Objective    To investigate the effect of chronic low-frequency electrical stimulation on the structural and metabolic changes of diaphragm of emphysema rabbits.     Methods    The rabbit model of emphysema was made by papain-inhaling of ultrasonic  atomizatio

n once a week for 3 weeks in 30 adult Japanese rabbits

6 receiving 10 Hz chronic  low  frequency electrical   stimulation

6 receiving 40 Hz

and 6 receiving（10＋40）  Hz. Other 6 emphysema rabbits and 6 normal rabbits served as control. An enzyme chemical method was used to observe the changes in the enzyme activities of sarcoplasmic reticulum Ca

2+

-ATPase

succinate dehydrogenase (SDH) and the lactate dehydrogenase (LDH) and changes in MHC in control group

emphysema group

and emphysema+chronic low frequency electrical stimulation group.     Results    Following chronic electrical stimulation using 40 Hz

10 Hz

and （10＋40）  Hz

the relative contents of MHC were increased in the diaphragmatic muscle of rabbits with emphysema. The percentage of MHC-Ⅰ was significantly increased in the 10 Hz group

while that of MHC-Ⅱ a was significantly increased in the （10＋40）  Hz group. Following chronic electrical stimulation using 40 Hz and （10＋40）  Hz

diaphragmatic muscle SR Ca

2+

-ATPase activity was increased in rabbits with emphysema (P0.05). In the 10 Hz group

Ca

2+

-ATPase activity was lower (P0.01). As compared with the control rabbits

SDH activity was increased in diaphragmatic muscle of rabbits with emphysema (P0.05)

while LDH activity did not change significantly. SDH activity was increased more significantly in the （10＋40）  Hz group than in the single 40 Hz or 10 Hz group (P0.05).     Conclusion    Different frequency electrical stimulation induces different adaptative changes in diaphragmatic muscle MHC and enzyme activity. It indicates that chronic electrical stimulation at a low and physiologic frequency may be the optimal frequency mode for the rehabilitation of diaphragmatic muscle of COPD patients undergoing external diaphragm pacing.