Abstract
The genioglossus is a major upper airway dilator muscle thought to be important in obstructive sleep apnea pathogenesis. Aging is a risk factor for obstructive sleep apnea although the mechanisms are unclear and the effects of aging on motor unit remodeled in the genioglossus remains unknown. To assess possible changes associated with aging we compared quantitative parameters related to motor unit potential morphology derived from EMG signals in a sample of older (n = 11; >55 years) versus younger (n = 29; <55 years) adults. All data were recorded during quiet breathing with the subjects awake. Diagnostic sleep studies (Apnea Hypopnea Index) confirmed the presence or absence of obstructive sleep apnea. Genioglossus EMG signals were analyzed offline by automated software (DQEMG), which estimated a MUP template from each extracted motor unit potential train (MUPT) for both the selective concentric needle and concentric needle macro (CNMACRO) recorded EMG signals. 2074 MUPTs from 40 subjects (mean±95% CI; older AHI 19.6±9.9 events/hr versus younger AHI 30.1±6.1 events/hr) were extracted. MUPs detected in older adults were 32% longer in duration (14.7±0.5 ms versus 11.1±0.2 ms; P = 0.05), with similar amplitudes (395.2±25.1 µV versus 394.6±13.7 µV). Amplitudes of CNMACRO MUPs detected in older adults were larger by 22% (62.7±6.5 µV versus 51.3±3.0 µV; P<0.05), with areas 24% larger (160.6±18.6 µV.ms versus 130.0±7.4 µV.ms; P<0.05) than those detected in younger adults. These results confirm that remodeled motor units are present in the genioglossus muscle of individuals above 55 years, which may have implications for OSA pathogenesis and aging related upper airway collapsibility.
Highlights
Obstructive sleep apnea is a common disorder that increases in prevalence with age, the mechanisms are unclear
Despite the fact that the genioglossus muscle is known to contain a high proportion of Type II muscle fibers and aging effects are pronounced for Type II fibers, [26,27], we recently found no evidence for increased Motor unit potential (MUP) durations associated with age in humans [17]
The number of motor unit potential train (MUPT) extracted per recording was lower for older adults compared to younger adults (2.760.3 versus 3.260.2; P,0.05, Dunns Method)
Summary
Obstructive sleep apnea is a common disorder that increases in prevalence with age, the mechanisms are unclear. Research into the motor control of the genioglossus is likely to provide insights into sleep apnea pathogenesis. Motor unit potential (MUP) analysis provides insight into the normal function of skeletal muscle and aids in the assessment of neuromuscular disorders [1]. Skeletal muscle remodeling is associated with physiological factors that can change the characteristics of MUPs [2,3,4]. MUPs with increased durations can be detected in many skeletal muscles, reflected as remodeled motor units as a result of denervation, collateral sprouting and reinnervation [5,6,7]
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