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Low DLCO (36%), shortness of breath, oxygen desaturation, all else pretty normal?

After complaining for years about exercise induced shortness of breath and after being prescribed inhalers which did no good, HMO performed a Pulmonary Function Test (PFT) with a gas diffusion component.  Previous tests did not perform the single breath carbon-monoxide test.  My oxygen saturation is normally in the low 90's.  It drops into the mid 80's when walking on flat surface at sea level at a reasonable walking pace.  Walking uphill, especially at altitude, taxes my breathing heavily and cause a cramp-like sensation in the upper abdomen.  After a short period of rest, oxygen saturation returns to my normal and the cramping sensation goes away.

PFT calculated DLCO at 41% and a second PFT calculated DLCO at 36% of predicted value.  Otherwise spirometry and lung volumes are normal.   COPD, interstitial lung disease, etc. have been ruled out through CT scans, Xrays and a triple lung wedge biopsy.  Right heart catherization was normal with a pulmonary artery pressure of 25/10.  Echocardiograms showed normal heart function, with 62% ejection fraction.  A small shunt estimated at 5.15% was seen on a nuclear medicine study.  However, even though bubble saline echocardiogram showed small shunt at rest, that shunt did not increase with exertion. CT angiogram showed no parenchymal disease nor evidence for a pulmonary embolus.  Vascular specialist said no evidence of vascular disease after reviewing CPET (cardiopulmonary exercise test).  CPET showed a reduced VO2 (doc said it was about 80% of normal for someone my age), but a normal anaerobic threshold, a reduced breathing reserve, and elevated Ve/VO2 and Ve/VCO2.  Vd/Vt was normal at rest with expected reduction with exercise, but dead space was lower than expected with exercise.  Blood tests have all been normal, including those looking for emphysema, sickle cell and the like.  Hemoglobin counts are normal.  

I have tried supplemental oxygen, but it appears to have little to no effect.

Long post I know, but case is odd.  Would appreciate if anybody has seen something like this or has some other insight to post back.
1 Responses
Avatar universal
Why is no one paying attention to the shunt?

Is it an asd?

Pulmonary Avm?
8 Comments
Thanks for your input.  Re: shunt - the echocardiogram under exercise with a saline bubble infusion did not show any increase in the shunt than what was seen under the no exercise condition.  Doc said that if the shunt were the cause, it would have been very evident.  At one point, he thought the shunt was the root of the problem as well, but the echo test and nuclear med scan ruled it out in his mind.  The location of the shunt still has not been identified.  

I will ask him about the asd and avm.
A shunt CAN and does cause your symptoms...

Did they look for a pda?

Were there bubbles seen after iv injection of agitated saline?
I looked back through my correspondences  with the pulmonologist re: shunt.  At my request, he wrote a summary of my case to the undiagnosed disease network research study.  In his letter he summarized the shunt issue like this:  

"Bubble study suggested a possible microscopic pulmonary AVG (I assume that is aortic valve gradient) with less than 10 bubbles visualized in the right atrium five cardiac cycles after injection of agitated saline during Valsalva.  The study was repeated after exercise, and the results were unchanged.  A significant shunt was not seen in a subsequent nuclear medicine study, with an estimated shunt percentage of 5.15%, considered normal."

At first, he was hopeful that the shunt would explain the issue; but, with each additional test result, became less enamored with the idea, eventually ruling it out as a cause.

He also ordered a CT scan with contrast dye to see if there was a visible aterio-venous malformation through which blood could be shunting.  But none was detectible.

I, too, had hoped that a shunt would be the cause as it sounds like something fixable.

My doc is retiring this week and my case is being referred to a teaching hospital outside the HMO network.  I plan to ask the new doc about the shunt possibility.  

I appreciate your thinking about my case.
I think you mean pulmonary avm?

Which is an arteriovenous malformation.

The amount of bubbles was indeed low...

However, were you supine during exercise or upright?

Because of the way blood distributes through out the lungs...

When you are prone your blood will essentially pool in zone 3 of your lung parenchyma...

But when you you are flat it is evenly distributed so if you were peddling while flat then the shunt may looked smaller than what it actually is bc of blood distribution.

Otherwise... what positions make you most symptomatic?

Hi Ayl:

Basically in the non-exercise saline bubble test, I don't recall if I was laying flat on my back or sitting.  On the exercise saline bubble test, I was standing (walking) on a treadmill.  They stopped the test when my oxygen saturation dropped.

Re: AVG - I just copied the comments from his letter to the undiagnosed disease network.  (Pulmonary AVM makes sense - I guess it was a typo on the part of his staff).

I generally understand a shunt as blood bypassing of lung's oxygenation system.  Is that correct?  And does the shunt percentage represent an estimation of the amount of blood that is going directly from the venous part of the blood system to the arterial part bypassing the lungs?  In my notes, I have the doc saying that everyone has some shunting, usually in the range of 2-3%.  So, if I understand correctly,  the calculation of a 5.15% shunt would indicate that 5% +/- of my blood is bypassing the lungs.  

In general, I experience symptoms walking uphill, moving objects from one location to another.  Worse at altitude.   Though when walking on flat ground at a reasonable pace, my oximeter reports ~86% oxygenation.  
In the lungs a pavm... its bypassing a  capillary bed... directly having arteries enter veins...

Have you had a cardiac mri?  Looking for extracardiac anamolies?
Cardiac MRI: No.  I am in the process of getting a referral to a tertiary facility.  I will bring that up with the doc.
Feel free to PM me so that I can tell you the best institutions to go to!
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