

What is the value of a typical MEP? (Include units)

Answer 2

80-100 cm H2O

Question 3

Name one condition in which inspiratory strength will be decreased.
What three conditions affect expiratory strength?
What two conditions affect both inspiratory and expiratory strength?

Answer 3

Inspiratory strength: Chest wall/spinal deformities
Expiratory strength: Neuromuscular diseases, emphysema, chronic bronchitis, cystic fibrosis, and inability to cough.
Neuromuscular diseases and emphysema affect both insp. & exp strength.

Question 4

What is the definition of DLCO?

Answer 4

Measurement of how well carbon monoxide can diffuse across the AC membrane.

Question 5

What is the normal DLCO value (Include units)

Answer 5

25 mLCO/min/mmHg STPD

Question 6

How do hemoglobin/hematocrit levels affect DLCO?

Answer 6

More or less sites are available on the hemoglobin molecule for CO binding.

Question 7

How does alveolar PCO2 affect DLCO?

Answer 7

Increases in PACO2 will increase DLCO because the PAO2 will be decreased.

Question 8

How does carboxyhemoglobin (COHb) affect DLCO? If there is a 1% increase in COHb, how much of an increase or decrease in DLCO will there be?

Answer 8

Increased COHb will decrease DLCO because of backpressure. 1% increase in COHb will decrease DLCO by 1%.

Question 9

How does body position affect DLCO?

Answer 9

Supine position will increase DLCO because of increased capillary blood flow compared to sitting upright.

Question 10

How does altitude affect DLCO?

Answer 10

Increasing altitude will increase DLCO due to decreasing PAO2.

Question 11

How much alveolar sample is collected for analysis?

Answer 11

0.5 - 1 liter

Question 12

With DLCO, what is a wash-out volume?

Answer 12

Volume discarded prior to collecting the alveolar sample. Normally 1 liter or less.

Question 13

Before taking a DLCO test, how long should the patient abstain from smoking?
What else should the patient avoid?

Answer 13

48 hrs

Avoid heavy exertion

Question 14

What is the formula for calculating DLCO?

Answer 14

V CO ML of CO diffusion per min
DLCO = ——- = —————————————–
PACO Alveolar partial pressure of CO

Question 15

How much do DLCO values increase during exercise?

Answer 15

2-3 times

Question 16

In what kind of diseases would you expect decreased DLCO values?

Answer 16

Restrictive diseases

Question 17

There is only one obstructive disease that will reduce DLCO. What is it?

Answer 17

Emphysema (Loss of surface area)

Question 18

How can air be introduced into the sample while doing a DLCO? What will this cause?

Answer 18

Tight seal not maintained or a leak is present.

Falsely increased DLCO

Question 19

When doing a DLCO, unidirectional valves must have: (x3)

Answer 19

Have low deadspace
Low resistance to flow to allow full inhalation & exhalation
Be easy to maintain to prevent increased resistance and leaks

Question 20

What if air dilutes the exhaled gas from a DLCO SB?

Answer 20

Both the calculated DLCO and the VA values will be erroneously increased.

Question 21

Will tracheal stenosis affect the DLCO SB? (Yes/No)

Answer 21

NO!
(Note that the DLCO SB is the most commonly used technique for measuring the diffusion capacity in the clinical setting.)

Question 22

What effect will polycythemia have on DLCO?

Answer 22

Polycythemia will increase the DLCO above 100% of predicted.

Question 23

When a patient does a DLCO SB (DLCO single breath), how big a breath does the patient need to take?

Answer 23

85% of the vital capacity

Question 24

What is the procedure for doing a DLCO SB?

Answer 24

1. Patient exhales to RV.
2. Patient inhales to TLC
3. Patient holds his breath for 10 seconds, then exhales rapidly.

Question 25

When a patient inhales when doing his DLCO SB, what is the composition of gas he inhales?

Answer 25

3% Carbon Monoxide
10% Helium
21% Oxygen
and some N2.

Question 26

Why does the patient inhale helium when doing a DLCO SB? (x2)

Answer 26

Corrects for trapped carbon monoxide in the RV.

Also serves as a carrier gas for carbon monoxide to the alveolar level.

Question 27

DLCO SB: The first portion of the exhaled sample is called ___. It is usually ___ mL.
This portion should be reduced to ___ mL if the FRC is small.
The next portion is collected. It is ___ to ___ mL.

Answer 27

“Washout volume” 750-1000 ml.
500 mL
500-1000 ml

Question 28

What data is collected and used to calculate DLCO? (x4)

Answer 28

Initial and final CO
Initial and final He
Inspired and alveolar volume
Breath hold time