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CP2.08_Ventilation Perfusion > Ventilation and Perfusion > Flashcards

Ventilation and Perfusion Flashcards

1
Q

What percentage of oxygen in arterial blood diffuses into tissues?

A

25%

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2
Q

Gas exchange begins where in the airway?

A
  • 17th division; respiratory bronchioles.
    • alveolar ducts appear at this level.
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3
Q

Anatomical dead space is:

A
  • the part of the airway proximal to the respiratory bronchioles that does not participate in gas exchange (the conducting pathway).
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4
Q

Anatomical dead space contains about what percentage of tidal volume?

A

30% of tidal volume.

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5
Q

What percentage of tidal volume participates in gas exchange?

A

about 70%

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6
Q

Rate of CO2 diffusion at the alveoli in comparison to oxygen diffusion:

A
  • CO2 diffusion 200X faster.
  • pulmonary capillaries have constant back and forth diffusion of CO2.
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7
Q

In the peripheral tissues, normal PO2 is roughly:

A

40mm Hg

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8
Q

In the peripheral tissues, normal PCO2 is roughly:

A

46mm Hg

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9
Q

The alveolar-arterial gradient is a measure of:

A
  • A-a O2 gradient
  • the difference between the alveolar concentration of oxygen and the arterial concentration of oxygen.
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10
Q

The alveolus contains which gases?

A
  • inhaled nitrogen, oxygen, water
  • exhaled CO2
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11
Q

Alveolar pressure (PA) is equal to:

A
  • Barometric pressure (Pb)
  • Sum of the partial pressures of N2, O2, H2O, and CO2.
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12
Q

Is there a difference between the partial pressure of CO2 in the alveolous and in arterial blood?

A
  • No.
  • CO2 is so diffusible that the partial pressures are equal.
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13
Q

Alveolar Gas Equation to determine alveolar O2 level:

A
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14
Q

FIO2 normal value =

A
  • fractional concentration of inspired O2 .
  • 0.21 when breathing normal air at any elevation.
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15
Q

PH2O normal value when air is fully saturated =

A
  • water vapor pressure
  • 47 mmHg when air is fully saturated
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16
Q

Respiratory quotient (R) normal value:

A
  • the ratio of CO2 production to O2 consumption
  • usually 0.8
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17
Q

The alveolar level of oxygen depends on (4):

A
  1. fraction of oxygen in inspired air (FiO2)
  2. barometric pressure (Pb)
  3. water vapor pressure (PH2O)
  4. amount of CO2 in alveolous (PaCO2/R)
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18
Q

Equation to determine PAO2 at sea level under normal conditions:

A

PAO2 = 0.21(760 - 47) - 1.25(PaCO2)

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19
Q

Simplified equation to determine PAO2 for a person breathing at sea level:

A

PAO2 = 150 - 1.25(PaCO2)

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20
Q

The alveolar-arterial (A-a) O2 gradient equation:

A

PAO2 - PaO2 (from ABG)

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21
Q

In a young healthy person, the A-a O2 gradient is normally:

A

<15 mmHg

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22
Q

Normal A-a O2 gradient in the elderly:

A
  • increases with age to about 30 mmHg
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23
Q

Calculate the A-a O2 gradient:

pH=7.40, PaCO2=40, PaO2=95

on room air at sea level

A

5 (Normal)

  • PAO2 = 150 - 1.25(40)
  • PAO2 = 150 - 50 = 100
  • A-a O2 gradient = 100 - 95 = 5
24
Q

Calculate PIO2 at a barometric pressure of 596 (high altitude/plane):

A
  • PIO2 = 0.21(Pb-47)
  • PIO2 = 0.21(596-47)
  • PIO2 = 115
25
Q

Calculate the A-a O2 gradient:

Pb = 596, PaCO2=40, PaO2=60 on room air

A

5 (normal)

  • PAO2 = 0.21(Pb - 47) - 1.25(PaCO2)
  • PAO2 = 0.21(596 - 47) - 1.25(40)
  • PAO2 = 115 - 50
  • PAO2 = 65
  • A-a O2 gradient = 65 - 60 = 5
26
Q

Calculate the A-a O2 gradient:

PaCO2= 68, PaO2=60

on room air at sea level

A

5 (normal)

  • PAO2 = 150 - 1.25(68)
  • PAO2 = 85
  • A-a O2 gradient = 65 - 60 = 5
27
Q

An increase in arterial PCO2 leads to:

A
  • alveolar hypoventilation
  • Arterial CO2 diffuses into the alveolus and displaces oxygen.
28
Q

The three causes of hypoxemia with a normal A-a O2 gradient:

A
  1. low barometric pressure (high altitude)
  2. decreased FiO2 (fire, CO toxicity)
  3. increased arterial CO2 (alveolar hypoventilation)
29
Q

Zones of the lung exist because:

A
  • gravity dependence of pulmonary perfusion.
  • gravity leads to blood flow being better in the base of the lungs than in the apex of the lungs.
30
Q

Draw the Regional Ventilation to Perfusion Ratios in the Normal Lung graph:

A
31
Q

Blood flow (perfusion) is highest in what part of the lung?

A

base of the lung (Zone 3).

32
Q

Ventilation is highest in what part of the lung?

A
  • slightly higher in the base of the lung (Zone 3) than in the other zones.
33
Q

V/Q ratio definition and importance:

A
  • alveolar ventilation (V) to pulmonary blood flow (Q) ratio.
  • Ventilation and perfusion matching is important to achieve ideal exchange of O2 and CO2.
  • Normal V/Q = 0.8.
34
Q

Normal V/Q ratio value:

A

0.8

35
Q

In what region of the lung does ventilation = perfusion?

A
  • an area in the middle region of the lung
36
Q

As you go toward the upper part of the lung, what occurs to V/Q (ventilation/perfusion ratio)?

A
  • increases.
  • more ventilation (V) than blood flow (Q).
37
Q

As you go to the lower part of the lung, what occurs to V/Q (ventilation/perfusion ratio)?

A
  • decreases
  • more blood flow (Q) than ventilation (V).
38
Q

If you have an alveolus that is not well ventilated, the defense mechanism of the body is:

A
  • hypoxic pulmonary vasoconstriction.
    • perfusion impaired to non-ventilated alveolus so that impaired ventilation is matched with impaired perfusion.
    • blood diverted to well-ventilated alveoli.
39
Q

Hypoxic pulmonary vasoconstriction in pneumonia:

A
  • Perfusion less in consolidated part of the lung since pus/fluid blocking gas exchange.
  • blood diverted to other areas of the lung that are better ventilated.
40
Q

Overall purpose of hypoxic pulmonary vasoconstriction:

A
  • match ventilation to perfusion
  • allows for less of a decrease in systemic arterial oxygen saturation levels.
41
Q

V/Q Mismatch in Pneumonia effect on PaO2:

A
  • Ventilation and Perfusion are not matched.
  • Regions of poor ventilation but preserved perfusion.
  • PaO2 levels decrease; hypoxia.
42
Q

Calculate A-a O2 gradient:

PaCO2: 32, PaO2:60 on 21% FIO2

room air at sea level

A

50 (elevated; abnormal)

  • PAO2 = 150 - 1.25(32)
  • PAO2 = 150 - 40 = 110
  • A-a O2 gradient: 110 - 60 = 50
43
Q

Anatomical shunt:

A
  • Septal defects in the heart.
  • Deoxygenated blood mixes with oxygenated blood.
  • No matter how well you oxygenate the alveoli, oxygen levels in the blood will still remain low.
44
Q

Physiologic shunt in the lung:

A
  • bloodflow normal, ventilation zero.
  • V/Q ratio is zero.
  • No gas exchange; increased A-a gradient.

AIRWAY OBSTRUCTION

45
Q

A physiologic shunt in the lung can be due to:

A
  • airway obstruction
  • acute respiratory distress syndrome
46
Q

Dead space ventilation in the lung:

A
  • ventilation normal; bloodflow zero.
  • V/Q ratio is infinite.
  • No gas exchange; increased A-a gradient.

BLOODFLOW OBSTRUCTION

(PULMONARY EMBOLISM)

47
Q

The three conditions that cause hypoxemia with an increased A-a gradient:

A
  1. V/Q mismatch
  2. Shunting
  3. Dead space ventilation
48
Q

V/Q mismatch, shunting, and dead space ventilation all cause hypoxemia with an increased A-a O2 gradient. What distinguishes V/Q mismatch from shunting and dead space ventilation clinically?

A
  • Supplemental O2 corrects the hypoxemia in V/Q mismatch but NOT in shunting/dead space ventilation.
49
Q

Consequences of V/Q Mismatch:

A
  • Low PaO2 (Hypoxemia)
  • Increased A-a Gradient
  • Hypoxemia is corrected with supplemental O2
50
Q

Consequences of physiologic shunting (4):

A
  1. Low PaO2 (Hypoxemia)
  2. Increased A-a Gradient
  3. Low PaCO2 (Hypocapnia)
  4. Not corrected by oxygen therapy
51
Q

Why do you have Low PaCO2 (Hypocapnia) in physiologic shunting?

A
  • open capillaries around a poorly ventilated alveolus.
  • CO2 will just diffuse across out of the capillary.
52
Q

Alveolar Ventilation (VA) is the volume of air per minute that:

A
  • enters or exits the alveoli of the lung and participates in gas exchange.
53
Q

Dead space ventilation (VD) is the volume of air per minute that:

A
  • enters the conducting airways and does not participate in gas exchange.
54
Q

Total ventilation (VE)=

A
  • VE= VA+ VD
  • = alveolar ventilation + dead space ventilation.
55
Q

Minute ventilation =

A
  • = respiratory rate X tidal volume.
56
Q

What two conditions are always associated with Dead Space Ventilation?

A
  1. Low PaO2 (Hypoxemia)
  2. High PaCO2(Hypercapnia)
    • CO2 cannot diffuse across to the alveoli since xit never passes alveoli.
57
Q

As alveolar ventilation decreases, what occurs to PO2 and PCO2?

A
  1. PO2 drops (hypoxemia)
  2. PCO2 increases (hypercapnia)

CP2.08_Ventilation Perfusion (1 decks)

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