USMLE Step 1: How to solve V/Q mismatch questions, the A-a gradient

V/Q mismatch USMLE Step 1 up and down arrows.
Hey guys, in this video I'll show you an easy way to think about V/Q mismatch questions that have those up and down arrows. You have to understand that an A-a gradient is a representative metric of a mismatch between ventilation and perfusion; V/Q mismatch. Keep watching to learn more!
Instagram: / sugarnoor101

[@virajpanchal988]

Hey, can you make another video explaining the changes of PaO2 , SaO2 and HbO2 with CO and Meth hb? This video is great !

[@acingmedicine]

Sure Viraj, will add that to requests

[@drzainabtahir3554]

Uff.... Finally understood this topic.... Thanks alottttt.

[@acingmedicine]

You’re welcome I’m glad it helped!

[@thegryffindoctor]

Thank you so much- you literally explained most of resp physio in such a short video!

[@acingmedicine]

I'm so glad you found it helpful!

[@MalkAhmad02]

proud of you 🔥👏

[@acingmedicine]

Thank you so much Malak!! ❤️

[@srushtipatil6739]

Very helpful!

[@acingmedicine]

Glad you think so!

[@wingsnotstrings]

What’s your concept for the difference between A-a gradient and VQ ratio ? Because if I listen to only the first 2 mins of this video it looks like they’re both the same

[@acingmedicine]

A-a gradient is an index of V/Q mismatch. Because there's a disconnect between ventilation [how much air goes in the lungs] and Perfusion [how much of this air reaches the blood], the PAO2 becomes much higher than the PaO2, thus creating a gradient [which is called the A-a gradient]. I hope that makes sense.

[@wingsnotstrings]

@@acingmedicine yes indeed ! Thanks : )

[@TanTan-ch3vq]

V/Q is focused on the rate for air exchange, please note

[@jorgemd5544]

High Yield video! Thank you very much for all the great content! I have a question, Dr. Ryan says that in hypoxemia with a High A-a gradient there is no increase in CO2, how is that possible?

[@MsEsyC]

Can you do a similar video explaining the pathophysiology of the heart and major concept in cardiac physiology, especially pediatric Congenital conditions like tetralogy of Fallot, tricuspid atresia, VSD/ASD etc.? 😮

[@acingmedicine]

Alright sure

[@rubaalqudah5534]

Best explanation! thank you very much for sharing this.

[@acingmedicine]

Glad it was helpful!

[@solomonmpalanyi7226]

Am speechless whatever u touch turns into gold. Best explanation ever for this crap! Now I get it. Thanks lots Noor, and keep up the good work. You deserve an award in my opinion! Now I see why u had a 265, it’s the extra brain u got that most people lack!

[@acingmedicine]

Your comments always leave me speechless Solomon. Thank you so much, Looking forward to hearing that you got the score of your dreams! 💪🏻

[@Be1smaht]

What about atelectasis and can you explain DLCO

[@acingmedicine]

Atelectasis is a form of shunt due to decreased ventilation in the collapsed alveolus leading to low V/Q ratio DLCO is the diffusion capacity of Carbon Monoxide. We use this as an index to assess how fast diffusion occurs across the alveolar-capillary barrier. The thicker the barrier, the slower the gas exchange; hence, lower DLCO

[@ezatullaha.3502]

👍🏼

[@mustafaal-samhouri3846]

Wonderful, Thank you.

[@acingmedicine]

Anytime!💙

[@adamjerusalem366]

الله يرضى عنك

[@acingmedicine]

🤲 امين و عنك

[@octaviablink5706]

Very good video, thank you! May I ask what type of V/Q mismatch we would see in a patient with late stages of COPD? Would we have both increased/decreased and shunt?

[@acingmedicine]

With COPD the main problem is ventilation so V/Q is expected to be low resulting in shunt and hypoxemia.

[@octaviablink5706]

@@acingmedicine Thank you so much Noor. in case we have damaged areas with damaged pulmonary capillaries preventing perfusion, could we also be presented with a high V/Q ratio?

[@acingmedicine]

@@octaviablink5706 in that case yeah, that would be a deadspace

[@mathis20737]

Great video. Thanks!

[@acingmedicine]

Anytime!

[@samarelraie9066]

Thank you for sharing this 🤩🤩

[@acingmedicine]

Glad you liked it!

[@mahmoudhadhoud9133]

Does pnemonia cause a shunt or a vq mismatch?

[@acingmedicine]

it causes a VQ mismatch where ventilation is lower relative to perfusion. The extreme of the VQ mismatch in pneumonia would be a shunt. for example, If the entire alveolus collapses or is fully filled with pus then this part will be a shunt (as ventilation becomes zero so V/Q is zero)

[@mahmoudhadhoud9133]

This is what I have an issue with unfortunately..I associate V/Q mismatch with anything that obstructs the blood flow and I associate the shunt with alveoli obstruction.. how can pneumonia be a v/q mis mismatch if it does not obstruct the blood flow? Thank you so much for helping

[@acingmedicine]

Hi Mahmoud, a V/Q mismatch means Ventilation (V) doesn't match Perfusion (Q), whether V is more than Q in case of deadspace or Q is more than V in case of shunt. If V is zero then this is a shunt. If Q is zero then this is a deadspace (wasted ventilation because of no perfusion). However, it's not always a zero value. These are two extremes. it could be reduced but not to the extent of zero. In such a case we call it a mismatch. So, shunt and deadspace are the two extremes of V/Q mismatch.

[@mahmoudhadhoud9133]

Amazing

[@acingmedicine]

Thank you Mahmoud!

[@aseelalami]

Thankkkk uuuuuuuuu❤

[@acingmedicine]

you're welcome

[@kafge7798]

you mentioned nothing regarding v/q