Totally Implantable Wireless Ultrasonic Doppler Blood Flowmeters: Toward Accurate Miniaturized Chronic Monitors

Flowing Liquid-Based Triboelectric Nanogenerator Performance Enhancement with Functionalized Polyvinylidene Fluoride Membrane for Self-Powered Pulsating Flow Sensing Application

Pulsating flow, a common term in industrial and medical contexts, necessitates precise water flow measurement for evaluating hydrodynamic system performance. Addressing challenges in measurement technologies, particularly for pulsating flow, we propose a flowing liquid-based triboelectric nanogenerator (FL-TENG). To generate sufficient energy for a self-powered device, we employed a fluorinated functionalized technique on a polyvinylidene fluoride (PVDF) membrane to enhance the performance of FL-TENG. The results attained a maximum instantaneous power density of 50.6 µW/cm2, and the energy output proved adequate to illuminate 10 white LEDs. Regression analysis depicting the dependence of the output electrical signals on water flow revealed a strong linear relationship between the voltage and flow rate with high sensitivity. A high correlation coefficient R2 within the range from 0.951 to 0.998 indicates precise measurement accuracy for the proposed FL-TENG. Furthermore, the measured time interval between two voltage peaks precisely corresponds to the period of pulsating flow, demonstrating that the output voltage can effectively sense pulsating flow based on voltage and the time interval between two voltage peaks. This work highlights the utility of FL-TENG as a self-powered pulsating flow rate sensor.

A proof-of-concept real-time processing to characterize vascular flow

In dialysis patients, monitoring vascular flow of the surgically created arteriovenous fistula (AVF) is critical to indicate the success of the AVF as a dialysis access site. Current gold standard to quantify vascular flow involves external doppler evaluation which requires frequent visits to the clinic. In this paper, we present a proof-of-concept cost-efficient vascular flow monitoring system towards a wearable and robust blood flow monitoring system. The proposed system captures beat-to-beat blood flow from impedance plethysmography (IPG) signal and performs embedded computing to robustly map the changes in the IPG to peripheral blood flow. We present the proof-of-concept results for the embedded real-time blood flow computing from measurements obtained using a custom electrical bioimpedance hardware presented previously elsewhere. We anticipate the results serving as the first step towards potentially eliminating the need for using expensive and bulky systems that require specialized personnel to operate for peripheral blood flow monitoring. Clinical relevance-The study paves the way to engineering a ubiquitous blood flow monitoring system for patients who have a surgically created Arteriovenous fistula (AVF) for dialysis vascular access.

A Wireless Near-Infrared Spectroscopy Device for Flap Monitoring: Proof of Concept in a Porcine Musculocutaneous Flap Model

BACKGROUND

 Current near-infrared spectroscopy (NIRS)-based systems for continuous flap monitoring are highly sensitive for detecting malperfusion. However, the clinical utility and user experience are limited by the wired connection between the sensor and bedside console. This wire leads to instability of the flap-sensor interface and may cause false alarms.

METHODS

 We present a novel wearable wireless NIRS sensor for continuous fasciocutaneous free flap monitoring. This waterproof silicone-encapsulated Bluetooth-enabled device contains two light-emitting diodes and two photodetectors in addition to a battery sufficient for 5 days of uninterrupted function. This novel device was compared with a ViOptix T.Ox monitor in a porcine rectus abdominus myocutaneous flap model of arterial and venous occlusions.

RESULTS

 Devices were tested in four flaps using three animals. Both devices produced very similar tissue oxygen saturation (StO₂) tracings throughout the vascular clamping events, with obvious and parallel changes occurring on arterial clamping, arterial release, venous clamping, and venous release. Small interdevice variations in absolute StO₂ value readings and magnitude of change were observed. The normalized cross-correlation at zero lag describing correspondence between the novel NIRS and T.Ox devices was >0.99 in each trial.

CONCLUSION

 The wireless NIRS flap monitor is capable of detecting StO₂ changes resultant from arterial vascular occlusive events. In this porcine flap model, the functionality of this novel sensor closely mirrored that of the T.Ox wired platform. This device is waterproof, highly adhesive, skin conforming, and has sufficient battery life to function for 5 days. Clinical testing is necessary to determine if this wireless functionality translates into fewer false-positive alarms and a better user experience.

The Future of Cardiovascular Stents: Bioresorbable and Integrated Biosensor Technology

Cardiovascular disease is the greatest cause of death worldwide. Atherosclerosis is the underlying pathology responsible for two thirds of these deaths. It is the age-dependent process of "furring of the arteries." In many scenarios the disease is caused by poor diet, high blood pressure, and genetic risk factors, and is exacerbated by obesity, diabetes, and sedentary lifestyle. Current pharmacological anti-atherosclerotic modalities still fail to control the disease and improvements in clinical interventions are urgently required. Blocked atherosclerotic arteries are routinely treated in hospitals with an expandable metal stent. However, stented vessels are often silently re-blocked by developing "in-stent restenosis," a wound response, in which the vessel's lumen renarrows by excess proliferation of vascular smooth muscle cells, termed hyperplasia. Herein, the current stent technology and the future of biosensing devices to overcome in-stent restenosis are reviewed. Second, with advances in nanofabrication, new sensing methods and how researchers are investigating ways to integrate biosensors within stents are highlighted. The future of implantable medical devices in the context of the emerging "Internet of Things" and how this will significantly influence future biosensor technology for future generations are also discussed.

Ultrasonic sensor concept to fit a ventricular assist device cannula evaluated using geometrically accurate heart phantoms

Future left ventricular assist devices (LVADs) are expected to respond to the physiologic need of patients; however, they still lack reliable pressure or volume sensors for feedback control. In the clinic, echocardiography systems are routinely used to measure left ventricular (LV) volume. Until now, echocardiography in this form was never integrated in LVADs due to its computational complexity. The aim of this study was to demonstrate the applicability of a simplified ultrasonic sensor to fit an LVAD cannula and to show the achievable accuracy in vitro. Our approach requires only two ultrasonic transducers because we estimated the LV volume with the LV end-diastolic diameter commonly used in clinical assessments. In order to optimize the accuracy, we assessed the optimal design parameters considering over 50 orientations of the two ultrasonic transducers. A test bench was equipped with five talcum-infused silicone heart phantoms, in which the intra-ventricular surface replicated papillary muscles and trabeculae carnae. The end-diastolic LV filling volumes of the five heart phantoms ranged from 180 to 480 mL. This reference volume was altered by ±40 mL with a syringe pump. Based on the calibrated measurements acquired by the two ultrasonic transducers, the LV volume was estimated well. However, the accuracies obtained are strongly dependent on the choice of the design parameters. Orientations toward the septum perform better, as they interfere less with the papillary muscles. The optimized design is valid for all hearts. Considering this, the Bland-Altman analysis reports the LV volume accuracy as a bias of ±10% and limits of agreement of 0%-40% in all but the smallest heart. The simplicity of traditional echocardiography systems was reduced by two orders of magnitude in technical complexity, while achieving a comparable accuracy to 2D echocardiography requiring a calibration of absolute volume only. Hence, our approach exploits the established benefits of echocardiography and makes them applicable as an LV volume sensor for LVADs.

Automatic Early-Onset Free Flap Failure Detection for Implantable Biomedical Devices

OBJECTIVE

Up to 10% of free flap cases are compromised, and without prompt intervention, amputation and even death can occur. Hourly monitoring improves salvage rates, but the gold standard for monitoring requires experienced personnel to operate and suffers from high false-positive rates as high as 31% that result in costly and unnecessary surgeries. In this paper, we investigate free flap patency monitoring using automatic hardware-only classification systems that eliminate the need for experienced personnel. The expected flow ranges of the antegrade and retrograde veins for breast reconstruction are studied using a syringe pump to create the laminar flow seen in veins.

METHODS

Feature data extracted from the Doppler blood flow signals are analyzed for sensitivity, specificity, and false-positive rates. Hardware is built to perform the classification automatically in real-time and output a decision at the end of the observation period.

RESULTS

Experimental results using the hardware-only classifier for a 50 ms window size show high sensitivity (96.75%), specificity (90.20%), and low false-positive rate (9.803%). The experimental and theoretical classification results show close agreement.

CONCLUSION

This work indicates that automatic hardware-only classifiers can eliminate the need for experienced personnel to monitor free flap patency.

SIGNIFICANCE

The hardware-only classification is amenable to a monolithic implementation and future studies should study a totally implantable wirelessly-powered blood flow classifier. The high classifier performance in a short window period indicates that duty-cycled powering can be used to extend the safe operational depth of an implant. This is particularly relevant for the difficult buried free flap applications.

[Progress of monitoring methods and preventions of disorder of blood supplying of expanded flaps]

Objective

To summarize the monitoring methods and preventions of the disorder of blood supplying of expanded flaps, so as to provide some references for improving the survival of expanded flaps.

Methods

The domestic and abroad related literature about the disorder of blood supplying of expanded flaps was reviewed and analyzed.

Results

Handheld Doppler, digital subtraction angiography, computer tomographic angiography, magnetic resonance angiography, and fluorescein angiography can be used as reliable preoperative imaging methods in designing expanded flaps with rich blood supply. Several techniques can be used for monitoring the blood supply of expanded flaps during the early postoperative period including traditional monitoring via physical examination, monitoring via dynamic infrared thermography, near-infrared spectroscopy tissue oximeter, external and implantable Doppler, and more recently developed diffuse correlation spectroscopy. Surgical delay, bloodletting, leech therapy, hyperbaric oxygen, and so on can decrease the risk of necrosis in expanded flaps.

Conclusion

The survival of expanded flap is influenced by many factors. Preoperative design by using handheld Doppler and new imaging technology and postoperative early detection of blood supply can provide references of timely intervention, so that ischemic necrosis of the flaps can be reduced, and the success rate of surgery can be improved.