L21 Variation of V-Q Ratio Flashcards
Contraption
Inverted cylinder filled with water. then turned upside down as water leaks out and then fills container to a certain mark
-chick drinks water until water level goes down until just below the opening
Regional variation of the Ventilation-Perfusion (V./Q. Ratio)
V.= volume of air exhcanged per unit of time = 6Lmin-1 at rest 70kg male Q.= CO cardiac output/circulation per unit of time= 5L
Equation of motion of the thoracic system
DeltaP = DeltaV/C + V. x R
- change of pressure will cause a change of volume, depedning inversely on the compliance
- the change in pressure will also induce a flow, depending directly on the resistnace
Equation of motion of the thoracic system arranged for Ventilation
V. = (DeltaP - (DeltaV/C)) / R
Certain amount of ventilation is going to occur depending on the:
-change of pressure
-this change in pressure is going to be reduced by whatever it took to change the volume of the lung, given its compliance
-and since any flow is inversely proportional to resistance
Ventilation V. is enhanced in which regions?
Ventilation V. is enhanced in region of:
- High lung compliance (C Dinominator becomes so large that it is infinite, so deltaV/C is essentially= higher ventilation
- Low resistance to airflow (due to inverse relationship)
Effect of Regional Variation of Compliance of Regional Variation of V./Q. (V.)
Compliance of the lung can be likened to a slinky
- each lung is held in a gravitational field= therefore the top of the lung/slinky gets stretched more
- stretched to a point where it is beginning to get more stiff and resisting more stretch
Graph: Volume change as a function of pleural pressure (V.)
Very low pressures in the lung
for a given incriment of pressure in the lung (change 3cmH2O)
-will have a larger effect if applied to the base of the lungs vs applied near the top of the lung
-Lower= Same change in pressure caused a Regionally different (Larger) Change in Volume (depending on if youre near the base of the lung, or its apex)
-due to the straightforward effect of gravity (slinky)
**For any given (Q.) Blood Flow and (DeltaP) Change in pressure, V. (Ventilation) is greater at the base of the lung
-deal with the numerator (V.) by keeping the blood flow constant
Exception to Effect of Regional Variation of Compliance of Regional Variation of V./Q. (V.)
For any given (Q.) Blood Flow and (DeltaP) Change in pressure, V. (Ventilation) is greater at the base of the lung, except at very low lung volumes
- Where condition are reversed such that V./Q. Ventilation-Perfusion ratio –> 0
- still well circulated at the lower lung, but essentially 0 Ventilation (V.) so ratio goes to 0
How is Q. Measured
steady state: same net amount of oxygen coming in and out of the atmosphere–> body, as there is passing around circulation and being consumed by mitochondria
–> using “Fick Principle”
Circulation Equation: V.o2= Q. (Cao2 - Cv-o2)
–> Algebraic rearrangement to get Fick’s Principle:
Q. = V.o2/(Cao2 - Cv-o2) = Respiration/Circulation
Flow of Blood=Net flow of Oxygen/Difference in content of oxygen
-measure oxygen usage from the mouth
Ventilation Equation:
V.o2= V.Io2 - V.Eo2
Ventilation= the difference between the rate we inspire and exhale oxygen
-we exhale a substantial proportion of what we inhale, particularly at rest
Circulation Equation
V.o2= Q. (Cao2 - Cv-o2)
rate of oxygen consumption by tissues in a steady state = rate of blood flow x (difference in oxygen content b/w arterial side and what is going back on the mixed venous blood)
Effect of Regional Variation of Blood-flow on the Regional Variation of V./Q. (Q.)
subject vertical, Radioactive tracers in the blood
-Radiation counters behind, counting the rate of release of radiation
Base: higher blood flow, in comparison to the apex
-therefore apex gets less ventilation and less blood flow
** There is a greater blood-flow at the base of the lung
Diagram explaining the Regional Variation of Blood-Flow
Ventilation and Circulation system combined
Lung alveolus has alveolar pressure (filled with fluid and air)
Pressure in pulmonary artery, driving blood through ventilation
-pulmonary artery passes through capillary which is in close apposition to alveolus
-pressure in the alveolus effects the patency of the capillary
-if the alveolar pressure gets high enough, (by raising the outflow), will progressively compress this vessel (capillary) until the flow is pinched off ( can increase alveolar pressure so far that flow is zero)
Note: (if at same height then wont flow at all as there will be no pressure gradient)
*** Fluid-flow in ANY vessel is diminished if P(external) > P(fluid in the vessel)
-can pinch hose and stop water coming out
West Graph discussing Effect of Regional Variation of Blood Flow on the Regional Variation of V./Q.
PRessure in pulmonary artery has to drive blood through the entire pulmonary capillary network
-variation in airflow from apex to base, have strong possibility that apex is pinching off capillaries vs base allows cappillaries to expand further = variation in blood flow
Blood Flow is Q. Greatest at the base
Recall that V. Air flow is also greater at the base
Regional Variation of Ventilation-Perfusion V./Q. Ratio Graph
Rate at which Blood Flow changes (Q.) with vertical position is much steeper > than the rate at which ventilation changes with location
3rd rib= about the same
Blood flow changes more rapidly
Combine V./Q. ratio to get exponential curved line.
-curved line is Very Steeply curved, but this indicates the difference in gradient of these two lines
** Q. decreases more from base to apex than V. does.
*** Hence V./Q. increases from base to apex
-V./Q. is really good at the top (ventilation is better at the top and circulation is poorer at the top)
Consequences of Regional Variation of the Ventilation-Perfusion (V./Q.) Ratio
Mixed Venous Blood entering alveoli:(Pv-o2=40mmHg Pv-co2=45)
A: single alveoli nicely ventilated with room air (Po2=150mmHg Pco2=0 essentially) –> alveoli (Po2=100mmHg Pco2=40). lost driving pressure due to oxygen cascade.
-the difference in partial pressure b/w Pao2=100 and Pv-o2= 40 (the consumption) that allows Oxygen to diffuse from environment –> alveoli
-the difference in partial pressure b/w Pv-co2=45 and Pco2=40 that allows CO2 to diffuse from mixed venous blood/artery –> alveoli
Consequences of Regional Variation of the Ventilation-Perfusion (V./Q.) Ratio: Extreme V.=0
No Ventilation V.=0 (complete block to alveolus from environment) (Ventilatory Block)
**no ventilation. good perfusion. –> Decreasing V./Q. = 0/x= 0
Pao2=40 PaCO2=45
-alveoli has to survive on what comes from periphery/mixed venous blood (same as Pv-o2=40mmHg Pv-co2=45)
-cannot change these as no access to outside air
-these are only starting values, because as time goes on, O2 will still diffuse out of alveoli and CO2 will still diffuse in, so values will progressively increase
Consequences of Regional Variation of the Ventilation-Perfusion (V./Q.) Ratio: Extreme Q.=0
No blood Flow Q.=0
(complete block to the blood flow) continue pumping air in and out of the alveolus but not moving any across the aveolar-capillary wall
Pao2=150 PaCO2=0
**good ventilation. No perfusion –> Increasing V.A/Q = Infinite ratio
Consequences of Regional Variation of the Ventilation-Perfusion Overall summary
Ventilation Perfusion Ratio varies from 0–> normal –> Infinity
Consequences of Regional Variation of the Ventilation-Perfusion on SIMPLE graph (Partial pressure of CO2 as a function of Partial pressure of O2) along 0–> infinity line
Normal= PAo2=100mmHg and PAco2=40mmHg
Cut off circulation/perfusion = Q.=0
–>PAco2=0mmHg PAo2= 150mmHg. –> V./Q.=Infinity. needlessly moving air in and out
Cut off ventilation = V.=0
–>only mixed venousblood coming back. PAco2=45mmHg PAo2= 40mmHg. –> V./Q.=0.
Consequences of Regional Variation of the Ventilation-Perfusion on COMPLEX graph (Partial pressure of CO2 as a function of Partial pressure of O2) along 0–> infinity line
In the vertical orientation fo the lung, every region of the lung will be different
- potentially differs all over the lung (vertically, horizontally, front and back)
- every region on the will have a different V./Q. Ventilation/Perfusion ratio
- depending on the circumstance the Right lung can be very different from the Left lung
What is the V./Q. ratio in a healthy young adult?
-
Redress of Regional V./Q. inequalities by “local mechanisms”
Hypoxic Pulmonary Vasoconstriction
-the minute you start exercising and consuming oxygen in the limbs, all the vessels start to vasodilate to supply muscles with oxygen and blood to keep the mitochondria happy
-BUTTT:
oxygen is a vasoconstrictor
-therefore if you’re hypoxic it is probably going to vasoconstrict
- is a balance
-in the Systemic circulation: hypoxia induces vasodilation
-in the Pulmonary circulation: hypoxia causes vasoconstriction (w. smooth muscle in the periphery and the lung)
Hypoxic Pulmonary Vasoconstriction
Decreased tissue PO2 around underventilated alveoli constricts their arterioles, diverting blood to better ventilated alveoli
Blood flow diverted to better ventilated alvoli
-one alveoli has a wonder air supply, and the other alveoli doesnt
-as a consequence of poor ventilation, the poor air supply capillary is hypoxic and in turn has undergone vasoconstriction
-overall causes a Shunting of blood: as the 2x capillaries are in parallel
–> causing more blood to flow through the capillary running by the well ventilated avleolus
Paradox of Hypoxic Pulmonary Vasoconstriction
- in the Systemic circulation: hypoxia induces vasodilation
- in the Pulmonary circulation: hypoxia causes vasoconstriction (w. smooth muscle in the periphery and the lung) “hypoxic PULMONARY vasoconstriction”
Hypoxic Pulmonary Vasoconstriction graph
Blood flow as a function of varied Alveolar PO2
- increase PAo2= blood flow Q. increases
- if increase to an extreme not seen in a healthy person = blood flow Q. increases even more
- If we reduce the Alveolar Po2 we reduce the blood flow (the poorly ventilated alveoli has a lower Po2 –> less blood flow/hypoxic pulmonary vasoconstriction)
Deleterious consequences of Hypoxic Pulmonary Vasoconstriction
- Increased Resistance (pulmonary artery)
- cannot shut off BV without constricting vessels. constricting vessels increases resistance. increased resistance in lung = increases pulmonary artery resistance.
- -> Right heart has to work harder (already pretty week to start with) - Increased Pressure (pulmonary artery) (heart)
- increased Pressure in right heart to drive blood through the increased resistance - Increased Work (right heart)
- -> Hypertrophy of RV
- -> Right Ventricular Hypertension (doesnt have very long to live)
Chick explanation
as the air goes in and the bubble rises there is a “gloop sound”
Holding the water standing up: Air pressure
-air is pushing down on the water and holding it up
