Ventilation and Perfusion Flashcards
what is ventilation
movement of gases in and out of the lungs through airways
it is measured as change in volume per unit of time eg 5.5L/min
what is perfusion
blood flow through organs eg lungs
through blood besets measured as flow of blood / unit of time eg 650 ml/min
describe the regional differences in lung ventilation
apical alveoli are about 4 times larger than basal alveoli in upright posture due to gravity
basal alveoli can therefore expand more and have better ventilation than apical areas
describe the bronchial circulation of the lung
bronchial artery from the thoracic aorta
bronchial vein to the superior vena cava
takes up 2% of cardiac output
what are the blood pressures in the pulmonary artery, aorta, pulmonary vein, superior vena cava
PA - 15-30/4-12
A - 100 - 140/60-90
PV - 2-15
SVC - 2-8
what is the equation for cardiac output
HR x SV
describe the process of blood vessels branching from the pulmonary artery to the lungs
splits into left and right , then into extra-alveolar vessels while running through lung parenchyma
how many capillaries are there per alveoli approx
1000
what is emphysema and how does it affect gas exchange
widespread destruction and dilation of distal airway
regional destruction of vascular beds
poor gas exchange and hypoxia
greatly reduced surface area
where is the pulmonary circulation does gas exchange start
small arterioles
what is hydrostatic pressure
force exerted by weight of fluid (blood/water) due to gravity ie max hydrostatic pressure at the bottom of a glass of water than at the top
what is the difference in diameter of vessels in the lungs ie lung perfusion due to hydrostatic pressure
extra alveolar vessels: running through lung parenchyma, their diameter is affect by the lung volume
alveolar vessels - diameter dependant on many factors
describe what happens to the blood vessels in the zone 1 at the apex of the lungs
alveolar pressure is greater than pulmonary artery pressure which is greater than pulmonary venous pressure and the blood vessels collapse halting flow
alveolar dead space - good ventilation but not perfusion of blood ie no gas exchange
describe what occurs in terms of lung perfusion in zone 2 of the lungs
recruitment zone
higher pressure in the arterial due to higher hydrostatic pressure therefore blood flow is dependant on the arterial pressure and the alveolar pressure
how would haemorrhage or positive pressure ventilation affect lung perfusion
H - drop in P-arterial
PPV - rise in P alveolar
describe what happens in zone 3 of the lungs in terms of lung perfusion
distension zone
lung bases
hydrostatic forces raise and pressure in the arterial and venous are greater than in the alveolus therefore there is continuous blood flow
what is ventilation perfusion mismatch (V), (Q)
V/Q ratio
if the amount of ventilation Va to an area of lung is equal to the amount of perfusion Q the ration of Va/Q would be 1 - ideal situation
but the ratio varies from 3.3 at the apex of the lungs to 0.6 at the base - the normal average is 0.8
what is the V/Q ratio in zone 1
infinity or very high as good ventilation but poor perfusion
what is the equation for physiological dead space
anatomic dead space + alveolar dead space
what are the 3 types of dead space
anatomic dead space - conducting airways - no gas exchange (150ml approx)
alveolar dead space - unperfused areas
physiological - each breath that does not take part in gas exchange
what is a pulmonary embolism
blood clot from another area of the body which gets trapped in the lungs blocking blood supply
commonly from deep veins in the leg or pelvis
CAUSES ENLARGED DEAD SPACE
what is a shunt in the lungs
where there is bypass of gas exchange and no ventilation occurs but good perfusion ie V/Q is zero
what diseases cause pulmonary shunt
bronchial veins
pneumothorax
age related changes: areas low V/Q ration in the lungs
what is pneumothorax and how is it treated
air in the cavity between the lungs and chest wall causing lung collapse
treated by immediate needle decompression - chest drain connected to an underwater sealed system
