4. Ventilation Perfusion Distribution In The Lung

Front 1

What characteristics may be associated with pulmonary circulation?

Back 1

High flow, low pressure, low resistance circulation

Front 2

Why is pulmonary driving pressure and resistance relatively low?

Back 2

Need only pump blood up to apex of the lung (~10-15 cm above the level of the heart)

Front 3

Why are pulmonary capillary walls ver thin?

Back 3

To maximize diffusion - high pressures would cause fluid filtration into the alveoli - pulmonary edema

Front 4

What are some defining characteristics of pulmonary and system circulation?

Back 4

Pulmonary has low driving pressure/resistance (does not need to pump blood very far)
Systemic must pump blood up larger vertical distance to organs (brain)

Systemic arterioles have lot of smooth muscle and can constrict to divert blood flow to organs with greater flow requirements (increases R)
Pulmonary capillary walls thin to maximize diffusion

Front 5

What can pulmonary hypertension cause?

Back 5

Can cause water to be driven out of capillaries into interstitial layer and possibly into alveoli - pneumonia

Front 6

What is the use of the Xenon 133 tracer method?

Back 6

Determining vertical distribution of perfusion (pulmonary blood flow) in the lung

Front 7

What is the effect of gravity on ventilation/perfusion?

Back 7

Alveolar units at base are better ventilated than apical units
Base of lung is better perfused than apex

V/Q Ratio is lowest at base of lung

Front 8

What are the effects of the V/Q ratio on the pulmonary venous blood PO2 and PCO2?

Back 8

The base of the lug does not oxygenate blood as well as the apex

Front 9

What are some consequences of a low ventilation/perfusion ratio?

Back 9

The perfusion rate is fine, but there are issues with ventilation
Either there is no ventilation, or hypoventilation

Front 10

What are some consequences of a high ventilation/perfusion raio?

Back 10

Normal ventilation, but either no perfusion (physiological dead space) or hypoperfusion

Front 11

What is an increase in pulmonary vascular resistance (R) at low lung volume caused by?

Back 11

It is caused by less negative intrapleural pressure reducing lumen of extra alveolar vessels
At high lung volumes expanded alveoli compress vessels in alveolar walls

Front 12

What are the effects of 'HPV' Hypoxic Pulmonary Vasoconstriction?

Back 12

Automatically diverts blood away from poorly ventilated parts of the lung --> consolidated pneumonic lobule

Front 13

What are some issues with alveoli at high altitude?

Back 13

When all alveoli are hypoxic - causes pulmonary hypertension and edema

Front 14

Why do respiratory blood vessels vasoconstrict when experiencing hypoxia?

Back 14

To divert blood flow to areas of the lung that are well oxygenated
Prevent hypoxic blood entering the blood from leaving the lung

Opposite to response of systemic circulation -->Vasodilation increasing blood and oxygen flow to muscle

Front 15

What kind of response is HPV?

Back 15

Does not depend on nervous system or hormones
Innate response of pulmonary vascular smooth muscle and is present even in isolated pulmonary arteries

Front 16

What are some functions of pulmonary circulation?

Back 16

Potential reservoir of blood volume (can distend easily)
Mechanical filter for small blood emboli
Involved in phospholipid synthehsis (surfactant)
Protein synthesis
Metabolism of Carbohydrates
Metabolism of vasoactive substances --> ANG I converted to ANG II by ACE (angiotensin converting enzyme)

Front 17

What are some properties of the bronchial circulation?

Back 17

R-L shunt normally depresses PO2 in pulmonary vein blood
Can prevent excess pressure in pulmonary capillaries
Pulmonary artery atresia --> bronchial arteries enlarge and significant amounts of oxygenated blood reach body via bronchial circulation