Lung Testing E: Resp muscle strength, DLCO Flashcards
What is the value of a typical MIP? (Include units)
-60 cm H2O
What is the value of a typical MEP? (Include units)
80-100 cm H2O
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?
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.
What is the definition of DLCO?
Measurement of how well carbon monoxide can diffuse across the AC membrane.
What is the normal DLCO value (Include units)
25 mLCO/min/mmHg STPD
How do hemoglobin/hematocrit levels affect DLCO?
More or less sites are available on the hemoglobin molecule for CO binding.
How does alveolar PCO2 affect DLCO?
Increases in PACO2 will increase DLCO because the PAO2 will be decreased.
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?
Increased COHb will decrease DLCO because of backpressure. 1% increase in COHb will decrease DLCO by 1%.
How does body position affect DLCO?
Supine position will increase DLCO because of increased capillary blood flow compared to sitting upright.
How does altitude affect DLCO?
Increasing altitude will increase DLCO due to decreasing PAO2.
How much alveolar sample is collected for analysis?
0.5 - 1 liter
With DLCO, what is a wash-out volume?
Volume discarded prior to collecting the alveolar sample. Normally 1 liter or less.
Before taking a DLCO test, how long should the patient abstain from smoking?
What else should the patient avoid?
48 hrs
Avoid heavy exertion
What is the formula for calculating DLCO?
V CO ML of CO diffusion per min
DLCO = ——- = —————————————–
PACO Alveolar partial pressure of CO
How much do DLCO values increase during exercise?
2-3 times
In what kind of diseases would you expect decreased DLCO values?
Restrictive diseases
There is only one obstructive disease that will reduce DLCO. What is it?
Emphysema (Loss of surface area)
How can air be introduced into the sample while doing a DLCO? What will this cause?
Tight seal not maintained or a leak is present.
Falsely increased DLCO
When doing a DLCO, unidirectional valves must have: (x3)
Have low deadspace
Low resistance to flow to allow full inhalation & exhalation
Be easy to maintain to prevent increased resistance and leaks
What if air dilutes the exhaled gas from a DLCO SB?
Both the calculated DLCO and the VA values will be erroneously increased.
Will tracheal stenosis affect the DLCO SB? (Yes/No)
NO!
(Note that the DLCO SB is the most commonly used technique for measuring the diffusion capacity in the clinical setting.)
What effect will polycythemia have on DLCO?
Polycythemia will increase the DLCO above 100% of predicted.
When a patient does a DLCO SB (DLCO single breath), how big a breath does the patient need to take?
85% of the vital capacity
What is the procedure for doing a DLCO SB?
- Patient exhales to RV.
- Patient inhales to TLC
- Patient holds his breath for 10 seconds, then exhales rapidly.
When a patient inhales when doing his DLCO SB, what is the composition of gas he inhales?
3% Carbon Monoxide
10% Helium
21% Oxygen
and some N2.
Why does the patient inhale helium when doing a DLCO SB? (x2)
Corrects for trapped carbon monoxide in the RV.
Also serves as a carrier gas for carbon monoxide to the alveolar level.
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.
“Washout volume” 750-1000 ml.
500 mL
500-1000 ml
What data is collected and used to calculate DLCO? (x4)
Initial and final CO
Initial and final He
Inspired and alveolar volume
Breath hold time
