Pulmonary Blood Flow Flashcards
Overview of blood flow to the lungs
Same volume pumped, but decreased pressure due to lower resistance.
Alveolar capillaries
Receive blood from RV.
Blood has low O2/high CO2.
Involved in exchange of O2 and CO2 between blood and air.
Appears like a sheet of capillaries.
Extra-alveolar capillaries
Receive blood from LV. High O2/low CO2. Deliver O2 and CO2 to the tissue of the lungs. Returns to the heart via PVs. Contains venous admixture.
Venous admixture
Result of mixing of shunted non-reoxygenated blood with reoxygenated. Reduces PaO2 of arterial blood and increases PaCO2 to a small degree.
Pulmonary vascular resistance equation
PBP = CO x PVR
Pulmonary vascular resistance is determined by (4):
High number of capillaries.
Number of available capillaries at a given point in time.
Sympathetic ton/vasoconstricting forces.
Lung volume.
During exercise PVR:
Drops as more pulmonary capillaries open up to accomodate the increased CO.
At low or very high lung volumes, resistance:
Increases a little because stretch of this tissue compresses the capillaries.
Compare and contrast PVR w/ SR
Normal value
BP
Blood volume
PVR: Low normal value Low BP 5 L/min blood volume SR: Moderate normal value Higher BP 5 L/min
Zones of the lungs
Zone 1 - apex
Zone 2 - mid lung
Zone 3 - base
Zone 1
BP is reduced because it is slightly above the heart.
Alveoli are somewhat expanded.
Blood flow is less.
Zone 2
BP is a little higher due to being at level of heart.
Alveoli are average size.
Blood flow is normal.
Zone 3
BP is high due to being below the heart.
Alveoli are smaller.
Blood flow is greater than in other regions of the lung.
NO modulation of pulmonary blood flow
Made by epithelium.
Causes smooth muscle relaxation and vasodilation.
Significant role in normal pulmonary blood flow.
Endothelin 1 modulation of pulmonary blood flow
Made in lungs.
Vasoconstrictor.
A player in pathologic conditions - not under normal physiology.
Thromboxane A2
Essentially the same as Endothelin 1.
Starling forces control what?
How much fluid moves from capillary to the lung.
Hydrostatic pressure in the lungs
Fluid pushing against tissue/capillary walls.
Exists in the capillary (Pc) and tissue (Pt).
Pc
BP in the capillary that wants to push fluid into the alveoli.
Pt
In the rest of the body, this pushes fluid into the capillary.
Oncotic pressure in the lungs
Osmotic pressure of fluids involved.
Exists in plasma (PIc) and tissues (PIt).
Plasma oncotic pressure
Tries to pull water into the capillary.
Tissue oncotic pressure
Tries to pull water into the alveolus.
Forces wanting to move water from capillary to alveolus (3)
Pc - hydrostatic pressure in capillary
PIt - oncotic pressure in tissues
Pt - hydrostatic pressure in tissues
Forces wanting to move water from alveolus to capillary (1)
PIc - oncotic pressure in capillary
Largest Starling Force in the lung
Pc
Net result of Starling forces
Favors filtration of fluid into the alveoli.
This is bad for gas exchange.
How does the body correct for net filtration into the alveoli?
The lymphatic system.
Regional blood flow in the lung is determined by:
Gravity and amount of air in the region of the lung.
Renin origin an function
Kidney. Converts angiotensin (from liver) to angiotensin 1.
ACE origin and function
Lungs.
Converts angiotensin 1 to angiotensin 2.
Activates bradykinin (another vasodilator).
Why do people on ACE inhibitors commonly develop a cough?
Inhibits bradykinin which can build up in lungs and cause a cough.
O2 modulation of pulmonary blood flow
A decrease in oxygen causes hypoxic vasoconstriction which increases PVR.
