Lung Ventilation and Perfusion Flashcards

1
Q

What is alveolar ventilation?

A

Rate at which new air reaches respiratory areas

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2
Q

What does the alveolar air equation describe?

A

Idea case of what the partial pressure of oxygen should be in the alveoli

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3
Q

What is the alveolar - arterial (A-a) gradient

A

The difference between the ideal PAO2 and PaO2. It is normally 15mmHg

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4
Q

Describe the ventilation is distributed in the lung?

A
  • Alveoli in the top of lung are more expanded than those at the bottom as the pleural pressure is more negative at the apex. As inspiration beings, alveoli in the lungs are at different lung volumes. The underinflated alveoli at the base of the lung are more compliant so receive more of tidal volume
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5
Q

Describe the effects of gravity on ventilation

A
  • At the base, alveoli are compressed by the weight of tissue above where as at the apex, alveoli are forced to inflate by weight of lung tissue below
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6
Q

Describe the blood supply to the airways

A
  • Pulmonary and bronchial arteries - Bronchial veins exist but majority of blood drains into pulmonary veins via shunt. This causes venous admixture
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7
Q

Pulmonary capillaries are relatively leaky and alveolar walls are extremely thin so why do the alveoli not fill with fluid?

A
  • Normal pulmonary capillaries and lymphatics maintain a slightly negative pressure, so excess fluid will be sucked back into interstitial space from alveoli
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8
Q

Describe pulmonary blood flow in zone two

A

Apex to mid lung. P(PA) > P(A) > P(V). Intermittent blood flow only during pulmonary arterial pressure peaks

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9
Q

Describe pulmonary blood flow in zone three

A

P(PA) > P(V)> P(A). Mid to lower lung. Continuous blood flow during entire cardiac output. Distention of pulmonary capillaries

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10
Q

Describe pulmonary blood flow in zone four

A

P(PA) > P(V)> P(A). This occurs at the extreme base of lung. There is constriction of extra-alveolar vessels and the peak flow decreases.

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11
Q

When does ZOne 1 pulmonary BF occur?

A

When the P(A) is high or the P(PA) is low. So it doesn’t occur normally

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12
Q

What is the regulation of pulmonary blood flow?

A
  • Cardiac output, - PO2 and PCO2, results in arteries constricts so that blood is better diverted to better oxygenated areas - Very slight autonomic control
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13
Q

Describe what agents affect pulmonary vascular resistance

A

Add picture

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14
Q

Where do the bronchial arteries arise from?

A

Aortic arch, thoracic arch and their branches

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15
Q

Define ventilation-perfusion ratio

A

It is the ratio used to assess the efficiency and adequacy of matching ventilation and perfusion. It is V/Q where V = ventilation and Q = Perfusion.

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16
Q

What occurs if the V/Q is above/below 1

A

When it is above one then ventilation exceeds perfusion. When below 1 then perfusion exceeds ventilation

17
Q

What is the normal V/Q ration?

A

0.85

18
Q

What is arterial hypoxemia?

A

Abnormal P(ao2)

19
Q

What is hypoxia?

A

Insufficient O2 to carry out metabolic functions

20
Q

What are the 4 major causes of hypoxemia?

A
  • Anatomical shunt, - Physiological shunt, - V/Q mismatching, - Hypoventilation.
21
Q

Describe some anatomical shunts?

A

Means blood is bypassing lungs this means the hypoxia cannot be abolished by giving 100% O2. - Right to left shunt - Cyanotic congenital heart diseases (MOST COMMON)

22
Q

Describe some physiological shunts?

A
  • If airway completely blocked then the alveoli supplied by that airway recieves no ventilation but perfusion continues but as V = 0 then V/Q = 0. - Most common cause = Atelectasis
23
Q

Describe features of V/Q mmismatching

A

This is where there is not a complete block but there is varying degrees of constriction of the airways so varying amount of air getting in. Supplemental O2 will correct hypoxemia as poorly ventilated units will get enriched O2.

24
Q

Describe features of hypoventilation

A

Underventilation will bring less fresh gas to alveoli. If O2 levels decrease in alveoli then CO2 levels increase. This occurs in patients with respiratory muscle weakness (muscular dystrophy or diaphragmatic paralysis).