A simple and reliable method to calibrate respiratory magnetometers
and respitrace.
Banzett, Robert B., Susan T. Mahan, David M. Garner,andrew Brughera,
Stephen H. Loring.
Physiology Program, Harvard School of Public Health
APStracts 2:0330A, 1995.
We present a simple and reliable method to calibrate respiratory
Magnetometers and Respitrace_ to infer respiratory volume changes. As
in earlier methods, we assume two degrees of freedom in the chest
wall, and that volume displacement depends linearly on surface motion
at the rib cage and abdomen. Because the area of the rib cage is
larger, a given motion of its surface produces a greater lung volume
change, therefore the rib cage motion signal is given a larger gain
before the two signals are added to estimate volume. In contrast to
earlier methods, we use a "standard ratio" to weight relative
gains of the rib cage and abdomen signals for all subjects, rather
than determining a gain ratio for each individual subject. Our
procedure does not require subjects to perform the sometimes
difficult isovolume maneuvers used in the calibration method of Konno
and Mead (3), does not require statistical computation used in the
multiple breath linear regression method, nor does it produce the
occasional substantial errors in gain ratio that may occur with the
other methods. When using magnetometers the standard ratio is 4:1
(rib cage:abdomen), when using Respitrace the standard ratio is 2:1.
In 11 subjects, calibration using standard ratios was as accurate as
the isovolume and linear regression techniques. Accuracy during
normal breathing was nearly always within 10% (median 2%), but
occasional large errors occured with both instruments.
Received 20 October 1994; accepted in final form 10 July 1995.
APS Manuscript Number A1081-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 July 1995.