Aging increases upper airway collapsibility in Fischer 344 rats

1 Center for Research and Education in Special Environments, Departments of 2 Rehabilitation Sciences, 3 Exercise and Nutrition Sciences, 4 Physiology and Biophysics, and 5 Medicine, Division of Pulmonary, Critical Care, and Sleep Medicine, State University of New York at Buffalo, Buffalo, New York; and 6 Department of Medicine, Division of Pulmonary, Allergy, Critical Care and Sleep Medicine, The Ohio State University, Columbus, Ohio Submitted 12 February 2008 ; accepted in final form 22 August 2008 The upper airway muscles play an important role in maintaining upper airway collapsibility, and the incidence of sleep-disordered breathing increases with age. We hypothesize that the increase in airway collapsibility with increasing age can be linked to changes in upper airway muscle mechanics and structure. Eight young (Y: 6 mo) and eight old (O: 30 mo) Fischer 344 rats were anesthetized and mechanically ventilated, and the pharyngeal pressure associated with flow limitation (Pcrit) was measured 1 ) with the hypoglossal (cnXII) nerve intact, 2 ) following bilateral cnXII denervation, and 3 ) during cnXII stimulation. With the cnXII intact, the upper airways of older rats were more collapsible compared with their younger counterparts [Pcrit = –7.1 ± 0.6 (SE) vs. –9.5 ± 0.7 cmH 2 O, respectively; P = 0.033]. CnXII denervation resulted in an increase in Pcrit such that Pcrit became similar in both groups (O: –4.2 ± 0.5 cmH 2 O; Y: –5.4 ± 0.5 cmH 2 O). In all rats, cnXII stimulation decreased Pcrit (less collapsible) in both groups (O: –11.3 ± 1.0 cmH 2 O; Y: –10.2 ± 1.0 cmH 2 O). The myosin heavy chain composition of the genioglossus muscle demonstrated a decrease in the percentage of the IIb isoform (38.3 ± 2.5 vs. 21.7 ± 1.7%; P < 0.001); in contrast, the sternohyoid muscle demonstrated an increase in the percentage of the IIb isoform (72.2 ± 2.5 vs. 58.4 ± 2.3%; P = 0.001) with age. We conclude that the upper airway becomes more collapsible with age and that the increase in upper airway collapsibility with age is likely related to altered neural control rather than to primary alterations in upper airway muscle structure and function. obstructive sleep apnea; pharyngeal pressure; upper airway muscle Address for reprint requests and other correspondence: A. D. Ray, Dept. of Rehabilitation Sciences, State Univ. of New York at Buffalo, 515 Kimball Tower, 3435 Main St., Buffalo, NY 14214 (e-mail: adr{at}buffalo.edu )