After the bilateral phrenic nerves of the dogs were stimulated,the effect of amino-phylline on the function of normal and fatigued diaphragm was observed with the determination of transdiaphragmatic pressure-stmulation frequency curve (Pdi-F).and the analysis of the power spectrum of diaphragmatic electromyogram (DMGdi) at spontaneous breathing.After the administration of 10 and 20 mg/kg of aminophylline ,the PDi pf the normal diaphragm was increased and that of the fatigued diaphragm recovered.The Pdi-F curve of the fatigued diaphragm was shifted to the left,and the central frequency,the medium frequency,and the high/low frequency ratio were markedly increased.It is concluded that aminophylline at the therapeutic dosage can imporve the generation of the strength and enhance the recovery of the fatigued diaphragm.

After electrical stimulation of the phrenic nerve,the function of the diaphragm was assessed by measurement of the transdiaphragmatic pressure (PDi),establishment of the Pdi-sti-mulating frequency (F) curve,and analysis of the power spectrum on the diaphragmatic elec-tromyogram (EMGdi) at spontaneous breathing.Hypercapnia of the dogs was induced by forcing the animals to inhale a mixture of CO2 and air.The findings were as follows:(1) After acute hypercapnia,PDi rapidly and progressively decreased.The power spectrum of EMGdi was also reduced.The PDi-F curve was shifted to right.These findings suggest that the function of the diaphragm was severely damaged.(2) The decrease of pH value was the important cause of diaphragmatic fatigue.(3) The diaphragm in a static condition could reduce the damage of hypercapnia.(4) Cedi-lanid exerted certain effects on the prevention of diaphragmatic fatigue created by acute hypercapnia.