Lecture 12: Perfusion of the lung Flashcards

1
Q

Where is perfusion greatest in the lung?

A

Perfusion is greatest at the base of the lung

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2
Q

What is the average pulmonary pressure?

A

14mmHg

  • Pressure drops across the pulm. art to an arou nd 5mmHg in pulm. cap
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3
Q

What are some notes about lung circulation?

A

2 systems

  • High pressure bronchial -> drains into left heart (never 100% oxygenated when ejected then)
  • Pulmonary circuit
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4
Q

Describe capillaries of pulmonary circuit?

A

Not in tubes, they are wall structures giving a sheet like structure for cap. exchange.

Pillars support these walls.

Keeps walls thin and maximises exchange

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5
Q

How is pulmonary circulation controlled?

A

1) Physical factors affecting blood flow
2) Chemical control of pulmonary blood vessels
3) Autonomic control of pulmonary arterioles

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6
Q

What are the physical factors affecting blood flow?

A

Lungs can hold a lot of blood because of distension and recruitment of additional pulm. vessels (prevents oedema)

BUT

Conversely resistance decreases as pressure increases

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7
Q

Why is alveolar blood flow resistance U-shaped?

A

Total pulmonary vascular resistance is u shaped. It is produced by the total of alveolar and extra-alveolar resistance.

Low inflated lungs have high extra alveolar resistance provided by vessel resistance and alveolar contribution is low.

As lung volume increases, alveolar resistance increases but extra-alveolar resistance decreases (the inflated alveoli must crush vessels and drive vasodilation?).

U-Shaped because of this (total resistance)

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8
Q

Describe the chemical control of pulmonary blood vessels:

A
  • Broncho agitation
    = Decreased PO2 = Hypoxia

This results in a regional vasoconstriction to redirect blood to better oxygenated alveoli.

i.e If alveoli cant oxygenate blood then redirect blood flow.

(Opposite to systemic where hypoxia dilates)

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9
Q

What drives pulmonary vasoconstriction:

A

Vasoconstriction

1) Hypercapnia
2) Decreased pH
3) ANG 2
4) Adenosine

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10
Q

What drives pulmonary vasodilation

A

1) Bradykinin
2) Histamine
3) Vasopressin

All endothelium dependent and mediated by NO

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11
Q

What drives pulmonary hypertension?

A

Endothelial dysfunction and lack of NO

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12
Q

Describe the autonomic control of pulmonary arterioles;

A

1) Symp innervation
- Vasocon
- Reduce pulm. blood flow by 30%

2) Muscarinic
- Vasodilation
- M3 receptor, depend on endothelium

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13
Q

Wheres the highest blood flow in the lung?

A

At the base

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14
Q

What drives the un-even blood flow?

A

Alveoli at the top of the lung are large and have less capillary density

Alveoli are smaller at the base and have a higher cap. density therefore higher blood flow

THIS IS THANKS TO GRAVITY (also pressure gradient)

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15
Q

What is good about the un-even blood flow?

A

Built in capacity so that the apex of the lung can increase perfusion during exercise.

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16
Q

Describe the perfusion ventilation mis-match;

A

Blood flow and ventilation decrease through the lung. But the proportion they decrease are different (blood flow slope is greater) and they cross around 0.8 in health lungs

AS these factors change in disease or physiologically then the ventilation perfusion ratio changes…

ADD graph

17
Q

How is ventilation perfusion ratio calculated???

A

Minute ventilation = V(t) x Hz

Alveolar ventilation = (Tidal vol - dead space) x Hz

CO = HR x SV

Ventilation / perfusion ratio = Alveolar ventilation / CO

18
Q

Whats the clinical importance of Va:Q ratio?

A

Blocked airway: Drops to near 0
Blocked vessels: Rises to 3+

Can use to determine disease

19
Q

What are disease states of the pulmonary circuit?

A

Pulmonary hypertension

  • Right side HF
  • Hypoxia = vasocon

Pulmonary oedema

  • left HF
  • Systemic hypoxia
  • Breathlessness - dyspnoea