Blood flow, gas exchange, ventilation and perfusion

Question 1

Define bronchial circulation

Answer 1

Systemic circulation which supplies airways, lung tissue, smooth muscle and nerves.

Question 2

What % of systemic circulation goes to bronchial circulation

Answer 2

2%

Question 3

Where does deoxygenated bronchial blood drain into and what effect does this have?

Answer 3

PULMONARY VEIN - dilutes oxygenated blood

Question 4

Summarise pulmonary circulation

Answer 4

Opposite of systemic circulation.
High flow, low pressure
Cardiac output from right ventricle through pulmonary artery to capillaries to pulmonary vein and back to left ventricle.

Question 5

Summarise the main alveolar/arterial and venous partial pressures of CO2 and O2.

Answer 5

PAO2 = 100mmHg/13.3pKa
PaO2=100mmHg/13.3pKa
PACO2=40mmHg/5.3pKa
PaCO2=40mmHg/5.3pKa
PvO2 =40mmHg/5.3pKa 
PvCO2=46mmHg/6.2pKa
Arterial values reflect lung values and Venous values reflect tissue values

Question 6

Describe how gas exchange occurs in the lungs in terms of the partial pressure gradient

Answer 6

Gases move across the alveolar membrane to and from capillaries until they reach equilibrium

Question 7

Describe the movement of O2 and CO2 across the alveolar membrane

Answer 7

O2 diffuses over from 100mmHg to 40 mmHg

CO2 diffuses over from 46mmHg to 40mmHg

Question 8

Why are the two exchange rates of O2 and CO2 similar

Answer 8

Because the pp gradient for oxygen is much steeper but CO2 is a lot more soluble than O2

Question 9

How is movement across the alveolar membrane proportional to:

1. pp gradient
2. surface area
3. distance
4. alveolar wall thickness

Answer 9

1. directly
2. directly
3. most rapid over short distances
4. inversely

Question 10

State the effect of emphysema on gas exchange

Answer 10

Loss of alveoli leads to reduced gas exchanged
Normal or low PAO2
Low PaO2

Question 11

State the effect of fibrosis on gas exchange

Answer 11

Hindered expansion and ventilation
Low PAO2
Low PaO2

Question 12

State the effect of oedema on gas exchange

Answer 12

Fluid leaks from plasma to ISF leading to increased space between alveoli and capillaries
Normal PAO2
Low PaO2

Question 13

State the effect of asthma on gas exchange

Answer 13

Bronchial smooth muscle over constricts making it more difficult to get air into the lungs and ventilate
Low PAO2
Low PaO2

Question 14

Explain the relationship between ventilation and perfusion ratio

Answer 14

Ratio is ideally 1
Ventilation > perfusion - ratio is more than 1
Ventilation < perfusion - ratio is less than 1

Question 15

How is blood flow proportional to vascular resistance?

Answer 15

Inversely

Question 16

Describe the relationship between alveoli and blood vessels at the base of the lungs in terms of vascular resistance

Answer 16

Vascular restance at the base of the lungs is low so pulmonary pressure is higher than alveolar pressure so blood is pulled down to the base by gravity and the alveoli are compressed by blood vessels

Question 17

Describe the relationship between alveoli and blood vessels at the apex of the lungs in terms of vascular resistance

Answer 17

Vascular resistance is higher so the alveoli are more inflated so their pressure is greater than pulmonary arterial pressure which compresses the arterioles.
In reality, pressure auto regulation overcomes this by 75%

Question 18

Why is pulmonary arterial pressure more susceptible to the effects of gravity?

Answer 18

Because it is low pressure at 25/8mmHg

Question 19

State what happens when ventilation>perfusion

Answer 19

Overventilation
Alveolar dead space created where they are ventilated but not perfused
Elevated PAO2 leads to pulmonary vasodilation
Reduced PACO2 leads to BRONCHIAL CONSTRICTION (lets less CO2 out)
Response INCREASES PERFUSION
(reduces ventilation to lesser extent)

Question 20

State what happens when ventilation

Answer 20

Underventilation
Blood is poorly oxygenated. Shunt occurs by local mechanisms: capillaries near less well ventilated alveoli constrict and blood is diverted to better ventilated capillaries.
Elevated PACO2 leads to MILD BRONCHODILATATION to allow more air into the lungs
SYSTEMIC VESSELS DILATE to allow more oxygen to tissues in hypoxia.

Question 21

What is physiological dead space?

Answer 21

Anatomical dead space + alveolar dead space