In this project, where the main focus is chronic heart failure, the advantage of the continuous monitoring is to follow the action of the heart throughout the day and night. Thus, one can see how the heart reacts to different kinds of stresses, to different kinds of activities and to different sorts of medications. A continuous monitoring of a patient can also give the physicians the possibility to make a direct comparison of the actual patient condition with a past condition (one day, one week or one month earlier). Therefore continuous moni-toring is a major leap forward in the diagnosis and the treatment of cardiac congestive heart failure (CHF).

Prerequisite for this are very reliable monitoring instruments that detect the variables that are the most important for the diagnosis and also for the treatment to be followed.

Current monitoring of CHF consists in periodical assessments of cardiac parameters such as blood pressure, EKG, echocardiography and some blood markers. Carrying out these monitoring procedures is labour intensive and requires a well-trained cardiologist for the echo-cardiographic study. Furthermore, it is expensive to do, in terms of both the personnel costs and blood tests. Current monitoring only reveals a snapshot of the cardiac condition. As monitoring is periodical and not continuous, patients may suffer from major changes in their condition that remain undetected during the period of time which is not monitored.

Despite the technological advancements made in the past years, the design issues for deeply implanted devices remain numerous, especially concerning miniaturisation and power consumption. In addition, because of the body's dielectric nature, communicating with implants that are located deeply within the body, using conventional techniques like Radio Frequency (RF), may not work effectively.

Another important concern is the electromagnetic compatibility, which is associated to communication based on radio frequency. It is becoming more and more difficult to ensure a radio communication characterised by a high immunity to external sources. The ever-increasing number of wireless hot-spots associated with the use of wide frequency spectrum in modern radio devices, render the use of electromagnetic waves as a questionable transmission medium.

ULTRAsponder is aimed at developing systems and methods, not using RF or electromagnetic telemetry with their limitations, but acoustic waves (ultrasounds), for communicating with, and charging efficiently a network of transponders that are placed deep inside a human body. Such systems are small and light, allowing them to be placed either via open surgery or minimally invasive techniques. A transponder may include one or more sensors for monitoring a variety of parameters, such as temperature, pressure, strain or fluid flow and chemical, electrical or magnetic properties. It may also perform therapeutic functions such as drug delivery, defibrillation or electrical stimulation. As part of a network, several transponders can com-municate and exchange information to the external control unit, leading to address complex biological and clinical applications.

This project is also dedicated to external systems for controlling, charging and communicating with such a transponder network, and to methods using such systems. In addition, the external control unit acts as a gateway for the entire system.

The key objectives of ULTRA-sponder are the following:
• To develop innovative wireless data and energy transmission techniques for ultra low power sensor/actuator nodes immersed in aqueous media,
• To achieve small footprint, high flexibility, modularity and gen-erality, which can easily be adaptable to any implantable microsystem,
• To perform bidirectional acoustic wireless data transmission,
• To enable local low massive signal processing capabilities to reduce transmission time and data load,
• To develop ultrasonic transponders actuating and either intermittently or continuously monitoring param-eters for biological applications, where considerations are given to miniaturization, power consump-tion, functionality, production and cost aspects,
• To prove the concept by developing a new technology for a network of ultra-low power transponders deeply implanted inside the body for long term periods,
• To assess the overall system in a real environment for a particular application aimed at measuring physiological parameters and correlating them (data fusion) to perform advanced diagnostics.

In order to enhance the quality of life of people who need to wear implanted monitoring devices, ULTRAsponder intends to develop a minimally invasive technology to be integrated into a minuscule implant, requiring no antenna, cumbersome battery, or connecting leads.

The ULTRAsponder implantable transponder contains an energy exchanger which converts acoustic energy into electrical energy, a small local energy storage, a control and processing chip, and a sensor or actuator, all enclosed in a miniaturized biocompatible casing, hermetically sealed. The device may be equipped with an alarm function, to facilitate critical care monitoring in certain applications. When the device has to operate autonomously, i.e. without external power, it shall be able to operate at least for one week, which depends on the application. This longevity parameter dictates the power consumption level of the implant.

The ULTRAsponder solution will also incorporate a dedicated external control unit, capable of energising the transponder or transponder network and receiving information directly from the implanted transponders. This device should facilitate the communication with up to 10 implants and should provide its user with relevant data. For devices operating autonomously, a critical asset is power management during periodical charging of the implant(s). The charge status will be monitored continuously, and when the implant is fully charged, it will stop requiring energy from the control unit; the total charge time for the implanted transponder shall not exceed 30 min.

In addition to the technology breakthrough proposed by the project, in vitro experiments as well as animal trials will be performed to validate the concept. In vitro experiments with phantoms will be exercised before animal trials will be organised. The ultrasound propa-gation in the body will be studied and visualised, and models will be validated. Animal trials will be conducted in accordance with the “three R’s” rules (Reduction, Replacement, Refinement) wherever possible and will be in compliance with the national directives. In particular, the use of “technical phantoms” will be examined in the design and testing steps of the development cycle to minimise the number of animals.

It is a general principle in medicine that an early detection of a disease implies a better chance for a cure. Accordingly, the continuous monitoring of organs or diseases will alert the physicians at an earlier point and thereby allow an earlier and more efficient treatment to be initiated. This is particularly true for cardiac diseases. There is often a very short time period from a cardiac arrhythmia to a cardiac arrest. By continuous monitoring, the initial phase of life threatening arrhythmias can be detected and treated, possibly saving the patient’s life.