13- Pulmonary Circulation

Question 1

Difference between pulmonary and systemic arteries and veins include

Answer 1

1. wall thickness
   - less in pulmonary
2. compliance
   - greater in pulmonary
3. pressures
   - lower in pulmonary due to (see below)
   - Right ventricle and pulmonary artery are low and aortic is high
4. blood volume
   - about 10% of the blood volume will be in the pulmonary vasculature

Question 2

differences in pressure occur where?

Answer 2

systolic and diastolic differences in pressure in pulmonary arter

-but no differences after that

Question 3

pulmonary vasculature compliance

Answer 3

left atrial pressure increases before pulmonary artery pressure increases (by nearly 10mmHg)

-reflects high compliance of pulmonary vasculature

Question 4

distribution of blood flow in the lung of a healthy person in the upright posture

Answer 4

blood flow is NOT uniform

• blood flow is much less at top and much more at the bottom of the lung
• gravity is not the sole determinant of blood flow distribution

Question 5

effect of alveolar pressure on blood flow in the lung

Answer 5

No flow as PALV > than perfusion pressure

intermittent flow as perfusion Pressure > than PALV during systole only

Continuous flow as perfusion Pressure > than PALV

Question 6

Pulmonary vascular resistance is dependent on lung volume

Answer 6

pulmonary vascular resistance changes as lung volume changes

note that overall vascular resistance is least at FRC

Question 7

Passive influences on pulmonary vascular resistance (PVR)

Answer 7

1. Lung volume above and below FRC increase PVR (lengthening and compression of capillaries).
2. Increased pulmonary artery or left atrial pressure, blood volume or cardiac output decrease PVR (recruitment and distension of capillaries).
3. Gravity decreases PVR (recruitment and distension).
4. Increased interstitial pressure and viscosity (compression).
5. Increased alveolar or intrapleural pressure increase PVR (compression).

Question 8

how to decrease pulmonary vascular resistance?

Answer 8

increase pulmonary blood flow or blood pressure

-resistance is highest at low flow then when flow increases that causes recruitment and distension of pulmonary capillaries

Question 9

how to increase and decrease PVR

Answer 9

1. Increase PVR (vasoconstriction)
   - sympathetic stimulation
   - catacholamines
   - PGE2
   - thromboxane
   - endothelin
   - angiotension
   - Histamine
   - alveolar hypoxia
   - hypercapnia
   - acid pH
2. Decrease PVR (vasodilation)
   - parasympathetic stimulation
   - ACH
   - PGE1
   - NO Bradykinin

Question 10

rate at which gases reach equilibrium b/w alveoli and capillaries

Answer 10

they are different depending on whether the gases bind to a molecule

• N2O
• O2
• CO

*you need so much more CO cause it binds to Hb very tightly so in order for it to be in the plasma and be active then you need A TON OF IT *

Question 11

what assures that the alveoli remain dry?

Answer 11

the balance of hydrostatic and osmotic forces and the lymphatic pump normally assure that the alveoli remain dry