Journal of Applied Physiology, Vol 77, Issue 1 37-42, Copyright © 1994 by American Physiological Society
Upper airway stability and respiratory muscle activity during inspiratory loading in full-term neonates
S. Duara, M. Rojas and N. Claure
University of Miami School of Medicine, Department of Pediatrics, Florida 33101.
To investigate the role of genioglossus and posterior cricoarytenoid (PCA)
activity in stabilizing the extrathoracic airway (ETA) of full-term infants
during inspiratory flow-resistive loading (IRL), 10 unsedated full-term
infants were evaluated in quiet sleep. IRLs were randomly imposed (L2, 125
cmH2O.l-1.s; L3, 250 cmH2O.l-1.s). Ventilation, total respiratory
resistance (a correlate of ETA resistance), and moving time averages of
PCA, submental activity of the genioglossus (SM), and diaphragm
electromyogram were obtained. Results revealed no phasic activity in the SM
during baseline breathing or with either IRL. Phasic PCA activity was
always observed; burst duration increased with L2 and L3 (P < 0.01) and
commenced earlier in relation to the onset of inspiratory airflow with both
loads (P < 0.05). PCA activity always preceded that of the diaphragm and
invariably outlasted it other than with L3. The upper airway negative
pressure changes induced by IRL were insufficient to recruit SM activity;
other potential stimuli such as transcutaneous PO2, transcutaneous PCO2,
and pulmonary stretch receptor activation (increase in tidal volume)
remained unchanged. Ventilation decreased with both loads (L3: P <
0.01), esophageal and mouth pressures increased (P < 0.01), and
inspiratory time and inspiratory time divided by total time were both
prolonged (P < 0.01). Total respiratory resistance remained unchanged
with L2 but increased with L3 (P < 0.01). We concluded that ETA
narrowing may be induced in full-term infants during quiet sleep with
moderately large-sized IRL and that it is not entirely ameliorated by
activation of the SM or PCA or by arousal.
