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TU‐C‐M100J‐07: A Systematic Study On the Sources of Drift in a Turbine‐Based Spirometer Using a Breathing Simulator
Author(s) -
Ha J,
Perlow D,
Yu C
Publication year - 2007
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.2761338
Subject(s) - spirometer , piston (optics) , cylinder , turbine , mechanics , mechanical engineering , volume (thermodynamics) , airflow , reversing , simulation , breathing , spirometry , engineering , physics , medicine , thermodynamics , optics , exhaled nitric oxide , wavefront , asthma , anatomy
Purpose: To systemically isolate and quantify the contributions of different sources of signal drift in turbine‐based spirometry. Method and Materials: To get a repeatable response from the VMM‐400 spirometer, we used a breathing simulator made of an airtight cylinder. The cylinder's piston was driven by a motor to force the air in/out of the cylinder to the spirometer. A heating blanket was used to heat the cylinder, so that the in/out air would have different temperature. The piston position, thereby the cylinder air volume, was determined using a position sensor. Results: Our data show that even when the piston was driven sinusoidally and the heating blanket was off, the spirometer exhibits a drift per cycle of 3.4% of the maximum tidal air volume due to the differential response of its turbine blade. Reversing the direction of in/out flow simply changes the drift direction. With the heating on, the drift accumulates an additional 4% per cycle. The added drift is due to the expanded air volume from the heating. The most significant drift was observed when the piston was driven in a saw‐tooth pattern, either with a fast inhale followed by a slow exhale or visa versa. The difference in the measured volume between the two breathing phases can be as large as 60% or more due to the failure of the spirometer to register the volume in the low flow‐rate phase and the air needed to be spent on reversing the blade at the end of the fast‐changing phase. Conclusions: The drift due to the blade asymmetry and temperature stays the same per breathing cycle (3.4% and 4%), and can be corrected in real‐time. The drift due to breathing asymmetry can vary between cycles because of patient irregular breathing; the correction would most likely be complex (i.e., nonlinear).