van Lunteren E, Dick T E
Department of Medicine, Cleveland VA Medical Center, Pulmonary Section, Case Western Reserve University, 111J(W), 10701 East Boulevard, Cleveland, OH 44106, USA.
Respir Physiol. 2001;124(1):23-33. doi: 10.1016/s0034-5687(00)00182-1.
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.
呼吸运动单位（MU）可分为不同亚群，这些亚群在静息呼吸和刺激呼吸时的放电模式有所不同。对于膈神经/膈肌运动单位，亚群内部也存在差异，且晚发运动单位的差异大于早发运动单位。本研究通过记录麻醉猫的颏舌骨肌运动单位，对上呼吸道呼吸运动单位亚群内的差异程度进行了表征。吸气运动单位（I-MU，n = 21）的放电持续时间范围很广（变异系数（CV）= 42%）。相比之下，吸气-呼气运动单位（I/E-MU，n = 19）在吸气时放电持续时间范围较窄（CV = 13%），但在呼气时放电持续时间范围较广（CV = 36%）。I-MU和I/E-MU各单位的平均放电频率具有相似程度的差异（CV = 31 - 40%）。对于I-MU，放电持续时间与平均放电频率相关，而I/E-MU则无明显这种关系。单次呼吸末呼气气道阻塞减少了吸气时放电持续时间的异质性，增加了呼气时的异质性，而吸气末气道阻塞则减少了呼气时的异质性。总之，（a）接受呼吸驱动的颏舌骨肌运动单位亚群内存在相当大的差异；（b）I-MU和I/E-MU亚群内的差异程度不同；（c）单次呼吸气道阻塞可调节亚群内活动时间的差异。
