Proceedings of the 2005 IEEE Engineering in Medicine and Biology 27th Annual Conference Shanghai, China, September 1-4, 2005
Effects of Muscle Electrical Stimulation on Bone Mineral Density in the Hindlimb Bones of the Tail-Suspended Rats Liang Peng, Jing Bai, Boyuan Sun, Guangzhi Wang, Wei Liu, Shuping Zhang, and Ying Liang
Abstract—Bone mass loss caused by microgravity is considered as one of the worst influences to human body during long-term spaceflight. As one of the countermeasures to retain bone mass, muscle electrical stimulation is just started in spaceflight application and needs further research. This work is aimed to investigate the effects of muscle electrical stimulation based on the tail-suspended rat experiment. The statistical results of bone mineral density have shown that muscle electrical stimulation can retain bone mass to a certain extent under the condition of simulated microgravity.
I. INTRODUCTION
A
CCORDING to the scientific observation and research of spaceflight for many years, microgravity would make bone mass lost due to negative calcium balance. Bone mass loss always exists during spaceflight and bone mass recovery needs a long time after spaceflight [1, 2]. As bone is of great physiological importance, especially to the support, protection and movement of human body, bone mass loss would do harm to human body. So bone mass loss caused by microgravity is considered as one of the worst influences to human body during spaceflight, especially during long-term spaceflight. Because of the serious consequence of bone mass loss caused by microgravity, many countermeasures have been developed to retain bone mass, such as medicine therapy, physical training, artificial gravity and muscle electrical stimulation. Among these countermeasures muscle electrical stimulation is considered as a simple and effective method. The research of muscle electrical stimulation on the earth has shown that it can reduce bone mass loss effectively [3-5], but it is just started in spaceflight application and needs further research. This work is aimed to investigate the effects of muscle Manuscript received March 29, 2005. This work was supported by National Natural Science Foundation of China and Fundamental Research Foundation of Tsinghua University. Liang Peng is with the Biomedical Engineering Department, Tsinghua University, Beijing, 100084, China (e-mail:
[email protected]). Jing Bai is with the Biomedical Engineering Department, Tsinghua University, Beijing, 100084, China (phone: +8610-62786480; fax: +8610-62780650; e-mail: deabj@ tsinghua.edu.cn). Boyuan Sun is with the Biomedical Engineering Department, Tsinghua University, Beijing, 100084, China. Guangzhi Wang is with the Biomedical Engineering Department, Tsinghua University, Beijing, 100084, China. Wei Liu is with the Biological Sciences and Biotechnology Department, Tsinghua University, Beijing, 100084, China. Shuping Zhang is with the Biological Sciences and Biotechnology Department, Tsinghua University, Beijing, 100084, China. Ying Liang is with the Beijing Obstetrics and Gynecology Hospital, Capital University of Medical Sciences, Beijing, 100006, China.
0-7803-8740-6/05/$20.00 ©2005 IEEE.
electrical stimulation on Bone Mineral Density (BMD) in the hindlimb bones of the tail-suspended rats. II. MATERIALS AND METHODS 17 growing male Sprague-Dawley rats with the weight between 139~160 g were used in this work. The rats were randomly divided into three groups: 4 in the free active control group (A), 7 in the tail-suspended control group (B), and 6 in the tail-suspended and muscle electrical stimulation group (C). Microgravity was simulated by tail-suspension, which is the simulated method adopted widely on the earth [6, 7]. The experiment lasted for 26 days and the muscle electrical stimulation lasted for 1 hour everyday during the experiment. The stimulation place was the right gluteus medius muscle, which makes right femur abducent. The stimulation frequency was 50Hz, the impulse time was 100µs, the stimulation intensity was 3mA, the stimulation period was 2s, and the stimulation interval was 3s. After experiment all rats were anesthetized, and the BMD of femur and tibia in all rats were measured on a DPX-IQ Bone Mineral Density Scanner (LUNAR, USA) with the following technological parameters: 76kvp and 150µA. Then the BMD of femur and tibia have been analyzed by t-test to evaluate the effects of muscle electrical stimulation on retaining bone mass. III. RESULTS As shown in TABLE 1, in the case of the average BMD of femur, the value of A group was maximal and the value of B group was minimal. In the case of the average BMD of tibia, the value of A group was also maximal, and the value of C group was a little bigger than the value of B group. To the BMD of C group, the value of right femur was maximal and the value of left tibia was minimal. In the case of the BMD of femur, between the right and left BMD in the same group, the values of t-test in the three groups were calculated: PA=0.091, PB=0.076, and PC=0.233, respectively. As the values of PA, PB and PC were more than 0.05, the following analysis was performed between the average BMD of the three groups: PAB=0.004, PBC=0.227, and PAC=0.050, respectively. As the value of PAC was equal to 0.05, the following analysis was performed between the right BMD of C group, the left BMD of C group, and the average BMD of A group: PACR=0.080 and PACL=0.041. The values of PAB and PACL were less than 0.05 among these values of t-test. In the case of the BMD of tibia, between the right and left BMD in the same group, the values of t-test in the three
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TABLE I THE BMD VALUES OF FEMUR AND TIBIA IN THE THREE GROUPS BMD˄g/cm2˅ Group Femur (X±S) Tibia(X±S) Right 0.197±0.016 0.199±0.017 A Left 0.184±0.013 0.180±0.011 Average 0.190±0.013 0.189±0.013 Right 0.163±0.011 0.158±0.008 Left 0.167±0.012 0.155±0.016 B Average 0.165±0.011 0.157±0.010 Right 0.173±0.019 0.165±0.005 Left 0.169±0.018 0.154±0.010 C Average 0.171±0.017 0.159±0.006 X is the mean value of BMD and S is the standard deviation of BMD. The “Average” BMD is obtained after averaging the “Right” and “Left” BMD in the same rat.
groups were calculated: PA=0.064, PB=0.705, and PC=0.011, respectively. As the value of PC was less than 0.05, the following analysis was performed between the right BMD of C group, the left BMD of C group, the average BMD of A group, and the average BMD of B group: PACR=0.001, PACL=0.001, PBCR=0.046, PBCL=0.675, and PAB=0.001, respectively. The values of PC, PACR, PACL, PBCR, and PAB were less than 0.05 among these values of t-test. To the BMD of C group, between the BMD of right femur, the BMD of left femur, the BMD of right tibia, and the BMD of left tibia, the values of t-test were calculated: PFRFL=0.233, PFRTR=0.177, PFRTL=0.025, PFLTR=0.313, PFLTL=0.076, and PTRTL=0.011, respectively. The values of PFRTL and PTRTL were less than 0.05 among these values of t-test. IV. DISCUSSION From the analysis results of t-test, we can evaluate the effects of muscle electrical stimulation on retaining bone mass under the condition of simulated microgravity. Bone mass loss caused by microgravity is very serious. There are extreme significance of difference between the average BMD of the free active control group and the average BMD of the tail-suspended control group in the cases of both femur (P=0.004) and tibia (P=0.001). Muscle electrical stimulation can retain bone mass to a certain extent. In the case of the BMD of femur, there is no significance of difference between the average BMD of the tail-suspended control group and the average BMD of the muscle electrical stimulation group (P=0.227). And there is a significance of difference between the left BMD of the muscle electrical stimulation group and the average BMD of the free active control group (P=0.041). But there is no significance of difference between the right BMD of the muscle electrical stimulation group and the average BMD of the free active control group (P=0.080). It has shown that the bone mass of the right femur in the muscle electrical stimulation group can be improved a little by the muscle electrical stimulation. And in the case of the BMD of tibia, there are extreme significance of difference between the average BMD of the free active control group and the right BMD of the muscle electrical stimulation group (P=0.001), and between the average BMD of the free active control
group and the left BMD of the muscle electrical stimulation group (P=0.001). And there is no significance of difference between the left BMD of the muscle electrical stimulation group and the average BMD of the tail-suspended control group (P=0.675). But there is a significance of difference between the right BMD of the muscle electrical stimulation group and the average BMD of the tail-suspended control group (P=0.046). It has shown that the bone mass of the right tibia in the muscle electrical stimulation group can be improved a little by the muscle electrical stimulation, too. The interaction between muscles is prominent. To the BMD of the muscle electrical stimulation group, there are no significance of difference between the BMD of right femur and the BMD of left femur (P=0.233), between the BMD of right femur and the BMD of right tibia (P=0.177), between the BMD of left femur and the BMD of right tibia (P=0.313), and between the BMD of left femur and the BMD of left tibia (P=0.076). But there are significance of difference between the BMD of right femur and the BMD of left tibia (P=0.025), and between the BMD of right tibia and the BMD of left tibia (P=0.011). It has shown that although the place of muscle electrical stimulation is the right gluteus medius muscle, the bone mass of left femur and right tibia have also been improved besides right femur. As a preliminary research on the effects of muscle electrical stimulation, the results of this work are influenced by many factors, such as the living conditions of rats, and the technological parameters of muscle electrical stimulation. The following research will put emphasis on optimizing the technological parameters of muscle electrical stimulation, including the place, frequency, intensity and duration. REFERENCES [1] [2] [3]
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