ssrpk
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What happens to A-a gradient in COPD? (considreing - no atelactasis)
give ur reasoning!
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| Addicudo
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COPD ... dude ... A-a ratio ... would diff in b/w the conditions ..
BUt am making all this up .. didnt read it nywhere ..
Emphysema ... A-a ratio would DECREASE .. Reason - comparatively muCh less gaseous exchange surface left ! And uMmm same would go for Chronic bronchitis ...
But in Asthma - it would INCREASE ...... Reason - Air i.e containing Oxygen :wink: would stay in lonGggg and would cause a goOd amount of diffusion.
So uMmm .. I guesss am right ... Or else as I said .. I just made that up .. didnt read it any where !!!
Whats the answeerr ! ?
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| Addicudo
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Ahaha .. I have a feelling that I'm wrong at this question ! :?
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| ssrpk
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A-a gradient will remain normal......CO2 retention will diluite the oxygen content in the alveoli reducing the PO2 in alveoli as well as in the arterial blood.....it's just the problem with expiration of air trapped in the resp.unit
however if atelactasis develops then it will constitue pulmonary shunting and A-a gradient goes up.....
A-a gradient incrsases when there is defects in:
Va/Q-mismatch.........(atelactasis/dead space)
OR diffusion impairment.....eg:fibrosis
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| ssrpk
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sorry guyz i got confused a bit :oops:
A-a gradient will invariably iuncresa in COPD or any other primary lung disease!
A-a gradient remains normal only in case of central resp. depression eg. barbiturates or neuromuscular abnormality eg.kyphoscoliosis
it's the dilution effect while sampling out the Alveloar PO2 at the end of tidal expiration tht results in greater difference b/w arterial and alveolaer blood gas compartment!
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| somdatta.gupta
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With Reference to Kaplan Physio notes, ( HYPOVENTILATION in chapter FOUR CAUSES OF HYPOXEMIA)
the A-a gradient doesn't change with COPD. The A-a gradient - if it's normal - simply indicates that there is normal gas exchange occuring in the lungs. If it's abnormal, it indicates that there is abnormal gas EXCHANGE in the lungs over and on top of the COPD.
Explanation -
In COPD, the entire lung is retaining CO2. This elevates Alveolar CO2 as well. Therefore the Alveolar O2 decreases by the same amount. If there is normal gas exchange in the lungs, as there is in uncomplicated COPD, the pulmonary end capillary PO2 and the PaO2 is decreased by the same amount, as in the alveolar compartment.
In COPD, if the lungs are retaining CO2, the alveolar CO2 goes up. Say it goes up from 40 mm to 80 mm Hg. Then the PAO2 will be decreased from 100 to 60, the PaO2 is also decreased to 55-60 mm Hg. But the A-a gradient is normal.
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| SmokyWaters
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it shud remain normal ...
but in case of emphysema it increases
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