Easton P A, Abe T, Smith J, Fitting J W, Guerraty A, Grassino A E
Notre-Dame Hospital, University of Montreal, Quebec H2X 2P2; and Department of Medicine, Canada.
J Appl Physiol (1985). 1995 May;78(5):1985-92. doi: 10.1152/jappl.1995.78.5.1985.
Because costal and crural diaphragm segments have different functional characteristics, ventilatory stimulation with hypoxia or hypercapnia may elicit differential segmental function. We report measurements of diaphragm segmental length, shortening, and electromyogram (EMG) activity from 11 canines that were chronically implanted with sonomicrometry transducers and EMG electrodes and then studied a mean of 18 days postimplantation while awake and breathing spontaneously during CO2 rebreathing and progressive isocapnic hypoxia. Ventilatory responses to hypercapnia and progressive hypoxia were moderate at 1.13 +/- 0.31 (SD) 1. min-1. mm-1 arterial Pco2 and -0.98 +/- 0.51 l. min-1.%arterial O2 saturation-1. When tidal values for breathing pattern and segmental function were compared at matching tidal volumes that correspond to mean CO2 of 49.4 arterial Pco2 and 77% arterial O2 saturation, there was no significant difference in resting length, tidal shortening, or tidal EMG of costal or crural segments. Intrabreath profiles of flow, shortening, and EMG activity at matched tidal volumes showed that 1) inspiratory flow during hypoxia was significantly greater during early inspiration, 2) crural EMG activity preceded costal EMG activity in early inspiration during both hypercapnia and hypoxia, 3) both segments showed increased postinspiratory inspiratory activity with stimulated ventilation, and 4) postinspiratory shortening and EMG were greatest for the crural segment during hypoxia. These results suggest that costal and crural diaphragm segments exhibit differential function during chemical stimulation, especially during postinspiration.
由于肋部和膈脚部膈肌节段具有不同的功能特性，低氧或高碳酸血症引起的通气刺激可能会引发不同的节段性功能。我们报告了对11只犬膈肌节段长度、缩短程度和肌电图（EMG）活动的测量结果。这些犬被长期植入超声测量换能器和EMG电极，然后在植入后平均18天进行研究，期间清醒且自主呼吸，经历二氧化碳再呼吸和渐进性等碳酸血症低氧过程。对高碳酸血症和渐进性低氧的通气反应适中，分别为1.13±0.31（标准差）1.min⁻¹.mm⁻¹动脉血二氧化碳分压和-0.98±0.51 l.min⁻¹.%动脉血氧饱和度⁻¹。当在对应于平均动脉血二氧化碳分压49.4和动脉血氧饱和度77%的匹配潮气量下比较呼吸模式和节段性功能的潮气量值时，肋部或膈脚部节段的静息长度、潮气量缩短程度或潮气量EMG没有显著差异。在匹配潮气量下，呼吸过程中的流量、缩短程度和EMG活动的吸气内曲线表明：1）低氧期间早期吸气时的吸气流量显著更大；2）在高碳酸血症和低氧期间的早期吸气过程中，膈脚部EMG活动先于肋部EMG活动；3）在通气刺激时，两个节段的吸气后吸气活动均增加；4）低氧期间，膈脚部节段的吸气后缩短程度和EMG最大。这些结果表明，在化学刺激期间，尤其是在吸气后，肋部和膈脚部膈肌节段表现出不同的功能。
