Pulmonary Circulation Flashcards
Pulmonary circulation has low resistance and systemic circulation has high resistance. What qualities of both determine the level of resistance?
Pulmonary
- Arterioles have less smooth muscle
- Veins are wider and shorter
- Pulmonary vessel walls are thinner
Systemic
- Increased smooth muscle in the arterioles & the metarterioles.
Compare pulmonary and systemic circulation, in terms of preesure, resistance, and compliance.
Pulmonary
- Pressure: LOW
- Resistance: LOW
- Compliance: HIGH
Systemic
- Pressure: HIGH
- Resistance: HIGH
- Compliance: LOW
At rest, aorta pressure is approximately 95 mmHg. Why is it so high?
Because systemic capillaries are closed
During systemic circulation, what is the approximate pressure of the aorta and right atrium?
Aorta: 95 mmHg
Right atrium: 2 mmHg
*This makes the driving pressure aprroximately 93 mmHg
During pulmonary circulation, what is the approximate pressure of the pulmonary artery and left atrium, respectively?
Pulmonary artery: 15 mmHg
Left atrium: 8 mmHg
*This makes the net driving pressure approximately 7 mmHg
How is pulmonary vascular resistance calculated?
PVR= (MPAP-MLAP)/(PBF)
MPAP= Mean pulmonary artery pressure
MLAP= Mean left atrial pressure
PBF= Pulmonary blood flow
Why is pulmonary resistance so much lower than systemic resistance?
- Pulmonary blood vessels are shorter and wider than those in the systemic circulation
- Arterioles are also present in much higher numbers
- The pulmonary arterioles are less muscular than those in the systemic circulation
Which passive factors play a major role in pulmonary vascular resistance?
- Gravity
- Body position
- Lung volume
- Alveolar and intrapleural pressures
- Intravascular pressures
- Right ventricular output
NOTE: These factors play a major role in pulmonary vascular resistance without altering the tone of the pulmonary vascular smooth muscle
Transmural pressure difference
Pressure inside minus pressure outside the vessel
As transmural pressure difference ________ (increases/decreases), the vessel diameter increases and resistance falls.
Increases
NOTE: A negative transmural pressure difference can lead to compression or even collapse of the vessel.
More _______ (negative/positive) intrapleural pressure pulls open extra-alveolar vessels.
Negative
Alveolar vessel resistance is dependent on what two factors?
Transmural pressure
Lung volume
As lung volume __________ (increases/decreases), the alveolar walls become more stretched out.
Increases
NOTE: The alveolar vessel is stretched along the longitudinal axis and the alveolar vessel is crussed when viewed in cross-section. This raises vessel resistance
Pulmonary vascular resistance is lowest near the __________ and increases at both low and high lung volumes because of the combined effects of the alveolar and extralveolar vessels.
Functional residual capacity
How are low lung volumes achieved?
- Positive intrapleural pressures
- Compression of extraalveolar vessels
Total pulmonary vascular resistance
Extra-alveolar resistance + alveolar resistance
Functional Residual Capacity
The volume of air present in the lungs at the end of passive expiration.
Resistance to blood flow is higher at ______ (low/high) lung volumes because the traction on the vessel walls is decreased.
Low
Gravity-dependent Pulmonary Blood Flow in the Lung
Blood flow to alveoli is greater at the bottom of the lung than at the top, when in an upright position
NOTE: Blood travels through the more gravity-dependent regions of the lung at a faster rate
During exercise what happens to pulmonary vascular resistance? How can this be explained?
The pulmonary vascular resistance will decrease. This can be explained by the recruitment and distention of pulmonary capillaries that occurs in response to elevated blood flow and perfusion pressure.
What role does recruitment play in reduction of pulmonary resistance?
- As pressure increases:
- Closed vessels may now open
- Capillaries that were open but not conducting now begin to conduct blood
NOTE: The recruitment of additional parallel capillary pathways reduces overal vascular resistance
What role does distention play in reduction of pulmonary resistance?
- Once a vessel is open and conducting: furter pressure increases will increase transmural pressure
- This causes the vessel to dilate
How is derecruitment accomplished?
- Low right ventricular output
- High alveolar pressure
*This results in a decrease in surface area for gas exchange and may increase alveolar dead space
