FACTORS INFLUENCING IMPEDANCE DURING RADIOFREQUENCY ABLATION IN HUMANS

Impedance during radiofrequency (RF) catheter ablation procedures is dependent on a variety of parameters related to the catheter, cabling, reference patch, body size, and temperature. To examine the influence of body size, impedance was measured during clinical ablation procedures in 93 patients (Group I) with a wide range of body sizes. In 14 other patients (Group II), impedance was measured during variations in catheter tip size (5, 6 and 7 Fr), reference patch size (120 and 60 cm2), patch location (chest vs. thigh), and catheter tip tissue contact. The average impedance was also compared to average tip temperature in Group II patients. Impedance decreased with increasing catheter tip size, reference patch size and proximity of the patch to the heart. However, the effects of body geometry were complex. For example, using a chest patch, impedance increased with body surface area, but using a thigh patch it decreased, suggesting that lung volume may increase impedance, but body width may actually decrease it. An increase in tip tissue contact, relative to blood contact, increased the impedance, suggesting that impedance may be a useful measure of tip tissue contact. Finally impedance decreased with increasing tip temperature, suggesting that impedance may be useful as a real time measure of tissue and blood heating. The results are interpreted in terms of an electrical analog which suggests further that despite the lower total power when the same voltage is applied to a higher impedance, less voltage should be applied to achieve the same tissue effect when the measured impedance is higher.

A demand-supply framework for evaluating the effect of resource and service constraints on community disaster resilience

Tools that quantify community disaster resilience are essential for informed decision-making on community disas- ter resilience improvement measures. One of the major research gaps in quantifying community disaster resilience are community disaster recovery simulations. Such simulations enable an insight into factors that enable a rapid and efficient community disaster recovery and vice versa. The iRe-CoDeS framework presented in this paper, simulates community disaster recovery as a time-stepping loop, where at each time step the interplay of demand and supply of community components for various resources and services dictates components’ ability to operate and recover. Disaster resilience of a community is then quantified using a multi-dimensional metric, where each dimension represents the unmet demand of a community regarding a certain resource or a service, labelled Lack of Resilience (LoR). This paper presents how such a demand/supply approach can be applied to account for re- source and service constraints, impeding factors, that prolong component recovery and thus decrease community disaster resilience. Housing resilience of North-East San Francisco exposed to a Mw7.2 earthquake on the San Andreas Fault is quantified to illustrate the proposed approach. rWhale application framework recently devel- oped at the NHERI SimCenter is used for this purpose, presenting how such a regional simulation on the effect of natural disasters on communities can be extended using the iRe-CoDeS framework to simulate community disas- ter recovery and quantify community disaster resilience. It is shown that housing resilience quantification results obtained in the case study focused on a part of San Francisco are in accordance with the existing estimates of housing resilience. The evolution of the post-disaster community-level supply and demand for recovery resources and services is obtained, identifying how and when the unmet demand for these resources and services impedes community recovery. Lastly, the effect of community’s ability to mobilize resources and services needed for its recovery on its disaster resilience is investigated.