Ventilation/perfusion relationship Flashcards
What does ‘ventilation’ refer to?
ventilation refers to the air that reaches the alveoli - the mechanical act of moving air in and out of lungs
what is ‘pulmonary ventilation’?
minute ventilation = voulme of air breathed in and out in one minute =
what is more important? Pulmonary or alveolar ventilation?
alveolar = becuase it takes out the ‘dead space’ that is in the upper airway that doesn’t exchange gas
How do you determine alveolar ventilation?
what is ‘perfusion’?
The blood that reaches the alveoli
- The process by which CO2 from tissues is brought to lungs for removal
- The process by which deoxygenated blood passes through the lung and becomes oxygenated.
what are the waste products of respiration?
water, CO2, nitrogen?
what type of epithelial cells make up the alveolus?
type 1 alveolar cells
what is the only barrier between gas and blood?
the structual matrix
*when people have cystic fibrosis, they feel breathless b/c this region has increased in thickness therefore they are not properly exhanging
how do RBCs pass through the capillary component>?
single file
how does gas exchange occur in the lungs?
by simple diffusion from high to low concentration
what makes up the partial pressure of the gas leaving your lungs?
N2, O2 and CO2 (and H2O)
does the oxygen content in the alveoli fluctuate?
no, O2 arriving in alveoli replaces O2 diffusing out of alveoli to pulmonary capillaries - it doesn’t accumulate but remains the same
GAS DIFFUSES FROM HIGH TO LOW CONCENTRATIONS
how many alveoli are in the lungs?
•The lungs contain around 300-500 million alveoli and have a surface area of around 70 square metres (half a tennis court)
•
Major function : Gas Exchange
•The Lungs are ideally structured for gas exchange
what is the law of gas exchange?
Ficks Law of diffusion
The greater the surface area
and the shorter the distance ;
the greater the rate of diffusion
what occurs during rest and exercise to our gas exchange?
- During exercise the area available for exchange can be physiologically increased. decreasing the ‘thickness’ of membrane and allowing more gas exchange
- During rest ; some pulmonary capillaries closed
–Low pressure pulmonary circulation
•Increased cardiac output ; opening of capillaries.
pulmonary oedema reduces gas exchange how?
it increases the thickness of the barrier between capillaries and the alveoli - therefore you have a decreased gas exchange
the same thing happens in pulmonary fibrosis - but there is scar tissue etc between alveoli and the capillaries
what is the ventilation/perfusion ratio?
•The ratio of the amount of air reaching the alveoli (V)
–To the amount of blood reaching the alveoli (Q)
This ratio is very important - but the numbers themselves are useless
- 1L Air contains approx 200ml O2
- 1L Blood can hold approx 200ml O2
- our bodies have managed to take in as much oxygen as our blood can absorb
- Efficiency and Adequacy
if your V/Q is high what happens?
you’re taking in more oxygen than you’re absorbing and you’ll be saturated with oxygen
(high Pressure O2, low pressure CO2)
what is the cause of hypoxemia in cardiopulmonary disease?
the mismatch of the ration between V and Q is the most frequent cause of hypoxemia (reduced blood PO2 and low V/Q ratio)
does normal V/Q relationship indicate that ventilation and perfusion is normal?
no- sometimes it could be normal, but there are other clincial symptoms
•In lobar pneumonia,
–ventilation to the affected lobe is decreased.
–This produces hypoxic vasoconstriction in the pulmonary capillary bed supplying the lobe
–resulting in decreased perfusion.
–
•Therefore, the V/Q ratio is normal but both ventilation and perfusion are reduced.
how does the V/Q ratio differ between regions of the lung itself?
apex = very good ventilation here, but poor diffusion b/c of gravity
at base= perfusion is great, but ventilation is poor b/c we often do not breath deep enough
what is arterial hypoxemia?
–Arterial PO2 less than 80 mm Hg in an adult breathing room air at sea level.
