4 V/Q matching cont'd

Question 1

A-aDO2 means? equal to?

Answer 1

A-a gradient, difference between alveolar and arteriolar oxygen –> PAO2 - PaO2 (alveoli minus arteriolar)

Question 2

A-aDO2 predicts? aka it tells us what?

Answer 2

degree of shunt by comparing the partial pressure of O2 in the (A) alveoli to that in the (a) artery –> how well the oxygen is moving from the alveoli to the arterial blood.

Question 3

physiologic shunt?

Answer 3

bronchial circulation comes off of aorta then drains into pulmonary veins –> mixing of deoxygenated blood from bronchial circulation and oxy blood from returning pulmonary circulation = shunt

Question 4

efficiency of oxygenation at top vs. bottom?

Answer 4

more efficient at top of lung, less at bottom –> but note that you are oxygenating a lot more blood at the bottom

Question 5

an anatomic shunt occurs when?

Answer 5

venous blood flows back to the circulation downstream from the lung - ie the bronchial circulation

Question 6

intrapulmonary shunt occurs when?

Answer 6

venous blood flows through an unventilated, lung, heart defects (like VSDs) or shunt channels in the lung (the ones that open at very high outputs)

Question 7

dead space is when V/Q = ? what does it mean? what air is this?

Answer 7

when V/Q - infinity so you have ventilation, no perfusion) –> air which is inhaled, but doesn’t take part in gas exchange either because it either remains in conducting airways, or reaches poorly perfused/not perfused alveoli

Question 8

benefits of dead space (4)

Answer 8

retain CO2 = bicarb buffer. inspired air brought to body temp (increases Hb affinity of O2). humidify air = improved mucus quality. particulate matter trapped in that mucus.

Question 9

pulmonary circulation is __flow, ___ pressure –> what is pulm vascular resistance? what happens if pressure very high?

Answer 9

high flow, low pressure so pulm. vascular resistance is very low. pulm vasculature relatively fragile, will leak water/blood into lung parenchyma if pulm. cap. pressure gets too high

Question 10

heavy exercise: what happens to pulm. venous oxygen? what happens to pulm artery pressure? result?

Answer 10

PvO2 lower b/c more peripheral extracting of O2. higher cardiac output = more blood flow through lungs, so higher pulm artery pressure. would get leakage into interstitium and cause pulm edema but we have shunt channels from arteries to veins

Question 11

effect of lung volume on PVR

Answer 11

low volumes, at RV: total PVR determined mostly by arterial R. going up to FRC, then TLC: capillary resistance account for most of total PVR

Question 12

relative contributions to PVR

Answer 12

small arterioles make the most contribution to resistance

Question 13

hypoxic vasoconstriction is what?

Answer 13

during hypoxia and hypercapnia, pulmonary circulation increases resistance to blood flow: helps shift blood flow away from areas which aren’t ventilated

Question 14

explanation behind high altitude pulmonary edema

Answer 14

less atm. pressure so partial pressure O2 decreases –> hypoxic vasoconstriction, but not uniform so the parts that don’t vasoconstrict get a lot more blood flow = edema