Pulmonary circulation, edema, and pleural fluid

Question 1

What are the 3 circulatory systems in the lungs?

Answer 1

1. pulmonary circulation. High flow, low pressure.
   - the pulmonary artery has high compliance –> allows for stroke volume from the R ventricle with minimal increase in pressure
2. Bronchial circulation. High pressure, low flow
   - 1-2% of total cardiac output
   - oxygenated blood for all lung tissues
   - empties directly into the pulmonary veins, so the L ventricular output > R ventricular output
3. Lymphatic circulation
   - any particulate or leaked protein will be removed via the lymphatic system

Question 2

How is the blood flow distributed in the lungs?

Answer 2

Pulmonary blood flow is almost equal to cardiac output
- pulmonary blood flow distribution is controlled by O2 level –> if low, there will be vasoconstriction, to shunt blood away from the poorly ventilated parts of the lungs
- there is minimal autonomic control of the pulmonary blood flow, BUT, sympathetic stimulation can lead to vasoconstriction, especially in the large pulmonary capacitative vessels – veins –> allows for displacement of extra blood in the lungs to other parts of the body to counteract hypotension

Question 3

What are the 3 zone of pulmonary blood flow?

Answer 3

Zone 1: no blood flow. Alveolar pressure > arterial pressure > venous pressure
Zone 2: intermittent blood flow. During systole, the arterial pressure > alveolar pressure, but decreases during diastole (no blood flow)
Zone 3: continuous blood flow. Arterial pressure > alveolar pressure during all cardiac cycle. When a healthy person is lying down, all lungs are in zone 3

Question 4

How does pulmonary resistance decrease during heavy exercise?

Answer 4

1. increasing the number of open capillaries
2. by distending the capillaries and increasing the flow through each capillaries

Question 5

What are some important difference between pulmonary and peripheral circulation?

Answer 5

1. pulmonary capillary pressure is low
2. interstitial fluid pressure is also more negative
3. capillary permeability is high – more leakage of protein –> high interstitial fluid osmotic pressure
4. alveolar epithelium is very thin – easily ruptures if the interstitial fluid pressure goes about atmospheric pressure (0) – allows for fluid dumping into the alveoli

Question 6

What’s significance of the +1mmHg mean filtration pressure?

Answer 6

This means that the slight higher filtration pressure will cause a continual loss of fluid from the pulmonary capillaries into the lymphatics

Question 7

What are some causes of pulmonary edema?

Answer 7

1. left sided heart failure/ mitral valve stenosis –> leads to a back up of blood into the lungs –>greatly increases the pulmonary capillary pressure –> flooding of the interstitial spaces and alveoli
2. Damage to the alveolar epithelium (ex. noxious gas) –> leakage of fluids/ proteins into the interstitial space

Question 8

What are 3 safety factors that prevents pulmonary edema?

Answer 8

1. normal negative interstitial pressure: any slight increase in fluid will be “sucked” into the lung interstitium
2. lymphatic drainage system: can proliferate and expand greatly given some time to help with excess drainage
3. colloid osmotic pressure of the interstitial fluids will be decreased if there is an increased fluid loss during protein washout

Question 9

What are the 4 main causes of pleural effusion?

Answer 9

1. blockage of lymphatic drainage from the pleural cavity
2. cardiac failure, leading to excessively high peripheral and pulmonary capillary pressure
3. decrease plasma colloid pressure
4. increased capillary permeability