Lung circulation

Question 1

What two ways does blood circulate throughout the lung?

Answer 1

High pressure, low flow system: thoracic aorta -> bronchial arteries

Low pressure, high flow: pulmonary artery and branches -> alveoli
7 ml/mmHg, pulmonary artery tree has larger compliance than the bronchial arteries, because of their thinner wall 1/3 of the aorta

Question 2

Name the pressures for the:
Pulmonary arterial pressure
Mean pulmonary pressure
Left atrium pressure (diastole)

Answer 2

Pulmonary arterial pressure: 24/9 mmHg

Mean pulmonary arterial pressure: 15 mmHg

Left atrium pressure (diastolic): 8 mmHg

Question 3

How does failure of the left heart effect pressure in the pulmonary system and how? And the systemic system?

Answer 3

Increases blood volume as much as 100%
-increases pressure

Increases blood pressure

Left atrial pressure rises up to 40-50 mmHg (norm 1-5) causes increase in pulmonary artery pressure to increase.
Above 30 mmHg - pulmonary edema

No effect or mild effect on systemic system.

Systemic system has 9 times the blood volume than the pulmonary system

Question 4

What are the 3 zones lungs can be divided into? What are the parameters used to divide them?

Answer 4

Divided based on type of blood flow,

Zone 1: No blood flow - local alveolar capillary pressure never rises higher than alveolar air pressure
-pathological

Zone 2: intermittent blood flow - during systole

Zone 3: continuous blood flow

Question 5

What’s the typical flow in the lung of a standing person and how does it compare to when they are exercising?

Answer 5

Normal:
Apices: zone 2 -little/intermittent blood flow
Lower areas: zone 3 - more blood flow

During Exercise:
Apices get zone 3 flow

Question 6

By how much does blood flow in the lungs increase during exercise? And why is this possible?

Answer 6

Blood flow increases 4- 7 times in the lungs during exercise

Because of:
Up to 3x increased numbers of open capillaries
Flow rate increases up to 2x than normal, all capillaries are distended
Pulmonary arterial pressure increased (but very little)

Question 7

What’d the outward force between pulmonary capillaries and the interstitium? What type of pressure in needed in the interstitium? What keeps it there? What’s the total inward force? The mean filtration pressure?

Answer 7

Total outward force is 29
Total inward force is 28
Mean filtration pressure is 1 mmHg
The interstitium needs to have negative pressure, kept negative by pumping of the lymphatic system. Postive pressure in the interstitium will cause rupture of the alveolar epithelium

Pulmonary capillaries are releatively leaky to proteins

Question 8

When does pulmonary edema occur? What are the common causes?

Answer 8

When pulmonary capillary pressure increases higher than 25 mmHg

Common causes are left-sided heart failure, mitral vavle disease or damage to pulmonary blood capillary membranes due to infections or breathing toxins.

Question 9

What is pleural effusion? What causes is?

Answer 9

Pleural effusion is edema of the pleural cavity
Causes are:
Blockage of lymphatic drainage from pleural cavity
Cardiac failure
Greatly reduced plasma colloid osmotic pressure
Infection/inflammation

Normal level of pleural space: -7 mmHg, increased to -4 mmHg -> lung collapse

Question 10

How does bronchial obstruction and hypoxia affect blood flow?

Answer 10

Hypoxia increases pressure in the pulmonary artery.
Bronchial obstruction causes constriction of vessels supplying the poorly ventilated alveoli. CO2 accumulated which decreases the pH which causes vasoconstriction. Lack of oxygen causes the vessels to constrict.

Blood blow is reduces to the portions of the lung that are not getting air.

Question 11

What agents constrict the pulmonary arteries?

Answer 11

Norepinephrine
Epinephrine
Angiotensin II
some prostaglandins

Question 12

What agents dilate the pulmonary arteries?

Answer 12

Isoproterenol

Acetylcholine

Question 13

Which agents constrict pulmonary venules?

Answer 13

Serotonin, Histamine, E. Coli endotoxin

Question 14

What are the effects of the sympathetic vasoconstrictor nerve fibers on the lung?

Answer 14

Come from cervical sympathetic ganglia

Decreases pulmonary blood flow by 30%

Mobilizes blood from pulmonary reserve (400ml- also released when person stands up)

Question 15

Oxygen concentration in the alveoli is controlled by what factors?

Answer 15

Rate of absorption of oxygen into the blood

Rate of new oxygen entry into the lungs (alveolar ventilation)
- can never increase above 149 mmHg

Question 16

Carbon dioxide concentration is the alveoli is controlled by what factors?

Answer 16

Rate of carbon dioxide excretion (increases directly)

Alveolar ventilation (decreases inversely)

Question 17

What characteristics determine how fast a gas will pass through the respiratory membrane?

Answer 17

Membrane thickness
-edema, fibrosis increase mem thickness by 2 to 3x normal.

Membrane surface area

Dissuasion coefficient of gas in the substance of the membrane

Partial pressure difference of gas between the two sides of the membrane

Question 18

What is Va/Q ratio?
What’s the normal value?
Where does gas exchange occur?

Answer 18

Ventilation-perfusion ratio: alveolar ventilation/blood flow

Normal: 0.8 (4/5 L/min)

Gas exchange is completed. In the first third of capillaries

Question 19

I nthe Va/Q ratio, what does it mean when ventialation is zero but perfusion is still occuring

Answer 19

The blood gas composition is unchanged, happens during an airway obstruction

Question 20

What happens to the V/Q ratio when there is a vascular obstruction?

Answer 20

The ratio is infinity
There is still ventilation but no blood flow. The Q can approach but never be zero. hence infinity.

Pulmonary embolism, or other sort of block

Creates a physiological shunt, there is no gas comp change in alveoli
The greater the shunt the less blood gets oxygenated. Complete - none.