The Study Of Vibratton Transmission Characteristies Of Human Spine Surface By Using High-speed Camera And Image Tracking

Background:The dynamic response of human body to vibration stimulation is evaluated usually by the driving point frequency response functions in early stage,using force platform and accelerometer to calculate biomechanical response of human.After that,the transmissibility is the main method,using accelerometer to obtain acceleration or second-order integration for amplitude and calculate the transmissibility.Most of the researches are concerned with the parameter of amplitude,while the vibration phase is less concerned.Objective:This study aims to explore the linearity and non-linearity of vibration transmission in human spine under different vibration frequencies by using high-speed camera and image tracking to obtain vibration situations of each point on human spine surface and fit vibration functions of them then analyze the parameter of amplitude and phase;Explore how the spine respond to external vibration stimuli under the condition of its physiological structure and biomechanical characteristics.Process: Six male subjects fully exposed their back and were stuck 18 “+” points equidistantly in the surface of the whole spine by using double-sided adhesive,the first and the last point were located at the end of the sacrum and the fourth cervical vertebrae respectively.Subjects were seated on the vibrate platform with upper body upright and no backrest,then exposed to three vibration frequency(level 1?4 and 7).Then we used self compiled MATLAB program to track the position coordinates of 18 “+” points on thousands of images and to fit out the vibration equation of each point.Then we calculate the relative phase between the first point and each other point,as well as the phase difference between the vibration platform and each point.Results: 1.The higher the vibration frequency,the smaller the vibration amplitude of each mark point.At level 1(3.5Hz),the trend of amplitude change of 18 points is gentle and amplitude of each point is bigger than vibration platform's amplitude,which means the vibration response of each point is bigger than the vibration excitation.At level 4(6.2Hz),the amplitude change of 18 points has large fluctuation,the amplitude change in lumbosacral junction is the largest,in thoracic vertebra the change is very smooth.The vibration response of lumber vertebra and lower 1/3 thoracic vertebra are smaller than vibration excitation,while the vibration response of upper 2/3 thoracic vertebra and cervical vertebra are bigger than vibration excitation.At level 7(9.5Hz),the amplitudes of 01~17 points are all smaller than vibration excitation.The eighteenth point's vibration response is always bigger than vibration excitation at three frequencies.2.At level 1,the trend of relative phase change between 01~17 is smooth,especially between 03~14,which correspond the whole lumber spine and the lower 1/2 thoracic spine,the vibration transmission is close to linear.At level 4(6.2Hz),the relative phase change of 18 points is non-linear,in which there are two peak values respectively on 05 and 15,and the minimum value is on 10 point.The relative phase change at level 7 is very similar to level 4,the only difference is that the first peak at level 7 is on 06 point.The 05?06 points correspond to L4?L3,where the relativephase and relative vibration delay are the biggest.The 10 point corresponds to the end of thoracic spine,where the relative phase and relative delay are the smallest.3.The phase difference between each point and vibration platform increases with increase of frequency.At level1,the phase difference change between each point and vibration excitation is smooth,especially between 06~14 the change is close to linear.At level 4 and 7,the change of phase difference between each point and vibration excitation is non-linear,and the change trends at level 4 and 7 are similar.The phase delay at level 1 is the smallest,while the phase delay at level 4 is the biggest,the level 7's in the middle,which means the vibration transmission speed at 6.2Hz is slower than that of 9.5Hz.Conclusions: In this study,the linear and nonlinear characteristics of vibration transmission of human spine surface when accepting vertical vibration on the vibration platform can be explained by using high-speed camera.First,the higher the vibration frequency,the smaller the vibration response of each mark point on spine surface.At low frequency(3.5Hz),the vibration response of each point are all bigger than vibration excitation,at middle frequency(6.2Hz),the vibration response of each part of spine is non-linear.At higher frequency(9.5Hz)except for the cervical spine,the vibration response of spine is smaller than vibration excitation.Second,the vibration transmission of spine surface is very sensitive to frequency,at 3.5Hz(lower than human natural frequency)the vibration transmission of lumber and thoracic spine is linear,while at higher frequency(6.2 and 9.5 Hz)the vibration transmission of spine surface is non-linear.This study can be further combined with ankylosing spondylitis patients.It is expected that after several years of research,it can contribute to the establishment of early diagnosis index for ankylosing spondylitis.