Chapter 10 - PFT

Question 1

During forced expression, what is flow limitation determined by?

Answer 1

Determined by elastic recoil force of the lung and resistance of the airways upstream of the collapse point

Question 2

In restrictive diseases, what is the flow rate in relations to the absolute lung volume at the latter part of expiration?

Obstructive disease?

Answer 2

Restrictive - abnormally high because of increased lung recoil

Obstructive - low in relation to lung volume, scooped appearance

Question 3

What causes reduction in FEV1?

Answer 3

increase in airway resistance or a reduction in elastic recoil of the lung

Question 4

in MBW, How much is the concentration of N2 in a a breath compared to the previous breath?

Answer 4

The N2 concentration is FRC/[FRC + (VT-VD)] times that of the previous breath

Question 5

What is responsible for the long tail of the washout in MBW?

Answer 5

slow-ventilated spaces are responsible for the long tail

Question 6

How can inequality of the V/Q ratios be measured?

Answer 6

1. A-a difference
2. Shunt equation
   QPS/QT = (CiO2 - CaO2)/ (CiO2 - CvO2)
3. Alveolar dead space equation
   VD/VT = (PaCO2 - PECO2)/PaCO2

Question 7

What are two causes of an increased arterial PCO2?

Answer 7

V/Q mismatch (but not always)

Hypoventilation

Question 8

What is pendelluft?

Answer 8

Swinging air
Caused by airways with uneven time constants.
The effect is that one airway might be inspiring when another airway is expiring!

Question 9

What is the normal closing volume in a person?

Answer 9

10% VC

Question 10

What are the stages of a single breath washout?

Answer 10

1. Dead space
2. Mixture of dead space and alveolar gas
3. Pure alveolar gas
4. Closing volume - closing of airways at the base of the lung (apex being emptied)
   - relatively high concentration of inert gas because the apex is less well expanded and therefore it is less diluted