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

¹ Université de Caen - Basse-Normandie, Faculté de Médecine, Laboratoire de Physiologie, UPRES-EA 3917, France.; and CHU de Caen, Laboratoire des Explorations Fonctionnelles, France.
² CHU de Caen, Laboratoire des Explorations Fonctionnelles, France.
³ CHU de Caen, Service d'hygiène, France.
⁴ CHU de Brest, Service des Explorations Fonctionnelles, France.

^* To whom correspondence should be addressed. E-mail: normand-h{at}chu-caen.fr.

	Abstract

The ATS/ERS Task Force underlined that the use of in-line filters during respiratory function tests "is an area of controversy". Our aim was to measure the contamination occurring during forced expiration downstream from a screen pneumotachograph (SP) with and without an in-line filter (Pall PF30S). Forty healthy subjects performed 8 consecutive maximal expiratory manoeuvres into 4 sterile apparatuses (A1: no filter, no SP; A2: filter-only; A3: SP-only; A4 filter and SP) in random order. A blood agar plate was fixed downstream from the apparatus. Colony-forming units (CFU) were counted after 24 hrs of incubation at 37°C. Out of the 40 plates obtained with each apparatus, 13 were sterile with A1 (range 0-679 CFUs), 25 with A2 (0-49 CFUs), 30 with A3 (0-35 CFUs) and 39 with A4 (1 CFU in the only positive plate) (p<0.001). A1 and A2 and also A3 and A4 gave different values for the CFU number (p<0.01), but A2 and A3 showed similar contamination levels. We conclude that: 1) the in-line filter does not perform better than a SP; 2) It does not eliminate the need to decontaminate the pneumotachograph; 3) equipment placed downstream from an in-line filter and a SP is almost protected from contamination.