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28 Cards in this Set

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2 options in respiratory insufficiency:
-Adequete ventilation
-Inadequete ventilation
2 things that could cause inadequete ventilation
-Obstructions
-Restrictions
2 types of obstructions
-Allergic
-Anatomic
2 types of restrictions:
-lung compliance
-Chestwall compliance
2 Factors that alter lung compliance:
-elastic tissue
-surface tension
If there is respiratory insufficienc but Ventilation IS adequete, what 2 things could be functioning abnormally?
-Lung diffusion
-Blood
Formula for Diffusion Rate:
PAS
----
d x sqrt MW
What is P? A? S? d? MW?
Pressure gradient
Area for diffusion
Solubility
Distance
Square root of mw
How do you calculate diffusion capacity?
D
Dl = ------
PA - Pc
Diffusion capacity is what?
The diffusion rate divided by the difference in alveolar pressure minus mean capillary pressure
How do you measure capillary pressure?
you really can't without traumatizing the patient
So how do you estimate the alveolar-capillary pressure gradient?
By breathing .1-.2% CO for 5-6 minutes and collecting the expired gas over the last 2 min.
Formula for diffusing capacity using CO:
Minute CO ventilation
---------------------
Alveolar pressure of CO
What do you mix the CO with?
A reference gas like N2
Once you calculate the diffusing capacity for CO, how do you figure it out for o2?
Dl for O2 is:
Dl for CO x 1.23
What is 1.23?
The oxygen diffusion coefficient divided by the CO diffusion coefficient.
What is the normal value for oxygen diffusing capacity?
21 ml/min/mm Hg
What is the Diffusing capacity in a normal person that's exercising?
68
What is the Diffusing capacity in a diseased person?
8.3
How are the average capillary pressures of O2 in the lungs different when diffusing capacities are different?
They aren't all that different:
88 for normal
63 for exercising
70 for diseased
So when does a diffusion capacity impairment become important?
When the diseased person is exercising
Why does difusing capacity only become apparent when the diseased person is exercising?
Because the transit time for blood in the capillary to equilibrate w/ alveolar air is already at the max, and now it can't get any faster.
What is the normal capillary transit time?
75 sec - but equilibrium is reached within 25 sec
What is the capillary transit time during exercise?
25 sec
What is the capillary transit time when a person has a low diffusing capacity?
still 75, but now equilibration of the blood gases takes the whole time.
What factors affect diffusing capacity?
-Membrane diffusing capacity
-Capillary volume
-Blood oxygen affinity
So what 2 lung-related factors will cause inadequete ventilation?
-Diffusion impairment
-VQ mismatch
What 2 blood-related factors will cause inadequete ventilation?
-Abnormal hemoglobin
-Reduced blood volume