Heterogeneity within geniohyoid motor unit subpopulations in firing patterns during breathing.
Respiratory motor units (MU) segregate into subpopulations, which differ in firing patterns during resting and stimulated breathing. For phrenic/diaphragm MUs, diversity also exists within subpopulations, and is greater for late than early-onset MUs. The present study characterized the extent of diversity within upper airway respiratory MU subpopulations by recording geniohyoid MUs in anesthetized cats. Inspiratory MUs (I-MU, n=21) had a wide range of firing durations (coefficient of variation (CV)=42%). In contrast, inspiratory-expiratory MUs (I/E-MU, n=19) had a narrow range of firing durations during inspiration (CV=13%), but a wide range of firing durations during expiration (CV=36%). Mean firing frequency had similar degrees of diversity among units for I-MU and I/E-MU (CV=31-40%). For I-MU firing duration correlated with mean firing frequency, whereas no such relationship was apparent for I/E-MU. Single-breath end-expiratory airway occlusion decreased heterogeneity in firing duration during inspiration and increased it during expiration, whereas end-inspiratory airway occlusion decreased heterogeneity during expiration. In conclusion, (a) there is considerable diversity within geniohyoid MU subpopulations receiving respiratory drive; (b) the degree of diversity within subpopulations differs for I-MU and I/E-MU; and (c) diversity within subpopulations in timing of activity is modulated by single-breath airway occlusion.
van Lunteren
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Department of Medicine, Cleveland VA Medical Center, Pulmonary Section, Case Western Reserve University, 111J(W), 10701 East Boulevard, Cleveland, OH 44106, USA. exv4@po.cwru.edu
Dick
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D000402:Airway Obstruction / Q000503:physiopathology; D000818:Animals; D002415:Cats; D003964:Diaphragm / Q000503:physiopathology; D004576:Electromyography; D012016:Reference Values; D012132:Respiratory Muscles / Q000502:physiology* / Q000503:physiopathology; D012143:Respiratory Physiological Phenomena