Submitted on February 12, 2008
Accepted on August 22, 2008
Aging Increases Upper Airway Collapsibility in Fischer 344 Rats
Andrew Donald Ray1*, Toshiyuki Ogasa2, Ulysses J Magalang2, John A Krasney3, and Gaspar Andrew Farkas4
1 Center for Research and Education in Special Environments, State University of New York at Buffalo, Buffalo, New York, United States; Rehabilitation Sciences, State University of New York at Buffalo, Buffalo, New York, United States
2 Medicine, Division of Pulmonary, Allergy, Critical Care and Sleep Medicine, The Ohio State University, Columbus, Ohio, United States
3 Physiology and Biophysics, University at Buffalo, School of Medicine and Biomedical Sciences, Buffalo, New York, United States
4 Exercise and Nutrition Sciences, University at Buffalo, Buffalo, New York, United States
* To whom correspondence should be addressed. E-mail: adr{at}buffalo.edu.
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 decrease in airway collapsibility with increasing age can be linked to changes in upper airway muscle mechanics and structure. Eight young (Y: 6 months) and eight old (O: 30 months) Fischer-344 rats were anesthetized, mechanically ventilated and the pharyngeal pressure associated with flow limitation (Pcrit) was measured with: 1) 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 to their younger counterparts (Pcrit =-7.1±0.6 (SE) vs. -9.5±0.7 cmH2O, 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, Y: -5.4±0.5 cmH2O). In all rats, cnXII stimulation decreased Pcrit (less collapsible) in both groups (O: -11.3±1.0, Y: -10.2 ±1.0 cmH2O). 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 UA becomes more collapsible with age and that the increase in upper airway collapsibility with age is likely related to altered neural control rather to primary alterations in upper airway muscle structure and function.
