Pulmonary Blood Flow Flashcards by Berina Karisik

Which side of the heart does the pulmonary circulation receive blood from?

Right side whereas systemic receives from left

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What is the source of blood going to the pulmonary circulation?

Systemic veins

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What is the source of blood going to the systemic circulation?

Pulmonary veins

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What is the pressure in the ventricle in the pulmonary circulation?

25/0

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What is the pressure in the ventricle in the systemic circulation?

120/0

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What is the pressure in the artery in the pulmonary circulation?

25/15

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What is the pressure in the artery in the systemic circulation?

120/80

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What is the CO for both the pulmonary and systemic circulation?

3.5-5 L/min

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What is the PaO2 in the pulmonary circulation?

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What is the PaO2 for the systemic circulation?

100

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What is the PaCO2 in the pulmonary circulation?

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What is the PaCO2 in the systemic circulation?

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What response does the pulmonary circulation have to hypoxia?

Vasoconstriction

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What response does the systemic circulation have to hypoxia?

Vasodilation —> deliver more blood/O2

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What is hypoxic vasoconstriction?

Regional vasoconstriction in response to hypoxia through myogenic mechanism (no innervation required)

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What is the purpose of hypoxic vasoconstriction?

Direct blood to areas of lung with better oxygenation

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Describe the alveolar capillaries

Receive blood from the RV
Low O2 and high CO2
Involved in the exchange of O2 and CO2 between the blood and air

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Describe the extra-alveolar (aka bronchial) capillaries

Receive blood from the LV
High O2 and low CO2
Deliver O2 and CO2 to the tissue of the lungs

What are the two pathways of blood flow returning to the heart from the extra alveolar capillaries?

Flow into azygos vein and other nearby returning to RV
In the pulmonary veins -> leads to venous admixture which reduces the PaO2 of the arterial blood and increases the PaCO2 to a small degree

How does blood return to the heart from alveolar capillaries?

Pulmonary vein

What are the levels of blood gases in the veins in alveolar and extra alveolar vessels?

High O2 and low CO2

How is pulmonary blood pressure calculated?

CO x PVR

How does PVR compare with the rest of the body?

PVR is much lower than the rest of the body (about 1/10 of TPR)

What is PVR determined by?

High number of capillaries
How many are open at any given moment in time
Much less sympathetic tone/vasoconstricting forces

What happens to PVR during exercise?

Drops as more pulmonary capillaries open to accommodate the increased CO

PVR also depends on what?

Lung volume At low or very high lung volumes the resistance increases a little bc the stretch of the tissue compresses the capillaries (diameter of capillaries decreases a little)

What is BP in PVR compared to systemic resistance?

25/15 | Systemic 120/80

Describe blood flow in the apex of the lungs

Blood pressure is reduced bc it is slightly above the heart However the alveoli are expanded The blood flow is less

Describe blood flow in the middle of the lung

BP is a little higher bc we are at the level of the heart Alveoli are an average size Blood flow is “normal”

Describe blood flow at the base of the lung

BP is high because we are below the level of the heart Alveoli are smaller Blood flow is greater than in other regions of the lung

Regional blood flow is determined by what?

How gravity is acting on the blood and how much air is in that region of the lung

What are chemical modulators of pulmonary blood flow?

NO, endothelin 1 and thromboxane A2

What is the role of NO on pulmonary blood flow?

Made by endothelium (EDRF) Causes SM relaxation and vasodilation Significant role in normal pulmonary blood flow

What role does endothelin 1 play on pulmonary blood flow?

Also made in the lungs Vasoconstrictor Seems to be a player under pathologic conditions (not normal conditions)

What role does thromboxane A2 have on pulmonary blood flow?

Similar to endothelin 1 | Can be found in the pulmonary vasculature under the right (pathologic) conditions

What controls how much fluid moves from the capillary to the lung?

The starling forces (hydrostatic and oncotic pressures)

Which forces move water from the capillary to the alveolus?

Capillary hydrostatic pressure Tissue hydrostatic pressure Oncotic pressure of the tissues

Which forces move water from the alveolus to the capillary?

Capillary oncotic pressure

Which pressure is the greatest in the lung?

Hydrostatic pressure in the capillaries

What is the net result of starling forces in the lung?

Favor net filtration (movement) of fluid into the alveoli | But this is bad for gas exchange - solution = lymphatic system

The lymphatics are crucial in doing what?

Removing the filtered fluid from the alveolus

ACE not only converts angiotensin I into angiotensin II but it also does what?

Inactivates bradykinin | This is why people on ACE inhibitors can develop a cough

How do the lungs participate in the metabolism of arachidonic acid metabolites?

Both leukotrienes and prostaglandins/thromboxane A2 are produced by immune system activation in the lungs Prostaglandins E2 and F2-alpha are also almost completely removed from the circulation in the lungs as are the leukotrienes