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Spr2015_Week5 > Diffusion and perfusion > Flashcards

Diffusion and perfusion Flashcards

1
Q

Define solubility coefficient

A

tendency of any molecule to dissolve in a liquid

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2
Q

what is the variable for O2 saturation coefficient

A

alphaO2

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3
Q

what is alphaO2 at 37C in isotonic NaCl solution (approximates blood)

A

alphaO2 = 0.0013 mM/Torr

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4
Q

how do you calculate dissolved [O2] in blood

what is typical value at a typical arterial PO2 of 100 Torr

A

[O2] = alphaO2 x PO2

[O2] = 0.13 mM at PO2 = 100 Torr

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5
Q

why is so little O2 carried in freely dissolved form in blood ([O2] in blood only = 0.13 mM) (2 reasons)

A

1) O2 doesn’t dissolve well in blood
2) O2 binds quickly to Hb and taken out of freely dissolved form rapidly

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6
Q

what is alphaCO2 typically

A

alphaCO2 = 0.03 mM/Torr

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7
Q

why is alphaCO2 > alphaO2

A

1) CO2 = 20x more soluble in blood than O2

CO2 dissolves more readily than O2

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8
Q

what does oxy-hemoglobin dissociation curve reflect?

what is SaO2 at PaO2 = 100 Torr?

A

ratio of O2 saturation of Hb (SO2) at equilibrium to PO2 in blood

ratio of 9 mM oxy-hemoglobin to 9.1 mM artial O2 content

@ PaO2 = 100 Torr

SaO2 = 98%

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9
Q

For PO2 = 100 Torr (normal arterial O2 sat), SO2 = ___

A

SO2 = 97.5%

so in arterial blood, Hb is close to full saturation

any further incr in PO2 would not incr amount of O2 carried by Hb

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10
Q

what is mixed venous blood

what is PO2 of mixed venous blood

what is SO2 of mixed venous blood

what is PO2 of mixed venous blood at half saturation

what is SO2 of mixed venous blood at half saturation

A

mixed venous blood = blood from RV

PO2 = 40 Torr

SO2 = 75%

PO2 at half saturation = 26 Torr

SO2 at half saturation = 50%

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11
Q

why is oxy Hb curve steep between 20 to 60 Torr

A

curve is steep at moderate PO2

because O2 binding to Hb is a “cooperative” process

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12
Q

what is significance of steep drop in SO2 with decrPO2

A

allows peripheral tissues that see relatively unsaturated Hb to withdraw larger amounts of O2 for small drops in capillary PO2

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13
Q

what are criteria during which standard Oxy-deoxy Hb curve functions under

A

pH = 7.40

PCO2 = 40 Torr

Temp = 37C

[2,3 DPG] = 15 umoles/g Hb

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14
Q

situations that can lead to reduced PO2 levels

why?

A

situations that could prevent reaching 100 Torr

severe disease or moderate disease + exercise

O2 impedes diffusion slightly, O2 needs to be in dissolved state –> from alveolus to interstitial space –> blood, poor solubility slows this process and makes O2 diffusion susceptible to disease

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15
Q

how does moderate disease and exercise affect PO2 as you pass through capillary bed

why?

A

if you have moderate disease or exercise that impedes diffusion, then curve of PO2 vs. % capillary bed passed shifts down, still able to reach 100% PO2

with exercise, blood flows more quickly through pulm circulation

___

why? O2 impedes diffusion slightly, O2 needs to be in dissolved state –> from alveolus to interstitial space –> blood, poor solubility slows this process and makes O2 diffusion susceptible to disease

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16
Q

how does severe disease (DIFFUSION DISORDERS) affect CO2 levels in blood?

SAME OR DIFFERENT FROM O2

WHY?

A

severe disease DO NOT affect CO2 levels in blood

STILL REACH 40 TORR

–> DIFFERENT FROM O2 CURVE

–> BECAUSE DIFFERENCE IN SOLUBILITY

CO2 passes READILY from blood to interstitium to alveolar space without trouble so diffusion disorders don’t affect CO2 diffusion sufficiently

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17
Q

Factors that promote rapid gas transfer across an arbitrary tissue plane (O2 diffusion from alveoli and pulm capillaries)

A

1) difference in partial pressure of gas on two sides
2) tissue plane area (A)
3) tissue thickness (d)
4) constant k reflects tissue solubility and molecular weight of gas

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18
Q

equation for gas transfer rate (VG) = Flux gas

what is the equation called

A

Flux gas = VG = (P1-P2) x (A/d) x k (Fick’s Law)

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19
Q

simplify equation for VG (Fick’s Law) to solve for diffusing capacity Dm

A

Dm = (A/d) x k

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20
Q

what does large surface area (A) refer to?

one adult lung = ____ alveoli

surface area of lung = ____

A

refer to alveolar membrane

300 million alveoli

50-100 m2

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21
Q

what is thin membrane width (d) of alveolar membrane

thin membrane ___ diffusion

A

0.3 um

maximizes

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22
Q

what exists between alveoli and capillaries

A

PAO2- PcapO2

any O2 that transfers from alveolus to capillary keeps free O2 levels low and maintain pressure gradient for diffusion from alveolar air into blood

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23
Q

what ensures that PcapO2 remains low and the gradient (PAO2 - PcapO2) large

A

1) low solubility of O2 in blood
2) tendency of O2 to bind quickly to Hb

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24
Q

If PO2 reaches alveolar values in 1/3 of the time it spends in the pulmonary circulation, then why have all of that extra time for diffusion to occur

A

Safety net for

1) exercise when faster blood flow reduces time diffusion occurs
2) disease when O2 and CO2 transfer slows

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25
Q

how does interstitial disease affect rate of diffusion

A

thickens alveolar wall (incr d),

slows rate of diffusion

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26
Q

how does emphysema affect rate of diffusion?

A

destroy alveolar bed –> decr surface area (A) for diffusion (decr A) –> decr rate of diffusion

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27
Q

how does polycythemia affect rate of diffusion

A

diffusion increases

28
Q

how does anemia affect perfusion

A

anemia = perfusion decr

29
Q

changes in Hb concentration exert ___ effects on tissue oxygenation

why?

A

much larger

because alters O2 delivery to tissue rather than through changes in O2 diffusion

30
Q

variable for perfusion

define perfusion

A

perfusion = Q

perfusion = blood flow of pulm circulation available for gas exchange per minute

31
Q

perfusion equals ____

what is value of Q (perfusion) at rest)

A

cardiac output

Q = 5L/min

32
Q

why does pulmonary circulation have low blood pressure (2 reasons)

purpose?

A

1) vast number of vessels
2) normally dilated state

keeps work of right heart as small as possible for efficient gas exchange

33
Q

what is PAO2?

A

alveolar O2 tension

34
Q

significance of PAO2

A

most important factor in governing minute-to-minute regulation of pulm circulation

35
Q

what is the mechanism of alveolar O2 tension

A

1) O2 diffuses through thin alveolar walls into smooth muscles of microvessels
2) in response to low arterial PO2 –> constricts nearby arterials = hypoxic pulm vasoconstriction
3) decr local blood flow –> shift to other regions of lung

36
Q

define hypoxic pulm vasoconstriction

how does response to low O2 differ between lungs and peripheral circulation?

A

low alveolar PO2 constricts nearby arterioles

decr local blood flow –> divert O2 to other lung regions (that may not be diseased)

________

OPPOSITE OF LOW O2 IN REST OF CIRCULATION

IF LOW O2 IN LEG –> VASODILATION TO OFFSET low O2 in blood and provide O2 to leg

37
Q

chemical agents affecting regulation of perfusion (2)

A

1) thromboxane = most important vasoconstrictor = localized to region of O2 release
2) prostacyclin = prostaglandin I2 = vasodilator

38
Q

where does thromboxane exert its effect

A

regions of O2 release

39
Q

how does capillary recruitment affect perfusion in exercise

A

1) moderate exercise = passive regulation
2) recruit new capillaries and distension of previoulsy open microvessels
3) incr up to 200 mL blood and incr CO 3x

incr in BP in pulm circulation due to incr CO with exercise, allows lungs to accomodate greater CO

40
Q

effect of gravity on pulm blood pressure in lung

A

pulm blood presure low at apex of lung, high in base of lung

41
Q

significance of pulm blood pressure higher at base of lung

A

allows more capillaries to open –> higher blood flow

perfusion incr from apex –> bottom of lung

42
Q

what is V/Q ratio

significance?

A

ventilation/perfusion ratio

describes variability in ventilation and perfusion ratio through lung

43
Q

define alveolar dead-space in lung

V/Q = ?

A

volume of lung that does not engage in gas exchange

ventilation = normal

NO PERFUSION

MOST EXTREME VERSION OF HIGH V/Q (V/Q = INFINITY)

44
Q

define shunt

V/Q= = ?

A

volume of blood that does not engage in gas exchange

blood perfusion present

NO VENTILATION

most extreme version of low V/Q (V/Q = 0)

45
Q

IS A SMALL amount of shunt normal?

why?

A

yes, because some venous blood enters LA and LV by way of bronchopulm venous anastamoses and intracardiac Thebsian veins (1-2%)

46
Q

how does shunts affect arterial oxygenation? when does this happen?

A

DECR ARTERIAL oxygenation significantly when well-ventilated blood mixes with shunt blood

47
Q

how do shunts affect level of PCO2

A

NO INCR IN PCO2

because incr countered by central chemoreceptors that incr ventilation with incr in PCO2

because PaCO2 inversely related to VAdot –> total ventilation remains normal (VAdot) so PaCO2 stays same

V/Q mismatch affects arterial O2 evels but NOT AFFECT CO2

48
Q

why is arterial PCO2 lower than normal

A

because additional hypoxemic stimulus to ventilation

49
Q

causes of V/Q mismatch (3)

A

1) resistance problem (OBSTRUCTIVE DISEASE) = partial occlusion of bronchiole (CAN BE MILD, MOD, OR SEVERE)–> differ from hypoventilation that requires severe disease because body wants to maintain normal CO2
2) Pulmonary embolism (blood flow diverted to other parts of circulation, incr Q, decr V/Q)
3) gravity–> creates different V/Q ratio due to difference in V and Q at top and bottom of lung

50
Q

why does gravity lead to regional variations in ventilation/perfusion in upright person

what is the ratio of Vbottom/Vtop and Qbottom/Qtop

A

gravity has different effects on V/Q in different parts of lung

V/Q HIGH IN APEX

V/Q LOW IN BASE

Vbottom/Vtop = 2.5

Qbottom / Qtop = 6

(V/Qtop) / (V/Qbottom) = 4

blood pools in base of lung, incr BP, open up blood vessels, incr perfusion (Q) in lung

51
Q

what is significance of gravity’s effect on regional variations in V/Q in lung

A

creates 5-10 Torr difference between arterial PaO2 and alveolar PAO2

PAO2 > PaO2

(V/Qtop) / (V/Qbottom) = 4

52
Q

O2 is ___ soluble in blood

A

poorly because O2 forms poor chemical interactions with water molec

53
Q

ARterial O2 Content = CaO2 = ___ + ___

typical values for all variables?

A

O2 bound to Hb and freely dissolved O2

CaO2 = 20.7 mL O2/100 mL blood = 20.4 mL O2/100 mL Hb-Bound + 0.3 mL/100 mL free

54
Q

PaO2 only reflects which form of O2

A

reflects freely dissolved O2 ONLY not including Hb-bound

55
Q

Hb-bound O2 is ___ related to PaO2 via the oxy deoxy Hb curve

A

indirectly

56
Q

___ keeps delta P

A

O2 binding to Hb

57
Q

Define perfusion

Define minute perfusion (Qdot)

A

perfusion = blood flow in the lung

minute perfusion (Qdot) = blood flow in lung per minute = cardiac ouptut because heart directly enters pulm circulation

58
Q

Factors that affect perfusion

A

1) O2 tension (amount of O2 in blood vessel)
if portion of lung poorly ventilated (low O2 in bronchi –> blood vessel), then blood vesel constrict

2) Capillary recruitment
3) Gravity

59
Q

V/Q mismatch examples

1) if have obstructive disease
2) if have high ventilation or partial occlusion of blood vessel

A

1) Obstructive disease that obstructs bronchiole, low ventilation –> low V/Q
2) Ventilation is high or (Partial occlusion of blood vessel, low perfusion)–> high V/Q

60
Q

Problems in oxygenation can arise even if total ventilation and perfusion is normal

A

a

61
Q

ideal V/Q ratio

A

V/Q = 1

approximated by

VAdot = 4.2L

Qdot = 5L

62
Q

situation with low V/Q

A

introduce partial occlusion of bronchiole, decr ventilation

63
Q

situation with high V/Q ratio

A

regions of High V/Q result when you have low V/Q

body is interested in maintaing a near normal PaCO2 to maintain normal PH

64
Q

if we have blood entry with CVO2 = 15.7 mL O2/100 mL (mixed venous blood O2 level), what is CaO2 after passes through circulation?

A

small incr blood through portion with high V/Q (amount of incr is small relative to normal level of O2 in V/Q =1)

large deficit in O2 through portion of circuit with small V/Q (more than incr in branch with high V/Q)

because even at typical O2 level with normal ventilation, 98% O2 bound to Hb so few O2 binding sites available, LIMITING AMOUNT OF O2 THAT CAN BE ADDED TO BLOOD–> O2 SATURATION OF HB THAT LIMITS HOW MUCH O2 THE HIGH V/Q BRANCH CAN ADD

65
Q

Diagram with V/Q mismatch and how that affects O2 and CO2

A
66
Q

Causes of Shunts (2)

A

1) Lung defects (pneumonia)
2) Heart defects

67
Q

Pneumonia causes V/Q = 0.0 (accum leukocytes)

A

a

Spr2015_Week5 (19 decks)

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