| Diaphragm pacing is a ventilation technique assisted to respiration that has enjoyed development in the past 30 years rapidly. However, it is hampered by functional disorders of respiratory muscles in the clinical application. Diaphragm fatigue is one of them by which the effectiveness of the treatment is puzzled. It is for this reason that the patho genesis arid prevention of diaphragm fatigue have become a focus of interest among researchers in recent years. Objective: To explore the mechanism of diaphragm fatigue during diaphragm pacing and to find out the fatigue-resistant effect of Radix Astragali Injection by making a copy of dogs ,determining the amount of ATP~ ADP~ AMP(AXP)~. SOD-. MDA and the morphologic changes in diaphragm before and after diaphragm fatigue. Methods: 1. 8 healthy adult dogs were generally anaesthesized with thiopental sodium (25-30mg/kg);.. Then a slant incision was made on both sides of the neck to. reveal the. phrenic nerve. 1 silver line was buried in the nerve and fixed on and other placed in the neck subcutaneously for a ioop. A multi-branched tube was put into the stomach, with one extended to gastric pouch and another into esophagus respectively. After the gastric and esophagus pouch filled with water.The tube was connected to a 4-channel physiologic~ instrument for simultaneous and continuous recording of the pressure in the stomach and esophagus and then assessed the trans- diaphragmatic pressure. A small incision was made in the middle of upper -5- abdomen of the dog and a silver electric pole was placed along the diaphragm while the other end was connected to a tracer to trace the myoelectric changes. Continuous pulsed electric currents were applied to stimulate diaphragmatic nerve and so a model of diaphragmatic fatigue could be established. 2. The following relevant indexes of the model before and after diaphragm fatigue were assessed including: 1) changes in the trans- diaphragmatic pressures followed by injection of the experimental drugs after the electric stimulation stopped; 2) changes in the contents of ATP, SOD and MDA in the diaphragm; and 3) morphologic alteration in phrenic mitochondria released by transmission electron microscopy. 3. Statistical analysis was performed by using the software packages of SPSS 10.0. Results: Trans-diaphragmatic pressure was improved significantly by the Radix Astragali Injection (P0.000). The contents of ATP, ADP, AXP and SOD were significantly lower after the fatigue whereas that of MDA was higher in the fatigue group than in the normal (P0.000). There was no significant change in the content of AMP. Some mitochondria in diaphragm swelled while others showed reversible vacuolar degeneration. Conclusions: The results of the present study indicate that exhaustion and composite blockage of ATP in diaphragmatic cells, decrease in the substances directly supplied and the damage caused by free radicals to the mitochondriac membrane are contributive to the occurrence of diaphragm fatigue after diaphragm pacing. The Radix Astragali Injection has a significant resistant effect on diaphragm fatigue. This injection can directly affect diaphragm cells and dilate diaphragm vessels, which can improve contractability of the cells. Besides, it can serve as a powerful scavenger for -6-...
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