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CRRAB II Week 5 > Blood Flow & Metabolism > Flashcards

Blood Flow & Metabolism Flashcards

1
Q

What does the Pulmonary artery contain?

A

Mixed venous blood!

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2
Q

What is the PO2 in the pulmonary artery?

A

About 40 mmHg

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3
Q

What is the PCO2 in the pulmonary artery?

A

About 46 mmHg

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4
Q

How is most CO2 transported?

A

As bicarbonate

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5
Q

How does the pulmonary circulation travel?

A

It branches with the airways down to the terminal bronchioles -> then breaks into pulmonary capillaries for gas exchange

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6
Q

What are the pressures in the pulmonary capillaries?

A

Relatively low (25/8 mmHg normally)

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7
Q

What conditions significantly alter the low pressure in the pulmonary capillaries?

A
  • Pulmonary HTN (when pressure goes up)
  • Heart failure –> elevated pulmonary artery pressures
  • Anything that causes inadequate pumping from the left of the heart
  • Alveolar hypoxia (COPD) patients all have pulmonary HTN
  • High altitudes –> cause pulmonary HTN
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8
Q

What is the mean pressure in the pulmonary circulation?

A

15 mmHg

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9
Q

What is the cardiac output?

A

5L/min

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10
Q

What is the left atrial pressure?

A

5 mmHg

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11
Q

What is the resistance in the pulmonary capillaries if the flow is 5L/min, mean arterial pressure is 15 mmHg and the pressure is 5mmHg in the left atrium?

A

Resistance = Change in P/Flow

=15-5 mmHg = 10 mmHg/5L/min = 2!!

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12
Q

What is the pressure around the pulmonary capillaries?

A

During exhalation = couple mmHg

During inhalation = subatmospheric

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13
Q

What is the pressure around pulmonary capillaries known as?

A

Surrounded by alveoli.

Therefore, it’s alveolar pressure.

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14
Q

What happens to pulmonary vessels during inspiration?

A

They are pulled open!

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15
Q

Why do people die from tension PTX?

A

It crushes the venis in the lungs!

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16
Q

IMP: Are there any conditions that radically change the pressure in around the pulmonary capillaries?

A

Tension PTX (very high tension —–> compress blood flow), anything that increases pressure in the chest

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17
Q

How does pulmonary artery resistance relate to pulmonary artery pressure ?

A

Resistance decreases with an increase in pulmonary artery pressure

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18
Q

What causes pulmonary artery resistance to decrease with an increase in pulmonary artery pressure?

A
  • Recruitment of additional capillaries in conducting blood flow
  • Distention of capillaries conducting blood to allow more blood to flow
  • Expansion of the lung also reduces resistance
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19
Q

What does alveolar pressure do if it is greater than capillary pressure??

A

It can compress vessels to increase resistance!

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20
Q

What does NE, Serotonin and Histamine do to vessels?

A

Contracts pulmonary vessels to reduce their resistance.

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21
Q

What does Acetylcholine (ACh), Isoproterenol & Prostacyclin do to pulmonary vessels?

A

Relaxes/dilates pulmonary vessels to reduce resistance

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22
Q

What does the shorter length of the pulmonary circulation cause?

A

Shorter length –> allows it to have lower pressure (mean = 15 mmHg) and lower resistance
-Ex: in the short artery traveling from the RV to the pulmonary circulation

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23
Q

What does the longer length of the systemic circulation cause?

A

-Longer length –> higher resistance, higher pressure (mean = 100 mmHg)
It also has muscular arteries

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24
Q

What is pulmonary resistance??

A

Delta P/Flow = 15-5 = 10 mmHg/5 L/min (CO) = 2 mmHg/L/min

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25
Q

What does Fick’s Principle Measure?

A

Oxygen consumption

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26
Q

What is Fick’s Equation?

A

O2 consumption = Cardiac Output (CaO2 - CvO2)
C = concentration of O2
-Referring to systemic arterial & venous blood here

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27
Q

How do we calculate pulmonary blood flow?

A

Pulmonary blood flow = VO2/ (CaO2-CvO2)

VO2 = oxygen consumption

28
Q

If oxygen volume consumed is 250 ml/min (at rest) and oxygen concentration in blood is 20 ml/dL and 15 ml/dL in arteries and veins, what is pulmonary flow?

A

250/(20-15) = 250/5 = 50 dL = 5L

29
Q

Let’s say CO2 production is 200 mL/min and O2 consumption is 250 mL/min, what is the respiratory quotient?

A

200 mL/min / 250 mL/min = 0.8

30
Q

What does a 0.8 respiratory quotient indicate?

A

You aren’t producing as much CO2 as you’re using O2 –> this means you’re burning fat!

31
Q

What happens to the respiratory quotient when you exercise?

A

The number increases to 1 because your CO2 production is similar to your O2 consumption

32
Q

Where is there more blood flow in the lung?

A

More flow to the base of the lung than to the apex because of gravity

33
Q

How many zones of perfusion exist?

A

Three!

34
Q

What is the flow in zone 1 of perfusion? What are the pressures?

A

Palveolar > Parterial > Pvenous

  • No flow occurs in this region
  • This does not occur naturally but can occur in hemorrhage or positive pressure breathing
  • This area does not participate in gas exchange (physiologic dead space)
  • -> Most likely to occur at apex of lung
35
Q

What influences the flow in zone 2 of perfusion? What are the pressures?

A

Parterial > Palveolar > Pvenous

  • Blood flow in this region is determined by pressure differential between arteries and Alveoli
  • Venous pressure does not influence flow
  • Most likely to occur in the apical region of the lung
36
Q

What influences the flow in zone 3 of perfusion? What are the pressures?

A

Parterial > Pvenous > Palveolar

  • Flow is dependent on the arterial/venous pressure difference (i.e., normal situation in the circulatory system)
  • Occurs in the mid regions or base of lungs - Zone 3 is the “normal region”
37
Q

What does alveolar hypoxia do the blood vessels perfusing the hypoxic region of the lung?

A

Alveolar hypoxia will CONSTRICT the hypoxic region of the lung (diverts the blood to other non-hypoxic areas)

38
Q

How does alveolar hypoxia lead to blood vessel constriction in that area?

A
  • Mechanism independent of nerves
  • Appears to involve inhibiting voltage gated K+ channels
  • -> this would hypopolarize (depolarize) the membrane potential
  • Causes an increase in [Ca] leading to a vasoconstriction
39
Q

What are examples of when alveolar hypoxia and resultant blood vessel constriction occurs?

A

-High altitudes, newborns

40
Q

What forces control fluid movement out of the pulmonary vasculature?

A

Starling forces

41
Q

What is the equation that describes starling forces and the fluid movement in the lung?

A

Fluid escape = Kf (Pcap - Pint) - delta(picap - pi int)

42
Q

What is the ‘fluid escape’ or flow in the lungs?

A

constant (15 - ?) - constant (25 - ?) = -10 = fluid reabsorption

43
Q

Why is it good that fluid movement is shifted toward reabsorption in the lungs?

A

-It’s good for keeping the lungs dry

44
Q

What might leak out of the lungs? What does this cause?

A
  • Must be a slight leak of fluid out the lungs because there is lymphatic drainage (20 ml/hr)
  • This is .001/.01% of total flow
  • This should be much less than in systemic circulations because of the lower hydrostatic pressure (Pcap)
45
Q

How does oncotic and hydrostatic pressure change along the capillary

A

As the capillary moves from arteriole to venous the hydrostatic pressure drops and the oncotic pressure remains the same the whole time.

46
Q

What are situations where fluid movement would be increased (fluid movement into the lungs)?

A
  • Heart failure

- Pulmonary HTN

47
Q

What does too much fluid in the lung cause? What do patient’s experience?

A

Too much fluid escapes –> alveolar edema

-Experienced as shortness of breath

48
Q

What are 25% of hospital admissions due to?

A

Heart failure

49
Q

What are two functions of the lung relating to blood?

A
  1. Reservoir for blood
    - -> When we lay down, blood drains from the legs to the lungs
  2. Filter of blood
    - -> Thrombi in the legs (periphery) can not get to the brain (prevents PE from reaching brain and causing stroke!)
50
Q

What does the lung activate?

A

Angiotensin I to Angiotensin II (but this occurs in all blood vessels)
-Mediated by angiotensin converting enzyme

51
Q

What does the lung inactivate?

A

Bradykinin

–> mediated by angiotensin converting enzyme (it breaks down bradykinin)

52
Q

What does the lung accumulate?

A

Serotonin to remove it from the circulation

53
Q

What does the lung metabolize?

A

Prostaglandin E1, E2 and F2alpha

54
Q

What does the lung synthesize?

A

Prostaglandins & Leukotrienes (mediators of asthma)

  • -> bronchoconstrictors
  • Lung also removes leukotrienes from circulation
55
Q

What is a very important function of PGE in the lung in early life?

A

Keeps the patent ductus arteriosus open

56
Q

If you wished to treat a patent ductus arteriosus, what drug would be best?

A

Indomethacin (COX inhibitor)

57
Q

How does indomethacin close the patent ductus arteriosus?

A

It inhibits COX which normally stimulates PGE and PGE dilates/causes the ductus arteriosus to remain patent.

58
Q

Where is pressure lower, in the pulmonary or systemic circulation?

A

Pressure is MUCH LOWER in the pulmonary circulation

59
Q

When does resistance fall in the pulmonary circulation?

A

Resistance is extremely low and falls further upon increases in cardiac output because of recruitment and distention

60
Q

How is blood flow distributed?

A

Toward the base of the lung and away from the apex

61
Q

How do you define Zone 1 of the lung?

A

-Physiological dead space

Paleveoli >Parteriole > Pvenous

62
Q

How do you define Zone 2 of the lung?

A

Parteriole > Palveoli > Pvenous

63
Q

How do you define Zone 3 of the lung?

A

Parteriole > Pvenous > Palveoli

64
Q

What does poor ventilation do to blood flow?

A

Hypoxic pulmonary vasoconstriction reduces blood flow to poorly ventilated sections of the lung

65
Q

What mediates fluid movement out of pulmonary capillaries?

A

Fluid movement out of the capillary is mediated by the balance of pressures (hydrostatic and oncotic) –> not much movement out of capillary due to hydrostatic and oncotic pressures
–> low hydrostatic pressure makes lung less likely to experience edema than other circulations

CRRAB II Week 5 (12 decks)

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