Journal of Applied Physiology, Vol 53, Issue 4 977-984, Copyright © 1982 by American Physiological Society
Frequency spectra of flow and volume events for forced vital capacity
R. J. Lemen, C. B. Gerdes, M. J. Wegmann and K. J. Perrin
We determined the frequency content of forced expiratory flow-time (FT) and
volume-time (VT) curves by a fast Fourier transform to determine the
dynamic responses required of devices to reproduce these curves. We
analyzed 304 FT and VT curves from 15 normal (N) subjects (ages 8-34 yr),
15 cystic fibrosis (CF) patients (ages 7-36 yr), and 9 smokers (S, ages
20-63 yr). The highest frequency (HF) with significant amplitude content,
defined as the highest frequency with 5% or more amplitude of the
fundamental, for FT curves in N (mean +/- SD, 5.06 +/- 0.7 Hz) was
significantly (P less than 0.05) lower than in CF (6.43 +/- 0.9 Hz) and S
(6.49 +/- 1.8 Hz). These differences were due predominantly to flow
transients at high lung volumes in CF and S. No significant differences in
HF of VT curves were noted among N (3.0 +/- 1.4 Hz), CF (2.9 +/- 1.4 Hz),
and S (1.7 +/- 1.5 Hz). All subjects had HF for FT of 12 Hz or less and for
VT of 6 Hz or less. For spirometric recordings our results suggest that the
amplitude response of flow- and volume-measuring devices should be flat
(+/- 5%) up to 12 Hz for flow signals and up to 6 Hz for volume signals.
