Recently a CPET report for an individual whose primary complaint was tachycardia and DOE with minimal activity came across my desk. Since the patient had had an pneumonectomy (one lung removed) about a year ago there wasn’t much doubt the results would be reduced, the question was whether they were reduced more than they should have been. You might expect lung function to decrease by half following a pneumonectomy but because the remaining lung always expands to some extent FVC and TLC tend to be approximately 60%-65% of their pre-surgical volume. Although this increase in volume however does not increase the alveolar-capillary surface area the entire cardiac output needs to pass through the remaining lung which causes an increase in the pulmonary capillary blood volume. For this reason DLCO also tends to be about 65% of baseline.

When I review the results from a CPET I am used to considering a maximum minute ventilation (Ve) greater than 85% of predicted as an indication of a pulmonary mechanical limitation. Recently a CPET report came across my desk with a maximum minute ventilation that was 142% of predicted. How is this possible and does it indicate a pulmonary mechanical limitation or not? It is unusual to see a Ve that is greater than 100% of predicted. We derive our predicted max Ve from baseline spirometry and calculate it using FEV1 x 40. We have tried performing pre-exercise MVV tests in the past and using the maximum observed MVV as the predicted maximum Ve but our experience with this has been poor. Patients often have difficulty performing the MVV test correctly and realistically even if it is performed well the breathing maneuver used during an MVV test is not the same as what occurs during exercise. Since both Wasserman and the ATS/ACCP statement on cardiopulmonary exercise testing recommend the use of FEV1 x 35 or FEV1 x 40 as the predicted maximum minute ventilation we no longer use the MVV.

As New Year’s Day approaches it is a tradition for people look back to see what has happened during the last year and then look forward and guess what will happen during the next year. I’ve never done a New Year’s blog before but I’ve been mulling over a number of ideas for a while and this looks like a good place to explore them. I’ve had the opportunity over the last several years to research the history of pulmonary function testing. There are a couple of interesting lessons from the past that may be useful, particularly when we are trying to guess what direction pulmonary function testing is heading towards in the future.

Around 20 years ago I had to write the emergency evacuation plan for the pulmonary function lab. Like many other administrative duties I learned that I needed to do this when my new administrator asked where it was and whether I had documented that I had reviewed it with the lab staff. Since I didn’t even have a real procedure manual at the time (just reprints of pertinent articles and textbook chapters) I ended up getting a crash course in writing policies. Fortunately the manager of a nearby departments let me borrow their evacuation plan and I was able quickly to knock one out that met the requirements fairly quickly. Since then I’ve had to review it annually and update it every time the lab moved or when rooms were added or taken away.

The March 1, 2014 issue of the American Journal of Respiratory and Critical Care Medicine had an article on the use of the Lung Clearance Index (LCI) with bronchiectasis. The study showed that the LCI was as good as high-resolution computed tomography and more sensitive than FEV1 when assessing changes in airway status. This is one of the few articles I’ve seen on the LCI that was specifically about adults and wasn’t about cystic fibrosis.

Closing Volume (CV) is a measurement made from a single-breath nitrogen washout (SBNW) test. It was commonly performed decades ago and elevated values were considered to be an indication of small airways disease and an aid in the detection of the early stages of airways disease. It is hardly ever performed any more but I still occasionally see research studies that include this test and almost every test system that is capable of measuring lung volumes by nitrogen washout is also capable of performing a CV.

In 1844 John Hutchinson published his first paper describing his spirometer and his research on the Vital Capacity. He was the first person to use the word “spirometer” to describe his instrument and the first to use the term “vital capacity” to designate the maximum amount of air an individual can exhale after a maximal inhalation. Although he is remembered as the inventor of the spirometer, he was not the first person to use a gasometer to measure lung volumes nor was he the first to measure the vital capacity. What made his research different from those that came before him was partly the prodigious number of individuals whose vital capacity he measured but far more importantly that he was able to show a clear relationship between standing height, age and vital capacity which had not been previously apparent. This finding galvanized researchers in England, Europe and the United States and in many ways helped set the course of research into lung function for many decades to come.

I was reviewing a pre- and post-bronchodilator spirometry report that showed a relatively large increase in FVC but the change in FEV1 was not significant. It’s not impossible for a patient to show this kind of a pattern following a bronchodilator but it is somewhat unusual. Usually when I see this it means that the patient exhaled a lot longer post-BD than they did pre-BD. When I looked however, I saw that just the opposite was true, the expiratory time was actually shorter for the post-BD effort than it was for the pre-BD effort.

The current ATS/ERS guidelines require that an individual have a post-bronchodilator increase in FEV1 or FVC of at least 12% and 200 ml in order for it to be considered a significant response. Numerous studies have shown however, that many patients that don’t meet these criteria, particularly those with COPD, do have a clinically significant improvement with bronchodilators. The September 2014 issue of Chest had a point-counterpoint set of editorials on this standard and on assessing the response to bronchodilator in general. Both sides had a number of interesting things to say but to a large extent one side was talking apples (physiology) and the other side oranges (statistics). I actually think that both sides feel there are significant problems with the ATS/ERS standards, they just differ in what they think is wrong and in the best way to fix it.

Patients with COPD often have a ventilatory limitation as their primary limitation to exercise. A ventilatory limitation to exercise has traditionally been assessed by the breathing index or the breathing reserve: breathing index = Peak Ve / Predicted MVV breathing reserve = 1 – (Peak Ve / Predicted MVV) which are basically two different ways of saying the same thing. In either case a breathing index greater than 85% or breathing reserve less than 15% is an indication that a patient has reached a ventilatory limit to exercise. There is some disagreement as to whether the predicted MVV should come from a MBC test performed by the patient or from the patient’s FEV1 x 40. I have tried both approaches and my experience has been that FEV1 x 40 is the best indicator for a patient’s predicted MVV. This is also Wasserman’s (my go-to source for exercise testing) recommendation so this is what we use.