Journal of Applied Physiology, Vol 57, Issue 5 1439-1447, Copyright © 1984 by American Physiological Society
Frequency dependence of pulmonary compliance and resistance in patients with obstructive lung disease
J. Clement, H. Bobbaers and K. P. Van de Woestijne
The frequency dependence of pulmonary compliance and resistance was
investigated in 27 patients with obstructive lung disease. Compliance and
resistance were determined either by the conventional zero crossing (Cdyn)
and isovolume (RL) technique or by a modified Fourier analysis following a
smoothing procedure (auto- and cross-correlation function) yielding an
effective compliance and resistance, CL and RL. The latter technique was
used to calculate CL and RL from the fundamental and third and fourth
harmonics present in the flow and transpulmonary pressure signals. Three
breathing frequencies were investigated: 0.5, 1, and 2 Hz. Both Cdyn and
CL, calculated from the fundamental component, decreased progressively with
frequency. However, Cdyn showed less frequency dependence than CL. CL
calculated from the harmonics was significantly smaller than CL from the
fundamental at the same breathing frequency. RL, as well as RL calculated
from the fundamental, tended to increase with frequency. A decline of
resistance with frequency became apparent, however, when RL from the
fundamental was compared with RL obtained from the corresponding higher
order harmonics. These results suggest that the frequency dependence of
resistance can be masked by the usual procedure of breathing at several
frequencies. Instead the measurements should be performed at a single
frequency, for instance spontaneous breathing, by computing resistance from
the higher order harmonics present in the breathing signals.
