5 Blood Supply

Question 1

How do we denote alveolar air, arterial blood and mixed venous blood?

Answer 1

Alveolar air - A
Arterial blood - a
Mixed venous blood - ṽ (e.g. in a pulmonary artery)

Question 2

So how do we denote the partial pressure of alveolar air?

Answer 2

PAO2 (A in subscript)

Question 3

From what section of the heart do the L&R pulmonary arteries arise?

Answer 3

The right ventricle, they carry its entire cardiac output

Question 4

What section of the heart does pulmonary circulation return to?

Answer 4

Left Atrium

Question 5

Describe the pressure & flow of the pulmonary circulation?

Answer 5

High flow & low pressure

Question 6

What do systolic/diastolic mean?

Answer 6

Systolic refers to max blood presssure when the heart is contracted
Diastolic refers to min blood pressure when the heart is relaxed

Question 7

What are the normal systolic pressures?

Answer 7

Pulmonary systolic pressure = 25mmHg

Systemic systolic pressure = 120mmHg

Question 8

Whats the diference between the pressure of the pulmonary vein and artery that causes blood to flow? And why is it clinically important?

Answer 8

About 10mmHg

Because its so small it only takes a little patholgy to disrupt the blood flow. (Systemic is normally 100mmHg)

Question 9

what causes gas to move between the blood and lungs?

Answer 9

Gases move down the partial pressure gradient

Question 10

What effects the rate of diffusion of O2 across the membrane?

Answer 10

• Directly proportional to partial pressure gradient
• Directly proportional to gas solubility
• Directly proportional to surface area
• Inversely proportional to membrane thickness
• Most rapid over short distance

Question 11

What happens in emphysema?

Answer 11

• Destruction of Alveoli
• Surface area is reduced
• Gas exchange decreases
• PaO2 gets low

Question 12

What happens in fibrotic lung disease?

Answer 12

• Alveolar membrane thickens
• Gas exchange slows
• Also loss of compliance may decrease alveolar ventilation
• PAO2 may be reduced and PaO2 is reduced.

Question 13

How does pulmonary oedema affect gas exchange?

Answer 13

• Institial fluid increases
• Diffusion distance increases
• PAO2 is normal but PaO2 is low

Question 14

How does asthma affect gas exchange?

Answer 14

• Bronchioles constrict
• Airway resistance increases
• Alveolar ventilation decreases
• PAO2 & PaO2 are reduced

Question 15

What is the ideal ventilation-perfusion relationship?

Answer 15

Ideally Alveolar ventilation with match perfusion in L/min

Question 16

Where is pulmonary blood flow highest? whY?

Answer 16

The base of the lung

Arterial pressure exceeds alveolar pressure.so vascular resistance is low

Question 17

Where is pulmonary blood flow lowest? Why?

Answer 17

The apex of the lung

Alveolar pressure exceeds arterial pressure so the arterioles are compressed and vascular resistance increased.

Question 18

How much of the lung has an equal blood flow & ventilation?

Answer 18

Around 75% of the height of the lung has a 1:1 ratio of blood flow: ventilation

Question 19

Where does most of the bloowflow:ventilation mismatch occur?

Answer 19

At the apex

Question 20

When is it called when blood flow to a section of lung tissue exceeds ventilation?

Answer 20

A Shunt

Question 21

In a shunt how do the Partial pressures alter in the alveoli?

Answer 21

• PA CO2 increases

- PA O2 decreases

Question 22

What happens to blood flowing past a shunt?

Answer 22

It isnt oxygenated

Question 23

When detecting a shunt the body auto-regulates. How does it do this?

Answer 23

Hypoxia in alveoli detected

• > Relevant arterioles constrict
• > Less blood flows to underventilated parts of the lung
• > Increased PA CO2 also causes bronchodilation
• > Ventilation increases

Question 24

What normally happens to blood vessels when hypoxia is detected?

Answer 24

They would usually dilate to allow greater oxygen delivery.

Only in the pulmonary circulation will they constrict on hypoxia.

Question 25

What do we call it when an area of lung tissue has a greater ventilation than blood flow?

Answer 25

Alveolar dead space

Question 26

What happnes to alveolar partial pressures during alveolar dead space?

Answer 26

PA O2 increases

PA CO2 decreases

Question 27

How does the body regulate a solution to alveolar dead space?

Answer 27

• Increased PA O2 causes pulmonary vasodilation diverting blood to the highly ventilated areas
• Decreased PA CO2 causes bronchial constriction which reduces ventilation

Question 28

Define shunt:

Answer 28

Passage of blood through areas of the lung that are poorly ventilated

Question 29

Define alveolar dead space?

Answer 29

Alveoli that are well ventilated but insufficiently perfused

Question 30

What is physiological dead space?

Answer 30

The sum of Alveolar Dead Space + Anatomical Dead Space.