Marcelo Martins Werneck

New impedance spectrometer for scientific and clinical studies of the respiratory system

The simple techniques generally used to investigate the biomechanical properties associated with the respiratory process are able to identify only basic characteristics, just supplying an initial representation of the complex behavior of the respiratory system. A much more detailed description can be obtained by the forced oscillation technique (FOT). Requiring very little cooperation of the subject, this technique allows a noninvasive evaluation of the mechanical impedance of the respiratory system. Although the FOT has a great scientific and clinical potential, this is attended by technical difficulties and has yet to be put to widespread use. In this context, this work describes a new flexible, open architecture, virtual-instrument-based impedance spectrometer for the FOT. After the design details are described, the system accuracy is evaluated investigating mechanical models simulating normal and individuals with restrictive disease. This analysis revealed errors smaller than 4% in modulus and 7° in p...

Development of an evanescent-field fibre optic sensor for Escherichia coli O157:H7

An intensity-modulated fibre optic sensor was developed for Escherichia coli O157:H7. The interaction between the whole natural bacteria and the guided lightwave was carried out by means of evanescent-field coupling. A correlation between optical response and the current number of bacteria was achieved. The device sensitivity had been calibrated for initial number of bacteria (N(0)) from 10-800. The sensor sensitivity was 0.016 (+/-0.001) dB/h/N(0). The sensing mechanism starts together with the log phase leading the present sensor response to be five to ten times faster than conventional bacteriological techniques.

Effect of generator nonlinearities on the accuracy of respiratory impedance measurements by forced oscillation

Measurements of respiratory impedance by means of the forced oscillation technique (FOT) are usually made using a loudspeaker as the excitation device. Its nonlinear nature can introduce artifacts that coincide with the frequencies applied to excite the respiratory system, limiting the accuracy of the impedance estimation. In this paper, this hypothesis is evaluated in the case of both a traditional estimator and the unbiased estimator proposed byDaróczy andHantos (1982). A simulated study under apnoea conditions in the pressure range 0.5–3.0 cmH2O peak-to-peak reveals that loudspeaker nonlinearities introduce a characteristic pattern of dispersion in both the resistance and reactance curves that can be significantly decreased (p≃0.03, signtest) by reducing the nonlinearities. A simulation of spontaneous breathing shows the same pattern, and is observed in the case of traditional as well as unbiased estimators. The dispersion is quantified by the mean absolute distance between the theoretical and simulated data and decreases with the reduction of nonlinearities when impedance is estimated with a traditional estimator (from 6.63 to 4.72% in real estimates and from 6.78 to 3.47% in imaginary estimates) as well as with an unbiased estimator (real estimates from 4.84 to 1.57% and 5.61 to 2.06% in imaginary estimates). Studies with normal subjects show the same dispersion pattern, which decreases if the generator nonlinearities are reduced. These results supply substantial evidence that reducing generator nonlinearities can contribute to the production of more reliable mechanical impedance FOT measurements.

Aerobiological pathogen detection by evanescent wave fibre optic sensor

An evanescent field fibre optic sensor was employed for detecting and monitoring aerobiological pathogen contamination in hospital environment. Measurements of methicillin-resistant Staphylococcus aureus (MRSA) and Streptococcus pneumoniae colonies were detected in 6 and 13 h, respectively, faster than those obtained by means of conventional techniques. All of the bacteria growth phases were clearly time resolved by means of the optical sensor. The 0.33 cm2 sensitive surface area fibre optic transducer also exhibited reproducibility, was of easy construction and low cost, which greatly enhances its potential and usefulness.

An evanescent-coupling plastic optical fibre refractometer and absorptionmeter based on surface light scattering

To the best of our knowledge, an evanescent-coupling plastic optical fibre (POF) refractometer and absorptionmeter, based on surface light scattering, is described for the first time. The sensing elements were manufactured by machining random roughness, using side-polishing technique. Coarser polishing leads to stronger surface light scattering, allowing measurements of refraction index smaller than the fibre cladding value. The same device also works as an absorptionmeter, where refractive and absorptive mechanisms may compete with each other.

Improvements of resolution and precision of a wavelength-encoded electrical current sensor using an ultra-bright light-emitting diode transducer

A wavelength-encoded electrical current sensor for high voltage using ultra-bright green (525 nm) light-emitting diode (LED) transducer and plastic optical fibre (POF), linking to remote location, has been developed. The wavelength receiver is based on passive filtering by employing an OG530 edge filter. LEDs from three different manufactures were characterized in their optical chirp response range, aiming for a sensor resolution improvement. The sensor precision (stability) was improved against external perturbations on the POF link by using an in-line mode-scrambler. The environment temperature of the LED transducer was kept unchanged at ±2°C.

Research progress in fiber optic sensors and systems at the Federal University of Rio de Janeiro

As widely known, fiberoptics (FO) are being used in a large variety of sensor an systems particularly for their small dimensions and low cost, large bandwidth and favorable dielectric properties. These properties have allowed us to develop sensor and systems for general applications and, particularly, for biomedical engineering. The intravasculator pressure sensor was designed for small dimensions and high bandwidth. The system is based on light- intensity modulation technique and use a 2 mm-diameter elastomer membrane as the sensor element and a pigtailed laser as a light source. The optical power out put curve was linear for pressures within the range of 0 to 300 mmHg. The real time optical biosensor uses the evanescent field technique for monitoring Escherichia coli growth in culture media. The optical biosensor monitors interactions between the analytic and the evanescent field of an optical fiber passing through it. The FO based high voltage and current sensor is a measuring system designed for monitoring voltage and current in high voltage transmission lines. The linearity of the system is better than 2 percent in both ranges of 0 to 25 kV and 0 to 1000 A. The optical flowmeter uses a cross-correlation technique that analyzes two light beams crossing the flow separated by a fixed distance. The x-ray image sensor uses a scintillating FO array, one FO for each image pixel to form an image of the x-ray field. The systems described in this paper use general-purpose components including optical fibers and optoelectronic devices, which are readily available, and of low cost.

Design and evaluation of a linear servocontrolled pressure generator for studies in respiratory impedance

A very common problem in respiratory impedance measurement is the unreliability of the data in the low frequency range. The use of unbiased estimators is a good alternative to overcome this problem, provided that the generator is linear. This, however, is not the case in the great majority of the generators described so far, because the loudspeakers are non-linear systems. The generator described in this work is designed to overcome this problem by the use of a feedback loop which controls the loudspeaker cone position. The evaluation of the proposed generator has shown an effective decrease of non-linearities. In addition, an improvement in the frequency response was achieved (open loop=23 Hz: closed loop=44 Hz). The closed loop band includes the most common frequency range (2 to 32 Hz) used in the literature.

Automatic calculation of vascular indexes with a microcomputer-based directional Doppler system

It is described a Doppler system which is accessed by a microcomputer. The flow waveforms can be shown at the computer video monitor and printed by a simple matrix printer. The system also averages the now signal in order to obtain a representative cycle and then calculates four vascular index used for diagnosing vascular diseases. Thirteen normal individuals and twenty pathologic patients were examined and their resulting indexes were compared.