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