Southwest Research Institute assistance to NASA in biomedical areas of the technology utilization program

The activities are reported of the NASA Biomedical Applications Team at Southwest Research Institute between 25 August, 1972 and 15 November, 1973. The program background and methodology are discussed along with the technology applications, and biomedical community impacts

Cerebrovascular Hemodynamics, Postural Stability, Gait Dynamics, and Falls in Older Adults

Injurious falls in community-living older adults are associated with standing up suggesting that cerebral hypoperfusion following a postural transition might be a contributing factor. A large population study has recently indicated that one fifth of older adults do not fully recover BP after standing from a supine posture. The purposes of this thesis were to provide a comprehensive assessment between posture-related cerebral hypoperfusion and impaired postural stability, altered gait and falls in older adults. This thesis measured arterial blood pressure regulation and cerebral tissue oxygenation (tSO2) during orthostatic stressors including 3 different transitions to standing in older adults (n=77, ages 69-100 years, average = 86.6±6.6 years) and 2 different transitions to walking in a sub-group of these older adults (n=27, ages 71-101 years, average = 86.8±5.3 years). Primary results included the finding that, like the altered blood pressure responses, 19.5% of older adults had low tSO2 on standing, and they had poorer postural stability. It was also found that a brief 10-s sitting-pause time improved tSO2 and postural stability when performing a supine-sit-stand. Prospective tracking of older adults for 6-months revealed a trend to an increased likelihood of a future fall in those who had the greatest drop in tSO2 on standing. Older adults with low tSO2 (≤60%) during walking had compromised gait dynamics (increased step-step variability). Although gait speed was not directly related to reduced tSO2, the increased mean gait cycle time and stance time associated with changes in OxHb of the older adults with low tSO2 were significantly associated with reduced gait speed. Increased vascular stiffness was associated with lower CBF and altered cerebrovascular hemodynamics while walking as well as lower gait speed. Collectively, the findings from these two investigations support a relationship between cerebral hypoperfusion induced by transitions from supine to upright posture and compromised standing and walking stability with consequences for increased fall risk

The role of physical activity, cardiorespiratory fitness and exercise on the autonomic and arterial systems of healthy adolescents

Cardiovascular diseases (CVD) are the leading cause of death worldwide and the atherosclerotic process that precedes CVD starts during childhood. Physical activity (PA), cardiorespiratory fitness (CRF) and exercise are well known as preventive strategies for CVD. One possible mechanism for such prevention is the role of PA, CRF and exercise on the arterial and autonomic systems. The aim of this thesis was to investigate using observational and experimental studies the role of PA, CRF and exercise on the autonomic and arterial systems of healthy adolescents. Chapter 4 systematically reviewed observational cross-sectional studies and provided level one evidence for a significant and positive association between resting parasympathetic function and moderate-to-vigorous PA in youth. Chapter 4 also indicated that gaps exist in the literature such as the associations between PA intensities, CRF and heart rate variability (HRV). These findings were furthered in Chapter 5 which showed that vigorous PA (VPA) and moderate PA (MPA) were positively related with HRV at rest and cardiac autonomic recovery following exercise in adolescents. In Chapter 6 a high-fat meal was used aiming to increase CVD risk in the postprandial state, and it was demonstrated that PA levels and CRF are not significantly associated with postprandial HRV and arterial stiffness in adolescents. Aiming to investigate possible associations between the vascular and autonomic system, measures of baroreflex sensitivity (BRS) were introduced. Chapter 7 showed that BRS and its autonomic and vascular components present a between-day coefficient of variation lower than 20% whilst within day coefficient of variations were lower than 34% in adolescents. In Chapter 8 acutely following high- and moderate-intensity interval exercise a decrease in blood pressure was observed concomitantly with decreases in BRS. This was mainly mediated by decreases in the autonomic modulation, and the duration of the decreases in blood pressure was higher following high-intensity interval exercise. Chapter 9 extended these findings by demonstrating that the changes in BRS following the ingestion of glucose was not altered by the high or moderate-intensity exercise performed before glucose ingestion. Chapter 10 showed that following four weeks of high-intensity exercise interval training no improvements were observed in BRS and its autonomic and vascular components at rest or acutely following exercise. Collectively, the present thesis contributes significantly to the literature by providing novel evidence in healthy adolescents on the role of PA intensities, CRF and exercise on the arterial and autonomic systems at rest, acutely following exercise and in the postprandial state. The results gathered in this thesis indicate potential of the autonomic and vascular function as targets of CVD risk reduction in youth.Coordenação de aperfeiçoamento de pessoal de nível superior - CAPES. Brazi

Investigation of vibrations at the skin surface caused by the flow disturbance in stenosed tubes

An occlusion in an artery (a stenosis) induces disturbances in the downstream flow and those disturbances produce mechanical waves that impinge on the vessel wall causing it to vibrate. These vibrations then travel through the soft tissues to the skin surface where they can be detected, thus providing a possible method for the non-invasive diagnosis of the underlying disease. Hence, in this study, the potential of measuring those disturbances was explored. Experiments were set-up to model the behaviour of carotid artery under different con-ditions. A 40:60 (by volume) glycerine-water solution was selected to simulate the vis-cosity of blood (approximately 4cP). A thin walled (250 μm - 350μm wall thickness) latex Penrose drain tube, with an external diameter of 6.35mm and a Young’s Modulus value of around 0.9MPa (for circumferential strains between 0.08 - 0.10), was used to mimic the carotid artery. Different severities (60%, 75% and 90% area reduction) of the stenoses, with a circular cross-section, were investigated. Two different types, axisym-metric and non-axisymmetric, were investigated to study the effects of asymmetry in the stenoses. The stenoses were 3D printed in an opaque VeroWhite material to mimic the occlusion. The stenosed artery was then embedded into a standardised neck phantom (filled with Parker Aquasonic 100 ultrasound gel) to mimic the soft tissues and the top of the phantom was sealed with a thin (50μm) polyurethane film (Platilon), with a stiffness value of approximately 21MPa, to simulate the skin. To detect the disturbance on the phantom surface, different equipment (including ac-celerometers, and a Laser Doppler Vibrometer [LDV]) were tested. The LDV proved to be the most reliable under all conditions and was chosen as the standard measurement method for all the phantom experiments. Having selected the appropriate materials and measurement techniques, the effects of flow rate, stenosis severity, stenosis symmetry and fluid viscosity were investigated. Both, steady and pulsatile flows were perfused through the phantom with flows ranging from 0-450ml/min for steady flow and 308-340ml/min for pulsatile flow. On modifying the viscosity of the fluid, it was seen that increasing the viscosity reduced the perturbations in the flow. This was expected due to the increased viscous forces in the flow, as the viscosity of the fluid increased. Furthermore, the experiments showed that, on increasing the flow rate, the stenosis severity, and/or introducing asymmetry in the stenosis, the post-stenotic perturbations in the flow were amplified and their zone of origin moved nearer to the stenosis. These features were confirmed by conducting bare tube experiments as well as some ultrasound scans in a modified phantom. On further investigation it was found that along with the positional dependence of these perturbations, their range of frequencies was increased with increasing flow rate, stenosis severity and/or stenosis asymmetry. In the phantom experiments the disturbances were barely detectable for an area reduc-tion of 60% and were weakly present at 75%. However, strong disturbances were seen for the highly (90%) stenosed tube. A possible cause of the unexpectedly small effect of the 75% stenosis was speculated to be the stenosis symmetry: in-vivo, atherosclerotic plaques are invariably not symmetrical. To show this, experiments were conducted with an asymmetric stenosis where higher level of disturbances were detected (even with the 75% stenosis severity), hence, emphasising the impact of stenosis symmetry. A preliminary computational simulation was also set-up to allow for future detailed modelling of the effects of changing the physical conditions on the signals arriving at the skin. The simulations (whose accuracy yet remains to be validated) showed similar effects of the increasing flow rates and the stenosis severity as the disturbances were amplified and moved nearer to the stenosis on increasing the value of either variable. Following this, an attempt was made to develop a fluid-structure interaction model to simulate the neck phantom and a sample simulation was set-up. This study developed a novel method for detecting the disturbances in the post-stenotic region, and the experimental results from this study suggest the feasibility of using LVD to infer the presence of a stenosis at an early stage before the symptoms are evident

Physical activity, physical function and arterial stiffness of people undergoing maintenance haemodialysis for stage 5 chronic kidney disease

This thesis addresses current issues regarding assessment of physical activity (PA) and physical function (PF) status of haemodialysis (HD) patients, specifically: What is the recommended wear time to provide a reliable accelerometer estimate of habitual PA and sedentary behaviour? Can similar outcomes from different accelerometers be used interchangeably? Do subjectively and objectively estimated PA outcomes agree closely enough to be pooled? Which PF assessments are potentially most ‘useful’? This thesis also explores potential risk factors of arterial stiffness, a strong predictor of mortality in this population. A PA reliability study involving 70 maintenance HD patients (55.9 ± 15.7 years) over a seven-day monitoring period indicated one dialysis day and two non-diaysis days with a minimum of eight hours wear per day would provide reliable estimates of PA and sedentary behaviour regardless of accelerometer employed, and allowed 90% sample retention. Concordance studies indicated broad agreement for similar outcomes obtained via ActivPAL and Actigraph GT3X accelerometers but they were not interchangeable. ActivPAL is recommended for monitoring steps taken and time seated, Actigraph activity count output for total/overall PA. Questionnaire and accelerometer estimated PA outcomes may not be used interchangeably or pooled. More of the shared variance of physical performance was explained by clinical, demographic and habitual PA factors than for self-reported functional status thus recommending the former. Age, blood pressure and HD vintage were determinants of arterial stiffness, however PA and cardiorespiratory fitness did not appear to be risk factors in this sample. This thesis makes clear recommendations regarding implementation of PA and PF assessment methods, and illustrates their application on sample retention, as well as characterising and potentially identifying individuals at risk of poor outcomes. Emergence of HD vintage as a risk factor for arterial stiffness underscores the need for further research into adjunctive lifestyle interventions to manage health threats in this population.sub_phyunpub2080_ethesesunpu

Sensing with Earables: A Systematic Literature Review and Taxonomy of Phenomena

Earables have emerged as a unique platform for ubiquitous computing by augmenting ear-worn devices with state-of-the-art sensing. This new platform has spurred a wealth of new research exploring what can be detected on a wearable, small form factor. As a sensing platform, the ears are less susceptible to motion artifacts and are located in close proximity to a number of important anatomical structures including the brain, blood vessels, and facial muscles which reveal a wealth of information. They can be easily reached by the hands and the ear canal itself is affected by mouth, face, and head movements. We have conducted a systematic literature review of 271 earable publications from the ACM and IEEE libraries. These were synthesized into an open-ended taxonomy of 47 different phenomena that can be sensed in, on, or around the ear. Through analysis, we identify 13 fundamental phenomena from which all other phenomena can be derived, and discuss the different sensors and sensing principles used to detect them. We comprehensively review the phenomena in four main areas of (i) physiological monitoring and health, (ii) movement and activity, (iii) interaction, and (iv) authentication and identification. This breadth highlights the potential that earables have to offer as a ubiquitous, general-purpose platform

Multidimensional embedded MEMS motion detectors for wearable mechanocardiography and 4D medical imaging

Background: Cardiovascular diseases are the number one cause of death. Of these deaths, almost 80% are due to coronary artery disease (CAD) and cerebrovascular disease. Multidimensional microelectromechanical systems (MEMS) sensors allow measuring the mechanical movement of the heart muscle offering an entirely new and innovative solution to evaluate cardiac rhythm and function. Recent advances in miniaturized motion sensors present an exciting opportunity to study novel device-driven and functional motion detection systems in the areas of both cardiac monitoring and biomedical imaging, for example, in computed tomography (CT) and positron emission tomography (PET). Methods: This Ph.D. work describes a new cardiac motion detection paradigm and measurement technology based on multimodal measuring tools — by tracking the heart’s kinetic activity using micro-sized MEMS sensors — and novel computational approaches — by deploying signal processing and machine learning techniques—for detecting cardiac pathological disorders. In particular, this study focuses on the capability of joint gyrocardiography (GCG) and seismocardiography (SCG) techniques that constitute the mechanocardiography (MCG) concept representing the mechanical characteristics of the cardiac precordial surface vibrations. Results: Experimental analyses showed that integrating multisource sensory data resulted in precise estimation of heart rate with an accuracy of 99% (healthy, n=29), detection of heart arrhythmia (n=435) with an accuracy of 95-97%, ischemic disease indication with approximately 75% accuracy (n=22), as well as significantly improved quality of four-dimensional (4D) cardiac PET images by eliminating motion related inaccuracies using MEMS dual gating approach. Tissue Doppler imaging (TDI) analysis of GCG (healthy, n=9) showed promising results for measuring the cardiac timing intervals and myocardial deformation changes. Conclusion: The findings of this study demonstrate clinical potential of MEMS motion sensors in cardiology that may facilitate in time diagnosis of cardiac abnormalities. Multidimensional MCG can effectively contribute to detecting atrial fibrillation (AFib), myocardial infarction (MI), and CAD. Additionally, MEMS motion sensing improves the reliability and quality of cardiac PET imaging.Moniulotteisten sulautettujen MEMS-liiketunnistimien käyttö sydänkardiografiassa sekä lääketieteellisessä 4D-kuvantamisessa Tausta: Sydän- ja verisuonitaudit ovat yleisin kuolinsyy. Näistä kuolemantapauksista lähes 80% johtuu sepelvaltimotaudista (CAD) ja aivoverenkierron häiriöistä. Moniulotteiset mikroelektromekaaniset järjestelmät (MEMS) mahdollistavat sydänlihaksen mekaanisen liikkeen mittaamisen, mikä puolestaan tarjoaa täysin uudenlaisen ja innovatiivisen ratkaisun sydämen rytmin ja toiminnan arvioimiseksi. Viimeaikaiset teknologiset edistysaskeleet mahdollistavat uusien pienikokoisten liiketunnistusjärjestelmien käyttämisen sydämen toiminnan tutkimuksessa sekä lääketieteellisen kuvantamisen, kuten esimerkiksi tietokonetomografian (CT) ja positroniemissiotomografian (PET), tarkkuuden parantamisessa. Menetelmät: Tämä väitöskirjatyö esittelee uuden sydämen kineettisen toiminnan mittaustekniikan, joka pohjautuu MEMS-anturien käyttöön. Uudet laskennalliset lähestymistavat, jotka perustuvat signaalinkäsittelyyn ja koneoppimiseen, mahdollistavat sydämen patologisten häiriöiden havaitsemisen MEMS-antureista saatavista signaaleista. Tässä tutkimuksessa keskitytään erityisesti mekanokardiografiaan (MCG), joihin kuuluvat gyrokardiografia (GCG) ja seismokardiografia (SCG). Näiden tekniikoiden avulla voidaan mitata kardiorespiratorisen järjestelmän mekaanisia ominaisuuksia. Tulokset: Kokeelliset analyysit osoittivat, että integroimalla usean sensorin dataa voidaan mitata syketiheyttä 99% (terveillä n=29) tarkkuudella, havaita sydämen rytmihäiriöt (n=435) 95-97%, tarkkuudella, sekä havaita iskeeminen sairaus noin 75% tarkkuudella (n=22). Lisäksi MEMS-kaksoistahdistuksen avulla voidaan parantaa sydämen 4D PET-kuvan laatua, kun liikeepätarkkuudet voidaan eliminoida paremmin. Doppler-kuvantamisessa (TDI, Tissue Doppler Imaging) GCG-analyysi (terveillä, n=9) osoitti lupaavia tuloksia sydänsykkeen ajoituksen ja intervallien sekä sydänlihasmuutosten mittaamisessa. Päätelmä: Tämän tutkimuksen tulokset osoittavat, että kardiologisilla MEMS-liikeantureilla on kliinistä potentiaalia sydämen toiminnallisten poikkeavuuksien diagnostisoinnissa. Moniuloitteinen MCG voi edistää eteisvärinän (AFib), sydäninfarktin (MI) ja CAD:n havaitsemista. Lisäksi MEMS-liiketunnistus parantaa sydämen PET-kuvantamisen luotettavuutta ja laatua

Sensing with Earables: A Systematic Literature Review and Taxonomy of Phenomena

Earables have emerged as a unique platform for ubiquitous computing by augmenting ear-worn devices with state-of-the-art sensing. This new platform has spurred a wealth of new research exploring what can be detected on a wearable, small form factor. As a sensing platform, the ears are less susceptible to motion artifacts and are located in close proximity to a number of important anatomical structures including the brain, blood vessels, and facial muscles which reveal a wealth of information. They can be easily reached by the hands and the ear canal itself is affected by mouth, face, and head movements. We have conducted a systematic literature review of 271 earable publications from the ACM and IEEE libraries. These were synthesized into an open-ended taxonomy of 47 different phenomena that can be sensed in, on, or around the ear. Through analysis, we identify 13 fundamental phenomena from which all other phenomena can be derived, and discuss the different sensors and sensing principles used to detect them. We comprehensively review the phenomena in four main areas of (i) physiological monitoring and health, (ii) movement and activity, (iii) interaction, and (iv) authentication and identification. This breadth highlights the potential that earables have to offer as a ubiquitous, general-purpose platform

A pervasive body sensor network for monitoring post-operative recovery

Over the past decade, miniaturisation and cost reduction brought about by the semiconductor industry has led to computers smaller in size than a pin head, powerful enough to carry out the processing required, and affordable enough to be disposable. Similar technological advances in wireless communication, sensor design, and energy storage have resulted in the development of wireless “Body Sensor Network (BSN) platforms comprising of tiny integrated micro sensors with onboard processing and wireless data transfer capability, offering the prospect of pervasive and continuous home health monitoring. In surgery, the reduced trauma of minimally invasive interventions combined with initiatives to reduce length of hospital stay and a socioeconomic drive to reduce hospitalisation costs, have all resulted in a trend towards earlier discharge from hospital. There is now a real need for objective, pervasive, and continuous post-operative home recovery monitoring systems. Surgical recovery is a multi-faceted and dynamic process involving biological, physiological, functional, and psychological components. Functional recovery (physical independence, activities of daily living, and mobility) is recognised as a good global indicator of a patient’s post-operative course, but has traditionally been difficult to objectively quantify. This thesis outlines the development of a pervasive wireless BSN system to objectively monitor the functional recovery of post-operative patients at home. Biomechanical markers were identified as surrogate measures for activities of daily living and mobility impairment, and an ear-worn activity recognition (e-AR) sensor containing a three-axis accelerometer and a pulse oximeter was used to collect this data. A simulated home environment was created to test a Bayesian classifier framework with multivariate Gaussians to model activity classes. A real-time activity index was used to provide information on the intensity of activity being performed. Mobility impairment was simulated with bracing systems and a multiresolution wavelet analysis and margin-based feature selection framework was used to detect impaired mobility. The e-AR sensor was tested in a home environment before its clinical use in monitoring post-operative home recovery of real patients who have undergone surgery. Such a system may eventually form part of an objective pervasive home recovery monitoring system tailored to the needs of today’s post-operative patient.Open acces

NONINVASIVE ASSESSMENT AND MODELING OF DIABETIC CARDIOVASCULAR AUTONOMIC NEUROPATHY

Noninvasive assessment of diabetic cardiovascular autonomic neuropathy (AN): Cardiac and vascular dysfunctions resulting from AN are complications of diabetes, often undiagnosed. Our objectives were to: 1) determine sympathetic and parasympathetic components of compromised blood pressure regulation in patients with polyneuropathy, and 2) rank noninvasive indexes for their sensitivity in diagnosing AN. Continuous 12-lead electrocardiography (ECG), blood pressure (BP), respiration, regional blood flow and bio-impedance were recorded from 12 able-bodied subjects (AB), 7 diabetics without (D0), 7 with possible (D1) and 8 with definite polyneuropathy (D2), during 10 minutes supine control, 30 minutes 70-degree head-up tilt and 5 minutes supine recovery. During the first 3 minutes of tilt, systolic BP decreased in D2 while increased in AB. Parasympathetic control of heart rate, baroreflex sensitivity, and baroreflex effectiveness and sympathetic control of heart rate and vasomotion were reduced in D2, compared with AB. Baroreflex effectiveness index was identified as the most sensitive index to discriminate diabetic AN. Four-dimensional multiscale modeling of ECG indexes of diabetic autonomic neuropathy: QT interval prolongation which predicts long-term mortality in diabetics with AN, is well known. The mechanism of QT interval prolongation is still unknown, but correlation of regional sympathetic denervation of the heart (revealed by cardiac imaging) with QT interval in 12-lead ECG has been proposed. The goal of this study is to 1) reproduce QT interval prolongation seen in diabetics, and 2) develop a computer model to link QT interval prolongation to regional cardiac sympathetic denervation at the cellular level. From the 12-lead ECG acquired in the study above, heart rate-corrected QT interval (QTc) was computed and a reduced ionic whole heart mathematical model was constructed. Twelve-lead ECG was produced as a forward solution from an equivalent cardiac source. Different patterns of regional denervation in cardiac images of diabetic patients guided the simulation of pathological changes. Minimum QTc interval of lateral leads tended to be longer in D2 than in AB. Prolonging action potential duration in the basal septal region in the model produced ECG and QT interval similar to that of D2 subjects, suggesting sympathetic denervation in this region in patients with definite neuropathy