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The infant lung function model: a mechanical analogue to test infant lung function equipment

¹ University Hospital of Berne, Inselspital, Berne, Switzerland, 3010 and ² Portex Anaesthesia, Intensive Care and Respiratory Medicine Unit, Institute of Child Health, London, UK

CORRESPONDENCE: U. Frey, Dept of Paediatrics, University Hospital of Berne, Inselspital, Berne, Switzerland. Fax: 41 316329484

Keywords: equipment and supplies, infant, model, plethysmography, respiratory function tests

Received: September 8, 1999
Accepted December 29, 2000

This work has been supported in part by Erich Jaeger GmbH, Hoechberg, Germany.

Abstract

To facilitate international multicentre studies and quality control of infant pulmonary function measurements, the European Respiratory Society-American Thoracic Society (ERS-ATS) working group for infant lung function testing aims to develop specifications for standardized infant lung function equipment and software. However, a standardized test device is also needed to test whether existing infant lung function equipment is able to meet these requirements.

The authors have built a "mechanical model baby" consisting of a linear pump which can reproduce prerecorded tidal flow waveforms with a precision of 0.5% (full stroke), enabling the simulation of tidal and forced flow patterns. This linear pump can be connected to a series of copper lung volumes (range 50–300 mL) with known time constants, so that lung volumes can be reproduced with a precision of ±1% at frequencies 10–120 bpm. Five airflow resistors were built using sinter material.

When assessed using flows 0–300 mL·s^–1 all resistors showed a quasilinear pressure/flow relationship, with slopes 1.0–5.6 kPa·L^–1·s. These resistances could be reproduced with a precision of ±2.5%. The infant lung model can also be used to assess frequency responses of infant lung function equipment, since the pump is capable of delivering low amplitude volumes up to 20 Hz in a pseudorandom noise manner.

In summary, based on error estimations, this infant lung model is able to test whether or not infant lung function equipment meets the requirements suggested by the European Respiratory Society-American Thoracic Society standardization group, that is: flow measurements within ±2.5%, volume and resistance measurements within ±5%, frequency response: magnitude attenuation <±10% and phase shift <±3 degrees at 10 Hz.