EFFECT OF VENTILATORY SUPPORT ON RESPIRATORY MUSCLE FATIGUE

通过对比双侧膈神经刺激对杂种犬膈肌疲劳的影响，探讨机械通气对杂种犬膈肌疲劳的影响。[方法]暴露膈神经并刺激颈部（破伤风刺激1秒，40Hz），通过附着在膈下表面的传感器测量双侧膈肌张力。分别在食管和胃处放置2根气囊导管，测量压差（Pdi）。采用机械通气吸气期（inspp .组，n=9）和呼气期（expp .组，n=9）同步进行强直膈肌刺激（强直膈刺激1sec，速率为12/min） 30min，诱导膈肌疲劳。分别在疲劳诱导前、疲劳后立即、疲劳后30min和60min测量肌肉抽搐和Pdi。通过破伤风频率为10、20、30、40、50和lOOHz时的肌肉抽搐情况来评估疲劳程度。[结果]两组疲劳诱导后肌痉挛和Pdi均有所降低，且刺激频率越高，肌痉挛和Pdi的下降幅度越小。肌痉挛和Pdi的抑制在两组间无显著差异。在某些频率下，Pdi的下降幅度小于肌痉挛的下降幅度。【讨论】吸气同步未能缓解膈肌疲劳。这可能是由于吸气流量低，不足以减轻膈肌的工作。在我们的研究中，我们采用了超极限刺激来诱导肌肉疲劳，这可能是导致疲劳不能缓解的部分原因。[结论]在临床环境中，实际吸气力的减少比呼吸相同步更重要。

We compared the diaphragmatic fatigue produced by bilateral phrenic nerve stimulation, which is synchronized to inspiratory and expiratory phase fo mechanical ventilation, to investigate the effect of mechanichal ventilatory suport on the diaphragmatic fatigue in mongrel dogs.[METHOD] Phrenic nerves were exposed and stimulated at neck region (tetanus stimulation for 1 sec at 40Hz), and bilateral diaphragmatic muscle tensions were measured through transducers attached to infradiaphragmatic surface. Two balooon-catheters were placed at esophgus and stomach, then pressure differences (Pdi) were measured. Diaphragmatic muscle fatigue was induced by tetanic phrenic stimulation (tetanic stimuli for 1sec at a rate of 12/min) for 30min synchronized to inspiratory phase (Insp.group, n=9) and expiratory phase (Exp.group, n=9) of mechanical ventilation. Muscle twitchs and Pdi were measured before induction of fatigue, immediately after fatigue, 30min and 60min after fatigue. Fatigue was assesed by the profile of muscle twitches at tetanic frequencies of 10,20,30,40,50 and lOOHz.[RESULT] Muscle twitches and Pdi in both group were reduced after induction of fatigue, where the higher the frequency of stimuli was, the smaller the depressions of muscle twitch and Pdi were. The depression in muscle twitch and Pdi did not differ significantly between two groups. The depression in Pdi were lesser than that in muscle twitch at some frequencies.[DISCUSSION] Inspiratory synchronization failed to relieve the diaphragmatic fatigue. This might be due to the low inspiratory flow, which was not enough to lessen the work of diaphragmatic muscle. In our study, we adopted the supramaximal stimulation to induce the muscle fatigue, and this might in part be a cause not to relieve the fatigue.[CONCLUSIONS] In clinical setting, the reduction of the actual inspiratory effort is more important than the synchronization to respiratory phase.