E. Cardiel

A Digital Goniometer based on encoders for measuring knee-joint position in an orthosis

Angular measurements of knee joint are a key factor in orthoses design, actually is very important for human gait analysis in order to obtain a deep knowledge of the musculoskeletal system performance. Video-based motion analysis systems have been used as measurement tools to quantify the angle and movement of knee joint. Though this technique is good, it requires special equipment and high computational cost. This work introduces a novel method of knee joint measurement. The design is mainly based on the contactless magnetic absolute encoder AS5040 (Austria Microsystems®, USA), and the microprocessor type PIC16F877A. The developed device has a resolution of 0.35 degrees, quite enough for an orthosis that requires knee position measurements. The reliability of the system was evaluated by making: 1) Static measurements by using a mechanical goniometer as reference, in which a correlation up to 0.999 was obtained. 2) Dynamical measurements by performing flexion-extension movements by a healthy subject and comparing the records with a commercial motion analysis system (APAS®, USA). A correlation of 0.9943 was obtained. Besides, trials were performed by three subjects under natural gait.

A pressure distribution measurement system for supporting areas of wheelchair users

Pressure ulcers are skin injuries caused by long term exposition to high pressures on support points that interrupt blood circulation reducing the transport of oxygen and nutrients to the cells. They mainly affect people with poor mobility that stay in seating position for long periods of time. In spite of the diversity of commercial prototypes of cushions, ulcers caused by pressure are still a problem for wheelchair users. This work describes the design of a measurement system of pressure distribution in sedentary position. The aim of the system is to record the pressure concentration in order to obtain specific information about the supporting areas, and with these data used as feedback, eventually to determine an efficient random stimulation sequence to provide, in the future, a system to prevent these referred injuries. The proposed system consists of a 12 air-cell division cushion. Each cell has a pressure sensor and an input for electro valves to inflate and deflate. The recording and control of the valves is carried out through a graphical interface designed in LabVIEW®. A calibration procedure for the designed cushion was made by comparing the greatest load values pressure with a commercial platform, similar results were obtained.

An alternating pressure sequence proposal for an air-cell cushion for preventing pressure ulcers

The distribution and release of pressure on ischial regions are two important parameters for evaluating the effectiveness of a cushion; especially the release of pressure over time on ischial tuberosities, which is significant for preventing pressure ulcers. The aim of this work is to evaluate the effect on interface pressure through the application of a proposed alternating pressure sequence for an air-cell cushion. Six healthy volunteers were asked to sit on the air cell cushion, in static and alternating modes, as well as on a typical foam cushion for 12 minutes. Interface pressure was monitored with a matrix sensor system. Interface pressure values on ischial tuberosities, user contact area and pressure distribution were analyzed. Results showed that IP on IT tends to increase in both foam and static cushions, while in alternating cushion IP on IT tends to decrease. User contact area was significantly larger in alternating cushion than in static or foam cushions. Moreover, there is a better pressure re-distribution with alternating cushion than with the other cushions. The goal of the alternating sequence is to redistribute pressure and stimulate the ischial regions in order to promote blood flow and prevent pressure occurring in wheelchair users.

Evaluation of suitability of a micro-processing unit of motion analysis for upper limb tracking

The aim of this study is to assess the suitability of a micro-processing unit of motion analysis (MPUMA), for monitoring, reproducing, and tracking upper limb movements. The MPUMA is based on an inertial measurement unit, a 16-bit digital signal controller and a customized algorithm. To validate the performance of the system, simultaneous recordings of the angular trajectory were performed with a video-based motion analysis system. A test of the flexo-extension of the shoulder joint during the active elevation in a complete range of 120º of the upper limb was carried out in 10 healthy volunteers. Additional tests were carried out to assess MPUMA performance during upper limb tracking. The first, a 3D motion reconstruction of three movements of the shoulder joint (flexo-extension, abduction-adduction, horizontal internal-external rotation), and the second, an upper limb tracking online during the execution of three movements of the shoulder joint followed by a continuous random movement without any restrictions by using a virtual model and a mechatronic device of the shoulder joint. Experimental results demonstrated that the MPUMA measured joint angles that are close to those from a motion-capture system with orientation RMS errors less than 3º.

Electrical stimulator for surface nerve stimulation by using modulated pulses

This work presents the design of an electrical stimulator based on modulated pulses. A reduction of the electrical impedance of the skin is pursued in order to facilitate the nerve stimulation with lower intensities of current and for reducing burning and painful effects as well. The stimulator is controlled by a PC through a graphic interface under the LabVIEW platform. Two outputs are available: a) monophasic rectangular pulses with programmable facilities in amplitude, frequency, and pulse width, which are used as the envelope; b) monophasic rectangular pulses with amplitude modulation and pulse width, amplitude and frequency of the carrier, all three adjustable.

Experimental Gastric Stimulator for Refractory Obesity Treatment

Morbid obesity and overweight have alarmingly increased their incidence around the world. They have become a disabling disease with major repercussions. A new and promising method to treat refractory cases of obesity has emerged in the last years. It uses electrical stimulation on vagus nerves to diminish gastric motility producing an early satiety sensation. In this work an experimental gastric stimulator is presented, intended to determine optimal values of intensity, and pulse width as well as better sites of stimulation and electrode-nerve attaching techniques. This device was designed considering a wide range in values to test the feasibility of the technique in vivo and in situ conditions. The device was submitted to a laboratory evaluation, as a first phase, but an implantable gastric pacemaker is pretended

Development of a system for measuring and controlling environmental parameters in an chamber for in vitro cell cultures experimentation

Cell cultures are essential in research. They need to be under appropriate conditions of temperature, humidity, and carbon dioxide to promote their growth. A system for monitoring and controlling the CO2 concentration, as well as for measuring and recording both temperature and humidity parameters inside of a conditioned chamber for experimentation with magnetic fields and recording the Transepithelial Electrical Impedance of cells, has been developed in this work. This system was designed to support the development of healthy growth of monolayer cultures and their survival. The system was based on the device K-33 BLG for CO2 concentration measurements and the sensor DHT22 for monitoring temperature and relative humidity. A graphical interface was developed for the control and monitoring of CO2, the exhibition of temperature and relative humidity values, the definition of set points parameter, and for alerting when thresholds are exceeded. The system is autonomous and can be adapted to several types of incubators. The validation was performed using three commercial incubators as a reference, and according to the performance results, this system can be used in experimental procedures.

A System for Simultaneous Finger Joints Goniometric Measurements Based on Inertial Sensors

In this work, a system to record continuously and simultaneously the flexion and extension of finger joints and to compute a range of motion of the hand joints is presented. The system is based on micro-inertial sensors and a graphical interface in LabVIEW with a mathematical algorithm for signal conditioning. Ten sensors were attached to fingers with adjustable velcro belts, eight on proximal and distal phalanges from index to little fingers, one on the proximal phalanx of the thumb and another on the hand dorsum. The evaluation protocol consisted of 3 sessions of 10 repetitions each, on both hands of 6 healthy volunteers where the angular trajectory was recorded during grasping a 7.8 cm diameter sphere. A statistical analysis was performed in order to determine the variation among the measurements. The purpose of this study was to demonstrate the suitability of this system for simultaneous measurements of range of motion during flexion and extension, considering that it can be used interchangeably in the two hands, regardless the size. The results showed that the developed system is suitable for registering objectively the range of motion of the hand.

A muscle fatigue monitor based on the surface electromyography signals and frequency analysis

People with lower-limb movement disorders often receive physical therapies for recovery. These procedures can cause muscle fatigue and pain without the patient noticing it. In this work the development of a system to monitor muscle fatigue is presented. It is based on the measurement of the median frequency shifting in the power spectrum density generated by surface electromyography recordings, as well as the Borg scale criteria related to pain, eventually caused by fatigue in healthy subjects. Electromyography signal processing was performed using non-parametric methods to determine the median frequency shifting, whereas the root mean square value in time domain, as indicators of muscle fatigue. Measurements were performed in rectus femoris and lateral gastrocnemius muscles of 16 healthy subjects when they were submitted to physical performance tests. Results showed fatigue in rectus femoris in 12% of cases when Welch method was applied, in contrast with 18% of cases of lateral gastrocnemius recordings when periodogram method was used.

Design of a platform to induce movement in the human body for equilibrium assessments

When a sudden change occurs in the condition of the environment and the body is forced to move away from equilibrium, it is said that a postural perturbation has happened [1]. Under this condition, a novel equilibrium assessment is used based on the stimulus-response technique, where a platform provides the stimulus through oscillating movements and the response is measured by an optic system that records the movements of the head. This signal is conditioned and submitted to processing under stability criteria used in control of systems. The result is an objective indicator, allowing an evaluation for absolute and relative stability of the human body.