Quick Question. How Can The Rv On Pft Be Low

Posted on Wed, 10 Apr 2019

Question: Quick question. How can the rv on pft be low at 68% of predicted but the FVC on spirometry and TLC from body box both normal? I had sarcoidosis 5 years ago and CT scan in 2016 show that it is gone. My doctor cleared me and said only to come back if I get sick.

Follow up: Dr. Dr. Jolanda (2 minutes later)

sorry forgot to attach copies of my PFT's. The only other thing was that my DLCO was down a bit but he said the the values are essentially the same.

Answered by Dr. Dr. Jolanda (26 minutes later)

Brief Answer:
Vr also slightly decreased

Detailed Answer:
Hello and welcome in HCM

I can understand your concern

I saw carefully your pfr results you have attached
So yes you have slightly low rv values but your TLC Is also slightly decreased if you see carefully 5.81 l instead of 6
58 l your predicted values. Dlco is slightly decreased too.

However in patients with sarcoidosis the most important thing is the difference in time of the above values which means that if these values stay constant during the time then we can say that you are stable.

So next time when you will do pfr evaluate carefully these values.

Do not worry you look stable according to pfr and specifically DLCO the most important indicator of the progress of sarcoidosis

Regards and feel free to contact me again

Dr Jolanda

Above answer was peer-reviewed by : Dr. Prasad

Follow up: Dr. Dr. Jolanda (49 minutes later)

I thought that PFT's are all based on a bell shaped curve so that the predicted value is the 50th percentile and that 80% to 120% essentially covers the 5th and 95% percentile. Since my TLC and FVC are both greater than 80% they were normal according my pulmonologist. The RV value seems out of line compared to my other tests. Since the RV is one component of the TLC that would mean that one of the other values is elevated? Assuming that is the FRC since since the RV is just the difference between calculated values and isn't measured directly.

Answered by Dr. Dr. Jolanda (1 hour later)

Brief Answer:
Read the following please

Detailed Answer:
Hi again

Yes you are right with your information

FRC is a calculated value not a measure one compound of ERV (expiratory residual volume) + Rv.If rv is low than the sum is low too.However generally we see dlco values because it is the first component that is affected in disease progression and lung volumes and capabilities are lowering later secondary to dlco.

Regards

Dr.Jolanda

Above answer was peer-reviewed by : Dr. Prasad

Follow up: Dr. Dr. Jolanda (2 hours later)

Thank you for the response. What I am trying to clarify is how accurate the RV result actually is. Isn't the TLC the combo of the FVC and TV. So if the TLC is normal and the FVC is normal shouldn't the RV be at a similar value? Hence how can the RV 68% of predicted but the TLC and FVC be at 88%. The RV is a lung volume so shouldn't the other lung volumes be reduced by a similar amount?

Answered by Dr. Dr. Jolanda (8 minutes later)

Brief Answer:
Please do not confound

Detailed Answer:
Hi

TLC = VC (Vital capacity) + FRC (Functional residual capacity)

VC = TV (TIDAL VOLUME) + IRV (Inspiratory residual volume)

FRC = ERV + VR

So the changes in vr do not mean that will be reflected with the same rate in other volumes

Fvc is dynamic and a measured volume of 6 seconds of expiration not all the expiration cycle so you can not calculate all the other volumes related to it in your opinion

Do not worry so much you are good actually

Regards

Dr
Jolanda

Above answer was peer-reviewed by : Dr. Prasad