Automatic real-time detection of myocardial ischemia with epicardial accelerometer was feasible. Automated ischemia detection analysis may be used for continuous monitoring of myocardial ischemia during cardiac surgery.
In coronary artery bypass grafting there is a risk of graft occlusion which may result in myocardial infarction. A three-axis acceleration sensor may give additional information about heart function during surgery and the first postoperative days. This paper describes the assembly and packaging of a three-axis micro acceleration sensor for use in clinical trials. The sensor was connected to a cable for power supply and signal output and moulded in silicone. Testing of the encapsulation showed leakage currents well below the 10 muA limit for direct cardiac applications. A hydrogen peroxide gas plasma method was used for sterilization. In animal experiments the sensor was sutured to the heart and no fatigue failures ensued due to the cycling strain forces from the heart. The sensor has been qualified for clinical trials.
Miniaturized 3D accelerometers placed on the heart can assess global and regional function in a closed-chest model. The technique may be used for continuous postoperative monitoring after cardiac surgery.
A small, standalone electrochemical hybrid sensor platform, combining flexible electronics and screen-printed electrodes, is demonstrated in the determination of capsaicin through adsorptive stripping voltammetry. The sensing scheme was simplified to be compatible with a low-cost device. The simplification involved eliminating the need for additional modification of the electrode and employing a coarsely stepped squarewave voltammetry, a technique which is applicable with less sophisticated instrumentation. This architecture was found to be suitable for concentrations up to at least 5000 µM with a detection limit of 1.98 µM. The screen-printed carbon graphite electrodes were made reusable through an ethanol rinsing protocol. The effect of ethanol/buffer volumetric ratio in the test sample greatly influenced the analytical data, and a fixed 10% (v/v) was chosen as a compromise between signal-to-noise ratio and not exceeding the solubility limit of the desired upper range.
Pseudo reference electrodes forms an essential part of electrochemical transducers, where they are used to maintain a reference potential for the system. Yet, little is known about their long-term stability, and any drift may cause undesired changes in the sensor signal. This paper investigates the stability of the reference potential of five material systems of screen-printed reference electrodes. Their potential was continuously monitored for a duration of 40 days in a phosphate buffered solution, and any signal changes were corroborated with EDX elemental analyses, SEM micrographs and cyclic voltammetry. The electrodes were considered to be stable as long as they remained within 30 mV of their initial potential throughout the study. It was found that Ag/AgCl electrodes with a 3:1 atomic ratio kept a stable reference potential (±2.2 mV), whereas Ag/AgCl electrodes with a 9:1 atomic ratio, despite showing good overall constancy of ±3.2 mV, seemed to statistically lose stability towards the end of the 40 day trial due to AgCl depletion through dissolution. The daily potential drift for the respective Ag/AgCl electrodes were −0.2 mV (3:1 ratio) and −0.1 mV (9:1 ratio), suggesting a proportionality between the amount of dissociated AgCl close to the electrode surface and the initial AgCl loading. Electrodes consisting of only Ag showed tendencies towards a mixed potential contribution, which reduced the long-term stability (±24.2 mV) as well as the longevity span (2 days). Ag/Pd electrodes proved to be more unstable (±29.7 mV), with an average lifetime of around 3.5 days. Pt had the greatest potential instability (±59.8 mV), rendering its average lifetime to less than a day. It was shown that electrodes which deviates from the Ag/AgCl equilibrium had the greatest potential variation with time.
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