MIE Medical Research Ltd Digital Analyser - Myometer Instruction Manual

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Ashley Lynch
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3 Getting Started Unpack your Digital Analyser and check that the following components are present: 1 x Digital Analyser Figure 1 1 x Myometer Transducer Figure 3 1 x Mains power supply cable 1 x CAS software and license dongle (if applicable) 1 x BNC to 9 pin connector lead to connect your computer to the Digital display unit 1 x CAS instruction manual (Doc124) in addition to this manual Referring to the illustrations overleaf, assemble the instrument as follows: 1. Connect the myometer transducer to the input marked TRANSDUCER (h) at the back of the Digital Analyser. Ensure that the plug is seated home fully and rotate the outer locking ring clockwise. 2. If you intend to use the system with a computer, connect the BNC connector of the computer lead, supplied with the instrument, to the BNC connector marked COMPUTER (i). Connect the 9 pin plug to the COM port of your computer. The system can be used with any type of computer with a compatible serial interface. However the supplied software has specific hardware and operating system requirements which must be met (refer to the CAS instruction manual for more information) 3. Check that the voltage shown on the instrument is compatible with your mains supply. If in doubt, consult with your supplier. 4. Connect the mains cable to the IEC mains input socket at the back of the display unit. 5. Switch on the Digital Analyser (g). The display should become active. 6. Set the display to zero by pressing the zero button (f). Even if the display initially reads zero, it is important that the zero button is depressed as the display does not indicate negative values. To install the CAS software, please refer to the CAS manual (Doc124). Doc Page 1

000 a N lb kg hold zero b c d e f * PRESS ZERO BUTTON BEFORE EVERY TEST * Digital Analyser g Figure 1: Digital Analyser (Front) TRANSDUCER h COMPUTER Figure 2: Digital Analyser (Rear) T-xx ma Tel :

4 000 a N lb kg hold zero b c d e f * PRESS ZERO BUTTON BEFORE EVERY TEST * Digital Analyser g Figure 1: Digital Analyser (Front) TRANSDUCER h COMPUTER Figure 2: Digital Analyser (Rear) T-xx ma Tel : Made in England by medical research ltd. Fax : support@mie-uk.com I j k WARNING This apparatus must be earthed CAUTION ISOLATE MAINS POWER BEFORE REMOVING COVER PLATE RATING 230 VOLTS HERTZ m l o p n q Figure 3: Myometer Transducer a b c d e f g h i j k l m n o p q digital display of force press to display force in newtons press to display force in pounds press to display force in kilogrammes press to store and display peak force value press and hold for 1 second to set display to zero before each test mains power switch input socket for transducer (grip handle or myometer) output socket to computers com port IEC mains input socket 230V: 2 x T-32mA mains fuses (5x20mm) or for 100/110V: 2 x T-63mA mains fuses (5x20mm) serial number - should match those on the transducer class B symbol Myometer transducer connect to the transducer input socket (h) on the analyser/display unit metal links adjust strap to the required length Doc Page 2

5 Introduction The Digital Myometer from MIE Medical Research Ltd. is a unique, precision instrument specifically designed to measure accurately the strength and endurance of the major muscle groups. This allows the accurate monitoring and assessment of function throughout physiotherapy, drug treatment or surgical management. Although the device may be used on its own, much more information may be obtained by linking it to a computer. Our CAS software demonstrates how powerful a tool the Digital Analyser can be in the analysis of muscle strength. First Principles In the past, the measurement of muscle strength has been fraught with problems. Many papers have shown that the repeatability of muscle strength is poor. Unfortunately, much of the work published relied on data produced by measurements on either a dynamometer or a crude mechanical device. First we must appreciate that we cannot measure muscle strength or fatigue directly as this requires an in-depth biomechanical analysis requiring the use of tensiometers, force platforms and knowledge of the internal structure of the subject, usually obtained from radiographs of the subject. An alternative measurement to that of the true muscle strength can be obtained by measuring the moment generated about a joint by the muscle of interest. Simple mechanical devices do not have the sensitivity to be able to detect the small changes in muscle strength measurements normally seen through the progress of disease or treatment. Usually, the gradations on mechanical devices are 2.5kg intervals. There are approximately 10 Newtons to the kilogram. This means that the crude mechanical device only measures at 25 Newton intervals. Although this may be perfectly adequate for testing sports people, many patients would find it very difficult to exert more than a few Newtons. The Digital Myometer is a general purpose tensiometer that can measure the tension in a restraining belt that is attached to the subject. The tension that is generated in the restraining belt will vary depending on the placement of the belt on the subject s limb. An example to demonstrate the difference between the true muscle force and the Myometer reading is shown later in Figure 5. In the example, the subject is sitting in a chair with the Myometer attached to the lower limb so as to measure the moment about the knee joint as generated by the quadriceps muscles. Doc Page 3

6 Special Features The Digital Myometer incorporates some unique features that ensure maximum accuracy and resolution. The myometer transducer is constructed so that you can securely anchor one end to wall bars, fixation points or any other convenient anchoring point. This ensures that you measure the true strength of the subject. In hand held devices, the instrument measures the weakest point in the chain. If the subject is stronger than the operator, then it can only measure the strength of the operator. An important point to note is that muscle strength varies with joint angle. Using a fixed anchor point ensures that the joint angle remains stable. The digital display indicates the applied force either in Newton force, kilograms or pounds. There is also a hold facility that locks the highest value on the display for a short while so that you can see the maximum grip value during a test. A reset button sets the display back to zero, (see quick reference guide). An output and connecting cable is also provided so that the instrument can be connected to a computer for detailed strength and endurance analysis. Doc Page 4

7 Instructions for Use MIE Medical Research Ltd The Digital Myometer is a precision instrument. It has been carefully designed to minimise any mechanical inaccuracies. However, muscle strength and endurance can vary in an individual due to physiological and psychological factors. It is, therefore, important to try to minimise these human factors as much as possible. Some human factors may include the following: Human Factor Limb position Fatigue Circadian Rhythms Pain Motivation Intra Operator Error Inter Operator Error Reason The orientation of the joints affects the mechanical advantage of muscles, e.g. strength varies with joint angle and rotation. Muscle strength and endurance reduces after several close successive tests. However, in many cases the second test indicates greatest strength. Research has shown that there are diurnal variations in muscle strength as well as more long-term variations, particularly with women. Muscle strength and endurance are greatly influenced by the degree of pain the subject experiences during the test and the pain threshold of that individual. Subjects may not exert maximum effort for numerous psychological reasons. It is important that the tester encourages the subject to ensure optimum results. The problem of intra operator error is increased when a formal test protocol has not been developed. Variations in the test procedure are a major cause of intra operator error. A formal test protocol and simultaneous training of operators minimises this error. However, other factors such as, how each operator encourages motivation, can also influence the results. The above table highlights the fact that although the instrument itself is very accurate, there are a number of outside factors that can affect the repeatability of maximum strength and endurance measurement. Therefore, a very important first step is to develop a test protocol according to your own needs and the type of subject that you are testing. Doc Page 5

8 Simplified Biomechanics of Muscle Strength Testing Figure 4, opposite, outlines an example in which the subject is sitting in a chair with the Myometer transducer attached to the lower limb so as to measure the moment about the knee joint as generated by the quadriceps muscles. Ellis (1982) demonstrated that the tension in the patellar ligament could be between 50% and 100% of the tension of the quadriceps tendon, depending on the knee angle. Let us assume that in this case that the quadriceps tension (Q) is 2000N and that the knee angle is at 90 of flexion. This would mean that the patellar ligament tension is 50% of the quadriceps tension, i.e. 1000Newtons. If the lever arm (d) between the tibio-femoral contact point (x) and the line of action of the patellar ligament (P) is 2cm, then the moment about the knee joint due to the quadriceps muscle would be 1000N x 0.02m = 20Nm. If the Myometer is attached to the leg at point (T 1 ) which is 20cm from the tibio-femoral contact point (x), then the tension measured would be 20Nm / 0.2m = 100N. We would therefore see on the Myometer display, the value of 100N. If however, the Myometer strap was moved 10cm lower down the leg to point (T 2 ) so that it is now 30cm from the tibio-femoral contact point (x), then the tension would be 20Nm / 0.3m = 66.6N. We would therefore see on the Myometer display, the value of 67N. This example illustrates that it is not sufficient to just record the Myometer tension, but also that the distance between the Myometer strap and the joint space must also be recorded. It also illustrates that although the quadriceps muscle tension may be 2000N, the tension in the strap, as measured by the Myometer, is considerably lower. Repeatable results can only occur if the lever arm (L) and the Myometer recording (T) are recorded and multiplied to obtain the moment about the joint. This data is usually sufficient to indicate muscle force, although it is not the true quadriceps force. It is important to remember that the moment about a joint may not be due to one muscle only. In the example illustrated, antagonistic muscle action by the hamstrings or the gastrocnemius may reduce the moment about the joint. It is important to bear in mind, therefore, that no myometer can measure true muscle force, but only indicate the moment about a joint. However, functionally it is perhaps more important to know this fact rather than the actual muscle force. Doc Page 6

9 Simplified Biomechanics of Muscle Strength Testing If Quadriceps Tension = 2000N 1) Moment about knee joint center = P x d = 1000N x 0.02m = 20Nm Myometer lever arm L 1 = 20cm L 1 X Patellar ligament tension P = 1000N Patellar ligament lever arm d = 2cm 2) T T T = = = 20Nm / L 20Nm / 0.2m 100N T 1 Additional myometer lever arm L 2 = 10cm 90 o L 2 3) T = 20Nm / L + L 2 T 2 T = 20Nm / 0.3m = 66.6N T 2 Figure 4: Simplified Biomechanics of Muscle Strength Testing Doc Page 7

10 Initiating the Test WARNING: It is essential that, before each test is made, the zero button on the digital display unit is pressed for at least 2 seconds even if the display indicates zero Before starting the test, please ensure that the strap is securely fastened. Place the subject s limb into the strap so that the plate is in contact with the limb. Ask the subject to apply a small load so as to tighten the straps. Adjust one or the other straps to position the joint accordingly. Measure the distance between the centre of the strap to the joint angle and make a note of it. If you are using the CAS software, you must enter this value before the test can commence. Make sure that the strap is adjusted to the same joint angle as previous tests for that subject, or according to your protocol. The MIE Clinical Goniometer 1 is ideal for this purpose. Choose the units you would like the force to be displayed as, on the Digital Display Unit, by pressing the appropriate button on the front panel. The preferred scientific unit of force is the Newton. CAS software displays data in Newton meters (Nm) only, irrespective of the units chosen on the digital display unit If you wish to display the maximum applied force, then it is necessary to activate the hold facility by ensuring that the hold button is pressed in. (in = on, out = off) It is now necessary to set the display to zero by pressing the zero button on the digital display unit for a minimum of 2 seconds. The Digital Display Unit cannot indicate negative values and so it is necessary to press the zero button even if the display already reads zero. The instrument is now correctly set and the subject can exert against the myometer transducer. To minimise the effects of fatigue, it is best if the subject attempts to exert their maximum as quickly as possible. If the subject is being tested in conjunction with the CAS software, then at the end of the test, the computer will make a short bleep. At this point, the subject should relax as quickly as possible, preferably without leaving any residual load on the transducer, i.e. minimal or no load applied to the dynamometer. 1 For information on the MIE Clinical Goniometer please refer to our website: Doc Page 8

11 Technical Specifications Parameter Display Range Maximum Force Resolution Accuracy Supply voltage Fuse Calibration Storage/transportation conditions Transportation Operating temperature range Specification Newtons 1000 Newtons 1 N 0.1kg - 1lb > 1% FSO 230V or 100/110V - see label on Digital Display Unit For 230V: 2 x T-32mA mains fuses (5 x 20mm) For 100/110V: 2 x T63mA mains fuses (5 x 20mm) Factory set recalibrate every 12 months +5º to + 45ºC <85% humidity Use original packing materials +5º to +45º C NOTE: If you have more than one instrument, please ensure that the serial number on the transducer matches that on the Digital Analyser Display Unit, otherwise calibration cannot be guaranteed. Multi-Myometers (instruments that have Pinch/Grip handles as well as Myometer transducers) components should all bare the same serial number. Manufactured by: MIE Medical Research Ltd. 6 Wortley Moor Road, Leeds, LS12 4JF United Kingdom. Tel: +44 (0) Fax: +44 (0) support@mie-uk.com Web Site: Doc Page 9

12 Notes Classification: Class 1 with a measuring function Type B Applied Part Suitable for continuous use Servicing: This instrument has no user serviceable parts. For repairs and calibration (due annually), return to manufacturer or an official MIE distributor. Cleaning: Clean the instrument using a dry cloth only. Transducers may be wiped down using a moist alcohol swipe. Ensure that the instrument is switched off during cleaning. Do not use water or any other electrically conducting materials. Exclusions: This instrument is not suitable for use with flammable gases. Not protected against ingress of water Not suitable for use in a sterile environment. Storage: This instrument should be stored in a dry room preferably in its original packing materials between +5º and + 45ºC <85% humidity. Electromagnetic or other interference: This instrument has been built and tested to comply with EN This instrument must be earthed. Do not operate the instrument without a transducer plugged in as this may adversely change its interference characteristics. If interference occurs from an external source, remove the source before using the instrument. Any computer port connected to this instrument must comply to IEC Doc Page 10

MIE Medical Research Ltd Digital Analyser - Multi-Myometer Instruction Manual

MIE Medical Research Ltd Digital Analyser - Multi-Myometer Instruction Manual Instruction Manual Doc 134-03 Copyright 1998-2004 MIE Medical Research Ltd Instruction Manual Overview The Digital Analyser Multi-Myometer from MIE Medical Research Ltd is a dual function dynamometer.