Flashcards in Pulmonary Circulation Deck (21)
How do pulmonary arteries differ from systemic arteries?
Pulmonary arteries are thinner and have a larger diameter than the systemic arteries
Why does gravity have an effect on lung perfusion?
Because pulmonary arterial pressure is so low
Outline the three zones of lung perfusion in the upright state
Apex - intermittent flow (only flows during systole)
Centres - pulsatile flow (flow greater in systole than diastole)
Bases - continuous blood flow
Describe the blood flow to the apices of the upright lung
No blood flow during expiration as the blood vessels here have very thin walls, so the arterioles and venules collapse during expiration when the alveolar pressure is greater than the arterial pressure
Describe the blood flow to the centre of the upright lung
The flow is pulsatile; flow increases during inspiration and decreases during expiration and average flow increases the further down the lung you go
How does average blood flow change the further down the lung you go?
Increases the lower you go down the lung
Describe the blood flow to the base of the upright lung
Flow occurs continuously as pulmonary arterial and venous pressures always exceeds alveolar pressure
What is the ventilation-perfusion ratio?
The ratio of the amount of air reaching the alveoli per minute to the amount of blood reaching the alveoli per minute
What is the ideal ventilation-perfusion ratio?
How can the distribution of blood flow be measured?
Using radioactive xenon; injected into venous blood and evolves into alveolar gas from the pulmonary capillaries, and therefore radiation counters measure the amount of xenon passing through each lung zone
How can you measure lung compliance?
Compliance = change in lung volume/change in pleural pressure of the lungs
How does the compliance of the bronchioles change throughout the lungs?
Bronchioles are stretchier/more compliant at the base of the lung and are stiffer at the apex
How may the apex of the lung be characterised?
More ventilation and less blood flow
How may the base of the lung be characterised?
Less ventilation and more blood volume
How does gas exchange differ between the apex and base of the lung?
Apex has high pO2 and low pCO2 (good gaseous exchange but low blood flow) whereas the base has low pO2 and high pCO2 (less efficient gas exchange but greater blood flow)
How may an airway obstruction affect the V/Q ratio?
V/Q ratio will be lower than normal as V will be smaller but will be divided by the same Q
How may a blood flow obstruction affect to V/Q ratio?
V/Q ration will increase as V will stay the same but Q will decrease, so the number will increase
What is the body's response to pulmonary hypoxia?
Causes local vasoconstriction in the lung area affected --> diverts blood away from the poorly ventilated, hypoxic lung regions towards more perfused regions.
How does pulmonary artery resistance change during exercise?
How do the pulmonary arteries change during exercise?
Pulmonary arteries and arterioles have thin walls --> become distended with increases CO at start of exercise --> stretching --> generates reflex relaxation of arterial smooth muscle --> vessels relax and enlarge.