5. Blood Supply, Gas Exchange, Ventilation and Perfusion Flashcards
(36 cards)
Where in the lungs is the greater volume change for a given change in pressure?
At the base
What happens to alveolar ventilation with height from base to apex?
It declines
What also declines from base to apex?
Compliance
Why does compliance decline?
The alveoli are more inflated at the FRC, at the base the lungs are slightly compressed by the diaphragm hence the greater compliance on inspiration
What brings about a larger change in volume at the base compared to the apex?
Any given change in intrapleural pressure
What are the two circulations in the body and how do they differ?
Pulmonary and Systemic
Pulmonary circulation is opposite from systemic circulation in function
It delivers CO2 to the lungs and picks up O2
Does the pulmonary vein or artery travel away from the heart?
Pulmonary Artery
What does the Bronchial circulation supply?
Supplies nutrients and O2 to the lungs
What does the Pulmonary circulation carry?
The entire cardiac output from the right ventricle
What is the flow and pressure of the pulmonary circulation?
High flow, Low pressure
Where is blood pressure higher? In the pulmonary or systemic circulation?
Systemic (~120mmHg)
Which side of the heart has a greater driving force to push blood?
Left
Where does gas exchange take place?
Between the alveoli and the blood capillaries
What happens to oxygen as it moves from the alveoli to the pulmonary vein?
It moves down the concentration gradient
This is the opposite for CO2
What do the abbreviations A,a and ṽ stand for?
A - Alveolar
a - Arterial blood
ṽ - Mixed venous blood (e.g pulmonary artery)
What does PaO2 and PACO2 stand for?
PaO2 = partial pressure of oxygen in arterial blood PACO2 = partial pressure of carbon dioxide in alveolar air
What are the normal mmHg and kPa figures?
Insert table
What is the rate of diffusion across the membrane directly proportional to?
The partial pressure gradient and to gas solubility specifically
Also to the available surface area and is inversely proportional to the thickness of the membrane
How many times greater is the gradient between O2?
10x greater
Why is the rate of diffusion more similar than expected for CO2 compared to O2?
CO2 is more soluble in water so can diffuse much more readily
What happens during Emphysema?
Destruction of alveoli reduces surface area for gas exchange
PO2 is low (alv)
What happens during Fibrosis?
Thickened alveolar membrane slows gas exchange causing loss of compliance which may decrease alveolar ventilation
O2 will be lower in the vein as the rate of diffusion is reduced
What happens during Pulmonary edema?
Fluid in interstitial space increases diffusion distance/ Arterial PCO2 may be normal due to higher CO2 solubility in water
What happens during asthma?
Does not alter the diffusion process but does impede ventilation
Increased airway resistance decreases airway ventilation
