Lung Testing D: Pulmonary Mechanics Flashcards
What’s the definition of airways resistance? (Raw)
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
What is the formula to figure out Raw?
Flow
What is a typical Raw value?
0.6-2.4 cmH2O/L/sec
What’s the technique to measure a patient’s 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.
How much of the total airway resistance happens in the:
Nose, mouth, upper airway:
Trachea, bronchi:
Small airways:
50%
30%
20%
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?
Small airways contribute only a small amount to total resistance.
Because of large airway involvement.
What test gives accurate readings even if the patient cannot or will not comply with the test?
Raw test
What has the greatest effect on Raw?
Gas density
What unit is Raw usually reported in?
It might also be reported as ___, which is measured in ___.
cm H2O/L/sec
Specific resistance, (abbreviated SRaw) measured in H2O/L
To eliminate artifact that occurs during Raw testing, what can you ask the patient to do during the test?
Use hands to eliminate jaw and cheek movement.
Gentle panting (can/cannot) affect the glottis. It also (can/cannot) cause airway compression.
Cannot
Cannot
What does a wide flow volume loop indicate? x2
Increasing Raw or slow respiratory rate.
What is the definition of Airway Conductance? (Gaw)
Flow per unit of pressure change
It’s the reciprocal of Raw. (Not compliance!)
How do you obtain a Gaw?
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.
What is a normal Gaw?
0.42-1.67 L/sec/H2O
When is it useful to obtain a SGaw? (x2)
- Helps to determine effectiveness of bronchodilator therapy in uncooperative or malingering patients.
- More appropriate test for small airway disease than Raw.
What is the definition of compliance (C)?
The volume change per unit of pressure change in liters/cm H2O or mm/cm H2O
What is C LT? (List normal values too)
What is C L?
What is C T?
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
What are two methods to obtain a C LT?
- If intubated, record Pplat at different lung volumes.
- If not intubated, you could intubate and record Pplat
- 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.
What is the procedure for inserting a catheter/ esophageal balloon? x2
- Insert the catheter, with balloon deflated, through the nose. Have patient swallow it until it enters the stomach.
- 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.)
How do you confirm placement of an esophageal balloon?
Observe positive pressure swings on inspiration and negative pressure swings on expiration.
How do you tell the optimum placement for an esophageal balloon?
How far is the tip of the balloon from the nose?
- The highest negative end inspiratory pressure that least affects the heart rate will be the best position.
- Typically the tip of the balloon is 35-45 cm from the nose.
When you’re sure the balloon is in the right position, what should you do?
Remove all the air, then inject 0.5 mL of air.
When the tap of the esophageal balloon is open, what will happen?
The balloon will tend to increase in volume.
