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Respiratory > 5 Blood Supply > Flashcards

5 Blood Supply Flashcards

1
Q

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

A

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

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2
Q

How do we denote the partial pressure of alveolar air?

A

PAO2 (A in subscript)

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3
Q

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

A

Right ventricle, carry entire cardiac output

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4
Q

What section of the heart does pulmonary circulation return to?

A

Left Atrium

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5
Q

Describe the pressure & flow of the pulmonary circulation?

A

High flow
Low pressure

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6
Q

What do systolic/diastolic mean?

A

Systolic is max blood pressure when heart is contracted
Diastolic is min blood pressure when heart is relaxed

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7
Q

What are the normal systolic pressures?

A

Pulmonary systolic pressure = 25mmHg
Systemic systolic pressure = 120mmHg

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8
Q

What is the difference between pressure of the pulmonary vein and artery that causes blood to flow?
Why is it clinically important?

A

About 10mmHg

Because its so small it only takes a little pathology to disrupt blood flow
(Systemic normally 100mmHg)

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9
Q

What causes gas to move between the blood and lungs?

A

Gases move down the partial pressure gradient

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10
Q

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

A

Directly proportional to:
- partial pressure gradient
- gas solubility
- surface area

Inversely proportional to membrane thickness
Most rapid over short distance

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11
Q

What happens in emphysema?

A

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

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12
Q

What happens in fibrotic lung disease?

A

Alveolar membrane thickens
Gas exchange slows
Loss of compliance may decrease alveolar ventilation
PAO2 may be reduced and reduce PaO2

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13
Q

How does pulmonary oedema affect gas exchange?

A

Interstitial fluid increases
Diffusion distance increases
PAO2 is normal but PaO2 is low

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14
Q

How does asthma affect gas exchange?

A

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

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15
Q

What is the ideal ventilation-perfusion relationship?

A

Alveolar ventilation matches perfusion in L/min

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16
Q

Where is pulmonary blood flow highest and why?

A

Base of lung
Arterial pressure exceeds alveolar pressure so vascular resistance is low

17
Q

Where is pulmonary blood flow lowest and why?

A

Apex of lung
Alveolar pressure exceeds arterial pressure
Arterioles are compressed and vascular resistance increased

18
Q

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

A

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

19
Q

Where does most of the bloodflow to ventilation mismatch occur?

A

Apex

20
Q

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

A

Shunt

(Blood gets shunted away)

21
Q

Define shunt:

A

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

22
Q

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

A
  • PA CO2 increases
  • PA O2 decreases
23
Q

What happens to blood flowing past a shunt?

A

It is deoxygenated

24
Q

How does the body auto-regulate a shunt?

A

Hypoxia in alveoli detected
-> Relevant arterioles constrict
-> Less blood flows to under-ventilated parts of lung

-> Increased PA CO2 also causes bronchodilation
-> Ventilation increases

25
Q

What normally happens to blood vessels when hypoxia is detected?

A

Systemic circulation - dilate to allow greater oxygen delivery
Pulmonary circulation - constrict to divert blood to better ventilated parts of lung

26
Q

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

A

Alveolar dead space

27
Q

Define alveolar dead space?

A

Alveoli that are well ventilated but insufficiently perfused

28
Q

What happens to PA during alveolar dead space?

A

PA O2 increases

PA CO2 decreases

29
Q

How does the body regulate alveolar dead space?

A
  • Increased PA O2 causes pulmonary vasodilation diverting blood to the highly ventilated areas
  • Decreased PA CO2 causes bronchial constriction which reduces ventilation
30
Q

What is physiological dead space?

A

Sum of Alveolar Dead Space + Anatomical Dead Space

Respiratory (30 decks)

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