Effects of a filter at the mouth on pulmonary function tests

Abstract

E Ef ff fe ec ct ts s o of f a a f fi il lt te er r a at t t th he e m mo ou ut th h o on n p pu ul lm mo on na ar ry y f fu un nc ct ti io on n t te es st ts sL. Fuso*, D. Accardo*, G. Bevignani*, E. Ferrante**, A. Della Corte*, R. Pistelli* Effects of a filter at the mouth on pulmonary function tests. L. Fuso, D. Accardo, G. Bevignani, E. Ferrante, A. Della Corte, R. Pistelli. ERS Journals Ltd 1995. ABSTRACT: The aim of this study was to verify whether the increase of resistance to airflow using a filter at the mouth could determine significant systematic errors of measurement or change the diagnostic performance in a respiratory physiology laboratory.The effect of the new filter Spirobac (DAR Spa, Italy) was assessed on out-patients referred to our laboratory for routine functional evaluation. The following tests were performed: maximal expiratory flow-volume curve, plethysmographic lung volume and airway resistance, bronchodilator test, and methacholine challenge test. Each test was performed randomly, twice with the filter and twice without.Significant differences between measurements with and without filter were found for forced vital capacity, forced expiratory volume in one second, airway resistance, and specific airway conductance (sGaw). These differences were unrelated to the average values of the measurements, except for sGaw. The limits of agreement were within the range of intraindividual short-term repeatability for almost all of the function indices. The overall concordance between tests performed with and without filter was 78% for bronchodilator test and 53% for methacholine test. However, in all the cases but one, the concordance of the methacholine test was inside the short-term repeatability.We conclude that the filter Spirobac has a statistically significant effect on the results of some pulmonary function tests. However, this is not considered to be clinically significant, since the changes due to the filter were within the intraindividual variability of repeated measurements for almost all the function indices and no appreciable classification error was found in diagnostic tests.

Bacterial colonization as a potential source of nosocomial respiratory infections in two types of spirometer

“…However, controversy exists regarding the potential alteration of pulmonary function test measurements when using these filters [19]. Significant differences between pulmonary function test measurements with and without the use of filters were found by FUSO et al [20]. However, the authors did not consider this to be clinically significant, since changes due to the filter were within the intraindividual variability of repeated measurements.…”

Clinical evaluation of a screen pneumotachograph as an in-line filter

“…At the present time, this aspect would seem not to have been taken into account by the lung equipment manufacturers, as for most equipment the presence of a filter is at best mentioned to correct the resistance measurements or the dead space of the equipment. Different heat and moisture exchange characteristics and resulting BTPS correction or different methods of BTPS correction may explain why, independently of the resistance, spirometry results are [12,13], or are not [3], affected by the presence of a filter. One advantage of this potential characteristic is that the need to heat the pneumotachograph to prevent vapour condensation can be reconsidered [31].…”

“…The appropriate placement of filters with ideally 100% effectiveness for trapping pathogenic organisms from exhaled air during pulmonary function testing would thus appear to be the most practical method for eliminating transmission of pathogenic organisms between patients [10], and, inasmuch as in-line filters have been shown to be effective in removing pathogens from the expiratory flow [11] without affecting the clinical utility of respiratory function tests [3,[12][13][14], their use might be encouraged in the clinical laboratory. Patient advocate groups, with the help of their medical committees, have published recommendations including the mandatory use of in-line filters during spirometry, and many laboratory managers have generalised the use of such filters.…”

General considerations for lung function testing

“…A low-impedance barrier device was found not to have a significant effect on FVC and FEV1 [14], whereas a barrier filter has been shown to cause small but significant reductions in FEV1 (-44 mL) and peak expiratory flow (PEF; -0.47 L?s -1 ), but did not appear to affect DL,CO, alveolar volume or TLC [15]. Although significant differences between measurements with and without filters have been demonstrated for FVC, FEV1, airway resistance and specific airway conductance (sGaw) [16], these differences were unrelated to the average values of the measurements (except for sGaw), and the limits of agreement were within the range of intra-individual short-term repeatability for almost all of the function indices. Thus, the effect of a filter with optimal characteristics is not considered to be clinically significant, and no appreciable classification error was found in diagnostic tests.…”