Understanding PFTs

[Beccamom]

I have been trying to become a more knowledgable advocate for my daughter and came across this website. It is not a .edu .gov etc. website. Can anyone with a better understanding of PFTs tell me if this worksheet makes sense to them?

<a href="http://noairtogo.tripod.com/pft.htm">http://noairtogo.tripod.com/pft.htm</a>
We switched pulmonologists to a CF specialist a year ago and he questioned both of my children's asthma diagnosis. When I looked at my daughterwhois in daignostic limbo for CFher PFTs high and low numbers through 8 years of results all show chronic bronchitis and no asthma.
When I looked at my healthier child's PFTs this worksheet shows she has no lung disease at all. I am hoping this isn't just too good to be true regarding my healthier child not having any lung disease. This would mean she only had sleep apnea from prematurity and never had asthma.
We have been slowly decreasing both of our children's "asthma" meds for the past year. The healthy child has remained just as healthy. My child in CF diagnostic limbo has made a 100% improvement off "asthma" meds and on hypertonic saline and mucus clearance vest IV antibiotics based on sputum cultures showing bacteria colonization etc.
Can I trust this workseet? Do those of you with CF or who have children with CF come up with obstructive lung disease based on your PFT scores being compared to this worksheet?
Jen

 

[Beccamom]

I have been trying to become a more knowledgable advocate for my daughter and came across this website. It is not a .edu .gov etc. website. Can anyone with a better understanding of PFTs tell me if this worksheet makes sense to them?

<a href="http://noairtogo.tripod.com/pft.htm">http://noairtogo.tripod.com/pft.htm</a>
We switched pulmonologists to a CF specialist a year ago and he questioned both of my children's asthma diagnosis. When I looked at my daughterwhois in daignostic limbo for CFher PFTs high and low numbers through 8 years of results all show chronic bronchitis and no asthma.
When I looked at my healthier child's PFTs this worksheet shows she has no lung disease at all. I am hoping this isn't just too good to be true regarding my healthier child not having any lung disease. This would mean she only had sleep apnea from prematurity and never had asthma.
We have been slowly decreasing both of our children's "asthma" meds for the past year. The healthy child has remained just as healthy. My child in CF diagnostic limbo has made a 100% improvement off "asthma" meds and on hypertonic saline and mucus clearance vest IV antibiotics based on sputum cultures showing bacteria colonization etc.
Can I trust this workseet? Do those of you with CF or who have children with CF come up with obstructive lung disease based on your PFT scores being compared to this worksheet?
Jen

 

[Havoc]

I am a 30yo CF patient and according to that quick guide, I do not have either obstruction or restriction. There are a lot of factors that affect PFT outcomes such as patient effort, the value set used to calculate % predicted (there are about 15), variations in height or weight with comparison to age and gender, etc.

What most of us are looking for with regard to our PFTs is trending. Once you have a good baseline when you are free from any current exacerbation, you can then compare that with newer PFTs. As an aside, don't get used to looking at % predicted, as it can be misleading for the reasons listed above. Rather, look at the raw data.

To give you an example, if I put in my age height, gender and weight and calculate what my FEV1 should be using various value sets, I get a range from 3.609L/sec to 4.401L/sec. So let's say that during my PFT I blew a 3.89L/sec FEV1. If you use the Knudson 1983 value set, I would have a 97.5% predicted, but if you use NHANES III, I would have a 94%. Not a huge difference, but you can see how these things might lead you to believe that there is a decline, when there isn't.

Now, let's change my weight. Say I had an exacerbation and my weight dropped 15 pounds, yet still blew a 3.89L/sec FEV1. Using Knudson 1983, I'm now at barely 96% and NHANES III I'm at barely 93%.

Height does the same thing (as kids grow, but perhaps maintain relatively the same weight). By adding 4 inches to my height, my 3.89L/sec takes me from 97.5% predicted (Knudson) to 76% and 78% (NHANES III).

That's a long answer, but this seems to be an area of confusion for a lot of patients and parents. Hopefully this will clear some of it up. Best practice is to look at the raw numbers and watch for trending away from your baseline.

 

[Havoc]

I am a 30yo CF patient and according to that quick guide, I do not have either obstruction or restriction. There are a lot of factors that affect PFT outcomes such as patient effort, the value set used to calculate % predicted (there are about 15), variations in height or weight with comparison to age and gender, etc.

What most of us are looking for with regard to our PFTs is trending. Once you have a good baseline when you are free from any current exacerbation, you can then compare that with newer PFTs. As an aside, don't get used to looking at % predicted, as it can be misleading for the reasons listed above. Rather, look at the raw data.

To give you an example, if I put in my age height, gender and weight and calculate what my FEV1 should be using various value sets, I get a range from 3.609L/sec to 4.401L/sec. So let's say that during my PFT I blew a 3.89L/sec FEV1. If you use the Knudson 1983 value set, I would have a 97.5% predicted, but if you use NHANES III, I would have a 94%. Not a huge difference, but you can see how these things might lead you to believe that there is a decline, when there isn't.

Now, let's change my weight. Say I had an exacerbation and my weight dropped 15 pounds, yet still blew a 3.89L/sec FEV1. Using Knudson 1983, I'm now at barely 96% and NHANES III I'm at barely 93%.

Height does the same thing (as kids grow, but perhaps maintain relatively the same weight). By adding 4 inches to my height, my 3.89L/sec takes me from 97.5% predicted (Knudson) to 76% and 78% (NHANES III).

That's a long answer, but this seems to be an area of confusion for a lot of patients and parents. Hopefully this will clear some of it up. Best practice is to look at the raw numbers and watch for trending away from your baseline.