Systems and methods for physiological signal enhancement and biometric extraction using non-invasive optical sensors

A system and method for signal processing to remove unwanted noise components including: (i) wavelength-independent motion artifacts such as tissue, bone and skin effects, and (ii) wavelength-dependent motion artifact/noise components such as venous blood pulsation and movement due to various sources including muscle pump, respiratory pump and physical perturbation. Disclosed are methods, analytics, and their uses for reliable perfusion monitoring, arterial oxygen saturation monitoring, heart rate monitoring during daily activities and in hospital settings and for extraction of physiological parameters such as respiration information, hemodynamic parameters, venous capacity, and fluid responsiveness. The system and methods disclosed are extendable to include monitoring platforms for perfusion, hypoxia, arrhythmia detection, airway obstruction detection and sleep disorders including apnea.Board of Regents, University of Texas Syste

In vivo non-invasive monitoring of optically resonant metal nanoparticles using multi-wavelength photoplethysmography

Nanotechnology has recently emerged as a powerful modality in many biomedical applications. In particular, several classes of nanoparticles have been employed as cancer therapy and imaging contrast agents. These particles can have architecture of varying complexity, depending on their specific application. These complex architectures are achieved by various chemical techniques usually performed in specific sequences to add complexity and functionality. One such class of nanoparticle, used in tumor treatment and as contrast agents in several optical imaging techniques, is the plasmon resonant metal nanoparticle. The most common metal used for these particles is gold because of its biocompatibility, lack of cellular toxicity, and simple surface chemistry. These particles have specific optical properties in the near infrared spectrum making them ideal for modern cancer therapy and optical imaging. Two examples of these particles are gold nanoshells and gold nanorods, both of which are highly absorptive and scattering at near infrared wavelengths. It is for this reason that they are often employed in photo thermal ablation of tumors using near infrared light. In this type of tumor treatment, the particles are injected intravenously and accumulate in the tumor. After accumulation, a near infrared laser is used to heat the particles and destroy the tumor. These gold nanoparticles must be modified with biocompatible stealthing compounds before they can be injected. This is because of the high efficiency of the body\u27s reticuloendotheial system, which will quickly eliminate materials foreign through cellular phagocytosis. Although techniques for quality control in manufacturing these nanoparticles are used to confirm proper surface modification, their in vivo behavior is very difficult to predict. It is for this reason that real time feedback in nanoparticle therapy is an urgent need and will greatly improve its efficacy. This dissertation reports the development of a non-invasive optical system capable of reporting the in vivo vascular concentration of these nanoparticles in near real time. The device, termed the pulse photometer, utilizes a technique similar to that used in pulse oximetry. This technique is photoplethysmography, which has many medical applications. One of these is determining the optical characteristics of pulsatile arterial blood, which are affected after the injection of these optically resonant particles. Several prototypes of this are presented in this dissertation. The culmination of this work is the prototype III pulse photometer capable of concurrent nanoparticle monitoring and oximetry. Final testing of this prototype revealed its ability to accurately determine the vascular optical density of gold nanorods compared to ex vivo spectrophotometry, a technique also verified in this dissertation, by statistical Bland-Altman analysis

Motion-Resistant Pulse Oximetry Processing Based on Time-Frequency Analysis

This paper proposes an alternative method for pulse oximetry processing based on time-frequency analysis. Instead of using the fast Fourier transform (FFT), the continuous wavelet transform (CWT) together with the median calculation was proposed for finding the frequency components of the normalized first derivative red and infrared photoplethysmographic signals. In order to estimate the arterial oxygen saturation (%SpO_2), the ratio of each red CWT modulus to each corresponding infrared CWT modulus was computed at each frequency, and then converted to the oxygen saturation by using the saturation equation obtained from calibration. All of the oxygen saturation data were plotted on a histogram. The greatest oxygen saturation with the most occurrences was considered to represent the %SpO_2. Experimental results showed that the proposed method was more resistant to the motion artifact than the conventional method.This paper proposes an alternative method for pulse oximetry processing based on time-frequency analysis.  Instead of using the fast Fourier transform (FFT), the continuous wavelet transform (CWT) together with the median calculation was proposed for finding the frequency components of the normalized first derivative red and infrared photoplethysmographic signals (PPG).  In order to estimate the arterial oxygen saturation (%SpO2), the ratio of each red CWT modulus to each corresponding infrared CWT modulus was computed at each frequency, and then converted to the oxygen saturation by using the saturation equation obtained from calibration.  All of the oxygen saturation data were plotted on a histogram.  The greatest oxygen saturation with the most occurrences was considered to represent the %SpO2. The experiments were held to evaluate the performance of the proposed processing method compared with the conventional pulse oximetry (CPO) processing.  The red and infrared PPGs were acquired from left and right index fingers simultaneously by using the PPG measurement system constructed in the laboratory.  During measurement, the left index finger was stationary, while the right index finger was performed the finger bend to induce the motion artifact (MA) in transient and periodic manners.  All detected PPGs were processed by the proposed method and the CPO processing.  The %SpO2 obtained from different processing methods and positions were compared.  Experimental results showed that the proposed method was more resistant to the MA than the conventional method

Motion-resistant pulse oximetry

The measurement of vital signs ? such as peripheral capillary oxygen saturation (SpO2) and heart rate (HR) levels ? by a pulse oximeter is studied. The pulse oximeter is a non-invasive device that measures photoplethysmography (PPG) signals and extracts vital signs from them. However, the quality of the PPG signal measured by oximetry sensors is known to deteriorate in the presence of substantial human and sensor movements contributing to the measurement noise. Methods to suppress such noise from PPG signals measured by an oximeter and to calculate the associated vital signs with high accuracy even when the wearer is under substantial motion are presented in this study. The spectral components of the PPG waveform are known to appear at a fundamental frequency that corresponds to the participant\u27s HR and at its harmonics. To match this signal, a time-varying comb filter tuned to the participant\u27s HR is employed. The filter captures the HR components and eliminates most other artifacts. A significant improvement in the accuracy of SpO2 calculated from the comb-filtered PPG signals is observed, when tested on data collected from human participants while they are at rest and while they are exercising. In addition, an architecture that integrates SpO2 levels from multiple PPG channels mounted on different parts of the wearer\u27s arm is presented. The SpO2 levels are integrated using a Kalman filter that uses past measurements and modeling of the SpO2 dynamics to attenuate the effect of the motion artifacts. Again, data collected from human participants while they are at rest and while they are exercising are used. The integrated SpO2 levels are shown to be more accurate and reliable than those calculated from individual channels. Motion-resistant algorithms typically require an additional noise reference signal to produce high quality vital signs such as HR. A framework that employs PPG sensors only ? one in the green and one in the infrared spectrum ? to compute high quality HR levels is developed. Our framework is tested on experimental data collected from human participants while at rest and while running at various speeds. Our PPG-only framework generates HR levels with high accuracy and low computational complexity as compared to leading HR calculation methods in the literature that require the availability of a noise reference signal. The methods for SpO2 and HR calculation presented in this study are desirable since (1) they yield high accuracy in estimating vital signs under substantial level of motion artifacts and (2) they are computationally efficient, (and therefore are capable to be implemented in wearable devices)

Investigation of Photodetector Optimization in Reducing Power Consumption by a Noninvasive Pulse Oximeter Sensor

Noninvasive pulse oximetry represents an area of potential interest to the army, because it could provide cost-effective, safe, fast and real-time physiological assessment in a combat injured soldier. Consequently, there is a need to develop a reliable, battery-powered, wearable pulse oximeter to acquire and process photoplethysmographic (PPG) signals using an optimized sensor configuration. A key requirement in the optimal design of a wearable wireless pulse oximeter is low power management without compromising signal quality. This research investigated the advantage gained by increasing the area of the photodetector and decreasing the light emitting diode (LED) driving currents to reduce the overall power requirement of a reflectance mode pulse oximeter sensor. In vitro and preliminary in vivo experiments were conducted to evaluate a multiple photodetector reflectance sensor setup to simulate a varying detection area. It was concluded that a reflection pulse oximeter sensor employing a large area photodetector is preferred over a similar transmission type sensor for extending the battery life of a wireless pulse oximeter intended for future telemedicine applications

Effect of respiratory-induced intensity variations on finger SpO(2) measurements in volunteers

Photoplethysmographic (PPG) signals were recorded from the fingers of 16 healthy volunteers with periods of timed and forced respiration. The aim of this pilot study was to compare estimations of arterial oxygen saturation (SpO2) recorded using a dedicated pulse oximetry system while subjects were breathing regularly with and without a mouthpiece containing a flow resistor. The experiments were designed to mimic the effects of mechanical ventilation in anesthetized patients. The effect of estimated airway pressures of ±15 cmH2O caused observable modulation in the recorded red and PPG signals. SpO2 values were calculated from the pre-recorded PPG signals. Mean SpO2 values were 95.4% with the flow resistor compared with 97.3% with no artificial resistance, with statistical significance demonstrated using a Student's t-test (P = 0.006)

Evaluation of a combined reflectance photoplethysmography and laser Doppler flowmetry surface probe

Photoplethysmographic (PPG) signals were recorded from the fingers of 16 healthy volunteers with periods of timed and forced respiration. The aim of this pilot study was to compare estimations of arterial oxygen saturation (SpO2) recorded using a dedicated pulse oximetry system while subjects were breathing regularly with and without a mouthpiece containing a flow resistor. The experiments were designed to mimic the effects of mechanical ventilation in manaesthetized patients. The effect of estimated airway pressures of ±15 cmH2O caused observable modulation in the recorded red and PPG signals. SpO2 values were calculated from the pre-recorded PPG signals. Mean SpO2 values were 95.4% with the flow resistor compared with 97.3% with no artificial resistance, with statistical significance demonstrated using a Student’s t-test (P = 0.006)