Optical aggregometry of red blood cells associated with the blood-clotting reaction in extracorporeal circulation support

Detecting Oxygenator Thrombosis in ECMO: A Review of Current Techniques and an Exploration of Future Directions

Extracorporeal membrane oxygenation (ECMO) is a life-support technique used to treat cardiac and pulmonary failure, including severe cases of COVID-19 (coronavirus disease 2019) involving acute respiratory distress syndrome. Blood clot formation in the circuit is one of the most common complications in ECMO, having potentially harmful and even fatal consequences. It is therefore essential to regularly monitor for clots within the circuit and take appropriate measures to prevent or treat them. A review of the various methods used by hospital units for detecting blood clots is presented. The benefits and limitations of each method are discussed, specifically concerning detecting blood clots in the oxygenator, as it is concluded that this is the most critical and challenging ECMO component to assess. We investigate the feasibility of solutions proposed in the surrounding literature and explore two areas that hold promise for future research: the analysis of small-scale pressure fluctuations in the circuit, and real-time imaging of the oxygenator. It is concluded that the current methods of detecting blood clots cannot reliably predict clot volume, and their inability to predict clot location puts patients at risk of thromboembolism. It is posited that a more in-depth analysis of pressure readings using machine learning could better provide this information, and that purpose-built imaging could allow for accurate, real-time clotting analysis in ECMO components.

Design and Fabrication of a Thin and Micro-Optical Sensor for Rapid Prototyping

Optical sensing offers several advantages owing to its non-invasiveness and high sensitivity. The miniaturization of optical sensors will mitigate spatial and weight constraints, expanding their applications and extending the principal advantages of optical sensing to different fields, such as healthcare, Internet of Things, artificial intelligence, and other aspects of society. In this study, we present the development of a miniature optical sensor for monitoring thrombi in extracorporeal membrane oxygenation (ECMO). The sensor, based on a complementary metal-oxide semiconductor integrated circuit (CMOS-IC), also serves as a photodiode, amplifier, and light-emitting diode (LED)-mounting substrate. It is sized 3.8 × 4.8 × 0.75 mm3 and provides reflectance spectroscopy at three wavelengths. Based on semiconductor and microelectromechanical system (MEMS) processes, the design of the sensor achieves ultra-compact millimeter size, customizability, prototyping, and scalability for mass production, facilitating the development of miniature optical sensors for a variety of applications.

Valve-Adjustable Optofluidic Bio-Imaging Platform for Progressive Stenosis Investigation

The clinical evidence has proven that valvular stenosis is closely related to many vascular diseases, which attracts great academic attention to the corresponding pathological mechanisms. The investigation is expected to benefit from the further development of an in vitro model that is tunable for bio-mimicking progressive valvular stenosis and enables accurate optical recognition in complex blood flow. Here, we develop a valve-adjustable optofluidic bio-imaging recognition platform to fulfill it. Specifically, the bionic valve was designed with in situ soft membrane, and the internal air-pressure chamber could be regulated from the inside out to bio-mimic progressive valvular stenosis. The developed imaging algorithm enhances the recognition of optical details in blood flow imaging and allows for quantitative analysis. In a prospective clinical study, we examined the effect of progressive valvular stenosis on hemodynamics within the typical physiological range of veins by this way, where the inhomogeneity and local enhancement effect in the altered blood flow field were precisely described and the optical differences were quantified. The effectiveness and consistency of the results were further validated through statistical analysis. In addition, we tested it on fluorescence and noticed its good performance in fluorescent tracing of the clotting process. In virtue of theses merits, this system should be able to contribute to mechanism investigation, pharmaceutical development, and therapeutics of valvular stenosis-related diseases.

Real-time, non-invasive thrombus detection in an extracorporeal circuit using micro-optical thrombus sensors

Introduction:

Real-time, non-invasive monitoring of thrombus formation in extracorporeal circuits has yet to be achieved. To address the challenges of conventional optical thrombus detection methods requiring large devices that limit detection capacity, we developed a micro-optical thrombus sensor.

Methods:

The proposed micro-optical thrombus sensor can detect the intensity of light scattered by blood at wavelengths of 660 and 855 nm. Two thrombus sensors were installed on in vitro circuit: one at the rotary blood pump and one at a flow channel. To evaluate the variation in the ratio of incident light intensity at each wavelength of the two sensors, R_fluct (for 660 nm) and I_fluct (for 855 nm) were defined. Using fresh porcine blood as a working fluid, we performed in vitro tests of haematocrit (Hct) and oxygen saturation (SaO₂) variation and thrombus detection. Thrombus tests were terminated after R_fluct or I_fluct showed a larger change than the maximum range of those in the Hct and SaO₂ variation test.

Results:

In all three thrombus detection tests, I_fluct showed a larger change than the maximum range of those in the Hct and SaO₂ variation test. After the tests, thrombus formation was confirmed in the pump, and there was no thrombus in the flow channel. The results indicate that I_fluct is an effective parameter for identifying the presence of a thrombus.

Conclusion:

Thrombus detection in an extracorporeal circuit using the developed micro-optical sensors was successfully demonstrated in an in vitro test.

Development of a real-time blood damage monitoring device for cardiopulmonary bypass system using near-infrared spectroscopy

The optical properties of hemoglobin could indicate the degree of hemolysis. We aimed to utilize this to develop a real-time blood damage monitoring device for cardiopulmonary bypass (CPB) systems. The real-time blood damage monitoring device comprised a near-infrared spectroscopy optical module with a fiber spectrometer and monitoring platform and computer software developed using LabVIEW 2017. The fiber spectrometer operated at wavelengths of 545, 660, and 940 nm and contained a detector fiber bundle (source-detector distance = 1.0-2.5 cm). CPB operation was simulated using an artificial heart-lung machine with a flow rate of 3, 4, or 5 L/min. Four hundred milliliter of anticoagulated porcine blood was continuously rotated for 4 h. The transmittance, reflectivity, and absorbance of the blood were measured using the optical device at a frequency of 25 Hz and then digitally averaged into 1-s interval. Samples of damaged blood were collected at regular intervals for in vitro hemolysis tests to calculate the normalized index of hemolysis (NIH). All experiments were repeated three times. We prepared 28 blood bags containing 400 ml of anticoagulant. Paired t test was used to examine the test-retest reliability of the differences between the three methods and control samples. Statistical tests revealed significant differences in the mean values between the test and control groups over time (P < 0.01). Relationship was established between the real-time monitoring results and the NIH values. An effective blood damage detection method that combined in vitro hemolysis tests and near-infrared spectroscopy was achieved. The results demonstrate the clinical potential of a real-time, low-cost, and reliable blood damage monitoring device to improve the safety of CPB operation.

Red blood cells aggregability measurement of coagulating blood in extracorporeal circulation system with multiple-frequency electrical impedance spectroscopy

Red blood cells (RBCs) aggregability A_G of coagulating blood in extracorporeal circulation system has been investigated under the condition of pulsatile flow. Relaxation frequency f_c from the multiple-frequency electrical impedance spectroscopy is utilized to obtain RBCs aggregability A_G. Compared with other methods, the proposed multiple-frequency electrical impedance method is much easier to obtain non-invasive measurement with high speed and good penetrability performance in biology tissues. Experimental results show that, RBCs aggregability A_G in coagulating blood falls down with the thrombus formation while that in non-coagulation blood almost keeps the same value, which has a great agreement with the activated clotting time (ACT) fibrinogen concertation (F_bg) tests. Modified Hanai formula is proposed to quantitatively analyze the influence of RBCs aggregation on multiple-frequency electrical impedance measurement. The reduction of RBCs aggregability A_G is associated with blood coagulation reaction, which indicates the feasibility of the high speed, compact and cheap on-line thrombus measurement biosensors in extracorporeal circulation systems.

Development of a real-time and quantitative thrombus sensor for an extracorporeal centrifugal blood pump by near-infrared light

We developed an optical thrombus sensor for a monopivot extracorporeal centrifugal blood pump. In this study, we investigated its quantitative performance for thrombus detection in acute animal experiments of left ventricular assist using the pump on pathogen-free pigs. Optical fibers were set in the driver unit of the pump. The incident light at the near-infrared wavelength of 810 nm was aimed at the pivot bearing, and the resulting scattered light was guided to the optical fibers. The detected signal was analyzed to obtain the thrombus formation level. As a result, real-time and quantitative monitoring of the thrombus surface area on the pivot bearing was achieved with an accuracy of 3.6 ± 2.3 mm². In addition, the sensing method using the near-infrared light was not influenced by changes in the oxygen saturation and the hematocrit. It is expected that the developed sensor will be useful for optimal anticoagulation management for long-term extracorporeal circulation therapies.