Detection of thrombosis in a magnetically levitated blood pump by vibrational excitation of the impeller

Abstract

The use of contactless support technology for the impeller has led to an increase in the durability of ventricular assist devices (VADs), and these have been in clinical use worldwide. However, pump thrombosis and stroke are still issues to be solved.We have developed a method for detecting the thrombosis in a magnetically levitated blood pump without the need for additional sensors or other equipment. In the proposed method, a sinusoidal current is applied to the electromagnets used for the magnetic bearing, resulting in vibration of the impeller. The phase difference between the current and displacement of the impeller increases with pump thrombosis. First, we describe the principle by which the pump thrombosis is detected.Pump thrombosis reduces the narrowest fluid gap in the pump and this gives rise to a change in the phase difference. Second, we report on experiments in which we changed the narrowest fluid gap using oriented polypropylene tape and showed that decreasing the narrowest fluid gap resulted in an increase in phase difference. For these experiments, the measurements were repeated three times for each condition.Third, we examine the relationship between the pump thrombosis and the phase difference evaluated by observations of the underside of the impeller when operating the pump with porcine blood. Since light was unable to penetrate the blood layer, the erythrocytes were removed for this observation. Only one observation was made.

Evaluation of real‐time thrombus detection method in a magnetically levitated centrifugal blood pump using a porcine left ventricular assist circulation model

“…The importance of the timing of inspection of the inside of the pump cannot be overemphasized. In previous in vitro experiments, the signal indicating pump thrombus formation was consistently enhanced over time 14,22 . This indicates that thrombus formation was not suppressed because the fibrinolytic system does not work in a simulated circuit.…”

“…Herein, we evaluated real‐time monitoring of pump thrombus in a mag‐lev pump without any additional sensors, by focusing on the phase difference between the impeller displacement and electromagnet current in a porcine left ventricular assist circulation model. This method enables thrombus detection simply by making the impeller of the pump to vibrate intentionally 14 . We previously conducted various in vitro experiments to verify the effectiveness of this method.…”

“…And we thought that applying the fibrinogen coating to the place where thrombi were most likely to occur was a device that can finish the experimental process quickly. Of course, this thrombus detection method can detect pump thrombi without fibrinogen coating 14,22 …”

“…The principle of detecting a pump thrombus in a mag‐lev pump has been described in previous studies 14 and is briefly explained here. In this method, a sinusoidal current is applied to the electromagnets of the magnetic bearing, causing the impeller to vibrate intentionally (Figure 1B).…”

“…The phase difference between the current and displacement of the impeller increases with the pump thrombus. This thrombus detection method has been shown to be successful and reproducible through simulated circuit experiments using porcine blood 14 . Using this method, pump thrombi were appropriately detected within a few hours during in vitro experiments.…”