Pulmonary Circulation 1

Question 1

Bronchial circulation supplies oxygen to _______

Answer 1

conducting airways

Question 2

Bronchial circulation originates from ___ and ___

Answer 2

aorta, intercostal arteries

Question 3

A typical source of the blood in hemoptysis (coughing up blood) is ____

Answer 3

bronchial circulation

Question 4

Bronchial circulation protects the lung from _____

Answer 4

infarction (e.g. PE, pneumonia)

Question 5

How can circulation be seen as a circuit? What is voltage, current, and resistance in circulation?

Answer 5

Voltage = pressure Current = blood flow Resistance = vascular resistance

V = I x R

Pulmonary artery pressure - left atrial pressure = CO x Pulmonary vascular resistance

In other words, the drop in pressure is equal to the product of cardiac output and pulmonary vascular resistance.

Question 6

Answer 6

C. 3 wood units

Question 7

Describe the different types of arteries that the blood flows through after the pulmonary artery.

Answer 7

After the pulmonary artery, the blood goes through large elastic arteries which absorb the pulsatile flow. Then the blood goes through muscular pulmonary arteries which regulat the blood flow before arriving at the pulmonary arterioles/pre-capillary vessels.

Question 8

Answer 8

A. The pulmonary circulation has lower resistance.

Question 9

How do you measure pulmonary artery pressure?

Answer 9

Method 1: non-invasive echocardiography (not very accurate, can have quite a lot of error)

Method 2: Pulmonary artery catheterization

Question 10

What is the Swan-Ganz catheter?

Answer 10

It is the catheter that is typically used these days for pulmonary artery catheterization. It is a “flow directed” catheter (inspired by sail boats).

Question 11

How do you take the pulmonary artery wedge pressure (aka occlusion pressure)?

Answer 11

You take the swan-ganz catheter all the way up through the pulmonary artery and you purposefully obstruct one of the pulmonary arteries. This makes a static water column distal to the obstruction where Q = 0 and change in pressure is 0. Measuring the pressure distal to the occlusion will give you an approximation of the left atrial pressure (and if there isn’t mitral valve problems it will also serve as an approximation for left ventricular end-diastolic pressure)

Question 12

When doing a pulmonary artery catheter, what 5 things can you measure?

Answer 12

1. Right atrial pressure
2. Pulmonary artery pressure
3. wedge pressure
4. cardiac output (thermodilution or laser doppler)
5. central venous oxygen saturation (light absorption)

Question 13

What are normal values found with PA catheter?

For: RA, RV, PA, PCWP, CO, PVR

Answer 13

RA = 0-5 mmHg

RV = 25/0 mmHg

PA = 25/10 mmHg (mean 15-20)

PCWP = 5-8 mmHg

CO = 5 L/min

PVR = 1-2 WU

Question 14

Explain this normal swan-ganz tracing diagram:

Answer 14

As the catheter goes from RA to RV, the systolic jumps up and the diastolic pressure should stay the same as long as tricuspid valve is normal. When going from RV to PA, the systolic stays the same but diastolic increases. Once the balloon wedges, it’s more complicated what the pressure does. The systolic pressure falls and the diastolic may or may not fall (depending).

Question 15

Answer 15

C. Pulmonic valve stenosis

Question 16

During stress/exercise, cardiac output can increase from 5 L/min to 20 L/min. However, the pulmonary pressures only increase about half as much as expected. How does this happen?

Answer 16

1. High capacitance. The pulmonary arteries are distensible vessels that can absorb the pressure.
2. Recruitment of unperfused vessels

Question 17

Explain the effects of gravity on pulmonary blood pressures:

Answer 17

You have the pressure going into the middle portion of the lung (25/8). If you’re sitting upright, there is a gradient across the lung so that the pressures at the top of the lung are lower than the pressures at the bottom of the lung. You have approximately 30 cm of water pressure in the entire lung which means that there is approximatley 15 cm of water from the top of the lung to the middle of the lung and 15 cm of water from the middle to the bottom of the lung.

So, the pulmonary artery pressure at the top of the lung has 15 cm of water pressure going against it so you subtract that from 25/8 and get 14/3 mmhg. At the bottom of the lung, you have 15 cm of water pressure sitting on top so the pressure is higher when you add the column of water bringing 25/8 to 36/19 mmhg.

Question 18

How does gravity affect air pressure in the alveoli?

Answer 18

Gravity affects the air pressure to a lesser degree than it affected blood.

Notice that the gravity does not affect alveolar pressure which is 0 at all levels.

Question 19

What are the physiologic zones of pulmonary blood flow?

Answer 19

Zone 1 is when P_A > P_a > P_v. In zone 1, the alveolar pressure is higher than the arterial and venous pressures so the capillaries are always collapsed. In healthy persons, there shouldn’t be any zone 1.

Zone 2 is when P_a > P_A > P_v. In zone 2, the alveolar pressure is between the arterial pressure and venous pressure. When arterial pressure drops under 0 mmHg (remember, alveolus pressure is always 0 mm Hg), the blood does not flow around the alveolus. When the arterial pressure is above 0, there is blood flowing through the capillaries around the alveolus.

Zone 3 (the bottom lobes of the lung) is when P_a > P_v > P_A. In zone 3, both arterial and venous pressure are greater than the alveolar pressure so the capillaries are always open and there is continuous blood flow through the capillaries.

Question 20

What are two ways that you can get a lot of Zone 1?

Answer 20

1. Mechanical ventilation. With mechanical ventilation, you are trying to send oxygen down into the lungs with positive pressure. This increases the pressure inside the alveoli. However, if you increase the alveolar pressure higher than the P_a and P_v, you end up with Zone 1 which is where the capillaries are collapsed.
2. Auto-PEEP. (Floppy airways in COPD cause airways to collapse during expiration. The patient can’t exhale all of what they inhaled due to the collapse and as they keep breathing, they keep stacking the air that isn’t being exhaled. This can increase the alveolar pressure and if the alveolar pressure is increased beyond P_a and P_v, you can end up with a lot of zone 1

Question 21

Answer 21

B. Increased pulmonary vascular resistance. During mechanical ventilation with positive pressure, you have an increase in P_A so you can imagine that the increased pressure of the alveolus causes the alveolus to press and squish the neighboring capillaries increasing vascular resistance.

Another way to think about this is with the Zones. If you increase P_A, you will have some Zone 3 areas turning into Zone 2, and some Zone 2 turning into Zone 1. You have more capillaries collapsing which is increasing vascular resistance.

Question 22

Answer 22

C. Some zone 2 lung will become zone 3.

If you give a dehydrated patient an IV bolus of fluid, there will be an increase of P_a and P_v. This means that some of Zone 1 will become Zone 2, and some of Zone 2 will become Zone 3.

Question 23

What is hypoxic pulmonary vasoconstriction and how is it helpful?

Answer 23

In areas of the lung where there is alveolar hypoxia, the local regulatory systems will cause vasoconstriction so that the blood can go to other areas of the lung that are not hypoxic. When there is a region with alveolar hypoxia, there is no use bringing blood to that area of the lung because there is no ventilation in that area (shunt). The vasoconstriction helps to bring the blood to other areas while working to correct the V/Q mismatch.

This is different from the systemic circulation where hypoxic regions cause vasodilation so that blood perfusion can increase bringing more oxygenated blood.

Question 24

True or False: Nitric oxide, prostacyclin, endothelin, and thromboxane are endogenous vasodilators and vasoconstrictors.

Answer 24

True

Question 25

Problems with pulmonary circulation can result in abnormal gas exchange. In terms of abnormal gas exchange, what are the 2 things that can result from this?

Answer 25

1. Hypoxia (low O₂)
2. Hypercapnia (high CO₂)

Question 26

What are the 2 types of pulmonary edema?

Answer 26

Cardiogenic, non-cardiogenic

Question 27

Where does fluid in the lung originate from?

Answer 27

Capillaries. The capillaries leak fluid into the interstitium and are taken up by the lymph vessels

Question 28

In the lung, fluid leave the capillary into the interstitium where it’s picked up by the lymph ducts. With this process in mind, how do you end up with excess fluid in the alveoli?

Answer 28

If the capillary is releasing fluid at a rate that the lymphatics cannot keep up with, there will be excess fluid that goes into the alveoli.

Question 29

What two factors determine how much fluid leaves the capillaries in the lungs?

Answer 29

1. hydrostatic pressure (pushes fluid out)
2. oncotic pressure (bringing fluid back in)

Question 30

With pulmonary edema, when you have a problem with the hydrostatic pressure, is it a cardiogenic or non-cardiogenic pulmonary edema?

Answer 30

Cardiogenic. Increased vascular pressure increases the hydrostatic pressure which pushes more fluid out of the capillaries

Question 31

With pulmonary edema, when you have a problem with increased permeability/oncotic pressure problem, is the pulmonary edema cardiogenic or non-cardiogenic?

Answer 31

non-cardiogenic. proteins leave the vasculature due to increased permeability

Question 32

How does pulmonary edema look on CXR?

Answer 32

There is fluid in the alveoli (pulmonary edema) and increased apical lung markings (cephalization)

Question 33

What happens to the pulmonary veins and lymph vessels when there is pulmonary edema?

Answer 33

They enlarge

Question 34

What are kerley B lines?

Answer 34

This is a radiologic finding that is often talked about but not often seen. They appear at the edge of the lung and are the lymphatics and veins swelling up.

Question 35

This is a classic example of what?

Answer 35

This is a classical example of noncardiogenic pulmonary edema due to ARDS. As you can see, there is bilateral alveolar infiltrates causing a “white out” of the lungs. This can happen following trauma.

Question 36

How can you tell the difference between cardiac and noncardiac pulmonary edema? (3 things)

Answer 36

Cardiogenic is caused by congestive heart failure while non-cardiogenic is caused by pneumonia/ARDS.

Cardiogenic will result in an elevated left atrial (PCWP) pressure while noncardiogenic left atrial pressure stays normal.

Cardiogenic pulmonary edema responds to diuretic treatment but noncardiogenic pulmonary edema does not.

Question 37

Answer 37

D. None of the above

Question 38

Answer 38

B. Diuretics

The elevated pulmonary capillary wedge pressure means that the pulmonary edema is cardiogenic so diuretics will help.

Question 39

Answer 39

C. Acute left ventricular infarction

This patient had a positive response to diuretics which means that the pulmonary edema is cardiogenic, thus, the LV infarction.