Pressure profiling of compression bandages by a computerized instrument

Transcription

1 Indian Journal of.fibre & Textile Research Vol. 37, June 2012, pp Pressure profiling of compression bandages by a computerized instrument A Das a, B Kumar, T Mittal, M Singh & S Prajapati Department of Textile Technology, Indian Institute of Technology, New Delhi , India Received 12 December 2010; revised received and accepted 4 May 2011 In the present study, a novel computerized instrument has been developed to record the applied pressure exerted by medical bandages in real time. The working of novel computerized instrument is based on the pneumatic principle, which is used to obtain pressure profiles of internal pressure exerted by the bandages over a period of time. The basic idea of this work is to design an online measurement system using differential pressure transmitter and digital process controller that provides a very accurate method of measuring pressure applied by compression bandages. This work also aims to identify different parameters affecting applied pressure profile of these bandages. A series of commercially available bandages have been studied and the effects of variables, namely fabric parameters (mass per unit area of bandage, tensile properties and thickness of bandage), number of bandage wraps or folds and extent of initial internal pressure have been studied. Bases on the results, certain characteristics have been recommended for choosing the ideal bandages. The bandages with higher mass per unit area and higher warp-wise extensibility show the faster and higher drop in internal pressure over a period of time. The reduction in internal pressure is minimised by increasing number of bandage wraps or folds. Keywords: Bandage, Differential pressure transmitter, Digital process controller, Internal pressure, Pressure profile 1 Introduction Wound healing is a natural process, and dressings and medication enhance the process. Unlike wound management, pressure garments and bandages are mainly used for managing third degree burns that not only affect the outer and inner layers of the skin but also deeper tissues. Pressure garments are used for the treatment of hypertrophic scars (overgrowth of scar tissue). The compression bandages are also used in the treatment of venous leg ulcers. The basic principle of this treatment is application of a certain pressure on the tissues surrounding the affected area. The success of this treatment depends to a great degree on the level of pressure applied and sustenance of this pressure during the course of the treatment. A number of studies 1-9 have been reported on the compressional properties of various types of compression bandages. However, most of this work has been done on prototypes based on strain gauges. Also, pressure measurements have been made by wrapping the bandages on hard surfaces, which fails to simulate the compressional characteristics of the human skin, thereby resulting in flawed pressure profiles. Also, the use of strain gauges shows a very pertinent problem as it results in alteration of the a To whom all the correspondence should be addressed. apurba@textile.iitd.ernet.in profile over which the measurement is being made, since after mounting the gauge it generally tends to protrude from the surface of the instrument. Finally, these systems also tend to give variable results because of the frequent calibration required by these systems due to continual distortion under the applied load. Piezoelectric sensor can also be used over a hard metallic surface to make pressure measurements. However, these sensors are found to be inappropriate as the repeatability of the readings is questionable and also the surface profile has to be modified in order to obtain the internal pressure signals properly. A lot of the work, done 7, 9 on medical bandages, is based upon the Laplace equation for measuring pressure across a cylindrical thin film. The Laplace equation for calculating internal pressure is given below: P = (T N 4620) / (C W) where P is the pressure in mmhg; T, the bandage tension in kgf; C, the circumference of the limb in cm; W, bandage width in cm; and N, number of layers applied. None of the above-mentioned studies, however, seem to have profiled the real time behavior of internal pressure of the medical bandages. Since these bandages are worn for extended periods of time, the pressure profiling over the time is an important

2 DAS et al.: PRESSURE PROFILING OF COMPRESSION BANDAGES BY A COMPUTERIZED INSTRUMENT 115 piece of information that needs to be investigated in order to reap the optimal amount of benefits from compression therapy or wound healing characteristics of medical bandage. Compression bandages find application in the treatment of venous leg ulcers 2, 10. The mechanism has already been explained in detail 2, 6. Pure blood flows from the heart to the legs through arteries taking oxygen and food to the muscle, skin and other tissues. Blood then flows back to the heart carrying away waste products through veins. The valves in the veins are unidirectional which means that they allow the venous blood to flow in upward direction only. If the valves do not work properly or there is not enough pressure in the veins to push back the venous blood towards the heart, the pooling of blood in the veins takes place and this leads to higher pressure to the skin. Because of high pressure and lack of availability of oxygen and food, the skin deteriorates and eventually the ulcer occurs 1. The present study is the continuation of our earlier study 11, wherein pressure profiling of medical bandages was done using manometer and video recording system. The present study is based on a novel computerized instrument which is capable to record the internal pressure exerted by bandages in real time. The basic idea of the present work is to design an online measurement system using differential pressure transmitter and digital process controller that provides a very accurate method of measurement of internal pressure applied by bandages. The simulation of human body hardness is done by adjusting the initial pressure of the bladder before wrapping the bandage. So, irrespective of the human body shape, ageing or toughness of tissues, the instrument is able to simulate the pressure profile. This work also aims to identify different parameters affecting compression characteristics of these bandages. A series of commercially available bandages have been used and the effects of variables, namely fabric parameters (mass per unit area of bandage, tensile properties, thickness of bandage), number of bandage wraps or folds and extent of initial internal pressure are studied. The interaction effect of these parameters on pressure profile of these bandages has also been studied. 2 Materials and Methods 2.1 Materials Different commercial compression bandages with different structural parameters were used for studying the internal pressure profiling with time. Similar test procedure was followed as reported earlier 11. These tests show how the pressure exerted by the bandage changes over a period of time, indicating the useful time period of the bandage; 24 h duration was taken for these tests. Nine different bandages were used in this study and the details of these bandages are given in Table 1. The study was done by wrapping the bandage around the mannequin leg, containing the air bladders filled with particular pressures, and then recording the pressure drop over specific time period by real time measurement at one second interval. This data was later compiled to give the pressure profiles of the bandages. 2.2 Methods Design and Development of Instrument The principle employed relates to the pressure changes in the fluid on application of an external pressure. The already commercialized instrument (KIKUHIME) works in almost similar principle 12. An air bladder was made and wrapped around the wooden mannequin leg, which is then inflated with air at a particular pressure (P 1 ) to simulate the human Bandage Mass per unit area g/m 2 Table 1 Details of the bandages used for the study Thickness mm Breaking load kg Breaking extension mm Initial modulus kg/mm 2 Warp Weft Warp Weft Warp Weft A B C D E F G H I

3 116 INDIAN J. FIBRE TEXT. RES., JUNE 2012 body hardness, and then the bandage was wrapped over the mannequin leg containing the bladders. Figure 1 shows the schematic diagram and the photograph of the instrument. This wrapping exerted some pressure (P) on the bladder, which was duly observed by the change in the pressure of the air in the bladder and the total pressure (P 2 ) was measured. Then by deducting the initial bladder pressure (P 1 ) from the final pressure reading (P 2 ), the pressure exerted by the bandage can be obtained. The advantage of this design is the compressibility (softness or resilience) imparted to mannequin surface due to the presence of the air bladders, giving a model simulating the human body. Two bladders were made (one for the ankle and one for below the knee) to simulate different body curvatures. The bladder pressure was measured using a differential pressure transmitter which has been connected to the computer via a digital process controller and a data acquisition card for retrieving data from the transmitter and storing the data online. Graphs for comparing the pressure profiles of different bandages can also be obtained subsequently. The technical details of the components used in the instrument are given below Differential Pressure Transmitter The Series-211 differential pressure transmitter can accurately measure positive, negative, or differential pressure and send the corresponding 4-20 ma output signal. It is not position sensitive and can be mounted in any orientation without compromising accuracy. It also features a power LED, so one always know when the transmitter is operating. The compact, lightweight design makes installation simple and easy. Two push on pressure connections are located on the front of the unit, labelled High and Low. For differential pressure measurement, the higher pressure should be connected to the High pressure port. For positive pressure, the Low pressure port should be left vented to atmospheric pressure. Periodically, it is necessary to recalibrate the gauge to maintain the accuracy. For zero gauge, the pressure connection needs to be removed from both pressure ports and to adjust the zero potentiometer until the output is 4 ma. To span the gauge, the full scale pressure to be applied to High pressure port and to adjust the span potentiometer until the output is 20 ma. The salient features of the pressure transmitter are compact design, LED power indication, 2-wire design, 4-20 ma output, ± 0.25% accuracy level, 0-90 mm Hg pressure range, -25 to 70 C operating temperature ranges, 2-wire output signal, and VDC power supply Digital Process Controller Masibus' Model 5006 is a simple, tough, reliable, cost effective yet a high performance indicating On/Off controller with single or dual programmable relay output. Relays can be configured for either alarm or control purpose. Model 5006 has one 4 digit display for process variable and optionally provides transmitter power supply eliminating the need for an additional power supply to excite field transmitters. Serial communication option makes it a smart controller that can communicate with PC for either remote configuration or data acquisition application. Fig. 1 (a) Schematic diagram of instrument, and (b) Photograph of experimental setup Analog- to-digital Card The digital process controller provides the pressure exerted by the bandage in analog form. Computers handle data in the digital form and thus require analog-to-digital convertor to convert analog signals into the digital form before it can be read. The VPL-FAD-12 card is used in the present instrument

4 DAS et al.: PRESSURE PROFILING OF COMPRESSION BANDAGES BY A COMPUTERIZED INSTRUMENT 117 which is one among the family of real time interface I/O boards that are compatible with personal computers. These boards are used to provide a direct interface between the computer and the analog world for a variety of data acquisition, analog outputs, digital I/O, and counter-timer pulse I/O application. The VPL-FAD-12 is a multifunction data acquisition board that has capabilities for various modes of analog input/output operation. 3 Results and Discussion The bandages were used to determine the impact of various parameters on the internal pressure profile of bandages. The pressure profiling was done for 24 h continuously after the wrapping of bandages. 3.1 Effect of Mass per Unit Area of Bandage The bandages B and H were chosen for studying the effect of mass per unit area of bandages on internal pressure profile. In bandages B and H, the other parameters like bandage thickness, breaking load and initial modulus are almost similar. The same number of wraps (i.e. 10 in the present case), and the initial total pressure of 60 mmhg were kept for both the bandages. The air bladder pressure before wrapping the bandage was kept at 40 mmhg; therefore the effective initial internal pressure exerted by the bandage was 20 mmhg. It can be observed from Fig. 2 that in the bandage with higher mass per unit area (bandage H), the internal pressure applied by the bandages decreases at a higher rate than in bandage of lower mass per unit area (bandage B). This may be partially due to the lower extensibility and relatively higher initial modulus of the bandage B than bandage H. Also, the presence of higher crimp and due to other structural parameters, the bandage H shows rapid stress relaxation. These result in higher drop in internal pressure in bandage H. 3.2 Effect of Bandage Extensibility To study the effect of bandage extensibility the bandages C and H have been selected. These two bandages have same mass per unit area and different extensibilities in both warp and weft directions. In warp direction the extensibility on bandage H is higher than that in bandage C, whereas in weft direction the trend is just opposite, i.e. bandage C has higher extensibility than bandage H. The initial modulus in warp direction is also comparable, but weft-wise the initial modulus of bandage C is higher than that of bandage H. The numbers of wraps and the total initial pressure have also been kept same for both the bandages (60 mmhg); therefore, the effective initial internal pressure exerted by the bandage remains 20 mmhg. Figure 3 shows the pressure profiles of bandages C and H with time. It can be observed that the bandages with higher warp-wise extensibility (bandage H) show the faster and higher drop in internal pressure applied by the bandages. Higher weft-wise initial modulus in bandage C may also be partially responsible for the proper maintenance of internal pressure with time. 3.3 Effect of Number of Wraps or Folds It has been reported 8 that as per the Laplace equation the internal pressure exerted by the bandages on the human limbs is directly proportional to the number of wraps of bandages and tension applied during the bandage wrapping. Effects of three different numbers of wraps or folds (6, 10 and 13) were studied. The total pressure exerted at the beginning of the experiments is maintained at constant level (60 mmhg), so that the effective initial internal pressure exerted by the bandage remains 20 mmhg for all the wraps by adjusting the tension during wrapping. Two different bandages (G and I) were selected randomly to study the effect of number Fig. 2 Effect of bandage mass per unit area on pressure profile Fig. 3 Effect of bandage extensibility on pressure profile

5 118 INDIAN J. FIBRE TEXT. RES., JUNE 2012 Fig. 4 Effect of number of wraps on pressure profile for (a) Bandage I, and (b) Bandage G of wraps on the internal pressure profile with time. Figure 4 show the internal pressure profiles of bandages G and I. It is evident that in bandages with higher number of wraps or folds, the internal pressure with lower number of folds decreases at higher rate than in the bandage with higher number of folds, i.e. with the increase in the number of folds the rate of drop in internal pressure reduces. This may be due to the reinforcement or support provided by the upper next successive layers to the bottom layers not allowing them to relax their stresses properly, so there is less and slower relaxation of the wrapped bandage. This helps in sustaining the pressure for a long period. Bandages G and I show similar trend with number of wraps. 3.4 Effect of Initial Internal Pressure on Pressure Profile During normal compression bandaging, with a certain bandage, it may so happen that the initial pressure is changed due to changes in tension applied during bandage wrapping. To study the effect of initial pressure applied by the bandage, two bandages (G and I) were selected randomly. The total initial pressure of the bandages was varied to 50, 60 and 70mmHg by changing the tension during wrapping. For bandages G and I the air bladder pressure values Fig. 5 Effect of initial pressure on pressure profile for (a) Bandage G, and (b) Bandage I before wrapping the bandages were kept at 40 mmhg and 20 mmhg respectively. Therefore, the effective initial internal pressures exerted by the bandage G were 10, 20 and 30 mmhg, while those for bandage I were 30, 40 and 50 mmhg respectively. All other parameters, like type of bandage and number of wraps were kept the same. The number of wraps was kept 10 during this study. Figure 5 show the internal pressure profiles with different levels of initial internal pressure for bandages G and I. It can be observed that the internal pressure profile with time is different for different bandages and also it depends greatly on the initial internal pressure applied by the bandage. The general trend is that the bandage with the higher initial internal pressure shows higher rate of drop of internal pressure with time. This is mainly due to the fact that the higher initial pressure means that the bandage is also at higher stress condition. This finally leads to higher stress relaxation with time, which, in turn, results in drop in internal pressure. 4 Conclusion 4.1 The work involved the design and development of a computerised instrument which measures the

6 DAS et al.: PRESSURE PROFILING OF COMPRESSION BANDAGES BY A COMPUTERIZED INSTRUMENT 119 internal pressure exerted by the bandage. The instrument is able to measure and record the internal pressure applied by compression bandages in real time. 4.2 In the bandage with higher mass per unit area the internal pressure applied by the bandage decreases at a higher rate than in the bandage with lowers mass per unit area. 4.3 The bandages with higher warp-wise extensibility show the faster and higher drop in internal pressure applied by the bandages. Higher weft-wise initial modulus in bandage C may also be partially responsible for the proper maintenance of internal pressure with time. 4.4 In bandages with higher number of wraps or folds, the internal pressure with lower number of folds decreases at higher rate than in the bandage with higher number of folds, i.e. with the increase in the number of folds the rate of drop in internal pressure reduces. 4.5 The internal pressure profile with time is different for different bandages and also it depends greatly on the initial internal pressure applied by the bandage. The higher initial internal pressure shows higher rate of drop of internal pressure with time. References 1 Anand S C & Rajendran S, Bandaging and Pressure Garments: An Overview (BCH Training Workshop, New Delhi, India), Anand S C & Rajendran S, Textile Materials and Products for Healthcare and Medical Applications (BCH Training Workshop, New Delhi, India), Maklewska E, Nawrocki A, Kowalski K & Tarnowski W, New tool for estimating the pressure under burn garment, paper presented at the Fourth International Conference and Exhibition on Healthcare and Medical Textiles, Bolton, UK, July Rajendran S & Anand S C, Design and development of threedimensional structures for single-layer compression therapy, paper presented at the Fourth International Conference and Exhibition on Healthcare and Medical Textiles, Bolton, UK, July Rithalia S & Leyden M, Intermittent pneumatic compression and bandaging: Is external pressure applied over bandage additive? paper presented at the Fourth International Conference and Exhibition on Healthcare and Medical Textiles, Bolton, UK, July Thomas S, A Structured approach to the selection of dressings, World Wide Wounds; com/1997/july/thomas-guide/dress-select.html (accessed on July 1997). 7 Thomas S, EMWA J, 1 (2003) Thomas S & Fram P, An evaluation of a new type of compression bandaging system, World Wide Wounds; New-Compression-Bandage.html (accessed on Sept 2003). 9 Sikka M, Ghosh S & Mukhopadhayay A, A study on the pressure profile of compression bandage and compression garment for the treatment of venous leg ulcers, paper presented at the Fourth International Conference and Exhibition on Healthcare and Medical Textiles, Bolton, UK, July Partsch H, A Position Document (European Wound Management Association, Medical Education Partnership Ltd, London), 2003, Das A, Alagirusamy R, Goel D & Garg P, J Text Inst, 101(6) (2010) Mosti G & Partsch H, Int Angiol, 29(5) (2010) 426.