Pulmonary circulation Flashcards
How compliant are the vessels of the pulmonary circulation?
Highly
What happens to blood flow in alveolar capillaries when PO2 drops? Why?
local vasoconstriction
To redistribute the blood to better aerated alveoli
What are the five scenarios mentioned in class that trigger abnormal hypoxic pulmonary vasoconstriction (HPV) response?
Airway obstruction Failure of ventilation Acute lung damage High altitude COPD
What triggers hypoxic pulmonary vasoconstriction?
Alveolar hypoxia
How do PA, Pa, and Pv relate to each other in the upper part of the lungs?
(recall that PA = alveolar pressure, Pa = arterial pressure, and Pv = veins).
PA > Pa > Pv
How do PA, Pa, and Pv relate to each other in the middle part of the lungs?
(recall that PA = alveolar pressure, Pa = arterial pressure, and Pv = veins).
Pa > PA > Pv
How do PA, Pa, and Pv relate to each other in the lower part of the lungs?
(recall that PA = alveolar pressure, Pa = arterial pressure, and Pv = veins).
Pa > Pv > PA
Conditions that affect blood vasculature affect what part of the lungs more, the base or the apex?
Base
Blood flow is greater in the base or the apex of the lungs?
Base
What happens to hydrostatic pressure in CHF? What does this cause?
increases
Causes increase in edema in the interstitium
Why does ventilation have to match perfusion?
Need to have blood flow with oxygen
What is the average value of V/Q?
0.8
What happens to the ventilation and perfusion when going from the base to the apex of the lung?
Both decrease, but perfusion drops more
What happens to the V/Q ratio when moving from the base of the lungs, to the apex? Why?
Increases
Q drops faster than V
Why does TB reactivate in the upper lung zones?
Because there is more ventilation relative to perfusion (it is an aerobe)
What is the V/Q ratio in the dead space?
infinite ventilation, no blood flow
What is the V/Q ratio in a shunt?
0 (no ventilation, but tons of blood flow)
What happens to the V/Q as you progress down the airway tree? Why?
more perfusion, less ventilation, thus gets smaller
What is the physiological shunt?
The bronchial circulation
If there is a communication between the left and right side of the heart, what always occurs? How?
Hypoxemia from RVH
Why doesn’t hypoxemia occur with right to left shunts right away?
Blood flow from left to right due to pressure initially, but RVH eventually wins, and causes non oxygenated blood to shunt from the right to the left
What happens to the V/Q ratio in PEs?
Infinite d/t normal ventilation, but 0 blood flow
Which side of the heart is affected more in a PE?
Right d/t blockage
What are the two major outcomes of a PE?
- Right to left shunting in areas of atelectasis
2. V/Q mismatch
What is the gold standard for PE detection?
V/Q (ventilation) scan
What is a ventilation scan?
Looking at lung perfusion with radioactive substance
What is the V/Q ratio in normal patients?
1.0, thus usually the curves will superimpose over one another
What is the function of the bronchial arteries? What effects does this have on systemic oxygen content?
Supply oxygen to the lung tissues.
This blood is then shunted to the left side of the heart, decreasing the overall oxygen content slightly
What is the function of the pulmonary circulation (capacitors or resistors)?
Capacitors
What happens to the bronchial arteries in CF?
Increase in size
What is the effect of persistent hypoxic vasoconstriction?
Vascular structural remodeling, leading to pulmonary arterial HTN (PAH)
In normal upright subjects at rest, blood flow
(BLANKS) from the apex of the lung to the base
of the lung.
In normal upright subjects at rest, blood flow INCREASES from the apex of the lung to the base
of the lung.
Are the effects of gravity felt equally in pulmonary veins and arteries?
Yes
Where is pulmonary edema seen in the lungs? Why?
Lower lobes d/t increase flow of blood there relative to the other parts
What is the effect of positive pressure ventilation on the upper part of the lungs (zone 1) relative to the Pa and PA?
PA»_space;>Pa, meaning that arteries could collapse
How permeable are pulmonary capillaries to proteins? What is the consequence of this?
Very
Higher propensity to develop interstitial edema
The capillary pressure in the pulmonary circulation favors what (filtration or reabsorption? What is the consequence of this?
Filtration
Thus lymphatics play a large role in pumping out this excess fluid
Why is there a negative hydrostatic pressure in the pulmonary interstitium? When can this become positive?
Lung expansion lowers it
Can become positive if there is inflammation of the capillaries
Which way does fluid flow between the alveoli and the interstitium? Why?
From alveoli to the interstitium d/t lower pressure in the interstitium
What is the effect of an increase in intravascular hydrostatic pressure in the pulmonary circulation?
Pulmonary edema
What is the effect of an decrease in capillary osmotic pressure in the pulmonary circulation?
Pulmonary edema
What is the effect of an increase in capillary permeability in the pulmonary circulation?
Pulmonary edema
In regions of dead space, alveolar gas has what composition relative to the inspire humidified air?
Same (all oxygen, no CO2)
When do right to left shunts occur?
If there is a defect in the
wall between the right and left ventricles
A defining characteristic of the hypoxemia caused by a right-to-left shunt is that it cannot be
corrected by having the person breathe a high O2 gas (e.g., 100% O2).
Why?
because the shunted
blood never goes to the lungs to be oxygenated.
Do left to right shunts cause hypoxemia? Why or why not?
No, because oxygenated blood flows into right ventricle to be oxygenated again.
What are the causes of a left-to-right shunt? (2)
Patent ductus arteriosus or traumatic injury
