Abstract-Ultra wideband (UWB) radio technology for wireless implants has gained significant attention. UWB enables the fabrication of faster and smaller transceivers with ultra low power consumption, which may be integrated into more sophisticated implantable biomedical sensors and actuators. Nevertheless, the large path loss suffered by UWB signals propagating through inhomogeneous layers of biological tissues is a major hindering factor. For the optimal design of implantable transceivers, the accurate characterization of the UWB radio propagation in living biological tissues is indispensable. Channel measurements in phantoms and numerical simulations with digital anatomical models provide good initial insight into the expected path loss in complex propagation media like the human body, but they often fail to capture the effects of blood circulation, respiration, and temperature gradients of a living subject. Therefore, we performed UWB channel measurements within 1-6 GHz on two living porcine subjects because of the anatomical resemblance with an average human torso. We present for the first time a path loss model derived from these invivo measurements, which includes the frequency-dependent attenuation. The use of multiple on-body receiving antennas to combat the high propagation losses in implant radio channels was also investigated. Index Terms-channel model, implant, in-body, in-vivo, path lossThis work is part of the MELODY Project-Phase II (Contract no. 225885), which is financially sponsored by the Research Council of Norway.

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Objective: A miniaturized accelerometer can be incorporated in temporary pacemaker leads which are routinely attached to the epicardium during cardiac surgery and provide continuous monitoring of cardiac motion during and following surgery. We tested if such a sensor could be used to assess volume status, which is essential in hemodynamically unstable patients. Methods: An accelerometer was attached to the epicardium of 9 pigs and recordings performed during baseline, fluid loading, and phlebotomy in a closed chest condition. Alterations in left ventricular (LV) preload alter myocardial tension which affects the frequency of myocardial acceleration associated with the first heart sound (f S1). The accuracy of f S1 as an estimate of preload was evaluated using sonomicrometry measured end-diastolic volume (EDV SONO). Standard clinical estimates of global end-diastolic volume using pulse index continuous cardiac output (PiCCO) measurements (GEDV PiCCO) and pulmonary artery occlusion pressure (PAOP) were obtained for comparison. The diagnostic accuracy of identifying fluid responsiveness was analyzed for f S1 , stroke volume variation (SVV PiCCO), pulse pressure variation (PPV PiCCO), GEDV PiCCO , and PAOP. Results: Changes in f S1 correlated well to changes in EDV SONO (r 2 = 0.81, 95%CI: [0.68, 0.89]), as did GEDV PiCCO (r 2 = 0.59, 95%CI: [0.36, 0.76]) and PAOP (r 2 = 0.36, 95%CI: [0.01, 0.73]). The diagnostic accuracy [95%CI] in identifying fluid responsiveness was 0.79 [0.66, 0.94] for f S1 , 0.72 [0.57, 0.86] for SVV PiCCO , and 0.63 (0.44, 0.82) for PAOP. Conclusion: An epicardially placed accelerometer can assess changes in preload in real-time. Significance: This novel method can facilitate continuous monitoring of the volemic status in open-heart surgery patients and help guiding fluid resuscitation.

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.