pulmonary circulation Flashcards
Describe the pulmonary circulation
pul artery = low oxygen blood
pul vein = high ox blood
function: perfusion of resp airways for GE
Comparison of the systemic circulation with the pulmonary circulation
different wall thickness: lumen ratio
pul circ - thinner walls because going to a smaller distance
in heart LV main compartment
RV ‘additional’ - less mechanically strong force and structure - shorter distance
circuit pressures in systemic and pul circulation `
LV give on/off pressure, systole/diastole
aorta - vascular compliance so make flow more pulsatile
blood goes from low to high pressure
pulmonary circuit similar process - under much lower pressure
cardiac parameters in systemic and pulmonary systems
pul has 10% of blood vol
blood is mainly in systemic/pul veins
pul has 15% pressure
pul has 10% of the pressure gradient - impacts the velocity
pul is a low resistance circuit - more resistance = faster, needs time to load
3 functions of the pulmonary circulation
GE
metabolism of vasoactive substances
filtration of blood
GE
deliver O2, take CO2 CO2 move quick - v diffusible anaesthetic moves from lungs to neurological system NO inert so travels in and out of lungs pulmonary transit time .75s
metabolism of vasoactive substances
endothelium that expresses ACE - convert ANG1 - ANG2 - vasoconstrictor
break down bradykinin (vasodilator)
only expressed at end of lungs or in the kidney
Filtration of the blood
filters things that get ‘caught’ before they reach the systemic arteries
eg venous thrombosis from stasis, ruptured fatty plaques, air bubbles
small embolus - eliminated in pul microcirc
large embolus - trapped in pul microcirc - local perfusion obstructed - can stop flow to entire lung - affects pressure and GE - better than in systemic `
embolus
mass in circulation capable of causing an obstruction `
embolism
event characterised by the obstruction of a major artery
in theory what should happen if CO (Q) is increased
increase MAP
therefore increase leakage
= pul oedema
reduced lung function
what actually happens when Q is increased in pul circ
pul artery distension - prevent increases in MAP
also the increase in pressure increases perfusion of the apex of the lung - increased throughput of the lung
both mean Q is increased with little increase in MAP
minimal fluid leakage
no onset of pul oedema
no detriment to pul func
pulmonary response to hypoxaemia
closure of O2 sensitive K+ channel reduced KJ efflux increased mem potential membrane depol = open V gated Ca channel vascular sm constriction
effect of breathing hypoxic air
global vasoconstriction RV work hard against resistance get stronger concentric hypertrophy septum change change in EDV on L affect in SV
beneficial effect of pul vasoconstriction with hypoxia
in foetus
perfusion matches inadequate ventilation
blood follows path of least resistance
increased flow through shunt (pul circuit is higher pressure)
first breath increases alveola PO2 - dilate the vessels
when is vasoconstriction as a result of hypoxia detrimental
COPD reduced ventilation increased resistance in pul circuit = pul hypertension RV hypertrophy congestive heart failure
Why is there a fluid balance in the lungs
vessels aren’t water tight
factors effect movement and move the water into the extracellular space
important components in the Starling eqn
hydrostatic pressure in the interstitium Pi
hydrostatic pressure in the capillary Pc
oncotic pressure in the interstitium (pi)i
oncotic pressure in the capillary (pi)c
describe the fluid balance in the lungs
plasma hydrostatic - highest when first get to capillary, forces fluid out
interstitial hydrostatic - tiny sucking force (ie negligible move out)
plasma oncotic - big sucking force into the vessel
interstitial oncotic - force out of the vessel
net movement out
small leakage
increase in interstitial hydrostatic pressure
pulmonary circulation can manage - uses -ve pressure to mop up the fluid
easier for the excess fluid to drain into the lymph and then drain into the capillaries
what happens if there is excess fluid
fluid exceeds ability of lymph to drain it
pulmonary oedema
effect of mitral valve stenosis on fluid balance
pressure build up from L of heart through pul circulation increased plasma hydrostatic pressure more fluid forced into the interstitium max lymph clearance rate exceeded pul oedema
effect of liver failure on fluid balance
plasma oncotic reduced - less plasma proteins made less fluid drawn into the capillary fluid accumulates in the interstitium lymph clearance exceeded oedema
effect of metastatic breast cancer on fluid balance
cancer spresd to lympoh nodes
tumours obstruct lymphatic drainage
lymph clearance compromised
oedema
effect of increase in systemic pressure on fluid balance
no effect
systemic circulation doesn’t affect pul circ
unless shared cause like hypovolaemia
