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Uncoupling of upper airway motor activity from phrenic bursting by positive end-expired pressure in the rat

¹Department of Life Science, National Taiwan Normal University, Taipei, Taiwan; ²Department of Physical Therapy, University of Florida, Gainesville, Florida; ³Department of Sports, Health and Leisure, Chihlee Institute of Technology, Taipei, Taiwan; and ⁴National Center for High-Performance Computing, Hsinchu, Taiwan

Submitted 23 August 2006 ; accepted in final form 27 October 2006

Phasic bursting in the hypoglossal nerve can be uncoupled from phrenic bursting by application of positive end-expired pressure (PEEP). We wished to determine whether similar uncoupling can also be induced in other respiratory-modulated upper airway (UAW) motor outputs. Discharge of the facial, hypoglossal, superior laryngeal, recurrent laryngeal, and phrenic nerves was recorded in anesthetized, ventilated rats during stepwise changes in PEEP with a normocapnic, hyperoxic background. Application of 3- to 6-cmH₂O PEEP caused the onset inspiratory (I) UAW nerve bursting to precede the phrenic burst but did not uncouple bursting. In contrast, application of 9- to 12-cmH₂O PEEP uncoupled UAW neurograms such that rhythmic bursting occurred during periods of phrenic quiescence. Single-fiber recording experiments were conducted to determine whether a specific population of UAW motoneurons is recruited during uncoupled bursting. The data indicate that expiratory-inspiratory (EI) motoneurons remained active, while I motoneurons did not fire during uncoupled UAW bursting. Finally, we examined the relationship between motoneuron discharge rate and PEEP during coupled UAW and phrenic bursting. EI discharge rate was linearly related to PEEP during preinspiration, but showed no relationship to PEEP during inspiration. Our results demonstrate that multiple UAW motor outputs can be uncoupled from phrenic bursting, and this response is associated with bursting of EI nerve fibers. The relationship between PEEP and EI motoneuron discharge rate differs during preinspiratory and I periods; this may indicate that bursting during these phases of the respiratory cycle is controlled by distinct neuronal outputs.

uncoupled activity; motoneurons; expiratory-inspiratory; preinspiratory

This article has been cited by other articles:

				K.-Z. Lee, D. D. Fuller, I-J. Lu, L.-C. Ku, and J.-C. Hwang Pulmonary C-fiber receptor activation abolishes uncoupled facial nerve activity from phrenic bursting during positive end-expired pressure in the rat J Appl Physiol, January 1, 2008; 104(1): 119 - 129. [Abstract] [Full Text] [PDF]