In patients with lung disease the use of supplemental oxygen during exercise increases oxygen consumption, endurance time and maximum workload, and decreases the sensation of dyspnea without increasing minute ventilation and maximum heart rate. My lab is occasionally asked to perform a CPET with an elevated FIO2 (hyperoxic CPET). We are capable of doing this but I’ve always had reservations, partly about the logistics involved in performing the CPET but more importantly with the interpretation of the results.

Although we routinely use mouthpieces, noseclips and occasionally masks for our testing, all of these alter respiration in one way or another. Opto-electronic plethysmography (OEP) is a completely non-invasive technique for measuring chest wall volume that also allows for regional differences in expansion and contraction of the thorax to be detected. The basic idea is simple and is the same as is used in cinematic motion-capture systems. Small (6-10 mm) reflective hemispheres are attached to a subject’s torso with double sided tape. A set of 4, 6 or 8 high-speed (60-120 frames/sec) CCD cameras are then used to monitor both the overall and the relative motion of the hemispheres while the subject breathes. The accuracy of these measurements is claimed to be on the order of 0.2 mm.

Since I started performing exercise tests I’ve used both treadmills and bicycle ergometers. There are a several reasons that make ergometers somewhat better for exercise testing than treadmills. Most importantly the reduced noise and physical motion makes it easier to get blood pressure measurements and better quality ECG’s. In addition the workload can be set fairly precisely and they are safer for patients. Treadmills do have some advantages however, since patients are usually able to achieve a higher maximum oxygen consumption (~10%) and for many individuals walking is more natural than riding a bicycle.

Reports are how patient test results are distributed. Paper versions have become less common because reports are now stored electronically in hospital information systems. Even if the way in which a report’s image is now stored, retrieved and distributed has changed, reports are still generated by our lab’s software systems and the ways in which this is done have not changed in any significant way for quite a while. Reports are the public face of any pulmonary function lab and they should be designed to be readable and pertinent. It is critically important for any lab to create and manage reports correctly. So why does our lab software make it so hard to do this?

I was reviewing PFT reports today and noticed that a patient appeared to have had the wrong gender entered in their demographic information. Specifically, the patient had an unambiguously masculine name but had been entered as female. Just to be sure I checked the patient’s on-line medical record and there he was listed as male. I had noticed from the trend report that the patient had been in the PFT lab numerous times. Since the basic patient demographics (name, date of birth, height, gender, etc.) are automatically forwarded into a new demographics record when a new PFT lab visit is created it struck me as odd that after all this time we had somehow managed to make a mistake with something as basic as gender. For this reason I thought it would be a good idea to see how far back this problem existed and started going back through the patient’s PFT records. About four visits ago the patient’s name suddenly changed to one that was unambiguously feminine.

Recently a patient was referred to my lab for a CPET by his oncologist. The patient had been complaining of excessive shortness of breath particularly when climbing only a few stairs. The patient recently had a full PFT panel (spirometry, lung volumes, DLCO) and the results had showed mild restriction with a mild gas exchange defect. The patient’s shortness of breath symptoms were far more severe than could be explained by his PFTs however, so he had been referred to Cardiology and had an ECG stress test. The stress test results were normal so Cardiology told the oncologist that the patient’s problems were probably not cardiac.

The static respiratory pressures, Maximal Inspiratory Pressure (MIP or PIMAX) and Maximal Expiratory Pressure (MEP or PEMAX) are a way to non-invasively assess respiratory muscle strength. Respiratory muscle weakness is present in a number of conditions, most notably neuromuscular diseases and disorders, but also malnutrition, cardiovascular disease, polymyositis, sarcoid and COPD. Strictly speaking, the maximal inspiratory and expiratory pressures are not generated solely by the respiratory muscles but also by the elastic recoil. The elastic recoil of the lung at TLC contributes up to 40 cm H2O towards MEP and the elastic recoil of the chest wall at RV contributes up to 30 cm H2O towards MIP. Even so, an individual cannot reach TLC or RV without the use of their respiratory muscles so the measurements are still valid regardless of how the pressures are generated.

I was reading James Hansen’s textbook on pulmonary function testing (one of my more interesting reads lately) and in passing he mentioned using the VA/TLC ratio as a way to measure ventilation inhomogeneity. The VA/TLC ratio has also been called the Va_,eff/VA_ ratio and the VA’/VA ratio by different researchers but regardless of what it is called it is the ratio between a single-breath TLC measurement (VA) taken from a DLCO test and a multi-breath (helium dilution or N2 washout) or plethysmographic TLC.

Recently I reviewed a set of completely irreproducible spirometry results. The patient had made eight attempts and the FVC, FEV1 and Peak Flow were different every time. In particular, there were frequent stops and starts during exhalation. I’ve always wondered why some patients have so much difficulty with what should be a simple test and although in this particular case it could simply be glottal closure I wondered if it could be Vocal Cord Dysfunction (VCD). For this reason I spent some time reviewing the literature.

I was reviewing a spirometry report and noticed something odd about the flow-volume loop, or more specifically the tidal loop, and this got me to thinking about what tidal loops can tell us about test quality, patient physiology and the ability of the technician to coach a spirometry test. There are at least a couple things wrong with this FVC test effort. First the exhalation time was only about 3 seconds so the FVC volume was likely underestimated by a fair amount. Second, it wasn’t reproducible and this was actually the patient’s the best test effort. What I noticed however, was that the tidal loop was shifted almost completely to the left.