Ch. 4 West

Question 1

The mean pressure in the main pulmonary artery

Answer 1

15 mmHg (very low!)
25/8 (sys/dia)

Question 2

Typical mean pressure in the aorta

Answer 2

100 mmHg

Question 3

Typical pressure in right atrium

Answer 3

2 mmHg

Question 4

Typical pressure in left atrium

Answer 4

5 mmHg

Question 5

Walls of the pulmonary artery and its branches are (thin/thick) and contain relatively little smooth muscle.

Answer 5

Thin- often mistaken for veins

Question 6

Since capillaries are so thin walled and relatively low pressure, they are liable to collapse or distend based on the pressures within and around them. The pressure around them is very similar to the pressure of _____

Answer 6

The alveolar pressure

Question 7

The pressure difference between the inside and outside of the capillaries is often called the ____ pressure.

Answer 7

Transmural pressure

Question 8

Arteries and veins (increase/decrease) their caliber as the lung expands

Answer 8

Increase

As the lung expands, these larger blood vessels are pulled OPEN by the radial traction of the elastic lung parenchyma that surrounds them.

Question 9

Alveolar vessels (i.e. capillaries and some of the slightly larger vessels in the corners of the alveolar walls) are subject to alveolar pressure, and become ___ when alveolar pressure increases.

Answer 9

They become compressed- basically they are the opposite of the larger vessels

Question 10

Vascular resistance

Answer 10

Vascular resistance = (input pressure - output pressure)/blood flow

Question 11

True/False: Increase in either pulmonary arterial or venous pressure causes pulmonary vascular resistance to fall

Answer 11

True

Question 12

Explain recruitment

Answer 12

Under normal conditions, some capillaries are either closed or open, but with no blood flow. As the pressure rises, these vessels begin to conduct blood, thus lowering the overall resistance.

Question 13

Explain distention

Answer 13

Widening of individual capillaries (from a flattened state to a more round state in cross-section) in response to increased pressure.

Question 14

True/False: recruitment and distention are often the main reason pulmonary vascular resistance decreases with exercise

Answer 14

True

Question 15

Explain how lung volume plays a role in vascular resistance

Answer 15

At high lung volumes, the larger vessels are pulled open and vascular resistance decreases.
On the other hand, vascular resistance is high when the lung volume is low.

Question 16

Explain critical opening pressure

Answer 16

If the lung is completely collapsed, the smooth muscle tone of the larger vessels is so effective that the pulmonary artery pressure has to be raised several cm of water above downstream pressure before any flow occurs at all- this is the critical opening pressure.

Question 17

List some substances which cause smooth muscle contraction and increase pulmonary vascular resistance

Answer 17

Serotonin
Histamine
Norepinephrine
Endothelin

Alveolar hypoxia
Thomboxane A2

Question 18

List some substances which cause smooth muscle relaxation on the pulmonary vessels

Answer 18

Acetylcholine
Calcium channel blockers
NO
PDE-5 inhibitors
Prostacyclin (PGI2)

Question 19

Fick principle/equation

Answer 19

Q = V(o2)/(CaO2 - CvO2)

Where Q = amount of blood passing through the lungs each minute
V(o2) = oxygen consumption (collected via spirometery or mouth piece and analyzer)
CaO2 = blood leaving the lungs
CvO2 = blood entering the lungs

Can be done also with dilution indicators or cold saline and temperature differential

Question 20

Zone 1 explanation

Answer 20

Top of the lung (least gravity-dependent)
There may be a region where the hydrostatic pressure in the arterial side of circulation is LESS than the pressure in the alveolus, which will then result in the capillary being squished flat, and no flow being possible.
This doesn’t happen under normal circumstances. It may happen however if the arterial pressure is reduced (sepsis/hypotension) or if the alveolar pressure is increased (PPV) - then we have alveolar dead space

Question 21

Zone 2 explanation

Answer 21

Further down in the lung than zone 1
Pulmonary arterial pressure increases due to hydrostatic forces, and exceeds alveolar pressure.
Under these conditions, blood flow is determined by the difference between arterial and alveolar pressures (not the usual arterial-venous pressure differential).
Venous pressure has no influence on flow unless it exceeds arterial pressure.

Question 22

Zone 3 explanation

Answer 22

In zone 3, venous pressure now exceeds alveolar pressure, and flow is determined as normal based off the difference between arterial and venous pressures.
The pressure within the capillaries increases down the zone, while the pressure outside them (alveolar pressure) remains the same. Recruitment and distention occur.A

Question 23

At low lung volumes, resistance of the extra-alveolar vessels becomes important as well. “Zone 4” is at the base of the lung, where the parenchyma is least expanded. The extra-alveolar vessels will be _____

Answer 23

They will have reduction of blood flow

Question 24

Zone 2 - flow is determined by what?

Answer 24

Difference between arterial and alveolar pressures

Question 25

Zone 3 - flow is determined by what?

Answer 25

Difference between arterial and venous pressures

Question 26

True/false: in zones 2 and 3, flow increases down each zone

Answer 26

True

Question 27

Explain hypoxic pulmonary vasoconstriction

Answer 27

Contraction of smooth muscle in the walls of the small arterioles in the hypoxic region of the lung.

The vessel wall becomes hypoxic. There may be some degree of inhibition of voltage-gated potassium channels, resulting in influx of calcium, resulting in smooth muscle contraction.

Question 28

Is hypoxic pulmonary vasoconstriction dependent on the CNS? Is it dependent upon the PaO2 or the FiO2?

Answer 28

It is dependent upon the PO2 of alveolar gas, NOT the PaO2

It is not dependent upon CNS connections

Question 29

Is hypoxic pulmonary vasoconstriction linear in response to the degree of alveolar hypoxia?

Answer 29

No- changes above 100 mmHg alveolar PO2 result in little change
Changes below 70 mmHg result in marked vasoconstriction

Question 30

List some pulmonary endothelial derived vasoactive substances and what they do

Answer 30

Nitric oxide: formed from L-arginine via catalysis by endothelial NO synthase (e NOS). NO activates soluble guanylate cyclase and increases synthesis of cGMP, which subsequently inhibits calcium channels, resulting in vasodilation - REDUCES hypoxic pulmonary vasoconstriction.

Endothelin-1 and thromboxane A2 are potent vasoconstrictors

Question 31

T/F: At higher altitudes, PO2 is reduced throughout the lung, and therefore generalized pulmonary vasoconstriction occurs leading to a rise in pulmonary arterial pressure.

Answer 31

True

Question 32

Fluid exchanges in the lung obey Starling’s law. The capillary hydrostatic pressure is higher at the bottom of the lung than the top of the lung. The interstitial edema seen in heart failure is characterized by fluid accumulation in the ______ an _____ spaces.

Answer 32

Peribronchial and perivascular spaces

Question 33

Name two other functions of the lung

Answer 33

As a reserve for blood (i.e. when a human goes from standing to laying down- the blood can be stored like a sponge in the lung circulation)

As a filter

Question 34

List some vasoactive substances which pass through the lung circulation without significant gain or loss of activity:

Answer 34

Epinephrine
Prostaglandin A1 and A2
Angiotensin II
Vasopressin (ADH)

Question 35

Which immunoglobulin does the lung secrete into the bronchial mucus to help defend against infection?

Answer 35

IgA

Question 36

Which two proteins make up the framework of the lung?

Answer 36

Collagen
Elastin

Question 37

Which vasoactive substances are completely removed or mostly inactivated by passing through the lung?

Answer 37

Bradykinin- up to 80% inactivated
Serotonin- almost completely removed (uptake for storage in the lung)
Norepinephrine- up to 30% removed
Prostaglandins E2 and F2α- almost completely removed
Leukotrienes- almost completely removed

Question 38

True/False: Pulmonary vascular resistance is low and falls even more then cardiac output increases due to distention and recruitment of capillaries.

Answer 38

True

Question 39

T/F: Pulmonary vascular resistance increases at very low or high lung volumes.

Answer 39

True