Exam 6: Pulmonary Circulation

Question 1

With regard to pulmonary circulation, describe what is meant by “shunting” of blood?

Answer 1

Blood will move to an area where it can properly diffuse when it is poorly oxygenated
Under normal and abnormal conditions in the lungs a small percentage of pulmonary blood is not oxygenated correctly. This is the shunt fraction

Question 2

List 5 difference between the pulmonary and systemic circulation

Answer 2

Systemic circulation
Wide variability in blood pressure, arterial to venous pressure difference is great, SVR and blood volume are highly variable, thick walled arteries

Pulmonary circulation
	Opposite of systemic
	Arteries are thinner walled
	PVR is less than SVR
	Autonomic control is less than that of systemic

Question 3

What is the blood volume of the pulmonary circulation?

Answer 3

450 mL, about 9-10% of total blood volume

Question 4

What are the factors that influence pulmonary blood volume?

Answer 4

Changes in posture
Changes in systemic vasomotor tone
Left heart failure

Question 5

Describe the effect of gravity on pulmonary blood flow

Answer 5

Gravity is the main driving force between the 3 zone of blood circulation
The structure of the vascular tree is the primary determinant of blood flow distribution in the mammalian lung

Question 6

Describe zone 1 of blood circulation

Answer 6

Dorsal; blood perfusion is least
Alveolar ventilation is high, but blood perfusion is low
High V/Q
This zone is where there is primarily alveolar dead space ventilation

Question 7

Describe zone 2 of blood circulation

Answer 7

Middle; blood perfusion is uniform

Alveolar ventilation and pulmonary perfusion are matched well; appropriate V/Q relationship

Question 8

Describe zone 3 of blood circulation

Answer 8

Ventral; blood perfusion is most
Pulmonary arterial pressures are higher than alveolar
Low V/Q
This zone is where the alveolar do not ventilate well and become atelectic

Question 9

What is hypoxic pulmonary vasoconstriction?

Answer 9

Caused by hypoxia
The effect of altitude on pulmonary vascular resistance and pulmonary arterial pressure, but it is not just an altitude phenomenon
Can result in pulmonary hypertension which results in right heart congestion

Question 10

Describe the effect of lung volume on pulmonary vascular resistance

Answer 10

At low lung volumes initially, PVR is high due to HPV
As alveoli expand, lung volume tends to increase pulmonary vascular resistance because the alveoli tend to squeeze the thin-walled pulmonary vessels that line the alveoli

Question 11

Write the Starling equation for fluid flux (given on exam), define its variables, and describe how changes in each will affect fluid flux from pulmonary capillaries.

Answer 11

Flux = K[(Pc – Pi) – σ(πc – πi)]
K: filtration coefficient
σ: reflection coefficient
Pc: capillary hydrostatic pressure
	Pushes fluid out of the capillary
Pi: interstitial hydrostatic pressure
	Pushes fluid into the capillary
πc: capillary oncotic pressure
	Draws fluid into the capillary
πi: Interstitial oncotic pressure
	Draws fluid out of the capillary

Question 12

What is pleural effusion?

Answer 12

Collection of large amount of free fluid in the pleural space

Question 13

What are the factors that can contribute to pleural effusion

Answer 13

Blockage of lymphatic drainage
Cardiac failure
Greatly reduced plasma colloid osmotic pressure
Infection

Question 14

Why does pulmonary vascular resistance fall during exercise?

Answer 14

Cardiac output and blood flow increase during exercise. This leads to an increased PaCO2 and a decreased PaO2. Minute ventilation will increase to blow off the excess CO2; likewise, HPV will decrease to optimize respiration during exercise