Ventilation-perfusion Relationships Flashcards

0
Q

What is hypoxaemia ?

A

Any situation where there is an abnormally low partial pressure of oxygen in the arteries

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1
Q

What is ventilation ?

A

It is the movement of air from the atmosphere through the ventilatory system

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2
Q

What are the 4 basic causes of hypoxaemia ?

A

Hypoventilation
Diffusion limitation
Shunt
Ventilation - perfusion inequality

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3
Q

What determines the partial pressure of oxygen in the alveoli ?

A

Rate of removal of oxygen by the blood

Rate of replenishment of oxygen by alveolar ventilation

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4
Q

What is hypoventilation ?

A

Situation where ventilation falls below the demands of the respiring tissue

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5
Q

What are the causes of hypoventilation ?

A
  • drugs that depress central respiratory centres= opiates and barbiturates
  • damage to the chest wall
  • paralysis of respiratory muscles
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6
Q

When does the diffusion limit become larger ?

A

During exercise or as a result of thickening of the blood-gas barrier

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7
Q

What is shunted blood ?

A

Blood entering arterial system without going through the ventilated areas of the lung

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8
Q

What are some of the causes of shunted blood ?

A

Abnormal vascular connection between small pulmonary artery and vein - pulmonary arteriovenous fistula
Cardiac atrial septal defect so venous and arterial blood mix

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9
Q

What happens to the resistance in the pulmonary circulation when pulmonary arterial pressure rises and why ?

A

It decreases
1- recruitment causes capillaries which were shut to open and conduct more blood
2- distension causes the capillary lumen radius to increase which decreases resistance

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10
Q

What is the relationship between the distribution of blood flow though an upright human lung ?

A

Flow decreases almost linearly from base to apex

Pressure gradient difference of about 23 mmHg which means there is more recruitment and distension at the base

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11
Q

What happens to blood flow throughout the lungs during exercise ?

A

Increases throughout lungs and the regional differences are reduced

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12
Q

What are the 3 main forces that affect blood flow through the lungs ?

A
  • hydrostatic pressure
  • arteriovenous pressure difference
  • alveolar pressure
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13
Q

Explain zone 1 of the flow zones in an upright lung…

A

The capillaries are squashed flat causing no flow - doesn’t occur under normal conditions
PA> Pa > Pv

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14
Q

Explain zone 2 of the flow zones in an upright lung…

A

Flow determined by difference between arterial pressure and alveolar pressure
Pa> pA>Pv

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15
Q

Explain zone 3 of the flow zones in an upright zone…

A

Flow determined by arteriovenous pressure difference

Pa> Pv > pA