Pulmonary circulation Flashcards
What is the pulmonary circulation?
Blood supplied to gas exchange surfaces for oxygenation
What is the Bronchial circulation?
Supplies the parenchyma
What are the major differences between the pulmonary and systemic circulations?
Wall thickness:lumen ratio is smaller in pulmonary arteries
- more compliant as pressure is lower, and stops uneccessary increase in blood pressure (prevents pulmonary hypertension)
Doesn’t need a high pressure circuit as close to heart
0.5L vs 4.5L
Lower resistance to increase flow
What are the three main functions of the pulmonary circulation?
Gas Exchange
Metabolism of vasoactive substances
Blood Filtration
What is the pulmonary transit time?
0.75s
What is metabolism of vasoactive substances?
Endothelial cells express ACE to convert AGTI to AGTII (vasoconstrictor) and break down bradykinin (vasodilator) allowing for vasoconstriction
What is pulmonary blood filtration?
Emboli (e.g. Air bubbles/ruptured fatty plaques/venous thrombosis) are caught in the pulmonary vessels, filtering out before reaches systemic arteries (can break down) - if large will be local perfusion obstruction
What are the effects of increasing cardiac output on Pulmonary vascular resistance?
Pulmonary circulation is low resistance, high capacity circuit (at resting Q = 5L/min) - increased Q should increase MAP and pulmonary oedema and reduce function BUT arteries distend due to greater compliance and perfusion to hypoperfused beds (towards the apex) increases, leading to negligible MAP change and minimal fluid leakage
What is the effect of increasing ventilation on Pulmonary vascular resistance?
Inspiration compresses alveolar vessels (compressible as no cartilage so alveolar size increases compresses) and expiration extra-alveolar vessels (thorax decreases in volume to pinch outside) - when really full or empty then resistance increases
What is the effect of Hypoxaemia on Pulmonary vascular resistance?
Systemically causes vasodilation but in pulmonary circulation causes vasoconstriction (O2 sensitive K+ channels close, decreasing the efflux of ions and increasing membrane potential until depolarisation and VSMC contraction) - stops blood flow through unventilated alveoli to match ventilation and perfusion
What are the foetal benefits of hypoxic vasoconstriction?
During foetal development to increase resistance in pulmonary circuit, and hence increase flow through shunts (first breath increases alveolar PO2 and dilates pulmonary vessels
What are the effects of hypoxic vasoconstriction in COPD?
Reduced alveolar ventilation and air trapping means all lung vessels constrict leading to pulmonary hypertension, right ventricular hypertrophy and CHF
What is the normal net movement of of fluid into the interstitium?
Should be approx. 1mmHg out, and steady fluid accumulation controlled by lymphatics, and if production exceeds maximum clearance then will produce oedema
What are the effects of mitral valve stenosis on the lungs?
Plasma hydrostatic pressure increases because pressures back up through pulmonary circulation, increasing pressure; causes net accumulation of fluid that exceeds lymphatic capacity leading to oedema and SOB on exertion
What are the effects of Liver failure on the lungs?
Liver synthesises plasma proteins, so reduced plasma oncotic force means reduced return to vessels and oedema development
