Journal of Applied Physiology, Vol 55, Issue 2 591-597, Copyright © 1983 by American Physiological Society
Noninvasive method for detecting laryngeal narrowing with low-frequency sound
K. Sekizawa, C. Shindoh, W. Hida, S. Suzuki, Y. Akaizawa, Y. Shimizu, H. Sasaki and T. Takishima
We measured laryngeal narrowing with low-frequency sound in human subjects.
A low-frequency sound of 800 Hz was forced into the mouth, and
sound-pressure amplitude above (SPAa) and below the vocal cord (SPAb) was
detected using two separate microphones at the anterior neck. If the
subject voluntarily narrowed the larynx at functional residual capacity,
the increased respiratory resistance (Rrs) was only caused by increased
laryngeal resistance, and SPAa was increased and SPAb was decreased. The
percent changes of SPAa (SPAa%) minus that SPAb (SPAb%) from the initial
values (SPAa% - SPAb% = Y) was proportional to the increase of Rrs from the
initial control state (X, cmH2O X 1-1 X s); Y = 22.4 X1.20 (coef of
correlation, r = 0.96, P less than 0.01). We confirmed similar proportions
in dogs by manually narrowing the vocal cord. When laryngeal resistance was
directly measured by tracheal puncture with a needle, the proportions
between Y and X were not significantly dependent on the increase of Rrs
below the vocal cord induced by methacholine inhalation in human subjects
and histamine injection in dogs. We concluded that the increase of
laryngeal resistance from the initial state could be detected noninvasively
by using low-frequency sound.
