Yelmen Nermin, Sahin Gulderen, Oruc Tulin, Guner Ibrahim
Department of Physiology, Istanbul University, Cerrahpaşa Medical School, 34098 Fatih-Istanbul, Turkey.
Yonsei Med J. 2007 Oct 31;48(5):856-64. doi: 10.3349/ymj.2007.48.5.856.
The purpose of this study was to investigate the activation of the respiratory centers during insufflation of the larynx with CO2 at different flow rates and concentrations.
The experiments were carried out in spontaneous air breathing rabbits, anesthetized with thiopental sodium (25 mg kg(-1) i.v.). The larynx was separated from the oropharyngeal cavity and the trachea. The tidal volume (VT) and respiratory frequency (f min(-1)) were recorded from the lower tracheal cannula. The respiratory minute volume (VE) was calculated, the action potentials from the right phrenic nerve were recorded and the inspiratory (TI) and expiratory (TE) periods and the mean inspiratory flow rate (VT/TI) were calculated. The larynx was insufflated at flow rates of 500 mL min(-1) and 750 mL min(-1), with 7 and 12% CO2-Air by means of a respiratory pump.
Insufflation of the larynx, with both gas mixtures, decreased the f and VT significantly. The TI and TE were found to increase significantly due to the decreasing in f. There was a significant decrease in VT/TI ratio. Following bilateral midcervical vagotomy, on the passing of both gas mixtures, significant decreases were observed in the VT, and the responses of f, TI and TE were abolished. After cutting the superior laryngeal nerve, the responses of the VT to both gas mixtures were abolished.
In conclusion, the results of this study purpose that the stimulation of the laryngeal mechanoreceptors by the effect of hypercapnia decreases the activation of the respiratory center.
本研究旨在探讨在不同流速和浓度的二氧化碳吹入喉部过程中呼吸中枢的激活情况。
实验在静脉注射硫喷妥钠（25mg/kg）麻醉的自主呼吸兔身上进行。将喉部与口咽腔和气管分离。从气管下部插管记录潮气量（VT）和呼吸频率（f，次/分钟）。计算每分钟通气量（VE），记录右侧膈神经的动作电位，并计算吸气（TI）和呼气（TE）时间以及平均吸气流速（VT/TI）。通过呼吸泵以500mL/分钟和750mL/分钟的流速，用7%和12%的二氧化碳-空气混合气吹入喉部。
两种气体混合物吹入喉部均显著降低了f和VT。由于f降低，TI和TE显著增加。VT/TI比值显著降低。双侧颈中部迷走神经切断后，两种气体混合物吹入时，VT显著降低，f、TI和TE的反应消失。切断喉上神经后，VT对两种气体混合物的反应消失。
总之，本研究结果表明高碳酸血症对喉机械感受器的刺激降低了呼吸中枢的激活。
