Blood flow, gas exchange, ventilation and perfusion Flashcards
Define bronchial circulation
Systemic circulation which supplies airways, lung tissue, smooth muscle and nerves.
What % of systemic circulation goes to bronchial circulation
2%
Where does deoxygenated bronchial blood drain into and what effect does this have?
PULMONARY VEIN - dilutes oxygenated blood
Summarise pulmonary circulation
Opposite of systemic circulation.
High flow, low pressure
Cardiac output from right ventricle through pulmonary artery to capillaries to pulmonary vein and back to left ventricle.
Summarise the main alveolar/arterial and venous partial pressures of CO2 and O2.
PAO2 = 100mmHg/13.3pKa PaO2=100mmHg/13.3pKa PACO2=40mmHg/5.3pKa PaCO2=40mmHg/5.3pKa PvO2 =40mmHg/5.3pKa PvCO2=46mmHg/6.2pKa Arterial values reflect lung values and Venous values reflect tissue values
Describe how gas exchange occurs in the lungs in terms of the partial pressure gradient
Gases move across the alveolar membrane to and from capillaries until they reach equilibrium
Describe the movement of O2 and CO2 across the alveolar membrane
O2 diffuses over from 100mmHg to 40 mmHg
CO2 diffuses over from 46mmHg to 40mmHg
Why are the two exchange rates of O2 and CO2 similar
Because the pp gradient for oxygen is much steeper but CO2 is a lot more soluble than O2
How is movement across the alveolar membrane proportional to:
- pp gradient
- surface area
- distance
- alveolar wall thickness
- directly
- directly
- most rapid over short distances
- inversely
State the effect of emphysema on gas exchange
Loss of alveoli leads to reduced gas exchanged
Normal or low PAO2
Low PaO2
State the effect of fibrosis on gas exchange
Hindered expansion and ventilation
Low PAO2
Low PaO2
State the effect of oedema on gas exchange
Fluid leaks from plasma to ISF leading to increased space between alveoli and capillaries
Normal PAO2
Low PaO2
State the effect of asthma on gas exchange
Bronchial smooth muscle over constricts making it more difficult to get air into the lungs and ventilate
Low PAO2
Low PaO2
Explain the relationship between ventilation and perfusion ratio
Ratio is ideally 1
Ventilation > perfusion - ratio is more than 1
Ventilation < perfusion - ratio is less than 1
How is blood flow proportional to vascular resistance?
Inversely
Describe the relationship between alveoli and blood vessels at the base of the lungs in terms of vascular resistance
Vascular restance at the base of the lungs is low so pulmonary pressure is higher than alveolar pressure so blood is pulled down to the base by gravity and the alveoli are compressed by blood vessels
Describe the relationship between alveoli and blood vessels at the apex of the lungs in terms of vascular resistance
Vascular resistance is higher so the alveoli are more inflated so their pressure is greater than pulmonary arterial pressure which compresses the arterioles.
In reality, pressure auto regulation overcomes this by 75%
Why is pulmonary arterial pressure more susceptible to the effects of gravity?
Because it is low pressure at 25/8mmHg
State what happens when ventilation>perfusion
Overventilation
Alveolar dead space created where they are ventilated but not perfused
Elevated PAO2 leads to pulmonary vasodilation
Reduced PACO2 leads to BRONCHIAL CONSTRICTION (lets less CO2 out)
Response INCREASES PERFUSION
(reduces ventilation to lesser extent)
State what happens when ventilation
Underventilation
Blood is poorly oxygenated. Shunt occurs by local mechanisms: capillaries near less well ventilated alveoli constrict and blood is diverted to better ventilated capillaries.
Elevated PACO2 leads to MILD BRONCHODILATATION to allow more air into the lungs
SYSTEMIC VESSELS DILATE to allow more oxygen to tissues in hypoxia.
What is physiological dead space?
Anatomical dead space + alveolar dead space
