Effects of fenoterol on inspiratory effort sensation and fatigue
during inspiratory threshold loading in normal subjects.
Suzuki, Junnichi, Shunsuke Suzuki, and Takao Okubo.
The First Department of Internal Medicine, Yokohama City University
School of Medicine, 3-9 Fukuura, Kanazawa-ku, Yokohama, Kanagawa 236,
JAPAN
APStracts 2:0477A, 1995.
We studied the effects of a single dose of fenoterol on the
relationship between inspiratory effort sensation (IES) and
inspiratory muscle fatigue induced by inspiratory threshold loading
in healthy subjects. The magnitude of the threshold was 60% of
maximum static inspiratory mouth pressure (PImax) at functional
residual capacity, and the duty cycle was 0.5. Subjects continued the
threshold loaded breathing until the target mouth pressure could no
longer be maintained (Tlim). The intensity of IES was scored using a
modified Borg scale. Either fenoterol, 5 mg, or placebo was given
orally 2 hours before loading in a randomized double-blind cross-over
protocol. Tlim with fenoterol (34.4 +/- 8.6 min) was longer than that
with placebo (22.2 +/- 7.1 min)(P < 0.05). The high-to-low
frequency power ratio of diaphragmatic EMG decreased during loading;
the decrease was less with fenoterol (P < 0.05). The Edi also
decreased with loading; the decrease was greater on fenoterol
treatment (P < 0.01). The PImax and maximal transdiaphragmatic
pressure (Pdi) were similarly decreased after loading on either
treatment. The intensity of IES rose with time during loading in both
groups, but was lower with fenoterol than with placebo (P <
0.05). The ratio of Pdi to integrated activity of EMG increased with
fenoterol (P < 0.05). Fenoterol treatment increased both
superimposed Pdi twitch (Ts) and Pdi twitch of relaxed diaphragm
(Tr), and decreased the value of (1-Ts/Tr). Thus, we conclude that in
normal subjects, fenoterol reduces diaphragmatic fatigue and
decreases the motor command to the diaphragm, resulting in a decrease
in IES during inspiratory threshold loading and a prolongation of
endurance.
Received 18 July 1994; accepted in final form 24 October 1995.
APS Manuscript Number A715-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 November 95