Dynamic Muscle Recorder

Transcription

1 Dynamic Muscle Recorder Team 17 By: Michael Petrowicz Farrukh Rahman James Porteus Client: Biomedical Engineering Department Dr. Enderle

2 Executive Summary The biomedical department requires a lab setup for their undergraduate juniors to measure and understand biological signals. The lab setup will require them to conduct experiments on frog gastrocnemius, use their data as inputs into a muscle optimization program and use the parameters to model the muscle themselves to gain a better understanding of what is taught in their anatomy class. This will also allow students to gain further knowledge and gain additional experience in fundamental software such as LabVIEW/simulink. Existing setups on the market cost thousands of dollars, while this project proposes the unit price per setup to extend no more than 300$. Using a 35% cost of prototype per unit, the budget for the development of the prototype is proposed at $850. The lab will consist of two experimental phases consisting of isometric and isotonic loading and electrical stimulation of the muscle. This stimulation will be done by either the National Instruments hardware already provided by the engineering department, or by using a power amplifier if sufficient current output is provided by the NI board. Force transducers as well as a physical apparatus to hold the muscle at isotonic length will be required to fulfill the experimental expectations. The data gathered will be fed into a muscle optimization program designed by Daniel Sierra, this program was initially written for neck muscles but will be optimized for the gastrocnemius. This program utilizing Matlab will calculate the parameters of the model, it will do this by using optimization. This involves minimizing the maximum tension of the muscle. These parameter values can be utilized by the students to simulate the model and gather theoretical graphs to represent the same relationships found experimentally. This type of modeling is very widely studied in industry and especially biomechanical research. Dozens of

3 methods and models exist for calculating the internal muscle tension for a variety of applications from medical rehab to athletic science. 1. Introduction 1.1 Background The undergraduate biomedical engineering department is in need of a muscle recorder setup for a class laboratory. The setup currently available is highly cost inefficient for the required laboratory as the current device costs several thousand dollars. The designed setup allow for students to explore the measuring, analyzing and muscle modeling biological signals. This will allow biomedical students to compare with what is learned in physiology and anatomy class and begin to understand the incorrect assumptions made in that class for simplicity. Electric potential is generated by skeletal muscle cells when they are neurologically activated. Electromyography is a technique implemented using a device which records this electrical activity within the muscles. When muscles generate electrical potential, they do so at a certain frequency (Hz.) and at a range of minute voltages (usually several microvolts). The frequency and magnitude of this signal has a correlation with how much internal force the muscle is producing. This information is valuable for several biomechanics applications such as medical diagnosis, or muscle rehabilitation

4 . Figure 1.1: example Electromyography (EMG) graph. 1.2 Purpose The designed setup must be simplified enough to be used by junior level undergraduates while still adequately meeting the functional requirements. Implementation will include electrically activating the muscle (simulating the brain activation signal), as well an isometric experimental procedure to present the tension to muscle length relationship and optimize the muscle length for maximum tension. Isotonic experiments will also be conducted to determine the force-velocity relationship in which the length of the muscle is held constant while the muscle is stimulated. This will allow the students to engage in measuring the biological signals as well as analyzing their significance. The data obtained from the experiments will be input into a muscle model program which will optimize the parameters. The students can use these parameters to simulate the muscle model and gain an understanding of the process involved as well as the relationships of biological signals to the mechanical attributes of skeletal muscle.

5 1.3 Previous work Products There are several products which have greater functionality and features then the device required for the undergraduate lab however the cost for these products is several times higher than the cost proposed for the designed lab setup. One type of device currently in the lab is the 305C-LR Dual Mode Lever System by Aurora Scientific. This is only the lever system for the lab, Aurora does sell the entire lab setup but at a cost that ranges several thousands of dollars. Other companies such as Medtronic, metron, neuromax have also created Devices which can detect the signal but do not have the full lab setup. These devices by themselves cost hundreds to thousands of dollars Patents General inventor based patents have been found for certain wireless EMG devices and for devices which can estimate the potential using noninvasive measures such as surface electrodes. In addition Microsoft with a collaboration of universities has filed a patent exploring using surface EMG technology as an interface device. (June 26, 2008) 2. Project Description 2.1 Objective The static and dynamic muscle recorder will be designed for use in an undergraduate BME laboratory session. It will be developed and used to test the muscle response of the frog gastrocnemius muscle. The experimental data obtained will then be used to optimize an existing

6 muscle model. The optimized muscle model will then be used to simulate the experimental results obtained previously. The muscle recorder will have the capability of performing two separate experiments. The first experiment is an isometric muscle contraction. In this setup, the length of the muscle is kept constant, the muscle is stimulated, and the force generated in the muscle is recorded. This is repeated at varying muscle lengths. To perform this experiment, an electric stimulator will be used to physically stimulate the muscle. An attached force transducer will then record the tension generated by the muscle during the isometric contraction. The results of the isometric test will be plotted to create a length-tension curve. The second experiment involves isotonic muscle contraction, in which the muscle is loaded and allowed to shorten during contraction. Experimental trials will consist of a constant loading of the muscle, stimulation of the muscle under the loading conditions, and recording of the change in length of the muscle during contraction. Subsequent trials are repeated under increased but still constant loading conditions. The stimulator is again used to stimulate the muscle in this part. In order to accurately measure the change in muscle length during the experiment, a lever system will be used. The lever arm will be attached to the gastrocnemius muscle on one end, and to the mass to be used as the load on the other end. There will be a rotation sensor attached to the lever arm which will allow for the measurement of angular displacement during the muscle contraction. When stimulated, the muscle will pull down the lever arm, creating a displacement from the initial horizontal calibration. The angle of displacement of the lever arm can then be related to the change in vertical length of the muscle through trigonometry.

7 The stimulator used will be voltage regulated and interfaced with National Instrument s LabVIEW program. The LabVIEW program will receive signals from the sensors and record the data in a text file. The lab students will be responsible for manipulating the data to determine the overall length-tension and force-velocity relationships for the muscle. The relationships and results obtained will be used in a program that will optimize parameters of a muscle model according to the results of the students specific muscle. model. Finally, a simulation of the experiment will be performed using the optimized muscle 2.2 Methods The teaching assistant (TAs) will pith a grass frog and remove each leg from the animal. One leg will be distributed to each lab group, which will dissect out the gastrocnemius muscle from the leg. This muscle will be used to perform the isometric and isotonic experiments of muscle contraction. A National Instruments interface will connect the experimental setup to a computer and the lab group will conduct and record the experiments using a custom written LabView interface. The lab group will then write a LabView protocol which will analyze the data and determine the length tension and force velocity curves for their muscle. These curves will be submitted to the TA and run through an optimization program to parameterize the muscle model proposed by Dr. Enderle for the lab groups muscle. These parameters will be returned to the lab group which will use them to simulate the isotonic experiment.

8 2.2.1 Animal Model The gastrocnemius muscle of the Northern Leopard Frog Rana pipiens will serve as the animal model for the experiment. Frogs will be purchased from Carolina Biological and scheduled to arrive one day before use in the laboratory. They will be housed in a terrarium until use and will not require feeding or care during this time. The TA will pith the animals at the start of the laboratory period and remove the legs using dissecting scissors. One leg will be distributed to each lab group. The lab group will then isolate the gastrocnemius muscle. First the skin must be peeled off the leg. This can be done by gripping the femur with one hand and using forceps to peel back the skin down the length of the leg. The thigh muscles can then be clipped off using dissecting scissors. At this point the en vivo length range of the muscle should be measured. The minimum length is measured after maximally dorsoflexing the foot and flexing the knee. The maximum length is measured after maximally plantarflexing the foot and extending the knee. The gastrocnemius can then be separated from the tibia using a probe and the Achilles tendon separated from the foot using a scalpel. A length of this tendon should be left attached to the distal end of the gastrocnemius. The tibia can then be cut close to the knee using dissecting scissors. Any remaining extraneous tissue should be removed using either dissecting scissors or a scalpel. The muscle will now be ready for testing (Fig 2.2 1).

9 Figure Until all data has been collected, the muscle preparation should be kept moist with amphibian Ringers solution. A squirt bottle of solution will be provided to each lab group for this purpose and lab groups should be careful not to wet any of the electronics Electrical Activation Activation of the muscle will be achieved by one of two possible means. In either case, the end fixture will consist of two wires which will contact opposite sides of the muscle. A voltage pulse train will be delivered to the muscle in order to achieve maximum fused tetanus contraction for each experiment. The exact voltage and frequency will need to be determined by each lab group as each muscle will respond differently. If the current output is sufficient, the voltage pulse train will be supplied directly from the National Instruments interface. If sufficient current cannot be provided by the National instruments interface, it will be used to control a power amplifier, which will supply the stimulatory voltage pulse train. The method of stimulation will be investigated and the suitable solution chosen.

10 2.2.3 Isometric Experiment The isometric experiment is designed to determine the active length tension relationship of the muscle. The muscle is stimulated to contract and held at constant length over the course of the contraction. The force time history is recorded from this experiment. The procedure is then repeated at different muscle lengths. The maximum force recorded at each length is plotted against the muscle length to construct the length tension curve (see Fig for example length tension curve). Figure 2.2.2: Example length tension curve The physical apparatus to conduct the isometric experiment will be rather simple, as there are no moving parts required. The muscle will be fixed between a load cell and a lower stage of adjustable height. The lower stage will consist of a clamp which will be used to secure the femur

11 of the muscle preparation. A small hook and Kevlar thread will be used to secure the tendon of the muscle preparation to the load cell (Fig shows the experimental apparatus). Figure A FlexiForce sensor, by Tekscan, will be used as the force transducer for the load cell. It will be sandwiched between two plates which will be squeezed together upon contraction of the muscle. The voltage output of the sensor will be connected to the National Instruments interface and recorded by the LabView program Isotonic Experiment The isotonic experiment is designed to determine the active force velocity relationship of the muscle. The muscle is stimulated to contract and the load is kept constant over the course of the contraction. The length time history is recorded from this experiment. The procedure is then

12 repeated under different loads. The maximum velocity of each contraction is calculated and plotted against the load to construct the force velocity curve (see Fig for example force velocity curve) Figure 2.2.4: Example force Velocity Graph The physical apparatus to conduct the isotonic experiment is as follows. The muscle will be fixed between a lever arm and a lower stage of adjustable height. The lower stage will consist of a clamp which will be used to secure the femur of the muscle preparation. A small hook and Kevlar thread will be used to secure the tendon of the muscle preparation to the lever arm. A mass hung on the other end of the lever will provide the constant load for the experiment. The lever will provide significant mechanical advantage to the muscle in order to reduce the effect of inertia on the experiment. The rotation time history of the lever during muscle contraction will be recorded by a rotation sensor, 1109-Rotation Sensor by Phidgets. The voltage output of the sensor will be connected to the National Instruments interface and recorded by the LabView program. (Fig shows the experimental apparatus).

13 Figure National instruments and LabView The LabView program provided to lab groups will allow them to control the electronic stimulator and acquire the force and rotation data from the isometric and isotonic experiments respectively. Lab groups must then write their own LabView or Matlab programs to process the data to determine the length tension and force velocity relationships for their muscle. The length tension and force velocity data will then be submitted to the TA for use in the optimization program.

14 2.2.6 Model Optimization The optimization program is a modification on that presented by Daniel Sierra, which will optimize the parameters of the muscle model presented by Dr. Enderle. The optimization will use the length tension and force velocity relationships determined by the lab group to estimate the model parameters (Fig shows the muscle model). After the optimization is complete the model parameters will be returned to the lab group. The optimization program will be written using the Matlab programming language by Mathworks Inc. Figure 2.2.6: Muscle model consisting of two ideal elastic elements, two ideal viscous elements, and an active state tension generator Simulation Using the optimized model parameters, the lab group will then simulate the isotonic experiment using Simulink by Mathworks Inc. to recreate the length time history of the experiment and the force velocity curve. In order to properly execute the simulation, the lab group must first analyze the model and determine the differential equations necessary to simulate the isotonic experiment. Once this has been performed the model can then be constructed in

15 Simulink and run under different load conditions to replicate multiple trials of the isotonic experiment. Multiple trials under different loads will allow the lab group to recreate the force velocity curve for their muscle. 3. Budget Specialized devices such as this are typically scratch built according to the need of the project. As there are not any other systems available that have the specific functionality as this device, there are no comparisons to be made in terms of price. There are certainly more advanced devices available that have greater functionality and that are in the price range of thousands of dollars, however this device has been specified not to exceed three hundred dollars. The device is estimated to be 35% of the prototype costs, which allows a maximum of $850 for the prototype. Table 3.1 Projected Budget Item Price Tekscan FlexiForce force sensor $65.00 (4 pack) Phidgets 1109 rotation Sensor $7.00 each Set of laboratory masses ~$20.00 Electrode stimulator ~$50.00 Power amplifier TBD Aluminum metal < $50.00

16 4. Conclusion In conclusion, the project proposed for the dynamic muscle recorder will fulfill the needs of the biomedical engineering department. They require a device which similar to the devices availible on the market however with limited functionality, but greater versatility and a price which is several times cheaper. This device will include the setup for entire lab class. It will include experiments to determine the relationships between the electrical and mechanical characteristics of skeletal muscle, and use NI and labview driven processes to conduct the experiment as well as gather the data. This data will be utilized to optimize a muscle model which the students can use to simulate the muscle characteristics and confirm with those determined experimentally. This data is important for biomechanical applications. There are a variety of methods, both accurate and inaccurate currently in use in determining the force a muscle exerts internally, This laboratory will be a good introduction for students to utilizing the skills they learn in previous classes in LabVIEW and simulink to conduct something meaningful which can be utilized in medical science for diagnostics or rehabilitiation.