3.2B. The pulmonary circulation. Ventilation-perfusion relationship. Flashcards
I. Pulmonary circulation
1. What are the functions of pulmonary circulation?
- Re-oxygenate the blood and release CO2
- To distribute metabolic products to and from the lung
I. Pulmonary circulation
2. What is the total blood volume of pulmonary circulation?
500mL (10% of total circulation).
I. Pulmonary circulation
5. Why is the drop in pressure is much smaller than in the systemic circulation?
- Pulmonary vessels = low resistance, few SMC (less than in systemic circulation)
- Driving force: which maintains the blood flow is the difference between the Pmean and pressure in left atria (14 – 8 = 6mmHg), which is about 15x smaller than the pressure difference in the systemic circulation
- Resistance is also 15x smaller, since flow is the same in pulmonary and systemic circulation
I. Pulmonary circulation
3. What is the mechanism of pulmonary circulation?
Deoxygenated blood is pumped into the pulmonary artery. The pulmonary blood flow is equal to the CO of the right heart, hence equal to the CO of the left heart.
I. Pulmonary circulation
4A. What is the value of pressure in the right ventricle?
25/0 mmHg
I. Pulmonary circulation
4B. What is the value of pressure in the pulmonary arteries?
24/9 mmHg
=> Pmean = 14mmHg
I. Pulmonary circulation
4C. What is the value of pressure in the Pulmonary capillaries?
~10 mmHg
I. Pulmonary circulation
4D. What is the value of pressure in the Pulmonary veins?
~9 mmHg
I. Pulmonary circulation
4E. What is the value of pressure in the left atria?
8 mmHg
II. Regulation of Pulmonary circulation
1. What are the 2 types of Pulmonary circulation regulations?
Passive and active
II. Regulation of Pulmonary circulation
2. What is the mechanism of passive regulation of pulmonary circulation?
- If we exercise, our CO is increased 3-4x more -> the increased circulation has to go through the lung, because the pulmonary and systemic circulation are serially connected
- This increased amount of flow will go through the lung, with a relatively small increase in pressure, CO increased = vessels dilate and resistance ↓
- This way, the pulmonary circulation can accommodate much larger blood flow than normal, without a major increase in BP
- Pulmonary circulation can accommodate ↑ blood flow
II. Regulation of Pulmonary circulation
3A. What is the mechanism of active regulation of pulmonary circulation?
Hypoxia (pO2↓) in pulmonary circulation causes vasoconstriction (reflex)
- Means that if we have a bronchus with low ventilation = pO2↓
-> local vasoconstriction (blood flow↓)
- If no ventilation, then due to the vasoconstriction, there will be no blood flow either
-> This reflex provides a balance between ventilation and blood flow
II. Regulation of Pulmonary circulation
3B. Hypoxia can occur in the whole circulation
-> How?
Hypoxia can occur in the whole circulation. This is the case for:
- people who live at high altitudes and have chronic hypoxia (pO2↓) and increased resistance in pulmonary vessels
- people with respiratory insufficiency (pO2↓ + pCO2↑) and have hypoxia in the whole lung
+) pulmonary resistance ↓
-> causes hypoxia = vasoconstriction in pulmonary vessels
-> increased resistance (whole lung in hypoxia)
-> pulmonary BP↑
-> makes work of right ventricle↑
+) have to pump against higher resistance with higher pressure
III. Circulation in the lung
1. What are the 2 blood supplies of the lung?
1) pulmonary circulation: for the uptake of O2 and removal of CO2 from the body
2) bronchial circulation
III. Circulation in the lung
2. What are the characteristics of bronchial circulation:?
bronchial circulation: to supply O2 for the lung tissue
- 1% of the total circulation
- Mixes venous blood with arterial blood of pulmonary veins; one of the factor which makes pO2 in the arteries a little bit lower than 100mmHg (95mmHg)
III. Effect of gravity on pulmonary blood flow
1. What is the Effect of gravity on pulmonary blood flow on zone 1?
Zone 1 (apex): (not realistic)
- Hydrostatic pressure (Phydro) is the lowest
- PA > Pa > PV, because the heart is a little bit below the apex
=> PA compresses the capillaries = no flow
(Blood flow is lowest at the apex of the lung and highest at the base of the lung)
III. Effect of gravity on pulmonary blood flow
2. What is the Effect of gravity on pulmonary blood flow on zone 2?
Zone 2: (real position of apex)
- Pa>PA>PV
- PA compresses the vessels, but not completely
=> Reduction blood
(Blood flow is lowest at the apex of the lung and highest at the base of the lung)
III. Effect of gravity on pulmonary blood flow
3. What is the Effect of gravity on pulmonary blood flow on zone 3?
Zone 3 (base):
- Pa>PV>PA
- Vessels are expanded into the alveolar space (vessels dilated)
=> Blood flow increased
(Blood flow is lowest at the apex of the lung and highest at the base of the lung)
III. Effect of gravity on pulmonary blood flow
4. Describe the blood flow from apex to base of ling?
From apex to base of lung, blood flow ↑ drastically (in standing position)
- At top: resistance↑, pressure↓ = Q↓
- At base: resistance↓, pressure↑ = Q↑
(Blood flow is lowest at the apex of the lung and highest at the base of the lung)
IV. Ventilation/perfusion ratio (mismatch)
2A. What is the difference in the intrapleural pressure between apex and base of lung? Explain
- -10 cmH2O at apex
- -2,5 cmH2O at base
=> 4x times larger alveoli at apex than base
- The intrapleural pressure is more negative at the top, because the weight of the lung (in standing position) pulls the pleural space downwards, making the pleural pressure more negative
- At the base, the weight of the lung puts positive pressure on the pleural space and makes the pleural pressure less negative
- The increased negative pressure at the top of the lung keeps the alveoli more open (larger alveoli), than those at the base (smaller alveoli)
- Less respiration at the alveoli at the top, since when they are expanded too much = less compliant
=> The same breathing, but volume change will be smaller, since alveoli are compressed too much
- More respiration will take place in the alveoli at the base, because the volume difference is larger
=> Alveoli are allowed to open and close completely, thus ejecting the old air for new air
IV. Ventilation/perfusion ratio (mismatch)
2B. What are intrapleural pressures at apex and base of lung?
-10 cmH2O at apex
-2,5 cmH2O at base
=> 4x times larger alveoli at apex than base
IV. Ventilation/perfusion ratio (mismatch)
2C. Why is The intrapleural pressure is more negative at the top than that at base?
- The intrapleural pressure is more negative at the top, because the weight of the
lung (in standing position) pulls the pleural space downwards, making the pleural
pressure more negative - At the base, the weight of the lung puts positive pressure on the pleural space and makes the pleural pressure less negative
IV. Ventilation/perfusion ratio (mismatch)
2D. What is the consequence of the increased negative pressure at the top of the lung?
- The increased negative pressure at the top of the lung keeps the alveoli more open (larger alveoli), than those at the base (smaller alveoli)
- Less respiration at the alveoli at the top, since when they are expanded too much = less compliant
=> The same breathing, but volume change will be smaller, since alveoli are compressed too much
IV. Ventilation/perfusion ratio (mismatch)
2E. More respiration takes place in the alveoli at the top
=> T/F? Why?
FALSE!!!
More respiration will take place in the alveoli at the BASE, because the volume difference is larger
=> Alveoli are allowed to open and close completely, thus ejecting the old air for
new air
IV. Ventilation/perfusion ratio (mismatch)
2F. More respiration will take place in the alveoli at the base
=> Why? What is the consequence?
More respiration will take place in the alveoli at the BASE, because the volume difference is larger
=> Alveoli are allowed to open and close completely, thus ejecting the old air for
new air
IV. Ventilation/perfusion ratio (mismatch) - Ventilation-perfusion relationship:
3. What is the relationship between ventilation and blood flow at top and base?
- AT TOP: more ventilation than blood flow
- AT BASE: more blood flow than ventilation
IV. Ventilation/perfusion ratio (mismatch) - Ventilation-perfusion relationship:
4. Explain the The ventilation-perfusion ratio (VA/Q) at top and base
- The ventilation-perfusion ratio (VA/Q) is higher at the top than at the base, because VA > Q
- If ventilation is too high (TOP) = ↑pO2 in blood
- If ventilation is not enough (BASE) = ↓pO2
IV. Ventilation/perfusion ratio (mismatch) - Ventilation-perfusion relationship:
5. What are the features of blood at top and base of the lung
- TOP – hyperoxic blood
- BASE – hypoxic blood
=> The blood gets mixed in the pulmonary veins
IV. Ventilation/perfusion ratio (mismatch) - Ventilation-perfusion relationship:
6. How can Ventilation-perfusion relationship relate to hypoxia?
- At the top of the lung, where pO2 is high, there is
little blood flow - At the base of the lung, where pO2 is low, there
is high blood flow - More hypoxic blood gets mixed with less
hypoxic (hyperoxic) blood
=> Result: average PAO2 < 100mmHg
(PAO2 (alveolar) = 100mmHg and PaO2 (arterial) = 95mmHg)
