Advances in Biomedical Devices_A comprehensive Exploration of Cardiovascular and Ophthalmic Applications

This review article discusses current technological advances in biomedical devices,emphasizing cardiovascular and ophthalmic application diagnostic,monitoring, and prosthetic instruments and systems. The scope encompasses various aspects, including implantable retinal prosthetic devices, portable device for carotid stiffness measurement, automatic identification algorithms for arteries, cuffless evaluation of carotid pulse pressure, wearable neural recording systems, and arterial compliance probes. Additionally, the paper explores advancements in pulse wave velocity measurement, real time heart rate estimation from wrist type signals, and the clinical significance of non invasive pulse wave velocity measurement in assessing arterial stiffness. The synthesis of these studies provides insights into the evolving landscape of biomedical devices, their validation, reproducibility, and potential clinical implications, emphasizing their role in enhancing diagnostics and therapeutic interventions in cardiovascular and ophthalmic domains.Comment:

Development and Evaluation of an Impedance Cardiographic System to Measure Cardiac Output and Other Cardiac Parameters, 1 July 1968 - 30 June 1969

Impedance cardiographic system to measure cardiac output and cardiovascular function

Sources of inaccuracy in photoplethysmography for continuous cardiovascular monitoring

Photoplethysmography (PPG) is a low-cost, noninvasive optical technique that uses change in light transmission with changes in blood volume within tissue to provide information for cardiovascular health and fitness. As remote health and wearable medical devices become more prevalent, PPG devices are being developed as part of wearable systems to monitor parameters such as heart rate (HR) that do not require complex analysis of the PPG waveform. However, complex analyses of the PPG waveform yield valuable clinical information, such as: blood pressure, respiratory information, sympathetic nervous system activity, and heart rate variability. Systems aiming to derive such complex parameters do not always account for realistic sources of noise, as testing is performed within controlled parameter spaces. A wearable monitoring tool to be used beyond fitness and heart rate must account for noise sources originating from individual patient variations (e.g., skin tone, obesity, age, and gender), physiology (e.g., respiration, venous pulsation, body site of measurement, and body temperature), and external perturbations of the device itself (e.g., motion artifact, ambient light, and applied pressure to the skin). Here, we present a comprehensive review of the literature that aims to summarize these noise sources for future PPG device development for use in health monitoring

NONINVASIVE NEAR-INFRARED DIFFUSE OPTICAL MONITORING OF CEREBRAL HEMODYNAMICS AND AUTOREGULATION

Many cerebral diseases are associated with abnormal cerebral hemodynamics and impaired cerebral autoregulation (CA). CA is a mechanism to maintain cerebral blood flow (CBF) stable when mean arterial pressure (MAP) fluctuates. Evaluating these abnormalities requires direct measurements of cerebral hemodynamics and MAP. Several near-infrared diffuse optical instruments have been developed in our laboratory for hemodynamic measurements including near-infrared spectroscopy (NIRS), diffuse correlation spectroscopy (DCS), hybrid NIRS/DCS, and dual-wavelength DCS flow-oximeter. We utilized these noninvasive technologies to quantify CBF and cerebral oxygenation in different populations under different physiological conditions/manipulations. A commercial finger plethysmograph was used to continuously monitor MAP. For investigating the impact of obstructive sleep apnea (OSA) on cerebral hemodynamics and CA, a portable DCS device was used to monitor relative changes of CBF (rCBF) during bilateral thigh cuff occlusion. Compared to healthy controls, smaller reductions in rCBF and MAP following cuff deflation were observed in patients with OSA, which might result from the impaired vasodilation. However, dynamic CAs quantified in time-domain (defined by rCBF drop/MAP drop) were not significantly different between the two groups. We also evaluated dynamic CA in frequency-domain, i.e., to quantify the phase shifts of low frequency oscillations (LFOs) at 0.1 Hz between cerebral hemodynamics and MAP under 3 different physiological conditions (i.e., supine resting, head-up tilt (HUT), paced breathing). To capture dynamic LFOs, a hybrid NIRS/DCS device was upgraded to achieve faster sampling rate and better signal-to-noise. We determined the best hemodynamic parameters (i.e., CBF, oxygenated and total hemoglobin concentrations) among the measured variables and optimal physiological condition (HUT) for detecting LFOs in healthy subjects. Finally, a novel dual-wavelength DCS flow-oximeter was developed to monitor cerebral hemodynamics during HUT-induced vasovagal presyncope (VVS) in healthy subjects. rCBF was found to have the best sensitivity for the assessment of VVS among the measured variables and was likely the final trigger of VVS. A threshold of ~50% rCBF decline was observed which can completely separate subjects with or without presyncope, suggesting its potential role for predicting VVS. With further development and applications, NIRS/DCS techniques are expected to have significant impacts on the evaluation of cerebral hemodynamics and autoregulation

Index to NASA Tech Briefs, 1974

The following information was given for 1974: (1) abstracts of reports dealing with new technology derived from the research and development activities of NASA or the U.S. Atomic Energy Commission, arranged by subjects: electronics/electrical, electronics/electrical systems, physical sciences, materials/chemistry, life sciences, mechanics, machines, equipment and tools, fabrication technology, and computer programs, (2) indexes for the above documents: subject, personal author, originating center

All-condition pulse detection using a magnetic sensor

A plethora of wearable devices have been developed or commercialized for continuous non-invasive monitoring of physiological signals that are crucial for preventive care and management of chronic conditions. However, most of these devices are either sensitive to skin conditions or its interface with the skin due to the requirement that the external stimuli such as light or electrical excitation must penetrate the skin to detect the pulse. This often results in large motion artefacts and unsuitability for certain skin conditions. Here, we demonstrate a simple fingertip-type device which can detect clear pulse signals under all conditions, including fingers covered by opaque substances such as a plaster or nail polish, or fingers immersed in liquid. The device has a very simple structure, consisting of only a pair of magnets and a magnetic sensor. We show through both experiments and simulations that the detected pulsation signals correspond directly to the magnet vibrations caused by blood circulation, and therefore, in addition to heartrate detection, the proposed device can also be potentially used for blood pressure measurement

STABILIZATION OF EXTENDED DIFFUSE OPTICAL SPECTROSCOPY MEASUREMENTS ON IN VIVO HUMAN SKELETAL MUSCLE DURING DYNAMIC EXERCISE

This research investigates various applications of diffuse correlation spectroscopy (DCS) on in-vivo human muscle tissue, both at rest and during dynamic exercise. Previously suspected muscle tissue relative blood flow (rBF) baseline shift during extended measurement with DCS and DCS-Near infrared spectroscopy (NIRS) hybrid optical systems are verified, quantified, and resolved by redesign of optical probe and alteration in optical probe attachment methodology during 40 minute supine bed rest baseline measurements. We then translate previously developed occlusion techniques, whereby rBF and relative oxygen consumption rV̇O2 are calibrated to initial resting absolute values by use of a venous occlusion (VO) and arterial occlusion (AO) protocol, respectively, to the lower leg (gastrocnemius) and these blood flows are cross validated at rest by strain gauge venous plethysmography (SGVP). Methods used to continuously observe 0.5Hz, 30% maximum voluntary isometric contraction (MVIC) plantar flexion exercise via dynamometer are adapted for our hybrid DCS-Imagent diffuse optical flow-oximeter in the medial gastrocnemius. We obtain healthy control muscle tissue hemodynamic profiles for key parameters BF, V̇O2, oxygen saturation (StO2), deoxyhemoglobin, oxyhemoglobin, and total hemoglobin concentrations ([Hb], [HbO2], and THC respectively), as well as systemic mean arterial pressure (MAP) and pulse rate (PR), at rest, during VO/AO, during dynamic exercise and during 15 minute recovery periods. Next, we began investigation of muscle tissue hemodynamic disease states by performing a feasibility pilot study using limited numbers of controls and peripheral arterial disease (PAD) patients using the translated methods/techniques to determine the ability of our technology to assess differences in these populations

The non-invasive assessment of the ischaemic limb, with particular reference to thermography.

Skin temperature (Tsk) has long been used in assessing limb circulation, and in recent years thermography has been used as an accurate way of measuring Tsk. However, apart from the general proposition that Tsk must be related to that of the blood, the precise relationship between the blood supply to a limb and its Tsk remains poorly understood. Without this knowledge full use cannot be made of thermography in the assessment of the limb with peripheral vascular disease. The purpose of these studies was to provide a scientific basis for the use of thermography on limbs. Previous work had indicated that Tsk was related to skin blood flow in the hand and foot, but not in the forearm or calf. This work has been confirmed and extended by studies on normal subjects at different ambient temperatures, and on subjects with a peripheral A-V fistula. I have shown that Tsk over the forearm and calf is related to the core temperature of the limb, i.e. to the arterial inflow. An attempt was then made to see if these findings could be used to interpret the abnormal thermograms found in a group of patients with intermittent claudication, and in a group with more severe peripheral vascular disease. In claudicants the regression line relating mean calf Tsk to total blood flow was parallel to, but higher than that in normal subjects, i.e. for the same blood flow, claudicants' Tsk was higher than in normal subjects. The reasons for this difference are not apparent. Thermograms in patients with more severe limb ischaemia were often difficult to interpret because of the confusion introduced by other pathologies. Thermography is a useful adjunct in the assessment of the ischaemic limb, but is unlikely to replace more conventional methods of investigation

Clinical investigation of plethysmographic variability index: A derivative index of pulse oximetry in anesthetized dogs

Plethysmographic Variability Index (PVI) is a derivative index of pulse oximetry that allows evaluating an individual\u27s intravascular volume status. Perfusion Index (PI) represents the strength of pulse signal at the anatomic site of measurement from which PVI is calculated using changes in PI over respiratory cycles. Plethysmographic Variability Index has been used to detect hypovolemia and predict fluid responsiveness in mechanically ventilated human patients however, fewer studies are available in spontaneously breathing patients. The use of PVI has not been explored extensively in dogs so far. The goals of this study were to establish a common range for PVI and assess relationship of the PVI, PI and various clinical variables in the anesthetized spontaneously breathing dogs. Values of PVI and PI derived from Masimo pulse oximetry were obtained at 5, 10, 15 and 20 minutes after anesthetic induction but before surgical stimulation together with cardiorespiratory variables that included heart rate, blood pressures (systolic, mean and diastolic blood pressures), respiratory rate and hemoglobin saturation of oxygen (SpO2) in 73 dogs with ASA 1-3 status admitted to the Purdue Teaching Hospital.^ Other clinical variables like body temperature, anesthetic protocol used, pre-induction packed cell volume (PCV) and total protein (TP) values, recumbency positions (sternal, lateral or dorsal recumbency) and rate of crystalloid fluids administration (5 vs 10 ml/kg/hr) were also obtained. Data were analysed using non-parametric Spearman\u27s rho coefficient and Kruskal Wallis one-way ANOVA by ranks to assess temporal relationship of PVI with all the clinical variables and with significant level set at P\u3c0.05. A common range of PVI was 5-43% with a median 18%. There was no significant correlation found between PVI and PI. Plethysmographic Variability Index positively correlated with the systolic blood pressure (rs=0.25; P\u3c0.001), mean blood pressure (rs=0.26; P\u3c0.001), diastolic blood pressure (rs=0.36; P\u3c0.001) and body temperature (rs=0.166; P=0.004). The other cardiorespiratory variables, recumbency positions, rate of crystalloid fluid administration, pre-operative PCV and TP values had no relationship with PVI. Premedication containing dexmedetomidine resulted in higher PVI (Kruskal-Wallis Test; P=0.001) and lower PI values (Kruskal-Wallis Test; P=0.004) and the opposite was true with protocols that contained acepromazine. It was concluded that while evaluating PVI for fluid response in the anesthetized dogs, various clinical factors should be taken into consideration