Although the authors of the Global Lung Function Initiative (GLFI) study acknowledge the effect of height on their reference equations the range and distribution of heights in its study populations was not included in the report. This was a similar problem for the NHANESIII reference equations since the height range was never reported within the text of the original report however it did include scatter graphs showing the range of heights. These graphs imply the height range was 162 to 194 cm (64” to 76”) for caucasian males and 145 to 180 cm (57” to 71”) for caucasian females. Using the extremes of these height ranges it is interesting to see how the GLFI reference equations compare to the NHANESIII reference equations.
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.
There are a number of CO2-related values that are useful when assessing exercise test results. Although End-tidal CO2 (ETCO2) is not a quantitative measurement in the same sense that minute ventilation or oxygen consumption is, it is still able to provide a lot of useful information about ventilatory efficiency and disease states.
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.
This has been a massive undertaking involving spirometry data from 72 different testing centers in 33 countries. The data has been subjected to rigorous quality control and an extensive, sophisticated statistical analysis and will likely become the standard reference equation set for spirometry testing in Pulmonary Function labs around the world.
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.
The first version of the modern spirometer (a counter-weighted volume displacement water seal spirometer) was developed by John Hutchinson in England around 1844. He performed vital capacity measurements on over 3000 people and in 1846 published a paper where he showed (among other things) the linear relationship of vital capacity to height. Different versions of Hutchinson’s spirometer were developed by other researchers in the following decades but even through the 1920’s the only measurement that was ever made with a spirometer remained just the vital capacity.