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### 12 Cards in this Set

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 What is VA (v dot A)? What is QC (Q dot C)? V-ventillation q- perfusion Why is it ideal for VA/QC to equal 1? Otherwise you have overventillation/underventillation/overperfusion/underperfusion What are the PO2 and PCO2 in an alveolus that is ventillated but not perfused? PO2 = 150 mmHg PCO2 = 0 These are atmospheric values. Alveoli that are ventillated but not perfused are called alveolar dead space since its a continuation of the airway. What is the PO2 and PCO2 in an alveolus that is perfused but not ventillated? This will have a mixed venous composition in the alveoli. PO2 - 40, PCO2- 45. What is the V/q ratio in a state of no ventillation. What is the V/q ratio in a state of no perfusion. No ventillation has a v/q = 0 No perfusion has a v/q = infinity What is venous admixture? Venous admixture occurs when you have a non ventillated alveolus. This means no gas exchange occurs. This deoxygenated volume is called venous admixture, since it mixes with the rest of the arterial blood. How does V/Q ratio differ throughout the lung V/Q ratios are highest in the upper lung, and decrease as you move down the lung. The average V/Q ratio is less than one because the lower lung has much more mass and therefore more alveoli. Over a large part of our lungs, we have uniform V/Q ratios that are necessary for ideal gas exchange. How does emphysema result in abnormal V/Q ratio in the lungs? Airways more readily collapse in emphysema -> not uniform filling/time constants -> abnormal V/Qs. What is a shunt? Shunt is the passage of deoxygenated blood from the venous circulation to the arterial side without picking up O2. Shunt is a problem in ventillation. What are some sources of the shunt? 2 Normal - thebesian circulation perfusing left ventricle, bronchial circulation emptying into pulmonary veins. 2 abnormal - atelectic/collapsed alveoli, congenital defects. How to calculate the fraction of CO that is shunted? Qshunt/Qtotal = (O2 content end capillary- arterial O2 content)/(O2 content end capillary- venous O2 content) At what point can inspiration no longer compensate for mismatches in Va/Qc Once the shunt exceeds 50% of cardiac output.