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Hi everyone.

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It's Mark again, and we are now gonna shift gears a

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little bit into the pattern recognition, but describe

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something that's more closely related to real estate.

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Remember real estate?

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It's about location.

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Location, and yes, location.

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So we've talked a lot about morphologic

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manifestations of diseases on a radiograph and CT.

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Next, we're gonna talk about the

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distribution and how you can use the

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distribution to really narrow your differential.

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So first, upper lobe diseases.

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These diseases occur in the high or upper lobes.

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We'll talk about the physiology and reasons

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why these diseases occur in the upper lobe.

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And one hint—it's almost never due to oxygen.

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So don't say it's because of high

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oxygen. No, that's not really true.

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So the distribution of diseases

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affects the pulmonary microbiome.

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What that means is that certain diseases can

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only grow or develop in certain parts of the lung

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because of that microenvironment—sort of like

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different seeds grow best in different soils.

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Here's the list of the differential based on

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the distribution. Usually, we separate it into

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acute symptoms (less than a week) and

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chronic symptoms (longer).

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We're gonna talk about the upper lobe,

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and the mnemonic I've made is SET PARK.

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I did my training up at McGill in Montreal, so

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I—you know, "park" is French, spelled with a "c."

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I like this one because the most

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common ones are right up front.

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On your differential card.

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This would be on this part right here,

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distribution of disease, upper lobe.

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And you can see the diseases

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that we're going to discuss.

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They're right here.

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Sarcoidosis, silicosis, e.g., extrinsic

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allergic alveolitis, TB, fungal.

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'Cause whenever you say TB, you always say fungal.

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And then you can see the rest

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here, a little less common.

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These upper lobe diseases are often

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lymphatic or inhalational-based.

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Okay.

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Cavitary tuberculosis up here and some here.

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Some budding tree, ill-defined

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nodular opacities in the upper lobe.

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Why does cavitary tuberculosis occur in the upper lobe?

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Posterior segment, apical segment,

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in the lower lobe superior segment.

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Why?

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I'll give you a hint.

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Don't say oxygen.

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I know.

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That's what you've been taught.

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Don't say oxygen.

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Let's go through the physiology quickly.

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Ventilation is about three times greater in

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the lower lobes relative to the upper lobes,

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so that means in the lower lobes, there's

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greater ventilation than the upper lobes.

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But the perfusion is about 18 times greater in

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the lower lobes than it is in the upper lobes.

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So the difference is even greater in taller patients.

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Now, what does that mean?

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That's why we talk about the ventilation-perfusion ratio.

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The V/Q ratio, as you go higher, the ventilation

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relative to the perfusion starts to go down.

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Even though ventilation is less in the upper

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lobe, it's profoundly less with perfusion.

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So what does this do?

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How does this affect the microenvironments?

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Well, first, upper lobes, you have reduced blood flow.

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Yes, relative to ventilation.

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You have reduced lymphatic production and flow.

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That's important.

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Actually, lymphatics are vital in

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removing antigenic debris and water.

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They're the sump pumps.

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There's higher oxygen, but there's also lower

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CO₂ because it's blown off more effectively.

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Well, how does that affect the pH?

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Well, the upper lobes are more alkaline in environment.

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Could that have an effect?

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Yeah.

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There's also a reduced cough efficiency in

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the upper lobes, but I won't get into that.

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So this patient has chronic renal failure, multiple

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calcified nodules and calcifications within the apices.

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Well, why are they in the apices?

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Well, you get the secondary hyperparathyroidism,

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calcium and phosphate ratios are off,

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and the calcium precipitates out.

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But calcium precipitates out in an alkaline environment.

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Nothing to do with high oxygen here, just

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it's more basic in the upper lobes, and

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that's where the calcium precipitates out.

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Now, let's talk about lymphatic clearance.

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This is not generally taught or

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emphasized, but it's really important.

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Lymphatics function, again, is to maintain

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fluid balance and remove particulates.

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How much lymphatic fluid is produced relates to the degree

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of pulmonary flow, as well as potentially chest

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wall motion, which is much greater anteriorly

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than it is posteriorly.

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There is very little lymphatic production and

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flow in the posterior parts of the lung, except in the

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lower lobes, and it does have a great effect on

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chronic exposure, diseases, and infections, as well

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as congestive heart failure and hydrostatic edema.

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So Goodman and Te Perez, Chest, 1983, looked at all

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sorts of reasons why people had cavitary tuberculosis

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in these particular places in the posterior lung.

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And what they found throughout their in vitro,

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in vivo, and high-risk population study

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was that oxygen was not a major determinant.

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It is actually hypothesized, and that's—I love

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the fact that they said hypothesis—but it's a good

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one and strongly associated with decreased lymph

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flow and production, and that had a very strong

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correlation to TB's localization, histoplasmosis,

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silicosis, chronic hypersensitivity pneumonitis.

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All of these are also—

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with chronic exposure—tend to have the scarring

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and injury in the upper lobes posteriorly.

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It's sort of like having a PPD, right?

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You get a PPD in the dermal aspect of your arm.

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There's no lymphatics there.

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If you had it placed in your subcutaneous tissue,

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lymphatics would take it and bring it here,

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where you would have your reaction here, but

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it'd be negative at your forearm injection site.

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So let's take a look.

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Congestive heart failure did CT angio—well, whatever.

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You can see the septal lines here.

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These are the so-called Kerley

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lines, but call 'em septal lines.

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They reflect lymphatic sump,

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pump flow, and movement of water.

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Well, you can take a look at their

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distribution in the lower lobes.

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They're everywhere, but as you go up

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in the lungs, look where they are.

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The septal lines are anterior but not posterior.

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And this is a more dependent part.

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You should have more there, but we don't because

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there's not as much lymphatic production and flow.

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So where does tuberculosis,

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cavitary tuberculosis, as well?

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It occurs in these areas that

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don't have as much lymphatic flow.

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So cavitary tuberculosis localization—it's

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similar to a PPD, although it's occurring in the lung.

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The antigen stays there longer, the

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infection stays there longer, there's more

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inflammation, and fewer cytokines are removed.

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This is where most of the inflammation and cavitation

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occurs because of poor lymphatic production.

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Chronic histoplasmosis—same thing.

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Remember, TB and fungal infections—always link 'em together.

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They're both granulomatous infections and have a

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great deal of overlap in how they look imaging-wise.

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So, a 34-year-old female—you can see that

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there are curved reticular opacities here.

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We talked about that in a previous session.

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You'll notice it has an upper lobe predominance,

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with upper lobes sparing the lower lobes.

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Upper lobe cysts and curved reticular

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opacities—well, you'd say, "Hmm, I'd think

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about some cystic disease in the upper lobes."

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You know, in this case, Langerhans cell histiocytosis.

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What you do is, you go to the card,

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look at the upper lobe disease, curved

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reticular pattern, and see which ones are in both.

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Cell histiocytosis, and the other one

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potentially could be Pneumocystis.

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Now, why does it occur in the upper lobes?

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Theoretically, when you breathe in noxious

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chemicals like tobacco smoke—it's one—it has a

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higher intra-alveolar concentration, and it is retained

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longer because there's much less blood flow.

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And as the blood flows, it pulls in the chemicals as well.

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It's pulled in quickly in the lower lobes, but

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not the upper lobes, so therefore, this noxious

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chemical, which can induce inflammation, sits

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in the alveoli much longer in the upper lobes.

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That's one of the main hypotheses on why

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emphysema and EG, in these inhalational diseases,

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tend to have a more upper lobe predominance.

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Last patient—28-year-old homeless with dyspnea.

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Dry cough for one week, fever for one week.

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What do you see?

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Well, you've got a bronchovascular

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and upper lobe disease process.

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Curved reticular

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opacities.

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Okay, so let's look.

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Okay.

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Upper lobe disease.

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Curved reticular

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opacities.

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Well, there's Langerhans cell

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histiocytosis, and there's Pneumocystis.

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These are the only two that are in both.

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So then you add the ground-glass, and

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now you see it's only Pneumocystis.

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What does this patient have?

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Pneumocystis pneumonia differential.

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I don't have one.

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So upper lobe diseases, lymphatic production, and

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flow, along with inhalation, are the most likely

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reasons why diseases occur in the upper lobes.

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Don't say oxygen.

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It is unlikely an important factor.

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And remember, the upper lobes are also more

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alkaline, which can also affect disease presentation.

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If you want more information, there's

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an article here that you can read that

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goes through this in much more detail.

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Thank you very much.