Objective To investigate the effect of chronic electrical stimulus (CES) of low frequency and physiological frequency on diaphragmatic subtype of myosin heavy chain (MHC) and mechanical characteristic in rabbits with emphysema.  Methods The rabbit model of emphysema was made by inhaling papain of ultrasonic atomization once a week for 3 weeks in 30 adult Japanese rabbits

6 receiving 10 Hz chronic low-frequency electrical stimulation

6 receiving 40 Hz

6 receiving 10 Hz plus 40 Hz. Another 6 emphysema rabbits and 6 normal rabbits served as control. The twitch tension (Pt)

titanic tension (Po)

time to peak tension (TPT)

half-relaxation time (1/2Rt)

fatigue index (FI) and fatigue recovery index (FRI) were measured and SDSpolyacrylamide gel electrophoresis was used to observe the changes in subtype of MHC in control group

emphysema group

CES groups respectively.  Results ①Following chronic electrical stimulus of 40 Hz

10 Hz

and (10+40) Hz

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

while that of MHC-I and MHC-IIa were significantly increased in the (10+40) Hz group. ②Following chronic electrical stimulation using 40 Hz and (10+40)Hz

diaphragmatic muscle Pt and Po were significantly increased in rabbits with emphysema

TPT and 1/2Rt were significantly reduced

and FI and FRI were significantly decreased (P0.01). In the 10 Hz group

Pt and Po were reduced (P0.05)

TPT and 1/2Rt increased

and FI and FRI decreased (P0.01). FRI and the decrease of FRI were more significant in the (10+40)Hz group than in the 40 Hz group (P0.01).  Conclusion Different frequency electrical stimulation induced different adaptative changes in MHC and mechanical characteristic. Chronic electrical stimulation using low and physiological frequencies can increase diaphragmatic muscle inotropy and the fatigue tolerance of diaphragmatic muscle. It indicates that it may be the optimal frequency mode for the rehabilitation care of diaphragmatic muscle of COPD patients with extraorgan diaphragm pacing.