Vent and Perfusion Flashcards
Pulmonary circuit different than systemic circuit how?
1) lower pressures and resistance
2) less smooth mm in pulm arteries and arterioles
3) SNS affect on pulm circuit are minimal
Pulmonary circuit has low resistance, why?
large cross sectional area of plum capillaries
Pulmonary circuit has low pressure, why?
resistance is low,
thin walled capillaries can not tolerate high pressure
Pulmonary vasculature characteristics? (2)
1) highly compliant Ѧ blood reservoir
2) can not autoregulate pressure and Po2
(compared to autoreg in systemic vascular beds)
Resistance of plumonary circ and blood flow affected by? (3)
1) vascular pressures
2) gravity
3) PAo2
↑ pulmonary vascular pressures results in what?
↓ pulmonary vascular resistance thru:
↑ distension or recruitment
Recruitment is?
in response to ↑ pulmonary pressure (arteries or veins),
more capillaries open to ↓ pulm vascular resistance.
Response is more useful at lower pressures.
Distention is?
in response to ↑ pulmonary pressure (arteries or veins),
capillaries already partially open are expanded to ↓ pulm vascular resistance.
Response is more useful at higher pressures
Gravity lowers pulmonary vascular resistance how?
distributes blood from apex to base of lung
↑ flow = ↓ resistance
What happens to PA, Pa and PV w/ change in lung position (relative to gravity)?
PA remains constant
Pa and PV both ∆
Gravity in Zone 1?
(apex)
vessels collapse = θ flow
contributes to alveolar dead space
PA > Pa > PV
Gravity Zone 2?
θ flow but
proportional to Pa - PA
Pa > PA> PV
Gravity Zone 3?
(base)
driving force is Pa - PV
PA dose not affect flow
Pa > PV > PA
Effects of hypoxic vasoconstriction (PAo2) on pulmonary vascular resistance?
↓ PAo2 below 70 mmHg ->
smooth mm contracts in pulm vasculature ->
blood sent to better ventilated alveolar ->
local control of vascular resistance
OPPOSITE of response of system circulation to hypoxia
Hypoxic vasoconstriction responsible for? (3)
1) plumonary HTN at high-altitude
3) chronic hypoventilation (COPD)
4) in utero keeps blood flow to fetal lungs at minimum
Alveoli at apex of lung:
Intrapleural pressure?
Volume?
Compliance?
-10 cm H2O
larger vol due to more neg intrapleural pressure
partially expanded so compliance is reduced
Alveoli at base of lung:
Intrapleural pressure?
Volume?
Compliance?
-2.5 cm H2O
smaller vol due to less neg pressure
more compliant Ѧ better ventilated
Vent/Perfusion ratio
ºV = vent reaching alveoli
(4.2 L/min)
ºQ = blood flow thru lungs
(cardiac output) (5 L/min)
ºV/ºQ = 0.84 in upright lung
Vent/Perfusion ratio
ºV = vent reaching alveoli
(4.2 L/min)
ºQ = blood flow thru lungs
(cardiac output) (5 L/min)
ºV/ºQ = 0.84 in upright lung
vent and perfusion ↓
from where to where?
base ( 3)
perfusion changes more rapidly than ventilation
High ºV/ºQ does what to:
ventilation and perfusion?
PAo2 and PAco2?
vent > perfusion
high PAo2
low PAco2
Low ºV/ºQ does what to:
ventilation and perfusion?
PAo2 and PAco2?
perfusion > ventilation
low PAo2
high PAco2
Apex ºV/ºQ ratio is?
Pao2?
Paco2?
high (3.0)
highest (130 mmHg)
lower (28 mmHg)
Base ºV/ºQ ratio is?
Pao2?
Paco2?
low (0.6)
lowest (89 mmHg)
higher (42 mmHg)
Wasted ventilation is?
Happens?
vent > needed to saturate blood delivered to alveoli
happens in alveoli w/ high ºV/ºQ
Shunt is?
ºV/ºQ?
O2 supplementation tx?
perfusion w/o ventilation:
e.g. bronchial blood flow, defective ventral septum
ºV/ºQ = 0
does not respond to supplemental O2,
non-vent alveolar are never ventilated
Areas w/ low ºV/ºQ add blood that is?
Respond to O2 tx?
poorly oxygenated
does respond to supplemental O2
O2 supplementation ↑ what?
Improves what?
FIo2 of inspired air
oxygenation in areas of low ºV/ºQ
