Respiratory physio question

[ask1288]

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Hi all, hope ur all having a swell time:

I have 2 physio questions, hopefully some of you may be able to assist

Regarding the ventilation-perfusion relationship, i have read: the upper part of the lung is less ventilated because the alveoli there are "more distended," but then, i have also read: the upper part of the lung is less perfused because there is "less distention." So I am confused about whether the alveoli are more or less distended in the upper part of the lung.

Also, regarding compensatory mechanisms to match ventilation and perfusion, why is there decreased surfactant and how does this help?

many thanks

 

[marr]

I think that "distention" is used correctly in regards to alveoli because overall upper part of the lung has more negative intrapulmonary pressure making alveoli "distended". In regards of "distention" used for perfusion, I think what the author is saying that blood can't open up more(recruit) arteries in the upper part of the lung. Hence, blood vessels in the upper lung aren't "distended".


I have no idea about the second half of your questions.


Hope this helps!!!

 

[scpod]

Hi all, hope ur all having a swell time:

I have 2 physio questions, hopefully some of you may be able to assist

Regarding the ventilation-perfusion relationship, i have read: the upper part of the lung is less ventilated because the alveoli there are "more distended," but then, i have also read: the upper part of the lung is less perfused because there is "less distention." So I am confused about whether the alveoli are more or less distended in the upper part of the lung.

Also, regarding compensatory mechanisms to match ventilation and perfusion, why is there decreased surfactant and how does this help?

many thanks

In the upright position, alveolar walls are distended by blood pressure inside them, but at the same time are compressed by alveolar air pressure on the outside. When the air pressure is greater than capillary blood pressure, caplillaries close and there is no blood flow. Near the lung apex both ventilation and blood flow are decreased, but blood flow much more so due to hydrostatic pressure and VA/Q can be 2.5 times greater than normal resulting in physiologic dead space (ventilation is still ok but blood flow is low, especially in diastole).

You've lost me with the second question.

 

[ask1288]

thanks y'all...never mind abt the 2nd qst...i figured it out
cheers

 

[fakin' the funk]

Regarding the ventilation-perfusion relationship, i have read: the upper part of the lung is less ventilated because the alveoli there are "more distended," but then, i have also read: the upper part of the lung is less perfused because there is "less distention." So I am confused about whether the alveoli are more or less distended in the upper part of the lung.

The way I think about this is:

higher pressure in basal capillaries due to gravity --> basilar alveoli are squeezed smaller --> basilar alveoli have more capacity to expand during inhalation --> basilar alveoli get more of the ventilation

it's a stretch, but that might help...