Reid S G, Milsom W K, Meier J T, Munns S, West N H
Department of Physiology, College of Medicine, University of Saskatchewan, 107 Wiggins Road, SK, S7N 5E5, Saskatoon, Canada.
Respir Physiol. 2000 May;120(3):213-30. doi: 10.1016/s0034-5687(99)00118-8.
This study examined the role of pulmonary vagal feedback on hypercapnic chemosensitivity and breathing pattern formation in cane toads (Bufo marinus). Decerebrate, paralysed toads were uni-directionally ventilated with air, 2.5% CO(2) or 5.0% CO(2) with the lungs inflated or deflated, before and after pulmonary vagotomy. Motor output from the mandibular branch of the trigeminal nerve served as an index of fictive breathing. As respiratory drive was increased, breathing frequency increased and breaths were clustered into discrete episodes separated by periods of apnea. Lung deflation tended to enhance episodic breathing while inflation biased the system towards apnea at low levels of respiratory drive and a pattern of continuous, small breaths at higher levels of respiratory drive. Following bilateral pulmonary vagotomy there was no increase in ventilation during hypercapnia and lung inflation/deflation had no effect on breathing pattern. In isolated brainstem-spinal cord preparations from the same animals, all variables associated with fictive breathing were unaffected by changes in superfusate pH from 8.0 to 7.6. The breathing pattern from the in vitro preparations was highly variable. This study demonstrates a crucial role for vagal feedback in modulating respiration and the respiratory responses to hypercapnia in B. marinus.
本研究考察了肺迷走神经反馈在甘蔗蟾蜍（海蟾蜍，Bufo marinus）高碳酸血症化学感受性及呼吸模式形成中的作用。在肺迷走神经切断术前和术后，对去大脑、麻痹的蟾蜍进行单向通气，分别给予空气、2.5% CO₂ 或 5.0% CO₂，同时使肺充气或放气。三叉神经下颌支的运动输出作为虚构呼吸的指标。随着呼吸驱动增加，呼吸频率增加，呼吸聚集成离散的发作，发作之间有呼吸暂停期。肺放气倾向于增强发作性呼吸，而肺充气在低呼吸驱动水平时使系统倾向于呼吸暂停，在高呼吸驱动水平时则呈现连续的小呼吸模式。双侧肺迷走神经切断术后，高碳酸血症期间通气量无增加，肺充气/放气对呼吸模式无影响。在来自相同动物的离体脑干 - 脊髓标本中，所有与虚构呼吸相关的变量均不受灌流液 pH 从 8.0 变为 7.6 的影响。体外标本的呼吸模式高度可变。本研究证明了迷走神经反馈在调节海蟾蜍呼吸及对高碳酸血症的呼吸反应中起关键作用。
