Pulmonary Circulation Flashcards
How does vascular resistance differ between systemic circulation and pulmonary circulation?
Systemic resistance is higher b/c left side of heart has to pump blood to whole body so there’s more resistance to overcome (also why pressure is higher)
Pulmonary resistance is lower b/c right side of heart only has to pump blood to pulmonary vasculature which is shorter so shorter vasculature leads to reduced resistance and requires less pressure to overcome resistance
Blood flow to the base of the lung is […] than the apex of the lung
Much higher
How does the volume of blood in pulmonary circulation compare to that in systemic circulation?
9-10% at any given point in time in pulmonary
84% in systemic
7% Heart
What is high altitude pulmonary edema?
When you are in high altitudes, there is lower oxygen concentration in the air, which can trigger a hypoxia response in the body. This will cause vasoconstriction in the pulmonary circulation to redistribute blood to zones of the lung that have higher V/Q ratio (zone 1). Zone 1 is more efficient at ventilation, but it was not designed to do a lot of ventilation (remember, ventilation is efficient but low in zone 1). Thus, redirection of blood flow to this area results in over perfusion and can lead to breakdown of the alveolar capillary basement membrane and cause edema in the alveoli (plasma, blood). Patients will cough up blood. Treated with O2.
How do you determine mean arterial pressure?
MAP = cardiac output (CO) x systemic vascular resistance (SVR)
Explain what this graph is showing.
PVR is lowest around FRC
Forced expiration to reach the reserve volume limit (RV) reduces tension on the alveolar walls and increases compression on extra alveolar vessels, resulting in a decreased diameter of the extra alveolar vessels and thus an increase in resistance.
Forced inspiration to reach the total lung capacity (TLC) reduces compression on the extra alveolar vessels and increases tension on the alveolar walls, resulting in a decreased diameter of the alveolar vessels and thus an increase in resistance.
Pulmonary ventilation is also greater at the base of the lung than at the apex. Why?
The lungs are suspended in the chest cavity. Gravity acting on the the mass of the lung with its blood supply pulls the lung downward and away from the chest wall. This creates a larger volume of the intrapleural space at the apex of the lung compared to the base, and thus a more substantial difference in pressure (transmural pressure) between the inside of the lung and the intrapleural space. This greater pressure gradient causes alveoli at the apex to be more expanded and thus less compliant than alveoli at the base of the lung. As such, alveoli at the base of the lung are able to expand more during ventilation and thus have a greater ventilation capacity.
How do the blood pressures of the systemic circulation and pulmonary circulation compare?
Systemic 120/80 with mean of 100
Pulmonary 25/8 with mean of 15
KEY TAKEAWAY: pulmonary is a low pressure system, systemic is a high pressure system
Shorter, thin walled vessels with decreased smooth muscle makes pulmonary arteries far more […] than systemic arteries
Distensible and compressible
How do the systemic vascular system and the pulmonary vascular system respond to hypoxia?
Peripheral chemosensors detect low oxygen in the blood and respond by doing the following to the:
- Pulmonary
- Increase ventilation –> respiratory alkalosis (producing more CO2, decreases pH due to increasing H+ concentration in blood)
- Vasoconstriction –> pulmonary hypertension
- Systemic
- Vasodilation –> deliver O2 that is available to crucial organs
- Increase sympathetic activation –> increased HR, CO, contraction velocity, BP
For each of the zones of the lung:
- Compare and contrast ventilation and perfusion
- What is the V/Q ratio
- What is the efficiency of gas exchange
Zone 1
- Ventilation (V) > Perfusion (Q)
- V/Q > 1
- Gas exchange is more efficient
- Partial pressure O2 high and partial pressure CO2 is low
Zone 2
- Ventilation ~ = Perfusion
- V/Q ~ 1
- Gas exchange is moderately efficient
Zone 3
- Ventilation < Perfusion
- V/Q < 1
- Gas exchange is less efficient
- Partial pressure CO2 is high and partial pressure O2 is low
In the pulmonary system, vessel resistance decreases with increasing pressure. What happens with blood pressure increases in the systemic circulation?
Increasing BP causes increasing vascular resistance
What are the symptoms of hypoxia?
What are the causes?
Why is there an uneven distribution of blood flow to the zones of the lung?
Pulmonary circulation is a low pressure system and the point of entry of blood to the lungs is not at the apex, so the blood has to flow against gravity to reach zone 1 of the lung and there is not enough pressure in the system to overcome the forces of gravity and perfuse zone 1 as much as it can perfuse zones 2 and 3, where gravity is working with the pressure system to pull blood down to the lower zones.
Pulmonary arteries have […] smooth muscles in their walls compared to systemic arteries
Less
What is this diagram showing?
As blood leaves the right ventricle, its undergoes pulsatile flow until it reaches the pulmonary capillaries (rise in graph = contraction of heart, decline = relaxation of heart). Once in pulmonary capillaries, it undergoes laminar flow back to left atrium.
How do changes in position and exercise affect blood flow to the different zones of the lung?
What are the west lung zones?
Upper, middle and lower zones that describe the uneven distribution of pulmonary blood flow and ventilation of the lungs
What effect does hypoxia have on the capillaries of the lungs?
Leads to vasoconstriction and the redistribution of blood flow to areas with higher ventilation
What happens to the resistance of pulmonary vasculature if the pulmonary pressure increases?
Resistance decreases due to:
- Recruitment
- Higher BP pushes open capillaries that are normally closed at baseline levels of respiration, which creates more parallel channels of blood flow and thus decreases resistance
- Distention
- Higher BP exerts more force on walls of pulmonary capillaries which causes increase in radius, which leads to decrease in resistance
