Lung Ventilation and Perfusion

Question 1

What is alveolar ventilation?

Answer 1

Rate at which new air reaches respiratory areas

Question 2

What does the alveolar air equation describe?

Answer 2

Idea case of what the partial pressure of oxygen should be in the alveoli

Question 3

What is the alveolar - arterial (A-a) gradient

Answer 3

The difference between the ideal PAO2 and PaO2. It is normally 15mmHg

Question 4

Describe the ventilation is distributed in the lung?

Answer 4

• Alveoli in the top of lung are more expanded than those at the bottom as the pleural pressure is more negative at the apex. As inspiration beings, alveoli in the lungs are at different lung volumes. The underinflated alveoli at the base of the lung are more compliant so receive more of tidal volume

Question 5

Describe the effects of gravity on ventilation

Answer 5

• At the base, alveoli are compressed by the weight of tissue above where as at the apex, alveoli are forced to inflate by weight of lung tissue below

Question 6

Describe the blood supply to the airways

Answer 6

• Pulmonary and bronchial arteries - Bronchial veins exist but majority of blood drains into pulmonary veins via shunt. This causes venous admixture

Question 7

Pulmonary capillaries are relatively leaky and alveolar walls are extremely thin so why do the alveoli not fill with fluid?

Answer 7

• Normal pulmonary capillaries and lymphatics maintain a slightly negative pressure, so excess fluid will be sucked back into interstitial space from alveoli

Question 8

Describe pulmonary blood flow in zone two

Answer 8

Apex to mid lung. P(PA) > P(A) > P(V). Intermittent blood flow only during pulmonary arterial pressure peaks

Question 9

Describe pulmonary blood flow in zone three

Answer 9

P(PA) > P(V)> P(A). Mid to lower lung. Continuous blood flow during entire cardiac output. Distention of pulmonary capillaries

Question 10

Describe pulmonary blood flow in zone four

Answer 10

P(PA) > P(V)> P(A). This occurs at the extreme base of lung. There is constriction of extra-alveolar vessels and the peak flow decreases.

Question 11

When does ZOne 1 pulmonary BF occur?

Answer 11

When the P(A) is high or the P(PA) is low. So it doesn’t occur normally

Question 12

What is the regulation of pulmonary blood flow?

Answer 12

• Cardiac output, - PO2 and PCO2, results in arteries constricts so that blood is better diverted to better oxygenated areas - Very slight autonomic control

Question 13

Describe what agents affect pulmonary vascular resistance

Answer 13

Add picture

Question 14

Where do the bronchial arteries arise from?

Answer 14

Aortic arch, thoracic arch and their branches

Question 15

Define ventilation-perfusion ratio

Answer 15

It is the ratio used to assess the efficiency and adequacy of matching ventilation and perfusion. It is V/Q where V = ventilation and Q = Perfusion.

Question 16

What occurs if the V/Q is above/below 1

Answer 16

When it is above one then ventilation exceeds perfusion. When below 1 then perfusion exceeds ventilation

Question 17

What is the normal V/Q ration?

Answer 17

0.85

Question 18

What is arterial hypoxemia?

Answer 18

Abnormal P(ao2)

Question 19

What is hypoxia?

Answer 19

Insufficient O2 to carry out metabolic functions

Question 20

What are the 4 major causes of hypoxemia?

Answer 20

• Anatomical shunt, - Physiological shunt, - V/Q mismatching, - Hypoventilation.

Question 21

Describe some anatomical shunts?

Answer 21

Means blood is bypassing lungs this means the hypoxia cannot be abolished by giving 100% O2. - Right to left shunt - Cyanotic congenital heart diseases (MOST COMMON)

Question 22

Describe some physiological shunts?

Answer 22

• If airway completely blocked then the alveoli supplied by that airway recieves no ventilation but perfusion continues but as V = 0 then V/Q = 0. - Most common cause = Atelectasis

Question 23

Describe features of V/Q mmismatching

Answer 23

This is where there is not a complete block but there is varying degrees of constriction of the airways so varying amount of air getting in. Supplemental O2 will correct hypoxemia as poorly ventilated units will get enriched O2.

Question 24

Describe features of hypoventilation

Answer 24

Underventilation will bring less fresh gas to alveoli. If O2 levels decrease in alveoli then CO2 levels increase. This occurs in patients with respiratory muscle weakness (muscular dystrophy or diaphragmatic paralysis).