Exam #3: Pulmonary Circulation

Question 1

How do pulmonary arteries structurally compare to the systemic arteries?

Answer 1

1) Shorter
2) More compliant
3) Thinner walled

This allows them to accomodate the entire cardiac output

Question 2

What is the bronchial circulation?

Answer 2

Circulation to the lung parenchyma itself

• Bronchial arteries provide oxygenated systemic blood to the lungs
• Bronchial veins carry 1/3 of the bronchial circulation back to the RA
• Remaining 2/3 goes to the LA via the pulmonary veins, which is responsible for the “physiological shunt” of blood

Question 3

What is the effect of bronchial circulation?

Answer 3

Physiological shunting of blood & drop in partial pressure of oxygen in systemic circulation compared to alveolar oxygen

Question 4

What is hypoxic pulmonary vasoconstriction (HPV)?

Answer 4

• Decreased alevolar Po2 i.e. alveolar hypoxia (<70 mmHg) causes local vasoconstriction, which is the OPPOSITE of what happens in systemic circulation
• Blood redistribution to better aerated alveoli i.e. serves to match ventilation & perfusion by redirecting perfusion to better oxygenated alveoli

Question 5

What causes HPV?

Answer 5

Airway obstruction 
Failure of ventilation 
Acute lung damage 
High altitude
COPD

Question 6

What is the long term effect of HPV?

Answer 6

Pulmonary arterial hypertension (PAH)

Question 7

What are the effects of gravity on the distribution of pulmonary blood flow? What is the clinical significance?

Answer 7

• Blood flow is greater in the bases of the lungs than the apex in the standing individual.
• Clinically, this is why you look for evidence of edema at the bases of the lungs

Question 8

Describe the structure of the pulmonary capillaries.

Answer 8

Thin walled
Leaky to protein
Low pressure
Form a sheet of flow

Question 9

Summarize the pulmonary capillary & interstitial fluid dynamics.

Answer 9

1) Normal outward forces are greater than inward forces, which provides a filtration pressure out of the pulmonary capillaries into the interstitial space
2) Pulmonary lymphatic pressure is negative relative to interstitial, which results in the recycling of fluid

Question 10

What causes an increased in interstitial hydrostatic pressure?

Answer 10

Edema

Question 11

What conditions will increase intravascular hydrostatic pressure?

Answer 11

Increased blood volume

Poor heart function

Question 12

What will decrease capillary osmotic pressure?

Answer 12

CKD

Liver disease

Question 13

What conditions will change capillary permeability?

Answer 13

Drug toxicity
Infection
Autoimmune disease

Question 14

What is the ventilation- perfusion relationship?

Answer 14

Matching ventilation (V) to perfusion (Q) is essential for ideal gas exchange

Question 15

What is the average normal for V/Q?

Answer 15

0.8

Question 16

Draw the V/Q graph.

Answer 16

N/A

Note that ventilation & perfusion decrease from the base of the lung to the apex, but perfusion decreases FASTER

Question 17

How do V & Q change from the base to the apex of the lung?

Answer 17

BOTH drop, but there is a higher V than Q at the apex than the base

Question 18

What pathological condition favors high V at the apex of the lung?

Answer 18

TB

Question 19

What is a V/Q defect?

Answer 19

Mismatch between V & Q.

Question 20

What is the V/Q relationship at the dead space? What pathologic condition results in dead space?

Answer 20

Infinity b/c no perfusion

- Pulmonary embolism; there is ventilation but no perfusion because the region is occluded by the emboli

Question 21

What does it mean that there is a high VQ?

Answer 21

• There is high ventilation relative to perfusion (high V compared to Q)
• Usually due to a decrease in blood flow

Question 22

What does it mean that there is low V/Q?

Answer 22

• There is low ventilation relative to perfusion, usually because ventilation is decreased

Question 23

What is the term for VQ= 0?

Answer 23

“Shunt,” this is a portion of the lung where the CO has been diverted

Question 24

What is a right to left shunt? What are the clinical features of a right to left shunt?

Answer 24

Shunting of blood from right heart to left heart e.g. in cases of LATE stage VSD or ASD

• Hypoxemia always occurs because blood is not going through the lungs
• Cannot be corrected with having the person breathe high O2 gas

Question 25

What is Eisenmenger Syndrome?

Answer 25

Refers to late stage septal defects that essentially have a reversal of shunting from left to right, to right to left

• Left to right shunting causes increased pressure to be pumped into the pulmonary arteries
• Vascular remodeling occurs that increases the thickness of these arteries, transmitting pressure back into right heart
• Eventually right pressure is greater than left & shut reverses direction

Question 26

Describe the pathophysiology of PE.

Answer 26

Right ventricular failure
Right to left shunting
V/Q mismatch

Question 27

What is the physiologic shunt?

Answer 27

This refers to roughly 2% of the CO that NORMALLY bypasses the alveoli

Question 28

What is a left to right shunt? What are the clinical features of a left to right shunt?

Answer 28

Shunting of blood from the left side of the heart to the right

• DO NOT cause hypoxemia
• E.g. patent ductus arteriosus & traumatic injury