Ch39 Pulmonary Circulation

Question 1

What are the two circulations in the lungs?

Answer 1

A high-pressure, low-flow circulation and a low-pressure, high-flow circulation

The high-pressure, low-flow circulation supplies systemic arterial blood to the trachea and bronchial tree, while the low-pressure, high-flow circulation supplies venous blood to the alveolar capillaries.

Question 2

What supplies systemic arterial blood to the lungs?

Answer 2

Bronchial arteries

These arteries are branches of the thoracic aorta and supply most of the systemic arterial blood to the lung’s supporting tissues.

Question 3

What is the function of the pulmonary artery?

Answer 3

Carries blood from the right ventricle to the alveolar capillaries for gas exchange.

Question 4

What is the typical blood volume of the lungs?

Answer 4

About 450 ml, which is approximately 9% of the total blood volume of the circulatory system.

Question 5

What is the mean pulmonary capillary pressure?

Answer 5

About 7 mm Hg.

Question 6

How does hypoxia affect pulmonary blood flow?

Answer 6

Decreased O2 levels cause vasoconstriction of adjacent arterioles, diverting blood flow to well-ventilated alveoli.

Question 7

What is the average systolic pulmonary arterial pressure?

Answer 7

About 25 mm Hg.

Question 8

True or False: The pulmonary arteries have thicker walls than the aorta.

Answer 8

False

The pulmonary artery has a wall thickness one-third that of the aorta.

Question 9

What happens to the pulmonary blood volume during increased pressure in the lungs?

Answer 9

It can vary from half-normal up to twice normal.

Question 10

Fill in the blank: The pulmonary veins empty their effluent blood into the _______.

Answer 10

left atrium.

Question 11

What causes blood to flow from the lungs into the systemic circulation?

Answer 11

Increased pressure in the lungs, such as when blowing out air.

Question 12

What is the function of lymphatics in the lungs?

Answer 12

Remove particulate matter and excess fluid from lung tissues.

Question 13

What does wedge pressure estimate?

Answer 13

Changes in pulmonary capillary pressure and left atrial pressure.

Question 14

What is the mean pressure in the left atrium?

Answer 14

About 2 mm Hg.

Question 15

How does the blood flow through the lungs compare to cardiac output?

Answer 15

It is essentially equal to the cardiac output.

Question 16

What causes pulmonary vasoconstriction during hypoxia?

Answer 16

Low O2 concentration may stimulate vasoconstrictor substances or decrease vasodilators like nitric oxide.

Question 17

What is the normal pulmonary arterial pressure in the uppermost portion of the lung compared to the heart?

Answer 17

About 15 mm Hg less.

Question 18

What is the effect of hydrostatic pressure gradients in the lungs?

Answer 18

They affect blood flow through different areas of the lungs.

Question 19

What are the characteristics of pulmonary arteries compared to systemic arteries?

Answer 19

Pulmonary arteries are shorter, have larger diameters, and are thinner and more distensible.

Question 20

What is the pressure range of the right ventricle?

Answer 20

Systolic: about 25 mm Hg, Diastolic: 0 to 1 mm Hg.

Question 21

Fill in the blank: The pulmonary arteries accommodate the stroke volume output of the _______.

Answer 21

right ventricle.

Question 22

What effect does left heart failure have on the pulmonary circulation?

Answer 22

It can cause blood to dam up in the pulmonary circulation, increasing pulmonary blood volume and pressures.

Question 23

What is the relationship between blood flow and ventilation in the lungs?

Answer 23

They are normally matched for optimal gas exchange.

Question 24

What is the average diastolic pulmonary arterial pressure?

Answer 24

About 8 mm Hg.

Question 25

What happens to blood volume in the lungs during exercise?

Answer 25

It increases due to enhanced blood flow.

Question 26

What is the mechanism for distributing blood flow in the lungs?

Answer 26

Vasoconstriction of blood vessels in poorly ventilated areas diverts blood to better-ventilated areas.

Question 27

What is the pulmonary wedge pressure typically measured at?

Answer 27

About 5 mm Hg.

Question 28

What are the three zones of pulmonary blood flow?

Answer 28

* Zone 1: No blood flow * Zone 2: Intermittent flow * Zone 3: Continuous flow ## Footnote Zone 1 occurs when alveolar air pressure is greater than capillary pressure. Zone 2 occurs during systole when arterial pressure exceeds alveolar pressure. Zone 3 has continuous flow as arterial pressure remains above alveolar pressure at all times.

Question 29

What characterizes Zone 1 blood flow?

Answer 29

No blood flow during any part of the cardiac cycle ## Footnote Occurs when alveolar pressure is consistently greater than capillary pressure.

Question 30

What characterizes Zone 2 blood flow?

Answer 30

Intermittent blood flow during peaks of pulmonary arterial pressure ## Footnote Blood flow occurs only when systolic pressure exceeds alveolar pressure.

Question 31

What characterizes Zone 3 blood flow?

Answer 31

Continuous blood flow through the alveolar capillaries ## Footnote Occurs when both systolic and diastolic arterial pressures remain greater than alveolar pressure.

Question 32

How does exercise affect blood flow in the lungs?

Answer 32

Increases blood flow through all parts of the lungs ## Footnote Exercise converts lung apices from a zone 2 pattern to a zone 3 pattern.

Question 33

What happens to pulmonary arterial pressure during heavy exercise?

Answer 33

Increases slightly due to increased number of open capillaries and distension ## Footnote Normally, the increase in blood flow is accommodated without large increases in pulmonary arterial pressure.

Question 34

What is the normal average pulmonary capillary pressure?

Answer 34

Approximately 7 mm Hg ## Footnote This value is estimated based on mean left atrial pressure and mean pulmonary arterial pressure.

Question 35

What is the typical time blood stays in the pulmonary capillaries at normal cardiac output?

Answer 35

About 0.8 seconds ## Footnote This time can shorten to 0.3 seconds with increased cardiac output.

Question 36

What is the colloid osmotic pressure of pulmonary interstitial fluid compared to peripheral tissues?

Answer 36

About 14 mm Hg, which is higher than in most peripheral tissues ## Footnote This difference influences fluid dynamics in the lungs.

Question 37

What keeps the alveoli dry under normal conditions?

Answer 37

Negative pressure in the interstitial spaces ## Footnote This pressure prevents fluid from entering the alveoli.

Question 38

What are the main causes of pulmonary edema?

Answer 38

* Left-sided heart failure * Damage to pulmonary capillary membranes ## Footnote Conditions that increase capillary pressure or impede lymphatic function can lead to pulmonary edema.

Question 39

What is the pulmonary edema safety factor?

Answer 39

Pulmonary capillary pressure must rise to at least the colloid osmotic pressure of plasma before significant edema occurs ## Footnote This helps to understand thresholds for edema development.

Question 40

What is the critical pulmonary capillary pressure level for significant pulmonary edema to occur?

Answer 40

At least equal to the colloid osmotic pressure of the plasma inside the capillaries ## Footnote This pressure must rise to a value that equals or exceeds the colloid osmotic pressure before edema can form.

Question 41

What happens when left atrial pressure rises above 23 mm Hg?

Answer 41

Fluid begins to accumulate in the lungs ## Footnote This occurs because the pulmonary capillary pressure exceeds 25 mm Hg.

Question 42

What is the acute safety factor against pulmonary edema in a person with a normal plasma colloid osmotic pressure of 28 mm Hg?

Answer 42

21 mm Hg ## Footnote This is derived from the normal pulmonary capillary pressure rising from 7 mm Hg to more than 28 mm Hg.

Question 43

How does chronic elevation of pulmonary capillary pressure affect the lungs' resistance to pulmonary edema?

Answer 43

Lungs become more resistant due to expansion of lymph vessels ## Footnote This can increase their capability of carrying fluid away from interstitial spaces by as much as 10-fold.

Question 44

How quickly can lethal pulmonary edema occur when pulmonary capillary pressure rises above the safety factor level?

Answer 44

Within hours, or even within 20 to 30 minutes ## Footnote This is particularly true if the pressure rises 25 to 30 mm Hg above the safety factor level.

Question 45

What maintains the negative pressure in the pleural space?

Answer 45

Pumping of fluid by lymphatics ## Footnote This negative pressure is crucial for keeping the lungs expanded.

Question 46

What is pleural effusion?

Answer 46

Collection of large amounts of free fluid in the pleural space ## Footnote It can be considered as edema of the pleural cavity.

Question 47

List the causes of pleural effusion.

Answer 47

* Blockage of lymphatic drainage from the pleural cavity * Cardiac failure leading to high capillary pressures * Reduced plasma colloid osmotic pressure * Infection or inflammation increasing capillary permeability

Question 48

What is the normal amount of fluid in each pleural cavity?

Answer 48

Only a few milliliters ## Footnote This amount is slight and is necessary to facilitate lung movement.

Question 49

What pressure must pleural fluid be to keep the lungs expanded?

Answer 49

At least as negative as −4 mm Hg ## Footnote Normal measurements show it is usually about –7 mm Hg.

Question 50

True or False: The pleural space is a physical space.

Answer 50

False ## Footnote It is considered a potential space due to its narrowness.