Journal of Applied Physiology, Vol 48, Issue 1 202-206, Copyright © 1980 by American Physiological Society
Smoothing of MEFV curves by digital filtering of flow as a function of volume
E. N. Bruce and A. C. Jackson
Noise in flow records limits the degree to which one can characterize local
features of maximum expiratory flow-volume (MEFV) curves, i.e., the volume
dependence of flow over small volume intervals such as 5-10% of the vital
capacity. Such noise includes instrument noise, cardiogenic pulsations, and
rapid flow oscillations due to audible turbulence. Noise removal by analog
filtering of the flow vs. time signal often is unacceptable because the
initial rapid onset of flow can be severely distorted. A digital technique
for directly filtering the flow vs. volume record that does not distort the
initial rapid flow transient has been developed. Flow values are determined
at 256 volume points equally spaced over the vital capacity. This sequence
of flow values is passed through a linear phase, finite impulse response,
Hamming window filter. The output sequence of filtered flow values, plotted
against the corresponding volumes, quantitatively retains the local shape
features of the MEFV curve without the noise.
