Jon P. Casamento

Intracellular calcium signaling by Jurkat T-lymphocytes exposed to a 60 Hz magnetic field.

To explore possible biochemical mechanisms whereby electromagnetic fields of around 0.1 mT might affect immune cells or developing cancer cells, we studied intracellular calcium signaling in the model system Jurkat E6-1 human T-leukemia cells during and following exposure to a 60 Hz magnetic field. Cells were labeled with the intracellular calcium-sensitive fluorescent dye Fluo-3, stimulated with a monoclonal antibody against the cell surface structure CD3 (associated with ligand-stimulated T-cell activation), and analyzed on a FACScan flow-cytometer for increases in intensity of emissions in the range of 515-545 nm. Cells were exposed during or before calcium signal-stimulation to 0.15 mTrms 60 Hz magnetic field. The total DC magnetic field of 78.2 microT was aligned 17.5 degrees off the vertical axis. Experiments used both cells cultured at optimal conditions at 37 degrees C and cells grown under suboptimal conditions of 24 degrees C, lowered external calcium, or lowered anti-CD3 concentration. These experiments demonstrate that intracellular signaling in Jurkat E6-1 was not affected by a 60 Hz magnetic field when culture and calcium signal-stimulation were optimal or suboptimal. These results do not exclude field-induced calcium-related effects further down the calcium signaling pathway, such as on calmodulin or other calcium-sensitive enzymes.

Calculation of induced current densities and specific absorption rates (SAR) for pregnant women exposed to hand-held metal detectors

The finite difference time domain (FDTD) method in combination with a well established frequency scaling method was used to calculate the internal fields and current densities induced in a simple model of a pregnant woman and her foetus, when exposed to hand-held metal detectors. The pregnant woman and foetus were modelled using a simple semi-heterogeneous model in 10 mm resolution, consisting of three different types of tissue. The model is based on the scanned shape of a pregnant woman in the 34th gestational week. Nine different representative models of hand-held metal detectors operating in the frequency range from 8 kHz to 2 MHz were evaluated. The metal detectors were placed directly on the abdomen of the computational model with a spacing of 1 cm. Both the induced current density and the specific absorption rate (SAR) are well below the recommended limits for exposure of the general public published in the ICNIRP Guidelines and the IEEE C95.1 Standard. The highest current density is 8.3 mA m(-2) and the highest SAR is 26.5 microW kg(-1). Compared to the limits for the induced current density recommended in the ICNIRP Guidelines, a minimum safety factor of 3 exists. Compared to the IEEE C95. 1 Standard, a safety factor of 60 000 for the specific absorption rate was found. Based on the very low specific absorption rate and an induced current density below the recommended exposure limits, significant temperature rise or nerve stimulation in the pregnant woman or in the foetus can be excluded.

Comparison of the Effect of ELF on c-myc Oncogene Expression in Normal and Transformed Human Cells

EWA CZERSKA? JON CASAMENT0,O JOHN NINGF MAYS SWICORDF HEBA AL-BARAZI? CHRISTOPHER DAVIS! AND EDWARD ELSONC aCenter for Devices and Radiological Health Food and Drug Administration Rockville, Maryland 20857 bDepartment of Electrical Engineering Universiv of Maryland College Park Maryland 20742 CDepartment of Microwave Research Walter Reed A m y Institute of Research Washington, District of Columbia 20307

Testing the Immunity of Active Implantable Medical Devices to CW Magnetic Fields up to 1 MHz by an Immersion Method

This paper presents a magnetic-field system and the method developed for testing the immunity of the active implantable medical devices to continuous-wave magnetic fields in the frequency range up to 1 MHz. The system is able to produce magnetic fields of 150 A/m for frequencies up to 100 kHz and strengths decreasing as l/f between 100 kHz and 1 MHz, with uniformity of the field within plusmn2.5% in the volume for tests. To simulate human tissue, the medical device, together with its leads, is placed on a plastic grid in a saline tank that is introduced in the magnetic field of the induction coil. This paper offers an alternative for the injection voltage methods provided in the actual standards for assessing the protection of the implantable medical devices from the effects of the magnetic fields up to 1 MHz. This paper presents the equipment and signals used, the test procedure, and results from the preliminary tests performed at the Food and Drug Administration-Center for Devices and Radiological Health on implantable pacemakers and neurostimulators. The new system and test method are useful for the EMC research on the implantable medical devices.

Medical device EMI: FDA analysis of incident reports, and recent concerns for security systems and wireless medical telemetry

FDA has evaluated reports of medical device malfunctions caused by electromagnetic interference (EMI), performed device testing, and developed standardized test procedures. Over 500 incident reports are suspected to be attributable to EMI affecting cardiac devices. More than 80 of these reports involve cardiac and other medical device interactions with electronic security systems. EMI presents a risk to patient safety and medical device effectiveness that is likely to continue as the use of electromagnetic energy in the medical device environment increases (e.g., cell phones, security systems). Developments can reduce these risks, such as the allocation of dedicated frequency bands for the new wireless medical telemetry service (WMTS) designed to protect transmissions of patient vital signs from interference by other intentional transmitters.

Performance Testing of Huber Needles for Coring of Port Septa

The Food and Drug Administration received complaints of Huber needles creating cores in the septa of ports of gastric banding devices. One of these complaints represented a cluster of similar events, even though no deviations from design specifications or recommended practices were subsequently identified by the manufacturer. The authors conducted this comparative investigation of off-the-shelf Huber needles and ports from several manufacturers to determine if engineering parameters could be identified that could account for the coring complaints. Huber needles from ten manufacturers were evaluated for coring using intravascular access ports from five manufacturers. A detailed optical analysis was also performed to identify needle features that would possibly account for coring. The majority of the tested needles performed as they should, i.e., they perforated the port septa without creating cores. However, needles that did produce cores were found to have sharp edges at the heel edge of the needle lumen, the edge of the ground bevel opposite from the needle tip that opens to the inner surface of the cannula tube. Manufacturing processes, which dulled or rounded the sharp heel of the bevel after bevel grinding, prevented coring. As a result of this investigation one manufacturer voluntarily recalled their product and another manufacturer implemented coring testing as part of their quality control. To prevent coring needles from entering the market as a result of manufacturing flaws, optical inspection of the heel edge and coring testing should be performed as part of routine quality control.

Changes in the susceptibility of a medical device resulting from connection to a full-size model of a human

The Radiofrequency (RF) susceptibility of an apnea monitor was evaluated while connected to a saline-filled, full-size model of an adult human. Experimental measurements were performed at an outdoor electromagnetic compatibility (EMC) test facility. The RF susceptibility of the apnea monitor increased by approximately 8 to 15 dB when its fully-extended patientmonitoring leads and electrodes were connected to the model, rather than being terminated with a resistor. This increase in electric field strength susceptibility of 2.5 to 5.6 times occurred in the 63 to 100 MHz range. This frequency range includes the resonant frequency of the model, and of actual adult humans. This finding has clinical significance due to the widespread presence of high power FM radio and VHF television transmitters in the U.S. and other countries.

Electromagnetic Compatibility Testing of Implantable Neurostimulators Exposed to Metal Detectors

This paper presents results of electromagnetic compatibility (EMC) testing of three implantable neurostimulators exposed to the magnetic fields emitted from several walk-through and hand-held metal detectors. The motivation behind this testing comes from numerous adverse event reports involving active implantable medical devices (AIMDs) and security systems that have been received by the Food and Drug Administration (FDA). EMC testing was performed using three neurostimulators exposed to the emissions from 12 walk-through metal detectors (WTMDs) and 32 hand-held metal detectors (HHMDs). Emission measurements were performed on all HHMDs and WTMDs and summary data is presented. Results from the EMC testing indicate possible electromagnetic interference (EMI) between one of the neurostimulators and one WTMD and indicate that EMI between the three neurostimulators and HHMDs is unlikely. The results suggest that worst case situations for EMC testing are hard to predict and testing all major medical device modes and setting parameters are necessary to understand and characterize the EMC of AIMDs.

Automated radiofrequency electromagnetic interference testing of apnea monitors using an open area test site

Medical devices that electronically sense physiological functions may be affected by external radiofrequency (RF) radiation from sources such as television and radio stations. When RF disrupts normal device function, it is referred to as electromagnetic interference (EMI). The Center for Devices and Radiological Health (CDRH) has been testing infant apnea monitors for susceptibility to EMI. Laboratory testing and user site surveys were conducted that confirmed susceptibility to EMI in infant apnea monitors. The field strength value above which device performance was compromised will be referred to as the devices threshold. An automated procedure has now been developed which enables us to obtain threshold EMI field-strength versus frequency plots and identify EMI regions by frequency band In addition, precise measurements at an outdoor open area test site have found that the ≃300-cm (≃10-ft) patient leads, when fully extended, act as significant receivers of RF signals below 50 MHz. Thresholds, averaged over the 10–54 MHz frequency range, were 0.22 V/m with minimums reaching 0.05 V/m for four of the nine monitors tested when 100% amplitude modulation at 0.5 Hz was imposed on the RF carrier. In the FM band (88–108 MHz) the thresholds averaged 0.88 V/m, with one model reaching a minimum of 0.08 V/m. These results were similar to our earlier laboratory data which were taken with the patient and power supply leads not fully extended in the RF exposure Held, indicating that testing with full lead length exposures may not be necessary at higher frequencies.

Performance Testing of Fast Read Digital Thermometers

Body temperature monitoring of humans has been an important tool for diagnosing infections, detecting fever, monitoring thermoregulation functions during surgical procedures, and assessing postsurgery recovery. Temperature is measured at various body sites including the pulmonary artery, rectum, bladder, distal esophagus and nasopharynx, sublingual surface of the tongue, under the armpit, tympanic membrane, and forehead. Inexpensive, off-the-shelf digital thermometers are generally used to measure temperature orally or under the arm. Currently, many such thermometers are available with a “fast read” capability, where they produce temperature readings in 5–10 s. In a previous study [1], we used a custom-designed, small thermistor bead-based thermometer (NIST traceable) and a computer data acquisition system to measure and record temperatures at a rate of 7 Hz (“reference thermometer”). Therefore, the reference thermometer records the temperature rise (transient data) from the initial contact with the skin until equilibrium. The small bead ensures rapid heat transfer and accurate temperature measurements. Relevant temperature measurements required at least 20 s, even with a sophisticated design and expensive support electronics. In this study we conducted clinical temperature measurement research on children to evaluate the accuracy of three off-the-shelf digital thermometers (brands A, B, and C) compared to our reference thermometer [1]. The off-the-shelf thermometers state that 5–11 s are required to produce a temperature measurement, depending on the brand. All of the off-the-shelf thermometers claimed an accuracy of 60.2 F; while one manufacturer (brand A) specified that the accuracy was achieved in a water bath. Also some manufacturers stated that the axillary measurements will be lower than the oral measurements: 1 F for brand A and 1–2 F for brand C. Our experience with our reference thermometer indicates that longer than 5–11 s would be needed to measure body temperature with the claimed accuracy. The purpose of this study was to investigate the accuracy of the fast read thermometers compared to our reference thermometer.