ICL 1.2: Pulmonary & Bronchial Circulation Flashcards
what are the 2 types of circulation in the lung?
- pulmonary circulation
2. bronchial circulation (from the systemic circulation!)
how does bronchial circulation works?
it provides blood to the trachea, pulmonary artery, upper respiratory tract from the systemic circulation
it comes from the descending aorta where the bronchial artery arises:
aorta –> bronchial artery –> bronchial capillary –> bronchial vein –> azygous vein –> SVC
why doesn’t the LA get 100% saturated blood from the lungs?
bronchial circulation has a bronchopulmonary vein which allows deoxygenated blood coming out of the bronchial circulation to get mixed with the pulmonary vein which has oxygenated blood from the lungs
so the blood coming from the lungs is 100% oxygenated but because it gets merged with the bronchopulmonary vein carrying deoxygenated blood, the % saturation decreases and is only 98% oxygenated when it reaches the LA
this isn’t important normally but in the cases of hypoxia this can be a huge deal and this “alveolar arterial gradient” is used to measure the degree of hypoxia
what is the pulmonary right-to-left shunt?
the lungs receive about 2% of the CO= 150 mL/minute through the bronchioles
2/3 of that blood, 100 mL, comes back to the pulmonary vein directly
so that’s why the output of the LV is just slightly higher than the RV because of this right to left shunt from the bronchiole circulation
what is the difference between the bronchial and pulmonary circulation?
BRONCHIAL CIRCULATION
1. high pressure, low flow circulation
- gets 2% of CO, so not a lot of blood goes through the bronchial circulation
- supplies blood from bronchi to terminal bronchioles
- arises from the aorta
PULMONARY CIRCULATION
1. low pressure, high flow circulation
- gets 100% of CO, all 5 L of blood go through the pulmonary circulation
- supplies respiratory bronchioles to alveoli
- arises from the heart, the RV
- the ONLY artery that carries deoxygenated blood!
what is the pressure in the pulmonary vs. systemic circulation?
PULMONARY RV = 25/0 PA = 25/8 capillary = 7-9 pulmonary vein = 5 LA = 5
SYSTEMIC LV = 120/0 aorta = 120/80 capillary = 30-45 peripheral vein = 15 RA = 0-2
the pulmonary circulation is a relatively low pressure system
mean pulmonary arterial pressure is 15 and if it’s higher than 25, it’s pulmonary HTN
what is pulmonary circulation?
the pulmonary circulation is defined as extending from the pulmonic valve to the left atrium and consists of the pulmonary outflow tract, the right and left main pulmonary arteries and their lobar branches, the intrapulmonary arteries, the pulmonary arterioles, capillaries, venules, and large pulmonary veins
what is the output of blood flow in the pulmonary circulation?
5 L/min
same as the CO!
what is the pressure difference in the pulmonary circulation vs systemic? how does it work?
pulmonary: PA - LA = (15-5) = 10 mmHg
systemic: (90-3) = 87 mmHg
how does this work? you are able to accommodate the same amount of blood at a lower pressure difference in the pulmonary circulation…the reason the pulmonary circulation works effectively at low pressures is primarily because of the low resistance
arterioles are the major resistance determinants in the cardiac system but with pulmonary circulation, arterioles have NO smooth muscle cells and no resistance! this absence of muscular arterioles provide a mechanism of lower resistance in the lungs
also, many of the lung capillaries remain closed and only open when required so they’re used when you need a mechanism to handle high pressures like pulmonary HTN so you recruit more capillaries to reduce the overall resistance
R = pressure difference/CO
how is the pulmonary circulation effected by gravity?
since pulmonary circulation works on low pressure, it’s more effected by gravity!
if you’re laying down gravity is working from anterior to posterior and has a big effect on lung circulation
usually, if you take one RBC, it takes 5 sec to completely go through the pulmonary circulation and out of this time, less than 1 second is spent in the capillary bed where the gas exchange happens
what is the capillary pressure in the pulmonary capillaries dependent on?
pressure difference = P(PA) - P(LA) = CO*resistance
P(PA) = CO*PVR + P(LA)
so if the CO is high like during exercise, pulmonary pressure will be higher
in the case of COPD or fibrosis or sleep apnea, PVR is increased so the pressure in the pulmonary artery increases
in the case of pulmonary venous HTN, heart failure or valve disease, left atrium pressure will be increased and the pulmonary pressure will be increased
how does pulmonary vascular resistance change as we breath?
every time we breath and change the lung volume, we change the PVR!
when we breath in, air is put into the alveoli which expand and put pressure on the vasculature surrounding the alveolar sac = compression of capillaries = increased PVR –> when this is happening during inspiration, you’re also expanding your chest cavity and the vessels not in contact with the alveoli get more space to dilate and they expand and their resistance decreases!
so during inspiration, extra-alveolar vessels have a decrease in resistance while alveolar vessels increase
which vessels are extra-alveolar?
- arteries
- arterioles
- venules
- veins
what are the components of the total resistance in the lungs?
it’s a combination of the resistance in the alveolar and extra-alveolar capillaries!
when you increase the pressure in the pulmonary artery, what happens to the pulmonary resistance?
P(PA) = CO*PVR + P(LA)
when we increase the pressure in the pulmonary artery, the PVR decreases
this is because there are less smooth muscles in the arterioles and they’re more compliant
also, in the lungs there are lots of capillaries that normally are closed but at increased pulmonary pressure or flow, these extra capillaries are recruited so that the resistance decreases and you can accommodate the increased flow without changing the pressure in the pulmonary artery
what is the formula for PVR? how does PVR effect pulmonary artery pressure?
PVR = length of tube/rˆ4
when you increase the pressure you’re recruiting more capillaries which increases the radius and decreases the PVR
P(PA) = CO*PVR + P(LA)
when you are exercising, the arterial pressure can be maintained by changing the pulmonary resistance! an increase in CO will increase pulmonary artery pressure but your body will try to reduce the resistance to maintain pulmonary artery pressure
if pulmonary vasculature wasn’t as compliant as it is, it would lead to pulmonary HTN very quickly – the ability to modulate PVR helps us keep the pulmonary artery pressure at a low pressure
what metabolic condition helps reduce pulmonary vascular resistance?
- low CO2 = low PaCO2
2. alkalemia
what 2 factors mainly effect pulmonary artery pressure?
- pulmonar vascular resistance
2. lung volume
what is the functional residual capacity of the lungs?
in the lungs, the resistance is a combination of alveolar and extra-alveolar vessels
if you inspire, you expand the lung and the pressure on the extra-alveolar vessels goes down but at the same time the alveolar vessels are being constricted
so the point at which both of these are at a minimum is called the functional residual capacity of the lungs! this is the point at which the PVR is minimal
if you increase the volume of the lungs past the FRC, the PVR will increase because alveolar resistance is increasing – if you decrease the volume from the FRC, the extra-alveolar vessels are compressed and the PVR will increase due to that –> so the PVR is at a minimum at the FRC!
what happens to vessel diameter in the lungs in conditions of hypoxia?
in the body, hypoxia is vasodilatory but in the lungs it’s vasoconstrictive!
this response is most prominent once the PO2 is below 70 mmHg
if you have an alveolar sac with less oxygen or it’s damaged so that both ways the oxygen is low, should you divert the capillaries to that area? capillaries are going to the alveolar sacs to get oxygen so why would you send it to an alveoli that doesn’t have enough oxygen?? so the lungs will constrict the capillaries in hypoxic areas of the lungs and divert them to somewhere else that has more oxygen!
so local hypoxia in the lungs is vasoconstrictive!!
if you go to areas of high altitudes where there’s really low oxygen, then there will be global vasoconstriction in the lungs but more often you will see local hypoxia from edema, etc.
which biological molecules vasoconstrict the lung vessels and increase PVR?
- noradrenaline
- adrenaline
- dopamine
- PGF2a
- histamine (H1)
- thromboxane
- serotonin
- angiotensin
which biological molecules vasodilate the lung vessels and decrease PVR?
- isoproteronol
- aminophyline
- ganglion blocker
- PGE, PGI2
- histamine (H2)
- ACh
- bradykinin
are the pulmonary vessels dilated or constricted under normal conditions?
pulmonary circulation is fully dilated under normal conditions, due to circulating vasodilators like NO, prostacyclin, arachidonic acid, that contribute to pulmonary vascular tone
what is the effect of SNS activation on the lungs?
SNS activation in the systemic circulation causes vasoconstriction and increased HR and CO
SNS activation has very little effect on the lungs because they’re smooth muscles!
what is the effect of PNS activation on the lungs?
PNS has a vasodilatory effect on both the lungs and systemic circulation
what are the 3 zones of perfusion in the lungs?
pulmonary circulation is effected by gravity and based on gravity plus the alveolar, arteriole and venous pressure, the lungs are split into 3 zones:
ZONE 1: PA > Pa > Pv
ZONE 2: Pa > PA > Pv
ZONE 3: Pa > Pv > PA
A = alveolar a = arteriole V = vein
what is happening in zone 1 of the lungs?
PA > Pa > Pv
the distance from the pulmonary artery to the apex is 15 cm which means you need 15 cm of pressure to raise the blood pressure from the pulmonary artery to the apex of the lung which is pretty high if you don’t have the pressure behind it to support this increase against gravity
this doesn’t happen easily…
since alveolar pressure is high, it means they’re fully expanded and the capillaries have very little flow since they’re being constricted = little to no flow in this zone
low perfusion, low ventilation but highest V/Q ratio because even though ventilation drops, perfusion drops to a greater degree
what is happening in zone 2 of the lungs?
Pa > PA > Pv
the pulmonary artery from the heart falls in zone 2
the arteriole pressure is higher than the alveolar pressure but venous is still the lowest
what is happening in zone 3 of the lungs?
Pa > Pv > PA
there’s maximum perfusion here because the alveolar pressure is the lowest!
what is one of the biggest complications associated with pulmonary circulation?
edema
this happens due to fluid imbalance
capillaries have no smooth muscles so hydrostatic pressure is the only thing regulating flow in the capillaries – if there’s more hydrostatic pressure inside the fluid will move out of the capillary
in capillaries, you have net movement outside when hydrostatic pressure is higher than the osmotic so the water goes out from the capillaries to the interstitial fluid
the alveolar walls are resistant to any movement of water and it won’t get into the air sacs – so generally the water coming out of the capillaries stays in the interstitium where the lymphatic system is supposed to deal with the extra drainage
but if you have high hydrostatic pressure in the pulmonary capillaries, the lymphatics will become overwhelmed and you’ll get edema! also, after a certain amount of swelling the alveolar sacs will also allow fluid into them which is really bad
what are the 2 types of pulmonary edema?
- cardiogenic
2. non-cardiogenic
what is cariogenic pulmonary edema?
fluid accumulating in the interstitial space or alveolar sac is just water, no protein!
this is happening because of an increase in pulmonary venous pressure which leads to an increase in hydrostatic pressure so fluid exits the capillaries at increased rates
endothelium is intact
can be due to LV failure, dysarythmia, etc.
how do you treat cariogenic pulmonary edema?
manage hydrostatic pressure by:
1. decrease BP in general
- increase lymphatic draining by reducing systemic venous pressure
- remove or displace fluid from alveoli
best approach is manage BP…
what is non-cariogenic pulmonary edema?
edvidence of alveolar fluid accumulation without hemodynamic evidence that suggest a non-cardiogenic etiology
so there’s no change in hydrostatic pressure, capillaries are running normally but the permeability has changed and fluid oozeses out!
there’s endothelial insult though so there’s protein in the fluid that’s leaking out
can be caused by inhaling toxic gas, aspiration, infection, high altitude
how do you treat non-cardiogenic pulmonary edema?
we have no known treatment to correct capillary permeability….
supportive measure while lung recovers
what is pulmonary HTN?
when the mean pulmonary artery is 25 mmHg when it’s normally 15 mmHg
this happens because the pulmonary artery is occlude due to smooth muscle hyperplasia and increased resistance
we don’t really know why this happens but there are gene mutations associated with it or it can be drug induced
what are the main symptoms of pulmonary HTN?
- right ventricle hypertrophy
- JVD
- lower extremity edema
- death from HF or arrhythmia
how do you treat pulmonary HTN?
- CCB
- digoxin
- diuretics
- oxygen
right side of circulation means what?
pulmonary circulation
compared with systemic circulation, the pulmonary circulation in healthy individuals has lower:
A. PaO2
B. BP
C. blood flow
D. vascular resistance
E. B and D
E. B and D
BP and vascular resistance
pulmonary edema is promoted by which conditions?
conditions with increased pulmonary capillary hydrostatic pressure
during moderate exercise in a healthy person, there is an increase in what?
pulmonary artery pressure increases! with higher CO, P(PA) = CO*PVR so if CO increases with exercise so will pulmonary artery pressure; pulmonary vascular resistance will decrease
PaO2 won’t increase because the amount of oxygen in blood is limited by the number of Hb molecules
CO is increased in exercise so there will be more blood flow in the pulmonary circulation so there will be faster gas exchange
CO2 increases in skeletal muscle with exercise but it doesn’t effect the blood concentration at a high degree because lung exchange has increased
what happens to PVR during blood loss due to hemorrhage?
increases
CO is going down due to blood loss there’s also less blood flow in the pulmonary circulation = pulmonary artery pressure decreases
so PVR will increase to try and maintain the pulmonary pressure
what is the best strategy to decrease the hydrostatic pressure of fluid in the capillaries accumulated due to vasoconstriction?
vasoconstriction the artery but dilate the vein
the blood will be pushing out of the capillaries quickly enough
