lecture 13 Flashcards
Exam 3
How do you find the concentration of a gas if we know the partial pressure of the gas and the total pressure?
[gas] = partial pressure of gas/ 760mmHg
For our class the total pressure will always be 760 mmHg!
What’s the concentration of nitrogen in lung air if the partial pressure of nitrogen is 569?
569/760 = 74.9 about 75%
The concentration of nitrogen in dry air is about 80%
What is the partial pressure of inspired (PI) nitrogen in the alveoli? What is the partial pressure of nitrogen in the alveoli after it has been in contact with the capillaries (PA)?
alveolar PIN2: 564 mmHg
after equilibration PAN2: 569 mmHg
Which PFT test is used to find the anatomical dead space?
Fowler’s test
What tells us the volume of anatomical dead space in Fowler’s test?
the midpoint of the transitional phase from where expiration begins and the alveolar plateau. Here we are expiring out the N2 in the deeper portions of the lungs and are hooked up to a nitrogen meter that can measure N2 concentration.
Which PFT measures how even ventilation is in the lungs?
The nitrogen washout test.
With the N2 washout test where would you expect to see the greatest amount of nitrogen dilution?
with the first breath
When is the nitrogen washout test usually stopped?
when the person is expiring out 2.5% N2
How fast should a healthy 20 year old be able to achieve diluting the pre-existing N2 out to 2.5%?
What is considered an abnormal result?
Should take about 3.5 minutes
If it takes greater than 7 minutes this is an abnormal result
Which PFT plots the rate of expired air from TLC –> RV as a function of volume and effort?
Flow volume loops
In the flow volume loop when is inspired air fastest?
probably at about the halfway point on the inspiration curve (bottom loop)
What transpulmonary pressure do we need to fill the lung all the way up to TLC?
30 cmH20
What is deficient in the lung of a COPD patient? How do they overcome this?
They don’t have good recoil pressure and rely on their abdominal muscles to push the air out.
What vent setting do you have to change for a patient with COPD? Why?
You have to increase the E time to allow more time for the air to get out of the lungs. Elastic recoil doesn’t work well with restrictive lung diseases and under anesthesia these patients cannot rely on accessory muscles to force air out of the lungs.
What is FVC?
Forced vital capacity, it looks at the forced expiratory flowrate (L/s)
What happens during forced expiration to the smaller airways? The larger airways?
There is a vulnerable point where the airway is most likely to collapse, just before the cartilage in the conducting zone. The larger airways remain patent with cartilage.
