A study in functional coordination of intercostal and abdominal muscles during forced expiration

用一种新设计的肌电放大器研究了用力呼气时呼吸肌的活动。该放大器在安全性、响应频率、增益、输入阻抗和噪声等方面都有较大的改进。初步的动物实验表明，高碳酸血症引起腹部运动神经元大运动单位的募集。本实验对11名健康志愿者的呼吸流量、肋间肌（IC）、腹外斜肌（EO）和腹内斜肌（IO）的肌电图进行了分析。在用力呼气期间的EMG活动的模式可以根据形状进行分类，即，锥形或山形。IC组9例受试者中有7例呈锥形，EO组6例中有2例呈锥形，IO组11例中有8例呈锥形。连续20次无间歇试验未改变流量-容量曲线、呼吸肌活性或频率成分（即H/L比值）。用力呼气时，当呼气回路短暂阻塞时，呼吸肌活动会短暂减少。从气道阻塞开始到肌电活动减少的时间间隔IC为61.5-100 msec，EO为61.5-106.5 msec，IO为58.0-92.3 msec。这些值在任何给定的主题中没有太大的不同。在这种短暂的气道阻塞的胸膜压力上升是轻微的，但口腔压力是大。结论：用力呼气的呼吸肌活动模式是预先确定的，并且对每块肌肉都是特异性的。重复试验至20次未引起呼吸肌疲劳。提示呼吸道或呼吸肌内受体的负反馈作用。

Activity of the respiratory muscle during forced expiration was studied with a newly designed EMG amplifier. This amplifier was improved in safety, response frequency, gain, input impedance and noises. The preliminary animal experiments demonstrated that hypercapnia produced recruitment of the large motor units for abdominal motoneurons. The rate coding was a predominant mechanism for phrenic motoneuron pool.In the main experiment, respiratory flow, EMG of intercostal muscle (IC), external oblique (EO) and internal oblique (IO) abdominal muscle were analyzed in 11 healthy volunteers. The pattern of EMG activity during forced expiration could be classified according to the shape, i.e., taper- or hill-shaped. The taper-shaped was found in 7 of 9 subjects for IC, 2 of 6 for EO, and 8 of 11 for IO. Twenty consecutive trials without intermission did not alter the flow-volume curve, activity of respiratory muscle or frequency component (i.e. H/L ratio). When expiratory circuit was obstructed for a short interval during forced expiration, activity of respiratory muscle reduced for a short period. The latencies from the onset of airway obstruction to the reduction in EMG activity were 61.5-100 msec in IC, 61.5-106.5 msec in EO, and 58.0-92.3 msec in IO. These values were not much different in any given subject. During such transient airway obstruction the rise in pleural pressure was slight but mouth pressure was large. Airway anesthesia with xylocaine did not altered the latency.In conclusion, pattern of respiratory muscle activity for forced expiration is predetermined and is specific for each muscles. Repetitive trials to 20 times did not cause respiratory muscle fatigue. Negative feedback from receptors in airway or in respiratory muscle was highly suggested.