4 V/q matching pulm circ Flashcards Preview

DMED 514 PULMO > 4 V/q matching pulm circ > Flashcards

Flashcards in 4 V/q matching pulm circ Deck (18)
Loading flashcards...
1
Q

definition of ventilation? perfusion?

A

V = rate at which gas enters or leaves the lung. P = process of delivery of blood to a capillary bed

2
Q

ventilation perfusion ratio definition? abbreviation?

A

V/Q ratio: measurement used to assess efficiency and adequacy of matching of these two variables in the lung

3
Q

why is V/Q matching important

A

ideally, oxygen provided via ventilation would be just enough to saturate the blood fully = ideal V/Q ratio would be 1

4
Q

in typical adult, 1 L blood has how much oxygen? how much in air? what is V/Q ratio?

A

200 mL/oxygen in blood, 210 mL in dry air –> but with humidified air the ideal V/Q ratio would be 1 (actually in reality is 0.8 ish)

5
Q

is ventilation uniform throughout lung? why?

A

not uniformly distributed: imbalance because intrapleural pressures different in different regions. most blood flow goes to lower lung, so bases heaver than apices = lung pull downward, intrapleural pressure at top is more negative than at bottom (stretched open more at top)

6
Q

apical alveoli vs. at base: size?

A

bigger aka more fully expanded at the top, since there is more negative pleural pressure

7
Q

how does intrapleural pressure change from top to bottom? w/ breathing?

A

top most negative, then gets less negative at bottom. breathe in = 3 cm H2O more negative

8
Q

where is ventilation greatest? because ventilation is proportional to?

A

ventilation higher at base of the lung. v = proportional to change in volume of alveoli (alveoli at bottom can expand more with less pressure change but at top are already expanded)

9
Q

is perfusion uniform throughout lung? why?

A

no: pulmonary arterial pressure increases from apex to base –> from top to hilum, 11 mmHg more, then at bottom 11 mmHg more than at hilum (column of blood 15 cm high exerts hydrostatic pressure of 11 mmHg)

10
Q

pulmonary venous pressure is also dependent on?

A

vertical height: so lowest at top, then gets more and more at bottom

11
Q

perfusion equation

A

Q = delta P / R –> amount of flow, aka perfusion, = pressure gradient divided by resistance

12
Q

describe flow from top to bottom of lung using equation

A

top no flow, because pressure favoring collapse > pulm arterial/inflow pressure –> arterioles collapse. going down, pulm. arterial pressure goes up and overcomes collapsing pressure = get flow. And you get more and more flow going down the lungs.

13
Q

in order for blood to flow through any vessel, what must be greater than what?

A

inflowing pressure > pressure favoring vessel collapse

14
Q

in normal lung, how much “collapsing” pressure is there?

A

there is a surrounding pressure of ~4 mmHg exerted on the small precapillary vessels (probably from elasticity of arteriolar smooth muscle)

15
Q

why is there a small drop in perfusion at the very bottom of the lung

A

venous + arterial pressures so high that fluid leaks out into interstitial = increased resistance to blood flow (recall Q = delta P /R)

16
Q

distribution of ventilation vs. perfusion

A

both increase from top to bottom –> but at top, more ventilation and at bottom more perfusion

17
Q

how do V/Q ratios change top to bottom

A

top: high V/Q, > 1 (more ventilation). bottom: V/Q < 1 since more perfusion

18
Q

V/Q ratios throughout lung –> impact on PAO2 (arteriolar oxygen)?

A

top of lung perfusion is lower than ventilation = higher PAO2, lower PACO2.. at bottom, perfusion greater so lower PAO2