After a couple years of waiting for the new methacholine standards to be released “any day now”, they were finally published in this month’s issue of the European Respiratory Journal. The standard is an open access article and can be downloaded by anyone. The length of time taken to develop the standard was acknowledged and although active ATS participation was withdrawn because the original timeline was not met, for the most part the original ATS participants continued with the task group and the standard has been officially endorsed by the ATS.

Inspiratory and expiratory flow rates are a function of driving pressure (i.e. the pressure difference between the alveoli and the atmosphere) and airway resistance. For this reason it would seem that airway resistance should be one of the most commonly performed pulmonary function tests but instead it is the outcome of airway resistance and driving pressure, i.e. the expiratory and inspiratory flow rates that are measured almost exclusively. One reason for this is that resistance measurements requires relatively expensive equipment such as a body plethysmograph or an impulse oscillometer as well as a fair amount of technical expertise.

I was contacted recently by an individual with some questions about the pulmonary function testing needed for a Social Security Disability evaluation. With a small amount of research I was able to answer their questions but this brought up an interesting point and that is that despite the number of patients we see every year my lab only rarely performs any pulmonary function testing for disability evaluations. The reason I know this is because the Social Security Administration (SSA) has very specific requirements for the content and form of pulmonary function reports and we are very rarely asked for these reports.

About a month or so ago I was corresponding with the manager of a small PFT lab and in response to one of their questions I had mentioned that there were no CPT codes for MIP/MEP. They responded with “what’s a CPT code?” so I guess this means that CPT codes aren’t as well known as I thought they were. CPT stands for Current Procedural Terminology and is managed by the American Medical Association. CPT codes are a relatively universal way to classify and describe all medical tests and procedures. They are also used by all insurance companies for medical billing so one downside to this is if there isn’t a CPT code for a test or a procedure, you can’t bill for it. CPT codes also include conditions that limit performing (or at least billing for) some tests in various combinations and to some extent this drives the way PFT tests are ordered and performed.

Okay, this may be wrong but at the moment I’m can’t seem to find a reason why it should be. A report like this came across my desk a couple of days ago. Observed: %Predicted: Post-BD: %Predicted: %Change: FVC: 4.59 94% 4.87 100% +6% FEV1: 3.38 89% 3.58 94% +6% FEV1/FVC: 73.6 95% 73.5 95% 0 Not particularly unusual and it would usually be interpreted as being within normal limits without a significant post-BD change. If you calculate the FEV1/VC ratio using the pre-BD FEV1 and the post-BD FVC however, it’s 89% of predicted and this indicates mild airway obstruction. But you’re not supposed to use the post-BD FVC this way, are you?

Over the last couple of weeks I’ve had an unusual number of patients with expiratory plateaus on their flow-volume loops. Expiratory plateaus are usually considered to be a sign of an intrathoracic central or upper airway obstruction and several of these patients had a diagnosis of tracheomalacia but many of them didn’t. Expiratory (and inspiratory) plateaus are mentioned in the ATS/ERS standards for interpretation but since there isn’t a specific definition (other than “plateau”), an expiratory plateau is a “know it when you see it” sort of thing.

I had finished reviewing a pre- and post-BD spirometry report yesterday and was about to toss it on my out pile when I noticed something a bit odd about the post-BD results. I pulled it back and spent some time trying to decide if the interpretation needed to be changed but after a lot of internal debate I finally let it go as it was. I’ve continued to think about it however, and although I’m not sure that was the right decision I still haven’t come up with a clear answer.

Recently I was reviewing a report that included helium dilution lung volumes. What caught my eye was that the TLC and the FRC didn’t particularly fit in with the results from the other tests the patient had performed. Test: Observed: %Predicted: FVC: 2.83 114% TLC: 3.03 71% FRC: 0.88 39% RV: 0.09 5% SVC: 2.93 118% VA: 3.64 88% When compared to the FVC and the VA (from the DLCO test) the lung volumes are significantly lower. In particular the FRC and RV are markedly reduced. This is somewhat unusual for helium dilution lung volume since most errors usually cause FRC, RV and TLC to be over-estimated instead of being under-estimated. When I checked the other reports for the day I found that two other patients that had had their lung volumes measured on the same test system also had a TLC, FRC and RV that were noticeably reduced. Obviously we had some kind of equipment problem with that test system but it took a bit of sleuthing before I found out what had happened.

The European Respiratory Society has just published the first standards for DLNO testing. This is a signal that DLNO is moving from a research setting into routine clinical testing. Although it is unlikely that most PFT labs will immediately jump into DLNO testing, the standard is still interesting because of an extensive discussion of DLNO, DLCO, DMCO and Vc measurements and physiology. The DLNO standards (and their supplementary material) are open-access and can be downloaded from the European Respiratory Journal .

Last week I ran across a couple errors in some DLCO tests that I don’t remember seeing before, or at least not as distinctly as they appeared this time. If I hadn’t been looking carefully I could have missed them but both sets of errors will be a lot more evident when the 2017 ERS/ATS DLCO standards are implemented. The first error has to do with gas analyzer offsets. What alerted me was a set of irreproducible DLCO results.