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pulmonary circulation Flashcards

1
Q

Normally, pulmonary circulation is a ____ (high/low) resistance, ____ (high/low) compliance system.

A

Low, high

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2
Q

Within the lungs, a decrease in PAO2 causes what process to occur within the vasculature in the area?

A

Hypoxic vasoconstriction

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3
Q

Within the lungs, hypoxic vasoconstriction serves what physiologic function?

A

• It shifts blood away from the poorly ventilated areas of the lung to those that are well ventilated

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4
Q

Name the perfusion-limited gases.

A

Oxygen (normal health), carbon dioxide, nitrous oxide

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5
Q

Under perfusion-limited conditions, where along the length of the pulmonary capillary do the partial pressures of a gas equilibrate?

A

Early (gas exchange is not limited by its ability to cross the membrane, only by the supply of blood)

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6
Q

A patient becomes hypoxic from a massive hemorrhage. Under these perfusion-limited conditions, how can pulmonary gas exchange be increased?

A

By increasing blood flow

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7
Q

Name the diffusion-limited gases.

A

• Oxygen (emphysema, fibrosis), carbon monoxide

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8
Q

Under what two conditions is oxygen a diffusion-limited gas?

A

Emphysema and fibrosis

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9
Q

Under diffusion-limited conditions, where along the length of the pulmonary capillary does the gas equilibrate?

A

It does not equilibrate (the characteristics of the gas cause it to diffuse slowly across the alveolar membrane)

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10
Q

A patient with untreated pulmonary hypertension presents with jugular venous distention, edema, and hepatomegaly. What caused this?

A

The patient is showing signs of cor pulmonale (right heart failure), a complication of pulmonary hypertension

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11
Q

What is the equation for diffusion of a gas across a membrane?

A

Vgas = A/T × Dk(P1 - P2), where A = area, T = thickness, DkP1 - P2) = difference in partial pressures

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12
Q

A patient has emphysema. Which variable is affected by his disease in the equation for gas diffusion, and how? (See image.)

A

The area of membranes available for gas transfer (A) is decreased in emphysema, causing a decrease in diffusion

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13
Q

In the equation for gas diffusion, which variable is affected by pulmonary fibrosis, and how?

A

Thickness of the alveolar membrane is increased in pulmonary fibrosis, causing a decrease in diffusion

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14
Q

How is pulmonary vascular resistance calculated?

A

PVR = pressure in the pulmonary artery - pressure in the left atrium)/cardiac output

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15
Q

How is left atrial pressure measured?

A

It is approximated by pulmonary wedge pressure

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16
Q

How do you measure pulmonary vascular resistance using flow and the difference in pressure across it?

A

R = ΔP/Q, where R is resistance, P is pressure, Q is flow

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17
Q

Pulmonary vascular resistance is ____ (directly/inversely) related to vessel length and ____ (directly/inversely) related to vessel radius.

A

Directly; inversely—R = (8ηl)/(πr4), where η = viscosity of blood, l = vessel length, and r = vessel radius

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18
Q

A patient’s cardiac output is 5 L/min. Ppulm artery is 10 mmHg, & PL atrium is 5 mmHg. What is the pulmonary vascular resistance?

A

PVR = (Ppulm artery - PL atrium)/cardiac output = ([10 mmHg - 5 mmHg])/5 L/min) = 1 (mmHg × min)/L

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19
Q

Matt’s pulmonary vascular resistance is 2 (mmHg × min)/L. If Ppulm artery is 20 mmHg and PL atrium is 8 mmHg, find the cardiac output.

A

CO = 6 L/min, as PVR = (Ppulm artery - PL atrium)/cardiac output = 2 (mmHg × min)/L = ([20 mmHg - 8 mmHg])/cardiac output)

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20
Q

Define the variables of the full alveolar gas equation: PAO2= PIO2 - PaCO2/R.

A

PAO2 = alveolar PO2, PIO2 = PO2 in inspired air, PaCO2 = arterial PCO2, R = respiratory quotient = CO2 produced/O2 consumed

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21
Q

How can the alveolar gas equation be simplified and approximated (assuming that the patient is breathing ambient air)?

A

PAO2 = 150 - (PaCO2/0.8)

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22
Q

By using the alveolar gas equation, what important measure of pulmonary function can be determined?

A

The alveolar-arterial gradient

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23
Q

What is the normal alveolar-arterial gradient?

A

10–15 mmHg

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24
Q

Explain why the alveolar-arterial gradient might be elevated. What three pathologic processes can cause this?

A

V/Q mismatches, diffusion limitations (fibrosis), and shunting (a rise in the A-a gradient may occur in hypoxemia)

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25
Q

A patient has a respiratory quotient (R) of 1.0. What does this tell you about current metabolic state?

A

The respiratory quotient (R) is a ratio of carbon dioxide produced to oxygen consumed

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26
Q

A patient breathes air with a PO2 of 100 mmHg. PaCO2 is 30 mmHg. With a respiratory quotient of 0.6, what is alveolar O2?

A

50 mmHg, as PAO2 = PIO2 - PaCO2/R = 100 mmHg - (30 mmHg/0.6)

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27
Q

A patient’s alveolar PO2 is 100 mmHg. Air PO2 is 150 mmHg. Assuming a respiratory quotient of 0.8, what is their arterial CO2?

A

40 mmHg, as = PAO2 = PlCO2 - PaCO2/R = 100 mmHg = 150 mmHg - (× mmHg/0.8)

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28
Q

Name five processes that can lead to hypoxemia (decreased arterial oxygen).

A

High altitude, hypoventilation, ventilation/perfusion ratio mismatches, diffusion limitations, and right-to-left shunting

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29
Q

Which two processes lead to hypoxemia with a normal A-a gradient?

A

High altitude and hypoventilation (e.g., opioid use)

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30
Q

Which three processes can lead to hypoxemia with an increased A-a gradient?

A

Ventilation/perfusion ratio mismatches, diffusion limitation, and right-to-left shunting

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31
Q

Name four processes that can lead to hypoxia (decreased oxygen delivery to tissue).

A

Decreased cardiac output, hypoxemia, anemia, and carbon monoxide poisoning

32
Q

Name two processes that can lead to ischemia (loss of blood flow).

A

Impeded arterial flow and reduced venous drainage

33
Q

What is the difference between hypoxemia and hypoxia?

A

Hypoxemia is decreased arterial partial pressure of oxygen, whereas hypoxia is decreased oxygen delivery to tissue

34
Q

A patient appears sedated and is breathing slowly after a painful surgical procedure. What is his likely A-a gradient?

A

The A-a gradient would be normal (he was likely given too much pain control with opioids, causing sedation and hypoventilation)

35
Q

A hiker is weak after rapidly ascending a mountain. What is his likely A-a gradient?

A

The A-a gradient would be normal in cases of hypoxemia caused by high altitudes

36
Q

A patient is found to have a diffusion limitation in his lungs. How is his likely A-a gradient affected?

A

It is increased

37
Q

A patient develops a pulmonary embolus. What is his likely A-a gradient?

A

This is a case of V/Q mismatch, which would cause an increased A-a gradient

38
Q

A patient is found to have a right-to-left shunt. How is his likely A-a gradient affected?

A

It is increased

39
Q

A patient has tuberculosis. This and other microorganisms that thrive in high-oxygen environments flourish in which part of the lungs?

A

The apex

40
Q

A woman chokes and aspirates a peanut. What is her ventilation/perfusion ratio likely to be?

A

Approaching 0, as airway obstruction creates a blood flow shunt which isn’t part of gas exchange (0 = “oirway” obstruction)

41
Q

A child chokes on a peanut. This airway obstruction leads to perfusion with no ventilation within an area of the lungs. What is this called?

A

A shunt

42
Q

A man suffers a pulmonary embolus. What is his ventilation/perfusion ratio likely to be?

A

Approaching ∞, as the pulmonary embolus is a blood flow obstruction, causing physiologic dead space (∞ = blood flow obstruction)

43
Q

Which zone of the lung is associated with wasted ventilation?

A

Zone 1

44
Q

Which zone of the lung is associated with wasted perfusion?

A

Zone 3

45
Q

In a hypoxic patient due to ____ (dead space/shunting), 100% oxygen does not improve the partial pressure of oxygen in the blood.

A

Shunting

46
Q

In a hypoxic patient due to ____ (dead space/shunting), 100% oxygen does improve the partial pressure of oxygen in the blood.

A

Dead space (assuming the dead space is

47
Q

What is the ideal ventilation/perfusion ratio for gas exchange?

A

1:1

48
Q

Within what part of the lung does ventilation/perfusion equal approximately 3?

A

The apex of the lung

49
Q

In the apex of the lung, there is wasted ____ (perfusion/ventilation).

A

Ventilation

50
Q

Within what part of the lung does ventilation/perfusion equal approximately 0.6?

A

The base of the lung

51
Q

Is ventilation greater at the base of the lung or the apex of the lung?

A

The base of the lung

52
Q

Is perfusion greater at the base of the lung or the apex of the lung?

A

The base of the lung

53
Q

A patient exercises. The vasodilation of the apical capillaries of the lung results in what change to the ventilation/perfusion ratio?

A

The ventilation/perfusion ratio approaches 1, maximizing gas exchange to meet the metabolic demands of exercise

54
Q

Once inside a red blood cell, carbon dioxide combines with which molecule to eventually become bicarbonate?

A

Water

55
Q

What enzyme catalyzes the conversion of carbon dioxide and water into carbonic acid?

A

Carbonic anhydrase

56
Q

Within a red blood cell, the carbonic acid formed from the combination of carbon dioxide and water dissociates into what two compounds?

A

Hydrogen and bicarbonate ions

57
Q

What is the fate of the bicarbonate that results from the deprotonation of carbonic acid within a red blood cell?

A

It gets exchanged out of the red blood cell for a chloride molecule that enters the red blood cell

58
Q

In the lungs, the oxygenation of hemoglobin promotes what?

A

The dissociation of a proton from hemoglobin and therefore a decrease in pH, which favors formation of carbon dioxide from bicarbonate

59
Q

Name the effect in which oxygenation of hemoglobin in the lungs promotes H+ dissociation, causing CO2 release from RBCs.

A

The Haldane effect

60
Q

A woman has lactic acidosis. How will this pH reduction in the peripheral tissues relative to the lungs shift the oxygen dissociation curve?

A

It will shift it to the right, favoring dissociation of oxygen from hemoglobin

61
Q

In peripheral tissue, the right shift of the oxygen dissociation curve causes oxygen unloading. What is this effect called?

A

The Bohr effect

62
Q

A hiker goes up to high altitudes for an afternoon. What happens to his ventilation, PaO2, and PaCO2?

A

PaO2 and PaCO2 decrease, as ventilation is increased

63
Q

A patient has been living high in the mountains for years. What happens to his erythropoietin levels?

A

In response to high altitude, erythropoietin levels are increased, as are hematocrit and hemoglobin

64
Q

A hiker ascends a mountain. What happens to his level of 2,3-bisphosphoglycerate?

A

In response to high altitude, the 2,3-BPG level increases

65
Q

What substance binds to hemoglobin so that hemoglobin releases more oxygen as a physiologic response to high altitude?

A

2,3-bisphosphoglycerate

66
Q

A hiker climbs up a tall mountain. What cellular change occurs in response to this?

A

An increase in the number of mitochondria occurs in response to high altitude

67
Q

A man ascends a mountain. Increased renal excretion of what substance occurs in response?

A

Bicarbonate

68
Q

The increased renal excretion of bicarbonate that is seen in response to high altitude compensates for what?

A

The respiratory alkalosis that occurs as a result of increased ventilation

69
Q

The increased renal excretion of bicarbonate that is seen in response to high altitude can be augmented using what?

A

Acetazolamide

70
Q

A man decides to live in the mountains for several years. In response, chronic hypoxic pulmonary vasoconstriction results in what condition?

A

Right ventricular hypertrophy

71
Q

A man undergoes an exercise test. What happens to carbon dioxide production in his muscles? Oxygen consumption? Rate of ventilation?

A

They are all increased

72
Q

A man undergoes an exercise test. What happens to the ventilation/perfusion ratio?

A

It becomes more uniform from apex to base

73
Q

A woman undergoes an exercise test. What happens to pulmonary blood flow?

A

It increases due to increased cardiac output

74
Q

A personal trainer undergoes strenuous exercise. How does the pH of the body change?

A

pH decreases during strenuous exercise due to lactic acidosis

75
Q

PaO2 and PaCO2 ____ (increase/decrease/stay the same) in response to exercise.

A

Stay the same

76
Q

When a patient exercises, the venous CO2 content ____ (increases/decreases), whereas venous O2 content ____ (increases/decreases).

A

Increases, decreases

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