Lung Ventilation and Perfusion Flashcards
What is alveolar ventilation?
Rate at which new air reaches respiratory areas
What does the alveolar air equation describe?
Idea case of what the partial pressure of oxygen should be in the alveoli
What is the alveolar - arterial (A-a) gradient
The difference between the ideal PAO2 and PaO2. It is normally 15mmHg
Describe the ventilation is distributed in the lung?
- 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
Describe the effects of gravity on ventilation
- 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
Describe the blood supply to the airways
- Pulmonary and bronchial arteries - Bronchial veins exist but majority of blood drains into pulmonary veins via shunt. This causes venous admixture
Pulmonary capillaries are relatively leaky and alveolar walls are extremely thin so why do the alveoli not fill with fluid?
- Normal pulmonary capillaries and lymphatics maintain a slightly negative pressure, so excess fluid will be sucked back into interstitial space from alveoli
Describe pulmonary blood flow in zone two
Apex to mid lung. P(PA) > P(A) > P(V). Intermittent blood flow only during pulmonary arterial pressure peaks
Describe pulmonary blood flow in zone three
P(PA) > P(V)> P(A). Mid to lower lung. Continuous blood flow during entire cardiac output. Distention of pulmonary capillaries
Describe pulmonary blood flow in zone four
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.
When does ZOne 1 pulmonary BF occur?
When the P(A) is high or the P(PA) is low. So it doesn’t occur normally
What is the regulation of pulmonary blood flow?
- Cardiac output, - PO2 and PCO2, results in arteries constricts so that blood is better diverted to better oxygenated areas - Very slight autonomic control
Describe what agents affect pulmonary vascular resistance
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Where do the bronchial arteries arise from?
Aortic arch, thoracic arch and their branches
Define ventilation-perfusion ratio
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.