Design and analysis of fingernail sensors for measurement of fingertip touch fouce and finger posture

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2002.Includes bibliographical references (leaves 142-148).A new type of wearable sensor for detecting fingertip touch force and finger posture is presented. Unlike traditional electronic gloves, in which sensors are embedded along the finger and on the fingerpads, this new device does not constrict finger motion and allows the fingers to directly contact the environment without obstructing the human's natural haptic senses. The fingertip touch force and finger posture are detected by measuring changes in the coloration of the fingernail; hence, the sensor is mounted on the fingernail and does not interfere with bending or touching actions. Specifically, the fingernail is instrumented with miniature light emitting diodes (LEDs) and photodetectors in order to measure changes in the reflection intensity when the fingertip is pressed against a surface or when the finger is bent. The changes in intensity are then used to determine changes in the blood volume under the fingernail, a technique termed "reflectance photoplethysmography." By arranging the LEDs and photodetectors in a spatial array, the two-dimensional pattern of blood volume can be measured and used to predict the touch force and posture. This thesis first underscores the role of the fingernail sensor as a means of indirectly detecting fingertip touch force and finger posture by measuring the internal state of the finger. Desired functionality and principles of photoplethysmography are used to create a set of design goals and guidelines for such a sensor.(cont.) A working miniaturized prototype nail sensor is designed, built, tested, and analyzed. Based on fingertip anatomy and photographic evidence, mechanical and hemodynamic models are created in order to understand the mechanism of the blood volume change at multiple locations within the fingernail bed. These models are verified through experiment and simulation. Next, data-driven, mathematical models or filters are designed to comprehensively predict normal touching forces, shear touching forces, and finger bending based on readings from the sensor. A method to experimentally calibrate the filters is designed, implemented, and validated. Using these filters, the sensors are capable of predicting forces to within 0.5 N RMS error and posture angle to within 10 degrees RMS error. Performances of the filters are analyzed, compared, and used to suggest design guidelines for the next generation of sensors. Finally, applications to human-machine interface are discussed and tested, and potential impacts of this work on the fields of virtual reality and robotics are proposed.by Stephen A. Mascaro.Ph.D

Doctor of Philosophy

dissertationFingernail imaging is a method of sensing finger force using the color patterns on the nail and surrounding skin. These patterns form as the underlying tissue is compressed and blood pools in the surrounding vessels. Photos of the finger and surrounding skin may be correlated to the magnitude and direction of force on the fingerpad. An automated calibration routine is developed to improve the data-collection process. This includes a novel hybrid force/position controller that manages the interaction between the fingerpad and a flat surface, implemented on a Magnetic Levitation Haptic Device. The kinematic and dynamics parameters of the system are characterized in order to appropriately design a nonlinear compensator. The controller settles within 0.13 s with less than 30% overshoot. A new registration A new registration technique, based on Active Appearance Models, is presented. Since this method accounts for the variation inherent in the finger, it reduces registration and force prediction errors while removing the need to tune registration parameters or reject unregistered images. Modifications to the standard model are also investigated. The number of landmark points is reduced to 25 points with no loss of accuracy, while the use of the green channel is found to have no significant effect on either registration or force prediction accuracy. Several force prediction models are characterized, and the EigenNail Magnitude Model, a Principal Component Regression model on the gray-level intensity, is shown to fit the data most accurately. The mean force prediction error using this prediction and modeling method is 0.55 N. White LEDs and green LEDs are shown to have no statistically significant effect on registration or force prediction. Finally, two different calibration grid designs are compared and found to have no significant effect. Together, these improvements prepare the way for fingernail imaging to be used in less controlled situations. With a wider range of calibration data and a more robust registration method, a larger range of force data may be predicted. Potential applications for this technology include human-computer interaction and measuring finger interaction forces during grasping experiments

Analysis and validation of an artifact resistant design for oxygen saturation measurement using photo pletyhsmographic ring sensors

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering; and, (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.Includes bibliographical references (leaves 99-103).Recent advances in continuous noninvasive health monitoring technologies provide clinicians and researchers with a previously unrealistic opportunity for closely tracking the developments and treatments of various pathologies both within and outside of a clinical setting. At the same time, miniaturized, wireless communication technologies have greatly enhanced the transmission of sensor data while reducing the size requirements for traditional, wearable sensors. The synergism of these innovations has led to the development of the Ring Sensor, a miniaturized, telemetric, photo plethysmograph sensor for continuous health monitoring. Previous work on the Ring Sensor has led to significant power savings in regards to data acquisition and transmission. Additionally, early long-term monitoring tests have indicated that the Ring Sensor is capable of acquiring a reliable waveform nearly 30% of the time. However, the utility of the Ring Sensor has remained somewhat limited. This thesis addresses several of the remaining issues associated with the Ring Sensor. The main design consideration associated with the Ring Sensor is achieving minimal power consumption while maintaining high signal quality. To this end, significant effort has been channeled to the development of an appropriate motion artifact model, representing the complex interplay between internal hemodynamics and external influences. Additionally, an artifact resistant, power-efficient, high-speed modulation scheme has been incorporated into the design of the Ring Sensor. It has been shown that this design significantly reduces the amount of data corrupted by motion while also minimizing the power consumed by the LEDs (one of the single largest power consuming elements).(cont.) This thesis also details the refinement of both the analog signal processing circuit and the redesigning of the sensor band for a more secure device interface. In particular, the order and type of filtering utilized by the Ring Sensor have been optimized for signal quality and stability. An improved sensor unit assembly provides a secure, pressurized contact with the patient's skin while protecting the optical components and wires from the external environment, while additional sensors, incorporated into both the sensor band and the ring unit, provide temperature and light feedback for signal quality assurance. In addition to these advancements, preliminary work towards sensor calibration for oxygen saturation measurements is provided. The thesis concludes with promising results obtained from field testing work conducted in the Massachusetts General Hospital's Pulmonary Function Testing Lab.by Phillip Andrew Shaltis.S.M

BEst (Biomarker Estimation): Health Biomarker Estimation Non-invasively and Ubiquitously

This dissertation focuses on the non-invasive assessment of blood-hemoglobin levels. The primary goal of this research is to investigate a reliable, affordable, and user-friendly point-of-care solution for hemoglobin-level determination using fingertip videos captured by a smartphone. I evaluated videos obtained from five patient groups, three from the United States and two from Bangladesh, under two sets of lighting conditions. In the last group, based on human tissue optical transmission modeling data, I used near-infrared light-emitting diode sources of three wavelengths. I developed novel image processing techniques for fingertip video analysis to estimate hemoglobin levels. I studied video images creating image histogram and subdividing each image into multiple blocks. I determined the region of interest in a video and created photoplethysmogram signals. I created features from image histograms and PPG signals. I used the Partial Least Squares Regression and Support Vector Machine Regression tools to analyze input features and to build hemoglobin prediction models. Using data from the last and largest group of patients studied, I was able to develop a model with a strong linear correlation between estimated and clinically-measured hemoglobin levels. With further data and methodological refinements, the approach I have developed may be able to define a clinically accurate public health applicable tool for hemoglobin level and other blood constituent assessment

Design and Testing Novel Wearable Instrumentation for Assessing Pelvic Floor Function and Exploring Continence Mechanisms

Urinary incontinence (UI) and fecal incontinence (FI) affect 20% of North Americans, with a higher prevalence in women and the elderly. The prevention and treatment of these conditions unfortunately leaves much to be desired, despite the $88B and$49B annual U.S. costs associated with managing UI and FI, respectively. Recent research suggests that the major problem lies with the sphincters themselves, rather than other structures. More needs to be learned about how age, injury and disease affect these sphincters. The literature is reviewed in Chapter 1, knowledge gaps are identified and testable hypotheses formulated. In Chapter 2, we describe the first subject-specific, 3-D, biomechanics model of the urethra capable of contracting the three individual muscle layers along their lines of action. This was developed to better understand how the different layers contribute to urethral closure during activities of daily living. Exploratory studies of the vascular plexus suggest a role in affecting functional urethral length. While this model helps one to understand which muscles contribute to continence, it could not provide insights into the amount of urine leaked which, after all, is what bothers women the most. In Chapter 3, we describe a novel approach for quantifying urine leakage both in and out of the clinic. While one can presently obtain micturition flowmetry in the seated posture in the clinic, this precludes the possibility of any information being gathered on leakage during activities of daily living (ADL). Instead, a patient must keep a leakage diary for several days, which unfortunately is prone to recall bias and other errors. Therefore, a novel wearable personal uroflowmeter (PUF) was invented and developed to attach over the urethral meatus in women to collect urine flow rate and leakage data during ADL leakage episodes. This was connected with a waist-mounted inertial measurement unit (IMU) to provide data on the pose and ADL associated with the volume of each leakage episode. Chapter 4 describes the first-in-human testing of the PUF in women in and outside the clinic, demonstrating the feasibility of wearable uroflowmetry. Moreover, theoretical studies of labia majora coaptation suggest that the labia can inadvertently form a potential reservoir for urine leakage during a sneeze or cough. This insight will help eliminate the confusion over the relationship between the ADL causing the passage of urine through the urethra (i.e., a cough) and that which later causes urine to leak from the labial reservoir (i.e., rising from a chair). A few incidents of this phenomenon were measured for the first time while testing the PUF in women. In terms of anorectal function, Chapter 5 reports the design and development of a disposable point-of-service instrumented anorectal manometry glove (“digital manometry”, DM) for testing anal sphincter and anorectal function at an order of magnitude lower cost than the standard high resolution anorectal manometry (HR-ARM). Chapter 6 reports first-in-human testing of the DM device in patients with and without FI and chronic constipation. Comparisons of the DM and HR-ARM results show reasonable agreement. In addition, the DM also provided myoelectric information useful for identifying paradoxical contraction of the anorectal muscle in patients with dyssynergic defecation. In summary, the dissertation provides novel and inexpensive approaches for a clinician or researcher to better document and understand incontinence.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/163121/1/attari_1.pd

Life Sciences Program Tasks and Bibliography

This document includes information on all peer reviewed projects funded by the Office of Life and Microgravity Sciences and Applications, Life Sciences Division during fiscal year 1995. Additionally, this inaugural edition of the Task Book includes information for FY 1994 programs. This document will be published annually and made available to scientists in the space life sciences field both as a hard copy and as an interactive Internet web pag

Reflectance photoplethysmography for non-invasive monitoring of tissue perfusion

Monitoring blood perfusion and oxygenation changes is of vital importance and for this reason many different techniques have been developed over the decades. Photoplethysmography (PPG) is an optical technique that measures blood volume variations in vascular tissue and it is well known for its utilisation in pulse oximetry for the estimation of arterial blood oxygen saturation (SpO2). In pulse oximetry, mainly the pulsatile component of the signal (AC PPG) is used while the continuous DC component is mostly excluded. Near Infrared Spectroscopy (NIRS) is another optical technique that measures changes in the concentration of oxygenated (ΔHbO2), deoxygenated (ΔHHb), and total haemoglobin (ΔtHb) from the variations in light attenuations at different wavelengths. The main motivation of this research is to explore the capability of Photoplethysmography in assessing tissue perfusion and oxygenation similarly as NIRS. The hypothesis underlining this research is that the DC component of the PPG signal contains information on the overall absorbed light and this part of the PPG signal, acquired at least two wavelengths, may be used to obtain ΔHbO2, ΔHHb, and ΔtHb as performed in NIRS. Therefore, DC PPG attenuations may be related to haemoglobin concentrations by the modified Beer-Lambert law (MBLL). In order to investigate this, novel reflectance, custom-made PPG sensors and measurement systems, including advanced signal processing algorithms, have been developed for the acquisition and analysis of raw PPG signals (AC + DC) from different anatomical locations. Three in vivo studies on healthy volunteers were carried out in order to investigate if ΔHbO2, ΔHHb, and ΔtHb estimated from PPG could indicate changes in blood perfusion and oxygenation. The studies consisted of vascular occlusions on the forearm, negative bed tilting, and whole body cold exposure. Raw PPG signals were acquired from different locations such as the forearm, fingers, and forehead, whereas simultaneous NIRS signals were used as a reference. The results showed that ΔHbO2, ΔHHb, and ΔtHb could be effectively estimated from PPG signals. These parameters indicated the changes in blood volumes and/or oxygenation, whereas comparison with NIRS signals showed good levels of correlation and trending. These promising results showed that DC PPG signals could be used to monitor changes in blood perfusion and oxygenation, extending the range of applications of Photoplethysmography

Condicionantes fisiológicos en la práctica del alpinismo de alto nivel

[spa] Las actividades realizadas en montaña, tanto recreativas como deportivas o profesionales, han experimentado un aumento en el número de practicantes de muy variado nivel que, entre otras cosas, ha supuesto una mayor incidencia de problemas médicos y deportivos. Un conocimiento más profundo de las adaptaciones fisiológicas al esfuerzo en montaña y de la incidencia y recuperación de las patologías ambientales derivadas podrá ayudar a prevenir los efectos negativos de la práctica del alpinismo y, al mismo tiempo, a facilitar logros y optimizar sus efectos positivos. Por eso, el objetivo de esta tesis es analizar diferentes variables del deporte del alpinismo para profundizar en la identificación de los riesgos, en especial considerando los ambientes fríos y el tiempo de exposición en la montaña. Los objetivos complementarios (secundarios) son: 1) Analizar la probabilidad y condicionantes de amputación tras las congelaciones a diferentes altitudes. 2) Identificar las diferencias en la respuesta cardiovascular y los requerimientos energéticos entre la progresión por nieve virgen y por una traza establecida. 3) Determinar la utilidad de un preparado tópico a base de nifedipino para el tratamiento de las secuelas de las congelaciones y la prevención de nuevas lesiones