Power saw noise levels during steel stud cutting tasks on commercial construction sites: a tool characterization from a worker exposure standpoint.

Construction framers who cut and install steel studs as part of their daily tasks are exposed to hazardous noise levels during their work shift in large part due to the power saws they use to cut steel studs. This investigation characterized the sound pressure levels of power saws used to cut steel studs on active construction sites. Further, the length of time it took to cut various studs on a construction site was investigated to understand worker exposure times to saw noise. In general, power saws used on the study sites to cut steel studs had a mean A-weighted equivalent continuous sound pressure level (LAeq) of 107.2 dB and a C-weighted peak sound pressure level (LCpeak) of 120.1 dB. Three of the saws-the chopsaw, the cut-off saw, and the grinder-had similar noise levels, whereas the cordless circular saw had higher noise levels. It took an average of 13.2 s to cut each stud, and workers in the study used power saws to cut steel studs for an average of 371.5 s per day. This average exposure time at the average recorded sound pressure levels (SPLs) suggests these saws can increase the risk of occupational noise-induced hearing loss, according to National Institute for Occupational Safety and Health (NIOSH) recommendations.

Behaviourally mediated predation avoidance in penguin prey: in situ evidence from animal-borne camera loggers.

Predator dietary studies often assume that diet is reflective of the diversity and relative abundance of their prey. This interpretation ignores species-specific behavioural adaptations in prey that could influence prey capture. Here, we develop and describe a scalable biologging protocol, using animal-borne camera loggers, to elucidate the factors influencing prey capture by a seabird, the gentoo penguin (Pygoscelis papua). From the video evidence, we show, to our knowledge for the first time, that aggressive behavioural defence mechanisms by prey can deter prey capture by a seabird. Furthermore, we provide evidence demonstrating that these birds, which were observed hunting solitarily, target prey when they are most discernible. Specifically, birds targeted prey primarily while ascending and when prey were not tightly clustered. In conclusion, we show that prey behaviour can significantly influence trophic coupling in marine systems because despite prey being present, it is not always targeted. Thus, these predator-prey relationships should be accounted for in studies using marine top predators as samplers of mid- to lower trophic-level species.

Characterizing medical care by disease phase in metastatic colorectal cancer.

PURPOSE: To characterize patterns of medical care by disease phase in patients with newly diagnosed metastatic colorectal cancer (mCRC). METHODS: Patients with mCRC newly diagnosed between 2004 and 2008 were selected from a large US national commercially insured claims database and were observed from initial mCRC diagnosis to death, disenrollment, or end of study period (July 31, 2009), whichever occurred first. The observation period was divided into three distinct phases of disease: diagnostic, treatment, and death. Within each phase, patterns of medical care were examined by the mutually exclusive service categories of inpatient, emergency room (ER), outpatient office and facility, outpatient pharmacy, chemotherapy, and biologic therapy, as measured by estimation of aggregate and category costs per patient per month. RESULTS: A total of 6,675 patients with newly diagnosed mCRC were analyzed. Mean age was 64.1 years; 55.5% were males. Mean costs per patient per month for diagnostic, treatment, and death phases were $16,895, $8,891, and $27,554, respectively. Inpatient care was the primary driver of medical care for both the diagnostic (41.7% of costs) and death (71.4% of costs) phases. The largest category of medical care for the treatment phase was outpatient care (45.0% of costs). Chemotherapy and biologic therapy accounted for 15.6% and 17.6% of costs in the treatment phase, respectively. CONCLUSION: Substantial differences in patterns of medical care were found between mCRC disease phases. Inpatient care was the key driver of medical care in the diagnostic and death phases compared with outpatient care in the treatment phase.

Characterizing medical care by disease phase in metastatic colorectal cancer.

OBJECTIVE: To characterize patterns of medical care by disease phase in patients with newly diagnosed metastatic colorectal cancer (mCRC). METHODS: Patients with mCRC newly diagnosed between 2004 and 2008 were selected from a large US national commercially insured claims database and were observed from initial mCRC diagnosis to death, disenrollment, or end of study period (July 31, 2009), whichever occurred first. The observation period was divided into 3 distinct phases of disease: diagnostic, treatment, and death. Within each phase, patterns of medical care were examined by the mutually exclusive service categories of inpatient, emergency department (ED), outpatient office and facility, outpatient pharmacy, chemotherapy, and biologic therapy, as measured by estimation of aggregate and category costs per patient per month. RESULTS: A total of 6675 patients with newly diagnosed mCRC were analyzed. Mean age was 64.1 years; 55.5% were males. Mean costs per patient per month for diagnostic, treatment, and death phases were $16,895, $8891, and $27,554, respectively. Inpatient care was the primary driver of medical care for both the diagnostic (41.7% of costs) and death (71.4% of costs) phases. The largest category of medical care for the treatment phase was outpatient care (45.0% of costs). Chemotherapy and biologic therapy accounted for 15.6% and 17.6% of costs in the treatment phase, respectively. CONCLUSION: Substantial differences in patterns of medical care were found between mCRC disease phases. Inpatient care was the key driver of medical care in the diagnostic and death phases compared with outpatient care in the treatment phase.

RF ablation at low frequencies for targeted tumor heating: in vitro and computational modeling results.

RF ablation uses RF current to heat and kill cancer applied via an electrode inserted under image guidance. Tumor has about half the electrical resistivity of normal tissue below 20 kHz, but similar resistivity above 500 kHz. We placed normal porcine liver tissue in contact with agar gel having similar resistivity as tumor within 20-450 kHz. A needle electrode was placed with half of the electrically active tip in each layer. We performed ablation with electric current applied for 12 min at 30 W, either at 20 or 450 kHz (n = 7 each), while measuring temperature via thermocouples 4 and 8 mm from the electrode. Mathematical heat-transfer models were created of an equivalent configuration and temperature profile determined at both frequencies. At 8-mm distance, at 450 kHz, tumor gel phantom and normal tissue obtained similar temperatures (57.5 ± 1.4 versus 58.7 ± 2.5 (°)C); at 20 kHz, tumor phantom obtained significantly higher temperatures than normal tissue (65.6 ± 2.0 versus 57.2 ± 5.6 (°)C, p < 0.01). Computer models confirm these results, and show the ablation zone diameter to be larger within the tumor phantom at 20 kHz compared to 450 kHz. Heating at low RFs may thus allow targeted heating of tumor tissue and reduced heating of normal tissue.

Sequential activation of ground pads reduces skin heating during radiofrequency tumor ablation: in vivo porcine results.

Skin burns below ground pads during monopolar RF ablation are increasingly prevalent, thereby hindering the development of higher power RF generators capable of creating larger tumor ablation zones in combination with multiple or new applicators. Our goal was to evaluate reduction in skin temperatures via additional ground pads in an in vivo porcine model. Three ground pads placed on the animal's abdomen were activated either simultaneously or sequentially, where activation timing was adjusted to equilibrate skin temperature below each pad. Thirteen RF ablations (n = 4 simultaneous at 300 W, n = 5 sequential at 300 W, and n = 4 sequential at 375 W) were performed for 12 min via two internally cooled cluster electrodes placed in the gluteus maximus of domestic swine. Temperature rise at each pad and burn degree as determined via histology were compared. Ablation zone size was determined via T2-weighted MRI. Maximum temperature rise was significantly higher with simultaneous activation than with either of the sequential activation group (21.4 degrees C versus 8.1 degrees C or 9.6 degrees C, p < 0.01). Ablation zone diameters during simultaneous (300 W) and sequential activations (300 and 375 W) were and 6.9 +/- 0.3, 5.6 +/- 0.3, and 7.5 +/- 0.6 cm, respectively. Sequential activation of multiple ground pads results in significantly lower skin temperatures and less severe burns, as measured by histological examination.

Sequential activation of ground pads reduces skin heating during radiofrequency ablation: initial in vivo porcine results.

PURPOSE: Radiofrequency (RF) ablation is a common treatment modality for inoperable liver cancer. Skin burns below ground pads during RF ablations are increasingly prevalent, hindering the development of higher-power RF generators capable of creating larger ablation zones. MATERIALS AND METHODS: 9 RF ablations (n=4 simultaneous, n=5 sequential) were performed with 300 W for 12 min via two internally cooled cluster electrodes placed in the gluteus maximus of domestic swine. Three ground pads placed on the animal's abdomen were activated either simultaneously, or sequentially where activation timing was adjusted to equilibrate skin temperature below each pad. Temperature rise at each pad was compared. Ablation zone dimensions were determined via MRI. RESULTS: Maximum temperature rise was significantly higher with simultaneous activation than with sequential activation (21.4 vs 8.1 degress C, p<0.01). Ablation zone diameters during simultaneous and sequential activation were 6.9+/-0.3 and 5.6+/-0.3, respectively. CONCLUSION: Sequential activation of multiple ground pads resulted in significantly lower skin temperatures during highpower RF ablation.

Effect of electrode thermal conductivity in cardiac radiofrequency catheter ablation: a computational modeling study.

PURPOSE: Radiofrequency (RF ablation) is the treatment of choice for certain types of cardiac arrhythmias. Recent studies have suggested that using gold instead of platinum as the electrode material for cardiac catheter ablation leads to larger thermal lesions due to its higher thermal conductivity. In this study we created computer models to compare the effects of different electrode materials on lesion dimensions using different catheters, insertion depths, and flow rates. MATERIALS AND METHODS: Finite element method (FEM) models of two cardiac ablation electrodes (7Fr, length 4 mm and 8Fr, length 10 mm) made of platinum, gold, and copper were created with tissue insertion depths of 0.75, 1.25, and 2.5 mm. Convective cooling was applied to the electrode and tissue based on measurements from previous studies at different flow rates. RF ablations were simulated with both temperature control and constant power control algorithms to determine temperature profiles after 60 s. RESULTS: With the constant power algorithm there was no difference in lesion dimensions between the electrode materials over the range of parameters. With the temperature control algorithm, lesion width and depth were only marginally larger ( approximately 0.1-0.7 mm) with the gold and copper electrodes compared to the platinum electrode for all parameter combinations. CONCLUSION: Our computer modelling results show only minor increases in thermal lesion dimensions with electrode materials of higher thermal conductivity. These observed differences likely do not provide a significant advantage during clinical procedures.

Electrical conductivity measurement of excised human metastatic liver tumours before and after thermal ablation.

We measured the ex vivo electrical conductivity of eight human metastatic liver tumours and six normal liver tissue samples from six patients using the four electrode method over the frequency range 10 Hz to 1 MHz. In addition, in a single patient we measured the electrical conductivity before and after the thermal ablation of normal and tumour tissue. The average conductivity of tumour tissue was significantly higher than normal tissue over the entire frequency range (from 4.11 versus 0.75 mS cm(-1) at 10 Hz, to 5.33 versus 2.88 mS cm(-1) at 1 MHz). We found no significant correlation between tumour size and measured electrical conductivity. While before ablation tumour tissue had considerably higher conductivity than normal tissue, the two had similar conductivity throughout the frequency range after ablation. Tumour tissue conductivity changed by +25% and -7% at 10 Hz and 1 MHz after ablation (0.23-0.29 at 10 Hz, and 0.43-0.40 at 1 MHz), while normal tissue conductivity increased by +270% and +10% at 10 Hz and 1 MHz (0.09-0.32 at 10 Hz and 0.37-0.41 at 1 MHz). These data can potentially be used to differentiate tumour from normal tissue diagnostically.

Probabilistic finite element analysis of radiofrequency liver ablation using the unscented transform.

The main limitation of radiofrequency (RF) ablation numerical simulations reported in the literature is their failure to provide statistical results based on the statistical variability of tissue thermal-electrical parameters. This work developed an efficient probabilistic approach to hepatic RF ablation in order to statistically evaluate the effect of four thermal-electrical properties of liver tissue on the uncertainty of the ablation zone dimensions: thermal conductivity, specific heat, blood perfusion and electrical conductivity. A deterministic thermal-electrical finite element model of a monopolar electrode inserted in the liver was coupled with the unscented transform method in order to obtain coagulation zone confidence intervals, probability and cumulative density functions. The coagulation zone volume, diameter and length were 10.96 cm(3), 2.17 cm and 4.08 cm, respectively (P < 0.01). Furthermore, a probabilistic sensitivity analysis showed that perfusion and thermal conductivity account for >95% of the variability in coagulation zone volume, diameter and length.

Effects of variation in perfusion rates and of perfusion models in computational models of radio frequency tumor ablation.

PURPOSE: Finite element method (FEM) models are commonly used to simulate radio frequency (RF) tumor ablation. Prior FEM models of RF ablation have either ignored the temperature dependent effect of microvascular perfusion, or implemented the effect using simplified algorithms to reduce computational complexity. In this FEM modeling study, the authors compared the effect of different microvascular perfusion algorithms on ablation zone dimensions with two commercial RF electrodes in hepatic tissue. They also examine the effect of tissue type and inter-patient variation of perfusion on ablation zone dimensions. METHODS AND MATERIALS: The authors created FEM models of an internally cooled and multi-tined expandable electrode. RF voltage was applied to both electrodes (for 12 or 15 min, respectively) such that the maximum temperature in the model was 105 degrees C. Temperature dependent microvascular perfusion was implemented using three previously reported methodologies: cessation above 60 degrees C, a standard first-order Arrhenius model with decreasing perfusion with increasing degree of vascular stasis, and an Arrhenius model that included the effects of increasing perfusion at the ablation zone boundary due to hyperemia. To examine the effects of interpatient variation, simulations were performed with base line and +/-1 standard deviation values of perfusion. The base line perfusion was also varied to simulate the difference between normal and cirrhotic liver tissue. RESULTS: The ablation zone volumes with the cessation above 60 degrees C perfusion algorithm and with the more complex Arrhenius model were up to 70% and 25% smaller, respectively, compared to the standard Arrhenius model. Ablation zone volumes were up to 175% and approximately 100% different between the simulations where -1 and +1 standard deviation values of perfusion were used in normal and cirrhotic liver tissue, respectively. CONCLUSIONS: The choice of microvascular perfusion algorithm has significant effects on final ablation zone dimensions in FEM models of RF ablation. The authors also found that both interpatient variation in base line tissue perfusion and the reduction in perfusion due to cirrhosis have considerable effect on ablation zone dimensions.

Sequential activation of a segmented ground pad reduces skin heating during radiofrequency tumor ablation: optimization via computational models.

Radiofrequency (RF) ablation has become an accepted treatment modality for unresectable tumors. The need for larger ablation zones has resulted in increased RF generator power. Skin burns due to ground pad heating are increasingly limiting further increases in generator power, and thus, ablation zone size. We investigated a method for reducing ground pad heating in which a commercial ground pad is segmented into multiple ground electrodes, with sequential activation of ground electrode subsets. We created finite-element method computer models of a commercial ground pad (14 x 23 cm) and compared normal operation of a standard pad to sequential activation of a segmented pad (two to five separate ground electrode segments). A constant current of 1 A was applied for 12 min in all simulations. Time periods during sequential activation simulations were adjusted to keep the leading edge temperatures at each ground electrode equal. The maximum temperature using standard activation of the commercial pad was 41.7 degrees C. For sequential activation of a segmented pad, the maximum temperature ranged from 39.3 degrees C (five segments) to 40.9 degrees C (two segments). Sequential activation of a segmented ground pad resulted in lower tissue temperatures. This method may reduce the incidence of ground pad burns and enable the use of higher power generators during RF tumor ablation.

Tumor ablation at low frequencies for preferential tumor heating: initial ex-vivo tissue studies.

PURPOSE: Radiofrequency (RF) ablation is a common treatment modality for inoperable liver cancer. Several studies have demonstrated that significant differences exist between the electrical properties of tumor and normal tissue, especially at lower frequencies. In this study, we investigated in an ex vivo setting whether the use of lower frequencies during ablation results in preferential heating of tumor tissue. MATERIALS AND METHODS: We created a setup consisting of adjacent layers (3 cm thick each) of tumor phantom (agar gel) and freshly excised normal porcine liver tissue in a saline bath. A standard RF needle electrode was placed such that half of the active electrode was in each layer. We applied 25 W of power at a frequency of either 20 or 325 kHz to the electrode for 12 minutes. Temperatures were recorded 6 and 10 mm from the electrode in both the phantom and normal tissue layers. RESULTS: The ratio of the temperature rise in the tumor phantom to the temperature rise in the normal tissue was significantly higher in the 20 kHz trials after 12 minutes at both 6 mm (1.50+/-0.27 vs. 1.02+/-0.16) and 10 mm (1.34+/-0.28 vs. 0.90+/-0.11) from the electrode (p<0.01). CONCLUSION: Tumor ablation at frequencies lower than currently used may preferentially heat tumor tissue, preserving normal tissue at the treatment site.

Sequential activation of multiple grounding pads reduces skin heating during radiofrequency tumor ablation.

PURPOSE: Radiofrequency (RF) tumor ablation has become an accepted treatment modality for tumors not amenable to surgery. Skin burns due to ground pad heating may become a limiting factor for further increase in ablation zone dimensions and generator power. We investigated a method were groups of ground pads are sequentially activated to reduce skin heating. METHODS: We compared conventional operation (i.e. simultaneous connection of all pads) to sequentially switched activation of the pads where different pad combinations are active for periods of approximately 0.3 - 8 s. The timing during sequential activation was adjusted to keep the leading edge temperature equal between the pads. We created Finite Element Method computer models of three pads (5 x 5 cm, 1 cm apart) placed in line with the RF electrode on a human thigh to determine differences in tissue heating during simultaneous and sequential ground pad activation. We performed experiments with three ground pads (5 x 10 cm, 4 cm apart) placed on a tissue phantom (1.5 A, 12 min) and measured pad surface and leading edge temperatures. RESULTS: Temperature rise below the leading edge for proximal, middle and distal ground pad in relation to active electrode location was 5.9 degrees C +/- 0.1 degrees C, 0.8 degrees C +/- 0.1 degrees C and 0.3 degrees C +/- 0.1 degrees C for conventional operation, and 3.3 degrees C +/- 0.1 degrees C, 3.4 degrees C +/- 0.2 degrees C and 3.4 degrees C +/- 0.2 degrees C for sequentially activated operation in the experiments (p < 0.001). CONCLUSION: Sequential activation of multiple ground pads resulted in reduced maximum tissue temperature. This may reduce the incidence of ground pad burns and may allow higher power RF generators.

In vitro measurements of temperature-dependent specific heat of liver tissue.

We measured the specific heat of liver tissue in vitro by uniformly heating liver samples between two electrodes. We insulated the samples by expanded polystyrene, and corrected for heat loss and water loss. The specific heat of the liver is temperature-dependent, and increases by 17% at 83.5 degrees C (p < 0.05), compared to temperatures below 65 degrees C. The average specific heat was 3411 J kg(-1)K(-1) at 25 degrees C, and 4187 J kg(-1)K(-1) at 83.5 degrees C. Water loss from the samples was significant above 70 degrees C, with approximately 20% of reduction in sample mass at 90 degrees C.

Haemostatic partial nephrectomy using bipolar radiofrequency ablation.

OBJECTIVE: To determine whether an electrode array with a bipolar radiofrequency ablation (RFA) energy source can be used to perform a haemostatic partial nephrectomy by simultaneously ablating and coagulating renal tissue. MATERIALS AND METHODS: Lower-pole partial nephrectomy was performed in 12 porcine kidneys using a bipolar RFA system. Intraoperative ultrasonography was used to identify and avoid the collecting system. Tissues were positioned between opposing electrodes and tissue impedance monitored using a proprietary feedback and control algorithm. Ablation time and power, lesion width and length, and tissue thickness were recorded. The kidneys were assessed in vivo to show haemostasis of the remaining renal unit. Collecting system integrity was assessed with methylene blue injection, and the resected tissue analysed histologically. RESULTS: Partial nephrectomies were successful in all 12 porcine kidneys; the mean nephrectomy specimen was 3.2 x 2.6 cm. The total ablation time (sem) per lesion was 211 (15) s and the mean power was 23 W. Methylene blue injection showed an intact collecting system in 11 of the 12 kidneys, and haematoxylin and eosin staining showed a mean zone of necrosis of 9 mm at the resection margin. Ultrasonography revealed flow to the remaining kidneys after RFA and the in vivo assessment of haemostasis revealed no abnormal bleeding or haemorrhage from the kidneys. CONCLUSIONS: Applying bipolar RF energy to an electrode array can enable transmural excision of renal parenchyma in vivo in a bloodless fashion without collecting system injury.

Measurement of temperature-dependent specific heat of biological tissues.

We measured specific heat directly by heating a sample uniformly between two electrodes by an electric generator. We minimized heat loss by styrofoam insulation. We measured temperature from multiple thermocouples at temperatures from 25 degrees C to 80 degrees C while heating the sample, and corrected for heat loss. We confirm method accuracy with a 2.5% agar-0.4% saline physical model and obtain specific heat of 4121+/-89 J (kg K)(-1), with an average error of 3.1%.

Large-volume radiofrequency ablation of ex vivo bovine liver with multiple cooled cluster electrodes.

Three methods of creating large thermal lesions with cool-tip cluster electrodes were compared. Three cluster electrodes were arranged 4 cm apart in a triangular array. Eight lesions were created ex vivo in fresh bovine liver (from a butcher) with each method: sequential ablation (three electrodes, 12 minutes each); simultaneous activation of electrodes (12 minutes); and rapid switching of power between electrodes (12 minutes), for which an electronic computer-controlled switch was developed. For sequential, rapid switching, and simultaneous methods, lesion volumes were 137.5 cm(3)+/- 22.2, 116.4 cm(3)+/- 15.2, and 22.3 cm(3)+/- 6.4 (P < .05), respectively, and final temperatures at lesion center were 80 degrees C +/- 5, 97 degrees C +/- 8, and 41 degrees C +/- 3 (P < .001), respectively. Because of electrical interference between electrodes, simultaneous method led to little heating at the center between the electrodes and created small discontinuous lesions. Rapid switching created large round lesions by employing multiple electrodes concurrently, which substantially reduced treatment time and resulted in more effective heating between electrodes.

Do complication screening programs detect complications present at admission?

BACKGROUND: A study was undertaken to verify the accuracy of computer algorithms on administrative data to identify hospital complications. The assessment was based on a medical records indicator that differentiated hospital-acquired conditions from preexisting comorbidities. METHODS: The indicators for identifying potential hospital complications were applied to all secondary diagnoses to distinguish hospital-acquired from preexisting conditions for all 1997-1998 discharges. RESULTS: Of the 95 defined complication types, cases were found with secondary diagnoses that met the criteria for 71 different complications. Sixty-nine of these complications had one or more cases with the trigger diagnosis coded as an acquired condition. Thirty-five complications had at least 30 cases with acquired conditions. Hospital complications add greatly to costs; for example, postoperative septicemia increased the hospital bill by more $25,000, added 13 hospital days to the stay, and increased hospital mortality by 16.6%. CONCLUSIONS: Current complication algorithms identify many cases where the condition was actually present on hospital admission. This fact, coupled with the known variability in coding between institutions, makes comparisons between hospitals on many of the complications problematic. Collection of the present-on-admission flag significantly reduces the noise in monitoring complication rates.

The value of pharmaceuticals--some direction for employers.

The costs of drugs keep rising. Are they worth it? Employers should consider value over cost, and make decisions based on diagnostics and research. They should thoroughly examine their organizations' experience to determine high-priority health conditions and do cost-effectiveness studies (using experienced consultants if necessary) that focus on all of the consequences of conditions and indicate the best medical and pharmaceutical therapies to treat them. Doing so should produce both human and financial dividends.