I. Litmanovitz et al., CENTRAL CHEMOSENSITIVITY AFFECTS RESPIRATORY MUSCLE RESPONSES TO LARYNGEAL STIMULATION IN THE PIGLET, Journal of applied physiology, 76(1), 1994, pp. 403-408
Stimulation of laryngeal afferent fibers triggers reflex apnea, which
can be very long in the neonatal period. The purpose of this study was
twofold: 1) to determine the effect of superior laryngeal nerve (SLN)
stimulation on expiratory as well as inspiratory muscle activity and
2) to compare the respiratory response to SLN stimulation under condit
ions that would appear to alter the level of central chemosensitivity
in anesthetized spontaneously breathing piglets. In protocol 1, we mea
sured electromyogram (EMG) responses from the diaphragm (DIA), triangu
laris sterni, and transversus abdominis muscles to graded SLN stimulat
ion; in protocol 2, we compared the DIA response to different levels o
f SLN stimulation during normocapnia, hypercapnia, and cooling of the
ventrolateral medullary surface (VMS). SLN stimulation performed durin
g normocapnia caused significantly greater inhibition of both expirato
ry muscles (triangularis sterni and transversus abdominis) than of the
DIA. During hypercapnia, laryngeal stimulation-induced inhibition of
all three muscles was significantly diminished, and the degree of inhi
bition for the three muscles became equivalent. Inhibition of the DIA
EMG was significantly greater with SLN stimulation during VMS cooling
than with a VMS temperature of 38 degrees C. We conclude that the magn
itude of respiratory inhibition induced by laryngeal stimulation durin
g early postnatal life is inversely related to the level of central ch
emical input and speculate that functional deficiency of structures lo
cated on the VMS may contribute to potentially life-threatening apnea
in infants.