Decoursey Ventilation and Perfusion Flashcards
What is the left right shunt?
This is the portion of CO that doesnt travel through pulmonary circulation. It’s 1-2% of CO and it comprised of the Thebesian veins(drain heart blood) and bronchial circulation (supply bronchi).
3 main differences in pulmonary and systemic
- Pulmonary has much lower pressure
- The right side has less work to do so it has thinner walls
- Low hydro static pressure minimizes the likelihood of filtering out of the capillaries into the airspace.
Where should fluid be in the lungs? what is it called when its else where
Very thin layer ling the interior the airspaces
Anywhere else it’s pulmonary edema
Possible causes of edema
- Increased capillary hydrostatic pressures (left heart fails so its not pushing blood out)
- Increased permeability of capillary endothelium
- Decreased plasma colloid osmotic pressure
- High altitude- generalized hypoxic vasoconstriction
- head unjury or heroin overdoes (mechanism unknown)
Explain why perfusion varies through the heart.
GRAVITY!
Palveolar is constant through the lung b/c air space is interconnected.
Top-PA> Pa so capillaries shut
Middle Pa>PA>Pv (capillaries close at the distal end until pressure builds up)
Bottom Pa>Pv>PA so this
What happens to pulmonary resistance when BP increase
Resistance decreases becuase of 2. Dilation- think poiseuilles equation 2. Recruitment opening previously closed vessels
The pulmonary vascular bed lack…..
Autonmic reflexes. Instead it has hypoxic pulmonary vasocontriction. This is intrinsic to smooth muscle
What is hypoxic pulmonary vasconstriction>
Aterioles vasoconstrict when they are in local hypoxia. At high altitudes constriction everywhere so increased hydrostatic pressure and there is pulmonary edema
4 other non respiratory functions of pulmonary circulation
- Angiotensin (ACE) in pulmonary endothelial cells converts Angio I to II
- INactivates vasoactive agents
- Filters out particulates and micrthrombi
- Provides “food” for lung parenchymal
Explain what happens to resistance when volume of the lung increases.
The extra alevolar vessels dilate so they reduce resistance
The capilarries narrow when volume increases so this increasing resistance
Explain why pressure is different through the lung. ADDDDDDDD
The Ppl is greater at the bottom because of gravity.
Where is ventilation the greaterst? compare to prfusion
Ventilation is greatest at the bottom. but the decrease in ventilation is much smaller than that of perfusion.
Wher is the V/R the greatest
At the Apex
What is the V/Q ratio normally?
.8 they should be nearly equal
Potential cuases of non-uniform ventialtion
- Uneven airways (emphysema, inflammation, bronchitis, bronchoconstriction, tumors, edema, mucous)
2 Due to uneven lung compliance- fibrosis, atelectasis, Edema, tumrs, COPD
- Non uniform perfusion- embolus, edmea, tumors, compression gravity
