Lee Kun-Ze, Chang Yu-Shuo
Department of Biological Sciences, National Sun Yat-sen University, Kaohsiung, Taiwan; Institute of Medical Science and Technology, National Sun Yat-sen University, Kaohsiung, Taiwan; Center for Neuroscience, National Sun Yat-sen University, Kaohsiung, Taiwan; and Department of Biomedical Science and Environmental Biology, Kaohsiung Medical University, Kaohsiung, Taiwan
Department of Biological Sciences, National Sun Yat-sen University, Kaohsiung, Taiwan;
J Appl Physiol (1985). 2014 Nov 15;117(10):1188-98. doi: 10.1152/japplphysiol.00723.2014. Epub 2014 Sep 25.
Persistent impairment of pulmonary defense reflexes is a critical factor contributing to pulmonary complications in patients with spinal cord injuries. The pulmonary chemoreflex evoked by activation of bronchopulmonary C-fibers has been reported to be abolished in animals with acute cervical hemisection (C2Hx). The present study examined whether the pulmonary chemoreflex can recover during the chronic injury phase and investigated the role of bronchopulmonary C-fibers on the altered breathing pattern after C2Hx. In the first protocol, bronchopulmonary C-fibers were excited by intrajugular capsaicin administration in uninjured and complete C2Hx animals 8 wk postsurgery. Capsaicin evoked pulmonary chemoreflexes in both groups, but the reflex intensity was significantly weaker in C2Hx animals. To examine whether spared spinal white matter tissue contributes to pulmonary chemoreflex recovery, the reflex was evaluated in animals with different extents of lateral injury. Linear regression analyses revealed that tidal volume significantly correlated with the extent of spared tissue; however, capsaicin-induced apnea was not related to injury severity when the ipsilateral-to-contralateral white matter ratio was <50%. In the second protocol, the influence of background bronchopulmonary C-fiber activity on respiration was investigated by blocking C-fiber conduction via perivagal capsaicin treatment. The rapid shallow breathing of C2Hx animals persisted after perivagal capsaicin treatment despite attenuation of pulmonary chemoreflexes. These results indicate that the pulmonary chemoreflex can recover to some extent following spinal injury, but remains attenuated even when there is moderate spinal tissue sparing, and that altered breathing pattern of C2Hx animals cannot be attributed to endogenous activation of bronchopulmonary C-fibers.
肺防御反射的持续受损是脊髓损伤患者发生肺部并发症的关键因素。据报道，在急性颈髓半横断（C2Hx）动物中，支气管肺C纤维激活所诱发的肺化学反射消失。本研究检测了肺化学反射在慢性损伤阶段是否能够恢复，并研究了支气管肺C纤维在C2Hx后呼吸模式改变中的作用。在第一个实验方案中，在术后8周对未受伤和完全C2Hx的动物经颈静脉注射辣椒素以兴奋支气管肺C纤维。两组动物中辣椒素均诱发了肺化学反射，但C2Hx动物的反射强度明显较弱。为了检测脊髓白质组织的保留是否有助于肺化学反射的恢复，对不同程度侧方损伤的动物进行了反射评估。线性回归分析显示潮气量与保留组织的程度显著相关；然而，当同侧与对侧白质比例<50%时，辣椒素诱发的呼吸暂停与损伤严重程度无关。在第二个实验方案中，通过经迷走神经周围注射辣椒素阻断C纤维传导，研究了支气管肺C纤维背景活动对呼吸的影响。尽管肺化学反射减弱，但经迷走神经周围注射辣椒素处理后，C2Hx动物的快速浅呼吸仍然持续。这些结果表明，脊髓损伤后肺化学反射可在一定程度上恢复，但即使有中度脊髓组织保留，其仍会减弱，且C2Hx动物呼吸模式的改变不能归因于支气管肺C纤维的内源性激活。
