Spirometry in Primary Medical Care: FEV1 and FVC
The reproducibility of FEV1 and FVC and their respective agreement with a gold standard is an issue for early diagnosis and follow-up of COPD patients in general practice. Schermer et al. performed a within subject comparison of FEV1 and FVC measured in 388 COPD-patients with a turbine flow spirometer. The values of FEV1 and FVC measured by general practice personnel were compared with the values measured by certified laboratory personnel, using the same type of turbine spirometer, as the reference test. In spite of equivalent reproducibility the agreement between measurement of lung function in general practices and in laboratories was limited. Training of general practice staff is thought to be the key for valid spirometric measurements. From a primary care practice point of view three questions remain.
Firstly, the validity of FVC measured with a turbine spirometer compared with the real life gold standard of an FVC measured with a pneumotachometer, that is currently used in the lung function laboratory, might be questioned. Godschalk et al. found that underestimation of FVC measured with a turbine spirometer was much more excessive than the underestimation of FEV1 when compared with the respective outcomes of FVC and FEV1, measured with a pneumotachometer. Inertia of the turbine spirometer explains the inaccuracy of the measurements in the very low flows at the end of the forced expiratory manoeuvre when the FVC is completed. Schermers’ choice for a ‘fairer’ comparison conceals the technical imperfection of the turbine spirometer compared with the gold standard of the pneumotachometer in the lung function laboratory. Unfortunately, flow volume curves made with turbine spirometers do not show this error and may therefore lead to wrong assumptions by the physician who uses a turbine spirometer. Systematic underestimation of FVC in primary care patients might result from the study as presented by Schermer et al. Do the authors agree with that?
Secondly, turbine spirometers are available for use in primary care settings, without and with ‘built in prompts’, ‘real time flow volume curves’, ‘patient instructions’ and ‘time indicators to monitor duration of expiratory flow’ as the authors state. However, sophisticated turbine spirometers seem to be in itself a barrier for their widespread use for measuring FEV1 and FVC in primary care patients. On the other hand, most common faults can be detected by observation of the well-instructed patient during his forced expiratory manoeuvre, rather than by an observer who concentrates on the flow volume curves only. In spite of the use of the flow volume curves by the general practice personnel in the study of Schermer et al. the results of FEV1 and FVC were not estimated interchangeable with the results of the laboratories, although measured with the same type of turbine spirometer. Based on the study of Schermer et al. the flow volume loop would appear be too sophisticated for the primary care setting. Therefore it would be better to encourage GPs to measure lung function in their practices, straightforward with a simple handheld spirometer. Wouldn’t it?
Thirdly, in COPD the patients’ own base-line values provide the best reference data. The study of Schermer et al. might underpin the relevance of frequent measurement of FEV1 and FVC. In order to promote lung function testing in primary medical care, could Schermer et al. provide us with some more detailed data on the limits of agreement of FEV1 and FVC measured by the practices and the lung function laboratories?
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