Implantable RF telemetry for cardiac monitoring in the murine heart: a tutorial review
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Implantable RF telemetry for cardiac monitoring in the murine heart: a tutorial review Robert Sobot Abstract Research and development of implantable RF telemetry systems intended specifically to enable and support cardiac monitoring of genetically engineered small animal subjects, rats and mice in particular, has already gained significant momentum. This article presents the state of the art review of experimental cardiac monitoring telemetry systems, with strong accent on the systems designed to work with a dual pressure–volume conductance-based catheter sensor. These commercially available devices are already small enough to fit inside a left-ventricle of a mouse heart. However, if the complete system is to be fully implanted and the subject allowed to freely move inside a cage, the mouse’s small body size sets harsh constrains on the size and power consumption of the required electronics. Consequently, significant portion of the research efforts is directed towards the development of low-volume and -power electronics, as well as RF energy harvesting systems that are required to serve as the energy source to the implanted telemetry instead of the relatively very bulky batteries. Introduction Congestive heart failure (CHF), a condition in which the heart fails to pump efficiently, is identified as one of the major cardiovascular diseases; e.g. in 2008 cardiovascular diseases accounted for 29% of all deaths in Canada [1]. In order to evaluate a heart’s functionality, cardiovascular researchers rely mostly on the shape and position of the heart’s pressure–volume (PV) loops [2], with genetically engineered small animal subjects, such as mice, rats, and rabbits being the most important models used for researching diseases. Similarly to piston in a car engine, a heart is described by PV loops, where a heart of a healthy person is capable of closing a PV loop with large surface, i.e. it is capable of generating a large stroke volume (SV); versus a failing heart that is capable of generating much smaller SV (Figure 1). Therefore, it is essential to collect simultaneous data related to both blood pressure (P) and volume (V ) of a heart on a beat-to-beat basis. To that end, one of the first micromachined (MEMS) type of P sensors suitable for blood pressure monitoring was reported in [3], and soon after Baan et al. [4,5] followed by Correspondence: [email protected] Western University, Electrical and Computer Engineering, London, Ontario, N6A 5B9, Canada
reporting the development of a catheter with the embedded conductance-based V sensor. Today, these two types of sensors are commercially available as a single-package dual-sensor device that is small enough to be implanted into a mouse heart [6,7]. However, the small size of a mouse body still presents great challenge if the supporting electronics and antenna are to be encompassed as well. Consequently, today’s biomedical researchers still rely on small, heavily distorted samples of PV data collected by the external data-collection unit during an open heart operati
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