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CRRAB 2 Week 3 > Pulmonary Blood Flow > Flashcards

Pulmonary Blood Flow Flashcards

1
Q

Are pressures in the pulmonary system relatively low or high? Average pressure?

A

LOW

25/8 normally, so mean pressure about 15 mmHg

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2
Q

Because the pulmonary pressure is low, what does that mean for resistance? What’s the average?

A

It means the resistance also has to be low in order to blood to get through - on average it’s around 2 mmHg (compared to the 100 mmHg on average in the systemic circulation)

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3
Q

What is the pressure around the pulmonary capillaries?

A

It’s about equal to alveolar pressure beecause the capillaries are surrounded by alveoli (basically air), not solid tissue

This means during exhalation it is a couple mmHg and during inspiration it is subatmospheric

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4
Q

If the pressure around the pulmonary capillaries is subatmospheric during inspiration, what happens to the radius of the capillary during inspiration?

A

they get pulled open so radius increases and resistance decreases

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5
Q

What are some conditions that would radically change the pressure surrounding the pulonary capillaries?

A

tension pneumothorax

positive pressure ventilation

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6
Q

Pulmonary artery resistance DECREASES with an increase in pulmonary artery pressure (which is not normal) because of what?

A
  1. you get RECRUITMENT of additional capillaries in conducting blood flow (increase surface area)
  2. Distention of the capillaries conducting blood to allow more blood to flow (increasing radius, decreases resistance(
  3. Expansion of the lung pulls the vessels open, increasing radius
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7
Q

When can alveolar pressure compress the vessels? This isn’t normal….

A

When the alveolar pressure is greater than the capillary pressure - like in a pneumothorax or positive pressure ventilation

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8
Q

What will norepinephrine, serotonin and histamine do to the vessels and resistance?

A

they will contract the vessels to increase resistance - IN THE PULMONARY SYSTEM

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9
Q

What will acetylcholine, isoproterenol and prostacyclin do to the pulmonary vessels and resistance?

A

They will relax the pulmonary vessels to reduce resistance

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10
Q

How do you measure pulmonary blood flow using the fick principle?

A

Pulmongary blood flow = VO2 (volume O2 consumption) / (CaO2 - CvO2)

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11
Q

How can you measure pulmonary blood flow using a dye?

A

you inject a dye into the pulmonary artery and measure concentration in arterial blood

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12
Q

From the equation R = 8nl/pi x r^4…

what are the two main variables that keep resistance low in the pulmonary system?

A

remember that the radius is the radius of all the vessels combined in the lung, so that’s a ton of radius and it’s to the 4th power!

length is super short in the pulmonary system - just from the heart to the lung which is practically nothing

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13
Q

Why does more blood flow to the base of the lung than to the apex?

A

easy - gravity

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14
Q

Describe zone 1 of perfusion in the lung. When does it occur?

A

It’s a zone where Palveolar > Parterial > Pvenous

NO flow occurs in this zone because the alveolar pressure is strong enough that is collapses the vessels

this does not occur naturaly but can arise from hemorrhage or positive pressure breathing

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15
Q

Does a region in zone 1 participate in gas exchange?

A

NO - no flow, no ga exchange

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16
Q

Where in the lung is a zone 1 most likely to occur?

A

at the apex

17
Q

`What does zone 2 of perfusion represent?

A

regions where Parterial > Palveolar > P venous

18
Q

What determines flow in zone 2? Why is this different from normal?

A

blood flow in zone 2 is determined by pressure differential between the arteries and the alveoli, which is different because venous pressure has no influence on the flow at all

19
Q

Where in the lung is a zone 2 most likely to occur?

A

in the apical region of the lung

20
Q

Describe zone 3 of perfusion?

A

This is what typically happens…

Parterial is greater than Pvenous is greater than Parterial

21
Q

What is flow dependent on in zone 3?

A

pressure difference between arterial and venous pressures. - the normal situations in the circulatory system

22
Q

Where in the lung does zone 3 occur?

A

the midregions and bases

23
Q

What happens to pulmonary vasculature during hypoxia? Why?

A

It constricts!!! Which is unique to the lungs!!

It does this because it’s in the body’s best interest to divert blood fllow away from an area of hpoxia in the hopes that it gets diverted to a region with better gas exchange

24
Q

What happens if there are no regions with better gas exchange?

A

you get pulmonary hypertension

25
Q

What’s the basic mechanism for the pulmonary constriction in response to hypoxia?

A

not totally worked out….but it’s independent of nerve signalling

involves inhibiting voltage gated K channels, which depolarizes the membranes and causes an increase in [Ca] leading to vasoconstriction

26
Q

How is fluid movement out of the pulmonary vasculature controlled?

A

starling forces -

fluid escape = K(Pc - Pint) - (Mc - Mint)

27
Q

What does the low pulmonary pressure value means for fluid filtration?

A

it keeps the lung dry!

Pcap in the lung is 15 and Mcap in the lung is 25, which means there’s a greater force keeping the fluid in the vasculature

good because no one likes pulmonary edema

28
Q

What are some conditions that would icnrease fluid escape into the lungs? What’s the symptom?

A

heart failrue or mitral stenosis - anything that causes an icnrease in pulmonary hydrostatic pressure

you get alveolar edema and shortness of breath

29
Q

What are two other functions of the pulmonary circulation besides gas exchange - not metabolic functions yet?

A

reservoir for blood (when we lay down)

filtration of blood - thrombi in the legs go to the lungs and can’t get through to the brain - good thing overall

30
Q

What are some metabolic functions of hte lungs?

A
  1. synthesizes ACE to convert ANG1 to ANG2
  2. inactivates bradykinin (with ACE)
  3. accumulates 5HT to remove form circulation
  4. Metabolizes prostaglandin E1, E2 and F2alpha
  5. Synthesizes prostaglandins and leukotrienes (importnat for asthma)
  6. Removes leukotrienes from the circulation

CRRAB 2 Week 3 (10 decks)

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