Airway Resistance and Conductance

Question 1

What is the definition of Raw?

Answer 1

Pressure required to generate 1 L/sec airflow

Raw = Ptransairway/flow = cmH2O/L/sec

Question 2

What is sRaw?

Answer 2

Raw relative to measured lung volumes

sRaw = Raw/Vtg

Question 3

What is the definition of Gaw?

Answer 3

Conductance
Flow generated per 1 cmH2O pressure drop
Reciprocal of Raw
Gaw = 1/Raw
Depends on lung volumes

Question 4

What is sGaw?

Answer 4

Gaw relative to measured lung volumes

sGaw = Gaw/Vtg or 1/(Raw x Vtg)

Question 5

What are the indications for measuring airway resistance/conductance?

Answer 5

Evaluation of resistance to airflow
Evaluation of reversibility
Evaluation of UAO
Evaluation of bronchial hyperreactivity

Question 6

What is the usefulness of Raw measurements?

Answer 6

Pre and post bronchodilator assessment (better indicator of reversibility that FEV1)
Determining the cause of hyperinflation

Question 7

What are the two steps in Raw measurement?

Answer 7

1. (open shutter) To measure flow and Pbox changes that occur with flow
2. (closed shutter) determining relationships between Pbox and Pa

Question 8

What is the significance of Raw/sGaw?

Answer 8

Raw normally accounts for 35% of the WOB
normal Raw = 0.6-2.4
Look at the absolute value of Raw rather than % predicted
sGaw less than 0,15-0.2 = obstruction (lower the value means more obstruction)