Photoplethysmography and its application in clinical physiological measurement

http://www.kresttechnology.com/krest-academic-projects/krest-major-projects/ECE/B-Tech%20Papers/67.pdf

ECG signal denoising and baseline wander correction based on the empirical mode decomposition

Oscillating-water-column wave energy converters and air turbines: A review

McDonaldʼs Blood Flow in Arteries

Photoplethysmography (PPG) is a noninvasive optical technique for detecting microvascular blood volume changes in tissues. Its ease of use, low cost and convenience make it an attractive area of research in the biomedical and clinical communities. Nevertheless, its single spot monitoring and the need to apply a PPG sensor directly to the skin limit its practicality in situations such as perfusion mapping and healing assessments or when free movement is required. The introduction of fast digital cameras into clinical imaging monitoring and diagnosis systems, the desire to reduce the physical restrictions, and the possible new insights that might come from perfusion imaging and mapping inspired the evolution of the conventional PPG technology to imaging PPG (IPPG). IPPG is a noncontact method that can detect heart-generated pulse waves by means of peripheral blood perfusion measurements. Since its inception, IPPG has attracted significant public interest and provided opportunities to improve personal healthcare. This study presents an overview of the wide range of IPPG systems currently being introduced along with examples of their application in various physiological assessments. We believe that the widespread acceptance of IPPG is happening, and it will dramatically accelerate the promotion of this healthcare model in the near future.

/pdf/photoplethysmography-revisited-from-contact-to-noncontact-2jla840amb.pdf

Photoplethysmography Revisited: From Contact to Noncontact, From Point to Imaging

A twin unidirectional impulse turbine topology for OWC based wave energy plants

Direct resistive sensor interface to a microcontroller has several advantages but has one prominent disadvantage, namely, the measurement is affected by the resistances of: 1) wires that connect the sensor to the port pins and 2) the internal resistances of the port pins of the microcontroller. A direct sensor-to-microcontroller interface scheme that compensates the effect due not only to resistances of lead wires but also the effect of microcontroller port pin’s internal resistance and any offset present in those pins is presented in this paper. Since the resistances of lead wires are compensated, automatic temperature compensation (temperature effect of lead wires) is also obtained. Simulation study and results obtained from a prototype built and tested establish the efficacy of the proposed method. A maximum error of 0.06% was observed from the prototype developed, when it was tested under room temperature, after interfacing it with the sensor Pt100, with a lead wire resistance $R_{\mathrm {LD}} = 21~\Omega $ . The error increased to a maximum of 0.08%, when the $R_{\mathrm {LD}}$ varied from 0 to $100~\Omega $ . When the same prototype was tested under elevated room temperature of 30 °C to 100 °C, the maximum error observed was 0.18%.

Improved Single-Element Resistive Sensor-to-Microcontroller Interface

To measure temperature using a thermistor as the sensing element, linearization to compensate for the inverse exponential nature of the resistance-temperature characteristic of the thermistor is required. A linearizing dual-slope digital converter (LDSDC) that accepts a thermistor sensor as input and provides a digital output that is directly proportional to the temperature being sensed is presented here. A logarithmic amplifier at the input of the LDSDC compensates for the exponential characteristics. The conversion logic of the underlying dual-slope converter is suitably modified to implement the required inversion and offset correction and thus obtain linearization over a wide range of input temperature. The efficacy of the proposed LDSDC is established through simulation studies and its practicality demonstrated with experimental results obtained on a prototype unit built and tested. Analysis of the proffered method to identify possible sources of errors is also presented.

Linearising dual slope digital converter suitable for a thermistor

A digital converter that directly translates variations in the capacitances of a differential-type capacitive sensor to a proportional digital value is described in this paper. A conventional dual-slope, analog-to-digital converter is suitably modified to obtain direct capacitance-to-digital conversion (CDC). Analysis of the proposed technique indicates that the effects of nonidealities and variations in circuit parameters on the performance of the CDC is either in the form of a gain error and/or an offset, both of which can be easily compensated. Simulation studies and experimental results obtained from a prototype built and tested prove the efficacy of the proposed scheme.

Digital Converter for Differential Capacitive Sensors

This paper presents the design and development of a virtual instrument for the measurement of haemo-dynamic parameters namely, pulse rate and oxygen saturation in arterial blood based on the popular photoplethysmographic (PPG) principle. A clip-on sensor, housing red and infrared (IR) light emitting diodes and suitable photo detectors is developed. The sensor is interfaced to a PC utilizing the audio channel of the sound card, thus dispensing with expensive analog to digital converter hardware. Since the frequency response of the audio channel is not suitable for the PPG waveforms of red and IR, FM modulation and demodulation are employed. An empirical relationship is developed for the computation of the oxygen saturation in arterial blood using the red and IR PPG data and the well-known and well-established extinction coefficients of haemoglobin with and without oxygen. Data acquisition and processing are accomplished under LabVIEW virtual environment.

V. Jagadeesh Kumar

Papers

A twin unidirectional impulse turbine topology for OWC based wave energy plants

Improved Single-Element Resistive Sensor-to-Microcontroller Interface

Linearising dual slope digital converter suitable for a thermistor

Digital Converter for Differential Capacitive Sensors

Virtual Instrument for the Measurement of Haemo-dynamic Parameters Using Photoplethysmograph