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Respiratory Part 9

QuestionAnswer
What does CO2 produced by cellular metabolism do? Diffuses into the blood where it can be carried in 3 different forms.
Name the 3 different forms CO2 can be carried as? 1) Dissolved CO2 2) Carboamino compounds 3) HCO3-
Dissolved CO2 Responsible for PCO2. CO2 dissolved in plasma is in equilibrium with CO2 in RBC.
Carboamino compounds CO2 reacts with the free amino groups on hemoglobin
HCO3- Both in RBC and plasma. Most of the CO2 produced by metabolism is carried in the plasma in the form of HCO3.
Chloride shift Bicarbonate will diffuse out of RBC & into plasma. Cl- comes in. RBC membrane is impermeable to + ions.
Haldane Effect The H+ is buffered by hemoglobin. The buffering capacity of Hb increases when it dissociates O2, b/c as Hb releases O2, it changes its shape and exposes more free NH2 groups.
What determines the volume of CO2 carried in the 3 forms? The PCO2 determines all of them. The relationship b/w the PCO2 and the total CO2 content is direct and nearly linear.
In hyperventilation do you expect to see lower or higher PCO2? Lower PCO2 in hyperventilation.
How does hyperventilation of healthy lung units affect VA/Qc mismatch and right to left shunt in CO2? Hyperventilation can significantly lower CO2 content of blood leaving the units so a VA/Qc mismatch does not necessarily lead to CO2 retention.
When does CO2 retention occur? As the disease worsens and there are fewer healthy lung units to hyperventilate/ patients doesn't want to hyperventilate.
How will overventilating the lungs affect PaCO2? It may be low if the units are overventilated like in asthma.
What kind of diseases always lead to CO2 retention? Non-pulmonary diseases where the entire lung is hypoventilated.
When VA/Qc=0, what does that indicate? A right to left shunt. A low VA/Qc means that there is not enough air in an alveolus for the amount of blood.
When VA/Qc=infinity, what does that indicate? Alveolar dead space. A high VA/Qc means that there is too much air in an alveolus for the amount of blood.
Describe the regional variation when the thorax is erect Units at the base are smaller and more compliant. The IPP is -2. Units at the apex are larger and stiffer. The IPP is -10.
Elastic limit Harder and harder to stretch the closer you get to the elastic limit. The apex is near the elastic limit.
Describe what happens during inspiration to the IPP at base and apex of lungs IPP becomes more negative and changes everywhere. More air goes to the base of the lungs and the base behaves as if more compliant. Alveoli at the base are relatively more compresed at FRC but expand better.
How much more air goes to the base of the lungs than to the apex? 4X more air goes to the base than the apex.
What is the consequence of the right ventricle developing a low pressure? Blood flow to the apex is compromised. Most of the blood ejected by the right ventricle goes to the base. Apex is relatively bloodless while blood pools at base.
How much more blood goes to the base of the lungs than to the apex? 10x more blood goes to the base than to the apex.
Describe the alveoli at the base compared to the apex Alveoli at the base are hypoventilated for the amount of blood flow. Alveoli at the apex receive too much air for the amount of blood perfusint them. High VA/Qc at the apex.
What is the PA/PaO2 at the apex and the base? Pa/PACO2? Apex: 130mmHg Base: 70mmHg Pa/PACO2, Apex: 28mmHg Base: 45mmHg