Norbert Stuban

Phantom with Pulsatile Arteries to Investigate the Influence of Blood Vessel Depth on Pulse Oximeter Signal Strength

This paper describes a three-layer head phantom with artificial pulsating arteries at five different depths (1.2 mm, 3.7 mm, 6.8 mm, 9.6 mm and 11.8 mm). The structure enables formation of spatially and temporally varying tissue properties similar to those of living tissues. In our experiment, pressure pulses were generated in the arteries by an electronically controlled pump. The physical and optical parameters of the layers and the liquid in the artificial arteries were similar to those of real tissues and blood. The amplitude of the pulsating component of the light returning from the phantom tissues was measured at each artery depth mentioned above. The build-up of the in-house-developed pulse oximeter used for performing the measurements and the physical layout of the measuring head are described. The radiant flux generated by the LED on the measuring head was measured to be 1.8 mW at 910 nm. The backscattered radiant flux was measured, and found to be 0.46 nW (0.26 ppm), 0.55 nW (0.31 ppm), and 0.18 nW (0.10 ppm) for the 1.2 mm, 3.7 mm and 6.8 mm arteries, respectively. In the case of the 9.6 mm and 11.8 mm arteries, useful measurement data were not obtained owing to weak signals. We simulated the phantom with the arteries at the above-mentioned five depths and at two additional ones (2.5 mm and 5.3 mm in depth) using the Monte Carlo method. The measurement results were verified by the simulation results. We concluded that in case of 11 mm source-detector separation the arteries at a depth of about 2.5 mm generate the strongest pulse oximeter signal level in a tissue system comprising three layers of thicknesses: 1.5 mm (skin), 5.0 mm (skull), and >50 mm (brain).

Optimal filter bandwidth for pulse oximetry

Pulse oximeters contain one or more signal filtering stages between the photodiode and microcontroller. These filters are responsible for removing the noise while retaining the useful frequency components of the signal, thus improving the signal-to-noise ratio. The corner frequencies of these filters affect not only the noise level, but also the shape of the pulse signal. Narrow filter bandwidth effectively suppresses the noise; however, at the same time, it distorts the useful signal components by decreasing the harmonic content. In this paper, we investigated the influence of the filter bandwidth on the accuracy of pulse oximeters. We used a pulse oximeter tester device to produce stable, repetitive pulse waves with digitally adjustable R ratio and heart rate. We built a pulse oximeter and attached it to the tester device. The pulse oximeter digitized the current of its photodiode directly, without any analog signal conditioning. We varied the corner frequency of the low-pass filter in the pulse oximeter in the range of 0.66-15 Hz by software. For the tester device, the R ratio was set to R = 1.00, and the R ratio deviation measured by the pulse oximeter was monitored as a function of the corner frequency of the low-pass filter. The results revealed that lowering the corner frequency of the low-pass filter did not decrease the accuracy of the oxygen level measurements. The lowest possible value of the corner frequency of the low-pass filter is the fundamental frequency of the pulse signal. We concluded that the harmonics of the pulse signal do not contribute to the accuracy of pulse oximetry. The results achieved by the pulse oximeter tester were verified by human experiments, performed on five healthy subjects. The results of the human measurements confirmed that filtering out the harmonics of the pulse signal does not degrade the accuracy of pulse oximetry.

Adjustable fetal phantom for pulse oximetry

As the measuring head of a fetal pulse oximeter must be attached to the head of the fetus inside the mothers uterus during labor, testing, and developing of fetal pulse oximeters in real environment have several difficulties. A fetal phantom could enable evaluation of pulse oximeters in a simulated environment without the restrictions and difficultness of medical experiments in the labor room. Based on anatomic data we developed an adjustable fetal head phantom with three different tissue layers and artificial arteries. The phantom consisted of two arteries with an inner diameter of 0.2 and 0.4 mm. An electronically controlled pump produced pulse waves in the arteries. With the phantom we investigated the sensitivity of a custom-designed wireless pulse oximeter at different pulsation intensity and artery diameters. The results showed that the oximeter was capable of identifying 4% and 2% changes in diameter between the diastolic and systolic point in arteries of over 0.2 and 0.4 mm inner diameter, respectively. As the structure of the phantom is based on reported anatomic values, the results predict that the investigated custom-designed wireless pulse oximeter has sufficient sensitivity to detect the pulse waves and to calculate the R rate on the fetal head.

Design Considerations of Small Size Reflective Type Pulse Oximeter Heads in Special Applications

Many pulse oximeter types are available on the market but development of reflective pulse oximeters is still required by health care players. An approach to determine optimal conditions of such measurements by means of objective methods and a pilot experiment is described in this paper. The optimal distance between the light sources and the detector and the optimal force to press a reflective pulse oximeter sensor head onto the skin are characterisable by the presented method and experimental setup. The preferable values are probably between 0.5-2 g/mm2 but the distance between the light sources and the detector shifts this value and changes the length of stabile region of performance as well, however, observed phenomena indicate, that pressure value alone is not enough to normalize results and compare pulse oximetry measuring heads having significant difference in size

Utilization of exhaust gas thermal energy – theoretical investigation

Even modern internal combustion engines have no more than 40% of efficiency. The remaining 60% of the energy gained from the burning fuel is considered as waste energy. Half of the waste energy is transferred to the environment by the exhaust system. As the exhaust gas has higher temperature than the environment the heat energy of the gas could be utilized. Although this idea is currently being researched by car companies to increase the fuel economy, our purpose with the present research is not to decrease the consumption but to generate electricity from the temperature difference based on the Seebeck effect. The produced electricity can power an emission reducing unit. The theoretical investigation of exhaust gas energetic utilization is described in the paper. The Seebeck efficiency of a 50 W nominal power Peltier element was determined with a measurement series. Based on the lower heating value (LHV) of diesel oil the achievable exhaust energy was calculated. A thermo picture was taken to determine the temperature gradient around the exhaust system on a real car. Finally the necessary Peltier element area was calculated

Wireless data transmission between personal computers

The paper presents a radio frequency data transmission system between PCs or other units communicating via the RS-232 interface. The main functionality of the proposed system is to transfer data between two PCs without any cable connection. The heart of the circuit is a Telecontrolli radio frequency module. The main task to control the data transfer is done by a PIC microcontroller. Since the wireless communication is noisy, a special error recognition and correction algorithm and a protocol using them were developed. Both are implemented in the microcontroller. The error correction algorithm is Hamming coding.

Operational tests of a wireless fetal pulse oximeter

Pulse oximeters are measuring the oxygen level of the arterial blood with a non-invasive method. The paper introduces the working principles and the build-up of modern pulse oximeters. The construction steps of a new kind of diagnostic tool, the wireless fetal pulse oximeter will be described also. Eliminating the catheter from the fetal blood oxygen monitoring system gives the possibility of free movement to the mother in labor. Furthermore, the uncomfortable feeling caused by the catheter can be reduced with this wireless device. With these advantages the wireless fetal pulse oximeter is a promising diagnostic tool for the labor rooms in the future. The radio range, the operation time, and the waterproof capability of the sealing of the prototype were examined in the paper.

Reducing Power Consumption of Wireless Pulse Oximeters

Purpose – To implement the signal processing algorithms into a data evaluation unit powered by mains electricity whilst the measuring head is powered by battery is a commonly used method of power management in measurement technology. As the measuring head no longer needs to deal with data evaluation, a processing unit with lower performance parameters is sufficient, thus reducing overall energy consumption. Although adopting this principle could save energy, it is still not used in today’s wireless pulse oximeters.