Lung Testing D: Pulmonary Mechanics

Question 1

What’s the definition of airways resistance? (Raw)

Answer 1

Raw is the difference in pressure between the mouth (atmospheric) and the alveoli, related to gas flow at the mouth.
It’s the ratio of alveolar pressure to airflow

Question 2

What is the formula to figure out Raw?

Answer 2

                                Flow

Question 3

What is a typical Raw value?

Answer 3

0.6-2.4 cmH2O/L/sec

Question 4

What’s the technique to measure a patient’s Raw?

Answer 4

Using body plethysmography, have patient “pant gently” at a rate of 1.5-2.5 breaths per second with the shutter opening allowing measurements to be made at FRC.

Question 5

How much of the total airway resistance happens in the:
Nose, mouth, upper airway:
Trachea, bronchi:
Small airways:

Answer 5

50%
30%
20%

Question 6

In patients with obstructive disease, Raw changes only a little bit. Why?
Even though they’re obstructive diseases, asthma and emphysema will give greater Raw. Why?

Answer 6

Small airways contribute only a small amount to total resistance.
Because of large airway involvement.

Question 7

What test gives accurate readings even if the patient cannot or will not comply with the test?

Answer 7

Raw test

Question 8

What has the greatest effect on Raw?

Answer 8

Gas density

Question 9

What unit is Raw usually reported in?

It might also be reported as ___, which is measured in ___.

Answer 9

cm H2O/L/sec

Specific resistance, (abbreviated SRaw) measured in H2O/L

Question 10

To eliminate artifact that occurs during Raw testing, what can you ask the patient to do during the test?

Answer 10

Use hands to eliminate jaw and cheek movement.

Question 11

Gentle panting (can/cannot) affect the glottis. It also (can/cannot) cause airway compression.

Answer 11

Cannot

Cannot

Question 12

What does a wide flow volume loop indicate? x2

Answer 12

Increasing Raw or slow respiratory rate.

Question 13

What is the definition of Airway Conductance? (Gaw)

Answer 13

Flow per unit of pressure change

It’s the reciprocal of Raw. (Not compliance!)

Question 14

How do you obtain a Gaw?

Answer 14

Same as Raw.
Using body plethysmography, have patient “pant gently” at a rate of 1.5-2.5 breaths per second with the shutter opening allowing measurements to be made at FRC.
For Gaw, take Raw and divide by 1.

Question 15

What is a normal Gaw?

Answer 15

0.42-1.67 L/sec/H2O

Question 16

When is it useful to obtain a SGaw? (x2)

Answer 16

1. Helps to determine effectiveness of bronchodilator therapy in uncooperative or malingering patients.
2. More appropriate test for small airway disease than Raw.

Question 17

What is the definition of compliance (C)?

Answer 17

The volume change per unit of pressure change in liters/cm H2O or mm/cm H2O

Question 18

What is C LT? (List normal values too)
What is C L?
What is C T?

Answer 18

Compliance of lungs and thorax, 0.1 L/cm H2O
Compliance of lungs only, 0.2 L/cm H2O
Compliance of thorax only, 0.2 L/cm H2O

Question 19

What are two methods to obtain a C LT?

Answer 19

1. If intubated, record Pplat at different lung volumes.
2. If not intubated, you could intubate and record Pplat
3. Or, if not intubated, you could use a spirometer through which a patient breathes at tidal volume before and after weights are added to the spirometer.

Question 20

What is the procedure for inserting a catheter/ esophageal balloon? x2

Answer 20

1. Insert the catheter, with balloon deflated, through the nose. Have patient swallow it until it enters the stomach.
2. Inject about 1 mL of air into the balloon. (Note at this time, you’re not positive that the balloon is in the right place.)

Question 21

How do you confirm placement of an esophageal balloon?

Answer 21

Observe positive pressure swings on inspiration and negative pressure swings on expiration.

Question 22

How do you tell the optimum placement for an esophageal balloon?
How far is the tip of the balloon from the nose?

Answer 22

1. The highest negative end inspiratory pressure that least affects the heart rate will be the best position.
2. Typically the tip of the balloon is 35-45 cm from the nose.

Question 23

When you’re sure the balloon is in the right position, what should you do?

Answer 23

Remove all the air, then inject 0.5 mL of air.

Question 24

When the tap of the esophageal balloon is open, what will happen?

Answer 24

The balloon will tend to increase in volume.

Question 25

How can the patient empty the esophageal balloon?

Answer 25

With the tap open, patient performs a valsalva maneuver and a 3 mL syringe is connected to the tap while the maneuver is maintained.

Question 26

What should you do if the balloon is too high in the esophagus?

Answer 26

Have the patient perform a Mueller maneuver against a closed shutter. This will cause a drop in the pressure difference between the mouth and esophagus.
Instruct the patient to pant.

Question 27

If there are variations in transpulmonary pressures detected by the esophageal balloon, what should you do?

Answer 27

If there are large pressure swings, the balloon should be advanced slightly until they disappear.

Question 28

What should you have the patient do to standardize the lung volume?

Answer 28

Patient should inhale to TLC.

Then have patient inspire again to measure pressure and volume at points of zero flow.

Question 29

How do you measure C L from an esophageal balloon?

Answer 29

Take measurement from the slope of the pressure volume curve over the segment from FRC to FRC + 0.5 L.

Question 30

At patient’s resting FRC, esophageal balloon pressure should be ___.

Answer 30

About -5 cm H2O.

Question 31

When is maximum elastic recoil pressure measured?

Answer 31

At most negative pressure attained TLC.

Question 32

How is static lung compliance obtained using an esophageal balloon?

Answer 32

Compare the difference between esopagea and mouth pressure to the absolut long volume with no airflow over the entire range available.

Question 33

What is a normal static lung compliance?

Answer 33

0.2 L/cm H2O

Question 34

What is a normal coefficient of retraction?

Answer 34

4-8 cm H2O/L

Question 35

What is the normal maximum static recoil pressure?

Answer 35

24.4-34.5

Question 36

Compliance taken during airflow are called ___ compliance.

Compliance taken during no airflow are called ___ compliance.

Answer 36

During airflow: Dynamic

Without airflow: Static

Question 37

What does it mean when the compliance is the same at static points and dynamic points?

Answer 37

It means the subject is normal.