Pulmonary Circulation

Question 1

What is the only vascular bed to receive the entire cardiac output?

Answer 1

pulmonary circulation

Question 2

Is the series circulation in parallel or series with the pulmonary circulation?

Answer 2

series

Question 3

Why is ischemic damage rare in the lung?

Answer 3

multiple supplies of O2

Question 4

Why is the pulmonary blood pressure lower than the systemic blood pressure?

Answer 4

vascular resistance is less than TPR

Question 5

Is the afterload lower in the left ventricle or right ventricle?

Answer 5

right ventricle

Question 6

What is the normal anatomic shunt and what percentage of CO does it carry?

Answer 6

Left to left shunt

1-2% of cardiac output

Question 7

Where does the lymphatic system drain into ?

Answer 7

caudal mediastinal lymph node and thoracic duct

Question 8

How are the valves of the lymphatic system regulated?

Answer 8

• By mechanical pumping during breathing

- by sympathetic activity

Question 9

Are there arterioles in the pulmonary circulation?

Answer 9

No

Question 10

Why does pulsatile pressure still exist in the pulmonary circulation?

Answer 10

Since resistance is so low

Question 11

What is the mean Ppa?
What Ppa indicates pulmonary hypertension?
What Ppa indicates pulmonary edema?

Answer 11

Mean = 11 mmHg
If Mean Ppa>20 - pulm hypertension
If mean Ppa>25 - pulmonary edema

Question 12

Diastolic P in pulmonary artery is nearly equal to what?

Answer 12

Left ventricular P

Question 13

What occurs during exercise in the pulmonary circulation?

Answer 13

• radius of the vessels increases and resistance therefore decreases passively
• Compliance of the vessels is high so P doesn’t increase much

(There is not autoregulation, this all occurs passively)

Question 14

Vessels in the alveoli are exposed to what type of P? Extraalveolar vessels are exposed to what type of P?

Answer 14

Alveolar vessels - alveolar P

extralveolar vessels - intrapleural P

Question 15

What occurs to the alveolar blood vessels during inflation?

Answer 15

• they are stretched and become narrower
• radius decreases and so resistance increases
• This reduces their pressure

Question 16

What happens to extraalveolar blood vessels in response to inflation?

Answer 16

• There is a more negative intrapleural P as the lung inflates
• their transmural P increases

Question 17

What is the relationship btwn alveolar and extra-alveolar vessels? How does this affect total resistance?

Answer 17

They are in series, so resistance is additive

Question 18

When is PVR at a minimum?

Answer 18

FRC

PVR increases at any other value

Question 19

During normal breathing what is the normal alveolar pressure, and what effect does this have on the alveolar vessels?

Answer 19

alveolar P fluctuates around zero and so all the vessels remain open

Question 20

During mechanical ventilation what happens to alveolar pressure? What does this mean for you as a physician?

Answer 20

It becomes slightly positive

• capillaries can collapse and inc their R
• must ventilate at lowest possible P near the FRC

Question 21

Name some vasodilators that affect pulmonary vascular resistance? (4)

Answer 21

• prostacycline
• histamine (bronchoconstrictor)
• calcium channel blockers
• Nitric oxide

Question 22

What happens in the lung when a certain area is not able to be ventilated and becomes hypoxic?

Answer 22

blood is shunted to a better ventilated region of the lung by hypoxic vasoconstriction

Question 23

Name some vasoconstrictors that affect pulmonary vascular resistance? (3)

Answer 23

• inc PCO2, low pH
• norepinephrine - weak effect
• angiotensin II

Question 24

In what part of the lung is blood flow greatest? Why?

Answer 24

at the base of the lung

-due to gravity and passive distension

Question 25

What happens to the pressure inside the capillaries as you distend down the lung?

Answer 25

it gradually increases | -due to the pressure from intrapleural fluid under the influence of gravity

Question 26

When a person is standing upright what is their apex pressure? What is their base pressure?

Answer 26

``` Apex= Ppa -10 Base= Ppa + 10 ```

Question 27

What zone does this describe and what occurs: | PA>Pa>Pv

Answer 27

Zone 1 - not normally present - capillaries will collapse and flow stops-no perfusion - can occur during blood loss or cardiac output decrease

Question 28

What zone does this describe and what occurs here: | Pa>Pv> PA

Answer 28

zone 3 - flow inc due to gravity and passive distension - capillaries are wide open

Question 29

How is flow determined in zone 3?

Answer 29

by the difference btwn PA-Pv

Question 30

What zone does this describe and what occurs here: | Pa>PA>Pv

Answer 30

Zone 2 | -partial collapse of capillaries on low pressure side but with maintenance of flow

Question 31

How would you determine the flow in zone 2?

Answer 31

Difference btwn Pa and PA | -Pv has no effect - it is downstream

Question 32

Describe what changes in the four starling filtration pressures cause pulmonary edema?

Answer 32

1. inc capillary permeability 2. inc in capillary hydrostatic pressure - mitral valve stenosis 3. dec interstitial hydrostatic P 4. dec colloid osmotic P

Question 33

Does high or low protein in the blood cause pulmonary edema?

Answer 33

low protein ---hypo

Question 34

In the equation: QS/QT = (C”c”O2-CaO2)/ (C”c”O2-CvO2), what occurs if QS =0?

Answer 34

normal condition of no shunt | CaO2 = C"c"O2

Question 35

In the equation: QS/QT = (C”c”O2-CaO2)/ (C”c”O2-CvO2), what occurs if QS =QT?

Answer 35

all blood is shunted - no oxygenation | CaO2 = CvO2

Question 36

In the equation: QS/QT = (C”c”O2-CaO2)/ (C”c”O2-CvO2), what occurs if QS =QT/2?

Answer 36

50% Shunt- aterial oxygen content is average of shunt and functional capillary content -CaO2 = (C"c"O2+ CvO2)/2

Question 37

Does shunting give more hypoxemia or hypercapnea?

Answer 37

more hypoxemia due to the O2 dissociation curve | -CO2 curve is linear

Question 38

Can breathing O2 rich gas help people with abnormal shunts?

Answer 38

NO - they physically cannot be oxygenated so this is just a waste