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Old 01-07-2012
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Lungs Lung Ventilation in the upper lobes

The upper lobes of the lung receive less ventilation and perfusion as compared to the lower lobes. Since the perfusion increases more than ventilation as you go inferiorly, the V/Q value falls. Secondary M. Tuberculosis has a propensity to survive in the upper lobes due to better ventilation....I thought the upper lobes were better ventilated...Both these statements to my knowledge are correct??

Can anyone clear up this confusion, these statements seem to be contradicting each other...Help!!
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Old 01-07-2012
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Quote:
Originally Posted by hishamsalahuddi View Post
The upper lobes of the lung receive less ventilation and perfusion as compared to the lower lobes. Since the perfusion increases more than ventilation as you go inferiorly, the V/Q vaue falls. Secondary M. Tuberculosis has a propensity to survive in the upper lobes due to better ventilation....I thought the upper lobes were better ventilated...Both these statements to my knowledge are correct??

Can anyone clear up this confusion, these statements seem to be contradicting each other...Help!!
Mycobacteria Tuberculosis is an strictly aerobe, loves 02 enviorment it thrives on it, that's why you see upper lobe cavitations from secundary TB.

About your question, Apex recieves ventilation but poor perfusion, in other words there is a wasted ventilation V/Q is = 3
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Old 01-07-2012
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Lungs have 3 areas/zones of ventilation:

1) where Pulmonary capillary Pressure in greater than Alveolar pressure all the time, the capillaries are open all the time and perfusion is best. This includes lower 7-10 cms of the lungs at standing position, at lying position and at exercise

2) where pulmonary capillaries collapse during diastole and open during systole, so blood flows intermittently. It occurs in standing from 7-10 cms above heart level to apex.

3) where alveolar pressure > pulmonary capillary pressure, capillaries remain collapsed and there is no blood flow.It occurs following hemorrhage and breathing against high air pressure e.g blowing a musical instrument.

Mycobacterium cannot survive at lower zones of lung due to high perfusion, so it survives at apex at intermittent zone of ventilation
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Old 01-13-2012
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I am kinda confused. Rapid review Pg 290 Edition 3 under secondary reactivaton tb goljan says " Secondary tb involves one or both apices in upper lobes- ventilation ( oxygenation ) is greatest in the upper lobes".

I understand what hishamsalahuddi understood- that ventillation at base is still greater than that at apex. Can doctorFH please explain why goljan would say a statement like this VS say something like what you said " mycobacterium can not survive with high perfusion".

Also, can you please explain why mycobacterium can not survive in high perfusion state? Thank you so much! Any help would be appreciated, exam is feb 3
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Old 01-14-2012
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Its quite obvious!!! Mycobacterium tuberculosis is a strict aerobe....

At upper zones of the lung the ventilation/perfusion gradient is high this means there is actually least amount of gaseous exchanhge that is taking place (physiological dead space), this means the oxygen that comes here resides here and is not replaced with CO2,

At lower zones although ventilation is higher but perfusion is also higher this means that there is gaseous exchange taking place and oxygen is continuously being replaced by CO2,

So Mycobacterium can actually hide at upper zones,please note that ths zone is imprtant in re-activation of TB rather than prmary TB...
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Old 01-15-2012
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Quote:
Originally Posted by doctorFH View Post
Its quite obvious!!! Mycobacterium tuberculosis is a strict aerobe....

At upper zones of the lung the ventilation/perfusion gradient is high this means there is actually least amount of gaseous exchanhge that is taking place (physiological dead space), this means the oxygen that comes here resides here and is not replaced with CO2,

At lower zones although ventilation is higher but perfusion is also higher this means that there is gaseous exchange taking place and oxygen is continuously being replaced by CO2,

So Mycobacterium can actually hide at upper zones,please note that ths zone is imprtant in re-activation of TB rather than prmary TB...
"this means there is actually least amount of gaseous exchanhge that is taking place (physiological dead space), this means the oxygen that comes here resides here and is not replaced with CO2, "

This sentence nailed the problem on the head, spot on. Thank you for such a clear and concise explanation doctorFH!!
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