A while back I reviewed the spirometry grading system that was included in the 2017 ATS reporting standards . My feeling was, and continues to be, that its usefulness is very limited because it’s mostly a reproducibility grading system that relies on a few easy-to-measure parameters. This doesn’t mean that a grading system can’t be helpful, just that it needs to be focused differently. In a clinical PFT lab many patients have difficulty performing adequate and reproducible spirometry, but that doesn’t mean the results aren’t clinically useful. Moreover, suboptimal quality results may be the very best the patient is ever able to produce. So what’s more important in a grading system than reproducibility is the ability to assess the clinical utility of a reported spirometry effort.

The issue of infection control has been a topic of a couple of discussions I’ve had lately. In particular, it was reported to me that a PFT lab had come under fire from a Joint Commission inspector who did not believe that filter mouthpieces were adequate and that “patient valves and circuits need to be sterilized between each patient”. Unfortunately with all the other things we have to worry about it’s all too easy to become blasé about infection control. This despite the fact that every hospital I’ve visited in the last dozen or so years has posted numerous signs about hand washing and the safe disposal of contaminated supplies. But maybe it’s because we’re inundated with reminders that we’ve developed a blind spot about it.

Over the last couple of years I’ve run across a number of test systems that do not include tidal loops along with the maximal flow-volume loop. I’ve wondered why this was done and because of this I’ve thought a lot about tidal flow-volume loops and what additional information, if any, they add to spirometry interpretation. One of my thoughts has been about the relationship between obesity and the IC and ERV. FVC and TLC are often reasonably preserved even with relatively severe obesity. FRC, on the other hand, is often noticeably affected with even minor changes in BMI (and interestingly this applies to reduced as well as elevated BMI’s). When FRC decreases because of obesity the IC usually increases and the ERV decreases and for this reason the IC/ERV ratio has been suggested as a way to monitor changes in FRC without having to actually measure lung volumes.

The 2005 ATS/ERS spirometry standard make it permissible and even recommends that the FVC and FEV1 be selected from different efforts. I disagree somewhat with their criteria for selecting the FEV1 but overall reporting composite results makes a lot of sense. In an ideal world we’d always get the best FVC and FEV1 in a single effort but what we more often get is a good FEV1 with a poor FVC or a poor FEV1 with a good FVC. So, it best serves the clinical needs of the patient to report the best elements from multiple spirometry efforts.

A couple days ago I pulled my copy of the Intermountain Thoracic Society manual on pulmonary function testing off the bookshelf and thumbed through it a bit. It was first published in 1975 and was the first major attempt towards standardizing the performance and interpretation of PFTs. My first thought was that we’ve come a long way since then. Most importantly our understanding of what spirometry can (and cannot) tell us has improved dramatically.

A set of guidelines for grading spirometry quality was included with the recently published ATS recommendations for a standardized pulmonary function report. These guideline are similar to others published previously so they weren’t a great surprise but as much as I may respect the authors of the standard my first thought was “when was the last time any of these people performed routine spirometry?” The authors acknowledge that the source for these guidelines is epidemiological and if I was conducting a research study that required spirometry these guidelines would be useful towards knowing which results to keep and which to toss but for routine clinical spirometry, they’re pretty useless.

One of the limitations of the single-breath DLCO is that the equation used to calculate results implicitly assumes that the entire breath-holding period occurs at TLC. Mathematically, what happens to the diffusion of carbon monoxide (CO) during inspiration and expiration is not a consideration: The different approaches towards measuring breath-holding time (BHT) make allowances for inspiration and expiration to one extent or another but realistically they should be considered fudge factors.

One of the recommendations in the 2017 ERS/ATS DLCO standards was that VA should be calculated using a mass balance equation. I’ve discussed this approach previously , but basically the volume of the exhaled tracer gas is accumulated over the entire exhalation and the amount of tracer gas presumed to remain in the lung is used to calculate VA. The conceptual problem with this for DLCO measurements is that VA is calculated using the entire exhalation but CO uptake is based solely on the CO concentration in the alveolar sample. Since VA calculated using mass balance tends to be larger than VA calculated traditionally in subjects with ventilation inhomogeneities this mean that DLCO calculated with a mass balance VA is also going to be proportionally larger as well.

The question that was actually posed to me a month or so ago was “when is RAW abnormal?” I didn’t have a good answer at the time since airway resistance (RAW) tests are not performed by my lab. The pulmonary physicians I work with don’t think that RAW is a clinically useful measurement and for a variety of reasons I don’t disagree with this. Nevertheless, RAW testing is routinely performed in many labs around the world so I thought it would be interesting to spend some time researching this.

This is the time of the year when it’s traditional to review the past. That’s what “Auld lang syne”, the song most associated with New Year’s celebrations, is all about. I too have been thinking about the past but it’s not been about absent friends, it’s been about trend reports and assessing trends. In the May 2017 issue of Chest, Quanjer et al reported their study on the post-bronchodilator response in FEV1. I’ve discussed this previously and they noted that the current ATS/ERS standard for a significant post-bronchodilator change of ≥12% and ≥200 ml penalized the short and the elderly. Their finding was that a significant change was better assessed by the absolute change in percent predicted (i.e. 8%) rather than a relative change.