Flashcards in CVS S9 - Incomplete Special Circulations Deck (11)
Describe how the pulmonary circulation is specialised to cope with the entire cardiac output
Has very low resistance due to short, wide vessels with lots of capillaries in parallel
Arterioles have relatively little smooth muscle which also reduces resistance
What is the normal pressure in the pulmonary artery?
What is the normal pressure in the pulmonary capillaries?
What is the normal pressure in the pulmonary veins?
What is the optimal ventilation/perfusion ratio?
What is hypoxic pulmonary vasoconstriction?
Alveolar hypoxia results in the vasoconstriction of pulmonary vessels
This increases resistance so causes decreased flow to less well ventilated areas and greater flow to the better ventilated alveoli
This helps maintain the ventilation/perfusion ratio of about 0.8
When can hypoxic pulmonary vasoconstriction be a problem?
In cases of chronic hypoxic vasoconstriction
This can cause right ventricular hypertrophy and heart failure due to increase in after load
Describe the forces which determine the formation of tissue fluid in the lung
Hydrostatic pressure of the blood within the capillary forces blood out
Colloid osmotic (aka oncotic) pressure exerted by large molecules in blood vessels draws fluid back in
As the pulmonary capillaries are low pressure, little fluid leaves the vessels but if pressure increases, oedema can occur
When sitting upright, gravity places greater hydrostatic pressure on the base of the lung
Describe the relationship between the mechanical work and oxygen demand of the myocardium
There is an almost linear relationship between the work done and the oxygen demand of the myocardium (as work increases, so does O2 demand)
Describe the coronary circulation
Left and right coronary arteries arise from the left and right aortic sinuses
These fill in diastole
There is a high capillary density in the myocardium to efficiently deliver oxygen
NO is constantly produced by the coronary endothelium to maintain high basal flow