I was reviewing a cardiopulmonary exercise test (CPET) recently. The test was part of a pre-op workup for a patient with lung cancer who also had a diagnosis of COPD. I had looked at the spirometry results first (we always do spirometry pre- and post-exercise) and seeing that the patient had severe airway obstruction (FEV1 < 50% of predicted) assumed the review would be relatively straightforward. I then saw just one exercise test value and knew immediately that this wasn’t going to be an ordinary test. That test value was the PETCO2 at anaerobic threshold, which happened to be 40.

The Global Lung Function Initiative (GLFI) was established by the European Respiratory Society in 2008 with the goal of establishing a truly worldwide set of reference equations for spirometry. Its results were released in the December 2012 issue of the European Respiratory Journal. Although the reference equations presently apply only to Caucasians, African-Americans and northern and southern Asians, it will likely be updated with Hispanic, African and Polynesian data within the next couple of years.

It’s always fascinating how a simple problem can blossom into something much more complicated. Ninety-five percent of the time when we need to report post test results for spirometry they are for post-bronchodilator. The remaining times they are for supine or post-exercise spirometry. At least once or twice a month however, we need to report two post results, not just one and this is where we run into problems. The most common scenario for this is when we need to report a baseline result and then both a post-exercise result and then a post-bronchodilator result. We need to do this when a patient bronchospasms during or following an exercise test and we find need to give them a bronchodilator after performing the post-exercise spirometry. Less commonly we are occasionally requested to perform both supine and post-bronchodilator spirometry as part of the same visit. Whenever either of these situations occurs we need to perform a number of work-arounds that end up taking extra time and effort.

Over forty years ago when I started to learn about pulmonary function testing I was taught about the nuts and bolts of the tests, not where the tests came from or how they came into existence. Spirometry and the FVC, FEV1 and FEV1/FVC ratio have always appeared to be the core elements of pulmonary function testing and seemed most likely to have been scratched on the wall of the first paleolithic PFT lab cave. I have been reviewing a lot of older research papers lately, including several historical reviews, and was quite surprised to find out how recent both FEV1 and the FEV1/FVC ratio really are.

I’ve had some concerns for a while now about how the CO and CH4 concentrations are being calculated from the DLCO analyzer calibration zero offsets and gains on our test systems. For this reason I’ve been looking carefully at all of the raw data from our DLCO tests and today I came across an oddball test result. There are several reason why this is probably not the best example for this particular problem that I could come up with but it illustrates an important point and it’s in front of me so I’ll go with it.

Expiratory flow limitation exists when increasing expiratory effort fails to increase the expiratory flow rate. This can been seen when a patient exhales along the same flow-volume curve during quiet, tidal breathing as they do during a forced expiratory effort. Tidal expiratory flow limitation (EFLt) is a key concept in understanding dyspnea, hyperinflation and orthopnea in patients with COPD and in assessing the functional severity of COPD. The notion that EFLt could be detected through flow-volume loops was proposed in the 1960’s but subsequent research has shown this approach to be unreliable for a variety of moderately esoteric reasons which include the differences in static lung recoil and airway resistance that occur following a deep inhalation, differences in time-dependent lung emptying and the viscoelastic forces in the lung. When tidal flow limitation as seen on flow-volume loops is compared to other techniques it is apparent that flow-volume loops overestimate the presence of EFLt by approximately one-third.

One of our testing systems has been leaking during the breath-holding period of DLCO tests. This has been an on-again, off-again problem caused by a leaking balloon valve. The odd thing about this is that the results from tests that show a patient leak are often higher than the results where they don’t. This is not the pattern I would have expected. My initial thought would be that in the DLCO tests with a leak, the patient is spending more time at a lung volume below TLC which in turn means a lower surface area. A lower surface area should lead to a lower DLCO but this doesn’t appear to be happening.

The issue of PFT staff licensure or certification has recently been a topic of discussion on the LinkedIn Pulmonary Function Studies group and the Diagnostics section of the AARConnect discussion board. The overwhelming majority of those posting comments have been in favor of some form of licensure or certification. CPFT (Certified Pulmonary Function Technician) and RPFT (Registered Pulmonary Function Technician) certification is discussed most often but not surprisingly on the AARConnect board most posters feel that RRT (Registered Respiratory Therapist) certification should be required as well.

FEV6 (the volume of air forcefully exhaled after 6 seconds) has been proposed as a replacement or surrogate for FVC in spirometry. Given that using FEV6 would simplify and speed up the spirometry test this is a seductive notion. The use of an expired volume with a fixed expiratory time as a replacement for FVC was proposed at least 25 years ago, although at that time FEV7 was proposed as being slightly more accurate than FEV6. The first reference values for FEV6 however, were not available until the results from NHANESIII study were made available in 1999 and most studies of FEV6 post-date that.

I’ll start by saying that I am not associated with Hans Rudolph Incorporated in any way. I just think they make a bunch of good products, and more specifically in this case, a DLCO simulator. For as long as I can remember I have always had intermittent problems with DLCO testing and I suspect that every PFT Lab has had them at some time. One of my current concerns has to do with how our test system’s software is calculating exhaled CO and CH4 concentrations from calibration data, but I’ve had other concerns at other times too. One way around to verify that your test system is actually performing the way it should is biological QC but a more precise way is to use a DLCO simulator.