Alterations of pulmonary vascular afterload in exercise-induced pre- and post-capillary pulmonary hypertension.

Exercise imposes increased pulmonary vascular afterload based on rises in pulmonary artery (PA) wedge pressure, declines in PA compliance, and resistance-compliance time. In health, afterload stress stabilizes during steady-state exercise. Our objective was to examine alterations of these exercise-associated stresses in states of pre- and post-capillary pulmonary hypertension (PH). PA hemodynamics were evaluated at rest, 2 and 7 min of steady-state exercise at moderate intensity in patients who exhibited Pre-capillary (n = 22) and post-capillary PH (n = 22). Patients with normal exercise hemodynamics (NOR-HD) (n = 32) were also studied. During exercise in all groups, PA wedge pressure increased at 2 min, with no further change at 7 min. In post-capillary PH and NOR-HD, increases in PA diastolic pressure and diastolic pressure gradient remained stable at 2 and 7 min of exercise, while in pre-capillary PH, both continued to increase at 7 min. The behavior of the diastolic pressure gradient was linearly related to the duration of resistance-compliance time at rest (r2  = 0.843) and exercise (r2  = 0.760). Exercise resistance-compliance time was longer in pre-capillary PH associated with larger increases in diastolic pressure gradient. Conversely, resistance-compliance time was shortest in post-capillary PH compared to pre-capillary PH and NOR-HD and associated with limited increases in exercise diastolic pressure gradient. During steady-state, modest-intensity exercise-specific patterns of pulmonary vascular afterload responses were observed in pre- and post-capillary PH relative to NOR-HD. Longer resistance-compliance time related to greater increases in PA diastolic pressure and diastolic pressure gradients in pre-capillary PH, while shorter resistance-compliance time appeared to limit these increases in post-capillary PH.

Load Distribution Analysis for Weight and Ballistocardiogram Measurements of Heart Failure Patients using a Bed Scale.

Ballistocardiogram (BCG) is an emerging tool with the potential to monitor heart failure (HF) patients. A close association of the weight to the BCG as an intermediate signal source requires a careful design, where events such as saturation of the weight signal can result in the loss of the BCG. This work closely examined the factors around the weight while load cells placed under each support of a bed collected the BCG (e.g., body weight, distribution over the four supports of the bed). Following the calibration of weights based on the location of the polls, the study examined the ratios of loads in head-foot and lateral directions. The head-foot ratio was also correlated to the height. Twelve non-obese HF patients were recruited, and the weight and BCG were appropriately measured, where the average error of the weight measurements was 0.45 ± 0.30%. The mean ratio of the loads between head to foot sensors was 3.2 ± 0.7 with a maximum ratio of 4.5, showing that the head-ward sensors supported greater body weight. The ratio of the loads between the right to left sensors was 1.2 ± 0.1. The height and the head-to-foot ratio had an inverse correlation (r = 0.52). Based on the analysis, the head-ward sensors should have a higher capacity of up to three times that of the foot-ward sensors to prevent any signal saturation. Mobility issues were observed in some subjects, attributing to the lateral imbalance. These novel findings based on the end-users (i.e., HF population) may allow better allocation of conditioning resources to obtain the BCG (e.g., optimally adjusted sensitivity).

Striatal Direct Pathway Targets Npas1+ Pallidal Neurons.

The classic basal ganglia circuit model asserts a complete segregation of the two striatal output pathways. Empirical data argue that, in addition to indirect-pathway striatal projection neurons (iSPNs), direct-pathway striatal projection neurons (dSPNs) innervate the external globus pallidus (GPe). However, the functions of the latter were not known. In this study, we interrogated the organization principles of striatopallidal projections and their roles in full-body movement in mice (both males and females). In contrast to the canonical motor-promoting response of dSPNs in the dorsomedial striatum (DMSdSPNs), optogenetic stimulation of dSPNs in the dorsolateral striatum (DLSdSPNs) suppressed locomotion. Circuit analyses revealed that dSPNs selectively target Npas1+ neurons in the GPe. In a chronic 6-hydroxydopamine lesion model of Parkinson's disease, the dSPN-Npas1+ projection was dramatically strengthened. As DLSdSPN-Npas1+ projection suppresses movement, the enhancement of this projection represents a circuit mechanism for the hypokinetic symptoms of Parkinson's disease that has not been previously considered. In sum, our results suggest that dSPN input to the GPe is a critical circuit component that is involved in the regulation of movement in both healthy and parkinsonian states.SIGNIFICANCE STATEMENT In the classic basal ganglia model, the striatum is described as a divergent structure: it controls motor and adaptive functions through two segregated, opposing output streams. However, the experimental results that show the projection from direct-pathway neurons to the external pallidum have been largely ignored. Here, we showed that this striatopallidal subpathway targets a select subset of neurons in the external pallidum and is motor-suppressing. We found that this subpathway undergoes changes in a Parkinson's disease model. In particular, our results suggest that the increase in strength of this subpathway contributes to the slowness or reduced movements observed in Parkinson's disease.

Dissociable Roles of Pallidal Neuron Subtypes in Regulating Motor Patterns.

We have previously established that PV+ neurons and Npas1+ neurons are distinct neuron classes in the external globus pallidus (GPe): they have different topographical, electrophysiological, circuit, and functional properties. Aside from Foxp2+ neurons, which are a unique subclass within the Npas1+ class, we lack driver lines that effectively capture other GPe neuron subclasses. In this study, we examined the utility of Kcng4-Cre, Npr3-Cre, and Npy2r-Cre mouse lines (both males and females) for the delineation of GPe neuron subtypes. By using these novel driver lines, we have provided the most exhaustive investigation of electrophysiological studies of GPe neuron subtypes to date. Corroborating our prior studies, GPe neurons can be divided into two statistically distinct clusters that map onto PV+ and Npas1+ classes. By combining optogenetics and machine learning-based tracking, we showed that optogenetic perturbation of GPe neuron subtypes generated unique behavioral structures. Our findings further highlighted the dissociable roles of GPe neurons in regulating movement and anxiety-like behavior. We concluded that Npr3+ neurons and Kcng4+ neurons are distinct subclasses of Npas1+ neurons and PV+ neurons, respectively. Finally, by examining local collateral connectivity, we inferred the circuit mechanisms involved in the motor patterns observed with optogenetic perturbations. In summary, by identifying mouse lines that allow for manipulations of GPe neuron subtypes, we created new opportunities for interrogations of cellular and circuit substrates that can be important for motor function and dysfunction.SIGNIFICANCE STATEMENT Within the basal ganglia, the external globus pallidus (GPe) has long been recognized for its involvement in motor control. However, we lacked an understanding of precisely how movement is controlled at the GPe level as a result of its cellular complexity. In this study, by using transgenic and cell-specific approaches, we showed that genetically-defined GPe neuron subtypes have distinct roles in regulating motor patterns. In addition, the in vivo contributions of these neuron subtypes are in part shaped by the local, inhibitory connections within the GPe. In sum, we have established the foundation for future investigations of motor function and disease pathophysiology.

Quantification of Resting-State Ballistocardiogram Difference Between Clinical and Non-Clinical Populations for Ambient Monitoring of Heart Failure.

A ballistocardiogram (BCG) is a versatile bio-signal that enables ambient remote monitoring of heart failure (HF) patients in a home setting, achieved through embedded sensors in the surrounding environment. Numerous methods of analysis are available for extracting physiological information using the BCG; however, most have been developed based on non-clinical subjects. While the difference between clinical and non-clinical populations are expected, quantification of the difference may serve as a useful tool. In this work, the differences in resting-state BCGs of the two cohorts in a sitting posture were quantified. An instrumented chair was used to collect the BCG from 29 healthy adults and 26 NYHA HF class I and II patients while seated without any stress test for five minutes. Five 20-second epochs per subject were used to calculate the waveform fluctuation metric at rest (WFMR). The WFMR was obtained in two steps. The ensemble average of the segmented BCG heartbeats within an epoch were calculated first. Mean square errors (MSE) between different ensemble average pairs were then retrieved. The MSEs were averaged to produce the WFMR. The comparison showed that the clinical cohort had higher fluctuation than the non-clinical population and had at least 82.2% separation, suggesting that greater errors may result when existing algorithms were used. The WFMR acts as a bridge that may enable important features, including the addition of error margins in parameter estimation and ways to devise a calibration strategy when resting-state BCG is unstable.

Ballistocardiogram Based Identity Recognition: Towards Zero-Effort Health Monitoring in an Internet-of-Things (IoT) Environment.

Ballistocardiography (BCG), a measure of body vibrations due to ejection of blood into aorta, has the potential to become a 'zero-effort' cardiovascular health monitoring technology, i.e., a technology that requires little or no engagement on part of the user for its operation. In order for any zero-effort monitoring technology to function without any input from the user, it is important that such a methodology can accurately perform identity recognition and thus continuously provide results and feedback to each user. However, most of the recent work on BCG has focused mainly on the estimation of parameters related to mechanical health and the use of BCG to identify a user has not been explored thoroughly. In this paper, we examine, using discrete cosine transform based features and multi-class linear classifier, the use of BCG heartbeats for identity recognition. We demonstrate from the BCG data of 52 healthy subjects collected using a modified floor tile that an average accuracy of 96.15% can be achieved for correct identification of each subject standing on the tile. Based on these results, we anticipate that such a BCG system, trained for a set of users, can be easily installed at different locations in the house and provide continuous and unobtrusive feedback to users for diagnostic monitoring and quantified-self.

Unobtrusive Detection of Simulated Orthostatic Hypotension and Supine Hypertension Using Ballistocardiogram and Electrocardiogram of Healthy Adults.

Effective management of neurogenic orthostatic hypotension and supine hypertension (SH-OH) due autonomic failure requires a frequent and timely adjustment of medication throughout the day to maintain the blood pressure (BP) within the normal range, i.e., an accurate depiction of BP is a key prerequisite of effective management. One of the emerging technologies that provide one's circadian and long-term physiological status with increased usability is unobtrusive zero-effort monitoring. In this paper, a zero-effort device, a floor tile, was used to develop an unobtrusive BP monitoring technique. Namely, RJ-interval, the time between the J-peak of a ballistocardiogram and the R-peak of an electrocardiogram, was used to develop a classifier that can detect changes in systolic BP (SBP) induced by the Valsalva maneuver on healthy adults (i.e., a simulated SH-OH). A t-test was used to show statistical differences between the mean RJ-intervals of decreased SBP, baseline, and increased SBP. Following the t-test, a classifier that detected a change in SBP was developed based on a naïve Bayes classifier (NBC). The t-test showed a clear statistical difference between the mean RJ-intervals of the increased SBP, baseline, and decreased SBP. The NBC-based classifier was able to detect increased SBP with 89.3% true positive rate (TPR), 100% true negative rate (TNR), and 94% accuracy and detect decreased SBP with 92.3% TPR, 100% TNR, and 95% accuracy. The analysis showed strong potential in using the developed classifier to assist monitoring of people with SH-OH; the algorithm may be used clinically to detect a long-term trend of symptoms of SH-OH.

Compositional Dependence of Phase Selection in CoCrCu0.1FeMoNi-Based High-Entropy Alloys.

To study the effect of alloy composition on phase selection in the CoCrCu0.1FeMoNi high-entropy alloy (HEA), Mo was partially replaced by Co, Cr, Fe, and Ni. The microstructures and phase selection behaviors of the CoCrCu0.1FeMoNi HEA system were investigated. Dendritic, inter-dendritic, and eutectic microstructures were observed in the as-solidified HEAs. A simple face centered cubic (FCC) single-phase solid solution was obtained when the molar ratio of Fe, Co, and Ni was increased to 1.7 at the expense of Mo, indicating that Fe, Co, and Ni stabilized the FCC structure. The FCC structure was favored at the atomic radius ratio δ ≤ 2.8, valence electron concentration (VEC) ≥ 8.27, mixing entropy ΔS ≤ 13.037, local lattice distortion parameter α2 ≤ 0.0051, and ΔS/δ² > 1.7. Mixed FCC + body centered cubic (BCC) structures occurred for 4.1 ≤ δ ≤ 4.3 and 7.71 ≤ VEC ≤ 7.86; FCC or/and BCC + intermetallic (IM) mixtures were favored at 2.8 ≤ δ ≤ 4.1 or δ > 4.3 and 7.39 < VEC ≤ 8.27. The IM phase is favored at electronegativity differences greater than 0.133. However, ΔS, α2, and ΔS/δ² were inefficient in identifying the (FCC or/and BCC + IM)/(FCC + BCC) transition. Moreover, the mixing enthalpy cannot predict phase structures in this system.

Performance Characteristics of an Independent Dose Verification Program for Helical Tomotherapy.

Helical tomotherapy with its advanced method of intensity-modulated radiation therapy delivery has been used clinically for over 20 years. The standard delivery quality assurance procedure to measure the accuracy of delivered radiation dose from each treatment plan to a phantom is time-consuming. RadCalc®, a radiotherapy dose verification software, has released specifically for beta testing a module for tomotherapy plan dose calculations. RadCalc®'s accuracy for tomotherapy dose calculations was evaluated through examination of point doses in ten lung and ten prostate clinical plans. Doses calculated by the TomoHDA™ tomotherapy treatment planning system were used as the baseline. For lung cases, RadCalc® overestimated point doses in the lung by an average of 13%. Doses within the spinal cord and esophagus were overestimated by 10%. Prostate plans showed better agreement, with overestimations of 6% in the prostate, bladder, and rectum. The systematic overestimation likely resulted from limitations of the pencil beam dose calculation algorithm implemented by RadCalc®. Limitations were more severe in areas of greater inhomogeneity and less prominent in regions of homogeneity with densities closer to 1 g/cm3. Recommendations for RadCalc® dose calculation algorithms and anatomical representation were provided based on the results of the study.

Perceptions of seniors with heart failure regarding autonomous zero-effort monitoring of physiological parameters in the smart-home environment.

BACKGROUND: Technological advances are leading to the ability to autonomously monitor patient's health status in their own homes, to enable aging-in-place. OBJECTIVES: To understand the perceptions of seniors with heart failure (HF) regarding smart-home systems to monitor their physiological parameters. METHODS: In this qualitative study, HF outpatients were invited to a smart-home lab, where they completed a sequence of activities, during which the capacity of 5 autonomous sensing modalities was compared to gold standard measures. Afterwards, a semi-structured interview was undertaken. These were transcribed and analyzed using an interpretive-descriptive approach. RESULTS: Five themes emerged from the 26 interviews: (1) perceptions of technology, (2) perceived benefits of autonomous health monitoring, (3) disadvantages of autonomous monitoring, (4) lack of perceived need for continuous health monitoring, and (5) preferences for autonomous monitoring. CONCLUSIONS: Patient perception towards autonomous monitoring devices was positive, lending credence to zero-effort technology as a viable and promising approach.

Influence of particle size and reactive oxygen species on cobalt chrome nanoparticle-mediated genotoxicity.

Patients with cobalt chrome (CoCr) metal-on-metal (MOM) implants may be exposed to a wide size range of metallic nanoparticles as a result of wear. In this study we have characterised the biological responses of human fibroblasts to two types of synthetically derived CoCr particles [(a) from a tribometer (30 nm) and (b) thermal plasma technology (20, 35, and 80 nm)] in vitro, testing their dependence on nanoparticle size or the generation of oxygen free radicals, or both. Metal ions were released from the surface of nanoparticles, particularly from larger (80 nm) particles generated by thermal plasma technology. Exposure of fibroblasts to these nanoparticles triggered rapid (2 h) generation of reactive oxygen species (ROS) that could be eliminated by inhibition of NADPH oxidase, suggesting that it was mediated by phagocytosis of the particles. The exposure also caused a more prolonged, MitoQ sensitive production of ROS (24 h), suggesting involvement of mitochondria. Consequently, we recorded elevated levels of aneuploidy, chromosome clumping, fragmentation of mitochondria and damage to the cytoskeleton particularly to the microtubule network. Exposure to the nanoparticles resulted in misshapen nuclei, disruption of mature lamin B1 and increased nucleoplasmic bridges, which could be prevented by MitoQ. In addition, increased numbers of micronuclei were observed and these were only partly prevented by MitoQ, and the incidence of micronuclei and ion release from the nanoparticles were positively correlated with nanoparticle size, although the cytogenetic changes, modifications in nuclear shape and the amount of ROS were not. These results suggest that cells exhibit diverse mitochondrial ROS-dependent and independent responses to CoCr particles, and that nanoparticle size and the amount of metal ion released are influential.

Considerations for thermal injury analysis for RF ablation devices.

BACKGROUND: The estimation of lesion size is an integral part of treatment planning for the clinical applications of radiofrequency ablation. However, to date, studies have not directly evaluated the impact of different computational estimation techniques for predicting lesion size. In this study, we focus on three common methods used for predicting tissue injury: (1) iso-temperature contours, (2) Cumulative equivalent minutes, (3) Arrhenius based thermal injury. METHODS: We created a geometric model of a multi-tyne ablation electrode and simulated thermal and tissue injury profiles that result from three calculation methods after 15 minutes exposure to a constant RF voltage source. A hybrid finite element technique was used to calculate temperature and tissue injury. Time-temperature curves were used in the assessment of iso-temperature thresholds and the method of cumulative equivalent minutes. An Arrhenius-based formulation was used to calculate sequential and recursive thermal injury to tissues. RESULTS: The data demonstrate that while iso-temperature and cumulative equivalent minute contours are similar in shape, these two methodologies grossly over-estimate the amount of tissue injury when compared to recursive thermal injury calculations, which have previously been shown to correlate closely with in vitro pathologic lesion volume measurement. In addition, Arrhenius calculations that do not use a recursive algorithm result in a significant underestimation of lesion volume. The data also demonstrate that lesion width and depth are inadequate means of characterizing treatment volume for multi-tine ablation devices. CONCLUSIONS: Recursive thermal injury remains the most physiologically relevant means of computationally estimating lesion size for hepatic tumor applications. Iso-thermal and cumulative equivalent minute approaches may produce significant errors in the estimation of lesion size.

Optical-thermal characterization of cutaneous transilluminators.

In recent years, there has been an increase in the popularity of light-emitting diode (LED)-based, battery-powered transilluminators (BPTs) for facilitating transdermal vascular access in adults and neonates. BPTs are believed to have lower potential for inducing skin burns than prior devices based on high-power broadband lamps; however, the optical and thermal outputs of BPTs are not well documented and safety limits for these devices are not well established. In this study, we characterize and assess the optical and thermal outputs of six BPTs that incorporate red, orange and white LEDs. Optical measurements included spectral irradiance and peak local irradiance. Thermal measurements included transient temperature readings for an exposure time of 4 min in ambient air and ex vivo tissue pre-heated to physiological temperatures. The greatest mean temperature rise produced in tissue by a non-white-light diode BPT was 2.5 degrees C, whereas a mean temperature rise of 9.1 degrees C was measured in a BPT that incorporated white-light diodes with relatively high irradiance levels. The dominant cause of temperature rise was most likely heat generation within the devices. Thermal damage analyses based on temperature limits and the Arrhenius equation indicate that although some of the devices studied approach the threshold for damage, none appear to exceed it under normal operating conditions. The results demonstrated that ambient air measurements may be suitable for identifying worst-case BPT temperatures. This study highlights the potential risk of LED-based medical devices as well as the need for additional research on related issues such as neonatal thermal injury thresholds.

Radio-frequency ablation in a realistic reconstructed hepatic tissue.

This study uses a reconstructed vascular geometry to evaluate the thermal response of tissue during a three-dimensional radiofrequency (rf) tumor ablation. MRI images of a sectioned liver tissue containing arterial vessels are processed and converted into a finite-element mesh. A rf heat source in the form of a spherically symmetric Gaussian distribution, fit from a previously computed profile, is employed. Convective cooling within large blood vessels is treated using direct physical modeling of the heat and momentum transfer within the vessel. Calculations of temperature rise and thermal dose are performed for transient rf procedures in cases where the tumor is located at three different locations near the bifurcation point of a reconstructed artery. Results demonstrate a significant dependence of tissue temperature profile on the reconstructed vasculature and the tumor location. Heat convection through the arteries reduced the steady-state temperature rise, relative to the no-flow case, by up to 70% in the targeted volume. Blood flow also reduced the thermal dose value, which quantifies the extent of cell damage, from approximately 3600 min, for the no-flow condition, to 10 min for basal flow (13.8 cms). Reduction of thermal dose below the threshold value of 240 min indicates ablation procedures that may inadequately elevate the temperature in some regions, thereby permitting possible tumor recursion. These variations are caused by vasculature tortuosity that are patient specific and can be captured only by the reconstruction of the realistic geometry.

Thermal modeling of lesion growth with radiofrequency ablation devices.

BACKGROUND: Temperature is a frequently used parameter to describe the predicted size of lesions computed by computational models. In many cases, however, temperature correlates poorly with lesion size. Although many studies have been conducted to characterize the relationship between time-temperature exposure of tissue heating to cell damage, to date these relationships have not been employed in a finite element model. METHODS: We present an axisymmetric two-dimensional finite element model that calculates cell damage in tissues and compare lesion sizes using common tissue damage and iso-temperature contour definitions. The model accounts for both temperature-dependent changes in the electrical conductivity of tissue as well as tissue damage-dependent changes in local tissue perfusion. The data is validated using excised porcine liver tissues. RESULTS: The data demonstrate the size of thermal lesions is grossly overestimated when calculated using traditional temperature isocontours of 42 degrees C and 47 degrees C. The computational model results predicted lesion dimensions that were within 5% of the experimental measurements. CONCLUSION: When modeling radiofrequency ablation problems, temperature isotherms may not be representative of actual tissue damage patterns.

Numerical evaluation of heating of the human head due to magnetic resonance imaging.

In this paper, we present a numerical model for evaluating tissue heating during magnetic resonance imaging (MRI). Our method, which included a detailed anatomical model of a human head, calculated both the electromagnetic power deposition and the associated temperature elevations during an MRI head examination. Numerical studies were conducted using a realistic birdcage coil excited at frequencies ranging from 63 to 500 MHz. The model was validated both experimentally and analytically. The experimental validation was performed at the MR test facility located at the Food and Drug Administration's Center for Devices and Radiological Health.

Effects of perfusion on radiofrequency ablation in swine kidneys.

PURPOSE: To evaluate the effect of vascular occlusion on the size of radiofrequency (RF) ablation lesions and to evaluate embolization as an occlusion method. MATERIALS AND METHODS: The kidneys of six swine were surgically exposed. Fifteen RF ablation lesions were created in nine kidneys by using a 2-cm-tip single-needle ablation probe in varying conditions: Seven lesions were created with normal blood flow and eight were created with blood flow obstructed by means of vascular clamping (n = 5) or renal artery embolization (n = 3). The temperature, applied voltage, current, and impedance were recorded during RF ablation. Tissue-cooling curves acquired for 2 minutes immediately after the ablation were compared by using regression analysis. Lesions were bisected, and their maximum diameters were measured and compared by using analysis of variance. RESULTS: The mean diameter of ablation lesions created when blood flow was obstructed was 60% greater than that of lesions created when blood flow was normal (1.38 cm +/- 0.05 [standard error of mean] vs 0.86 cm +/- 0.07, P <.001). The two methods of flow obstruction yielded lesions of similar mean sizes: 1.40 cm +/- 0.06 with vascular clamping and 1.33 cm +/- 0.07 with embolization. The temperature at the probe tip when lesions were ablated with normal blood flow decreased more rapidly than did the temperature when lesions were ablated after flow obstruction (P <.001), but no significant differences in tissue-cooling curves between the two flow obstruction methods were observed. CONCLUSION: Obstruction of renal blood flow before and during RF ablation resulted in larger thermal lesions with potentially less variation in size compared with the lesions created with normal nonobstructed blood flow. Selective arterial embolization of the kidney vessels may be a useful adjunct to RF ablation of kidney tumors.

An alternative method for determination of low-frequency specific absorption rate patterns in homogeneous phantoms.

We propose a new application of voltage gradient measurements to determine specific absorption rate (SAR) at low frequencies where quasi-static electromagnetic conditions apply. This method, which we call the voltage gradient method, relies on direct measurement of the voltage field rather than measurement of the electric field or thermal transients. The voltage gradient method is fast and can be implemented with voltmeters of moderate cost. We tested the voltage gradient method using normal saline, in a phantom with simple geometry, and a sine wave voltage source at 5, 10, 20 and 50 kHz. Compared to the SAR measured thermally in the same phantom, the voltage gradient method produced almost identical curves when normalized. When the results of the voltage gradient method were scaled to the same power level used for the thermal SAR, the agreement was compatible with typical thermal SAR accuracy.

Finite element analysis of hepatic radiofrequency ablation probes using temperature-dependent electrical conductivity.

BACKGROUND: Few finite element models (FEM) have been developed to describe the electric field, specific absorption rate (SAR), and the temperature distribution surrounding hepatic radiofrequency ablation probes. To date, a coupled finite element model that accounts for the temperature-dependent electrical conductivity changes has not been developed for ablation type devices. While it is widely acknowledged that accounting for temperature dependent phenomena may affect the outcome of these models, the effect has not been assessed. METHODS: The results of four finite element models are compared: constant electrical conductivity without tissue perfusion, temperature-dependent conductivity without tissue perfusion, constant electrical conductivity with tissue perfusion, and temperature-dependent conductivity with tissue perfusion. RESULTS: The data demonstrate that significant errors are generated when constant electrical conductivity is assumed in coupled electrical-heat transfer problems that operate at high temperatures. These errors appear to be closely related to the temperature at which the ablation device operates and not to the amount of power applied by the device or the state of tissue perfusion. CONCLUSION: Accounting for temperature-dependent phenomena may be critically important in the safe operation of radiofrequency ablation device that operate near 100 degrees C.