Impedance-gradient electrode reduces skin irritation induced by transthoracic defibrillation.

A new type of disposable external defibrillation electrode has been developed to reduce the skin irritation commonly associated with defibrillation and synchronised cardioversion. This design employs an impedance gradient to reduce the proportion of current delivered to the electrode periphery. The temperature distribution under the new electrode was compared with that of four other types of commercially available electrodes after repeated high-energy biphasic defibrillation discharges to domestic swine. Skin temperature distributions were acquired using non-invasive thermography. Measurements of the maximum temperature rise at each electrode site, taken 3.6s after the fifth defibrillation discharge, demonstrated that the new impedance-gradient electrode produced 50-60% less skin heating than two of the three uniform-impedance electrode designs. Histological examination of erythematous sites excised 24 h after defibrillation quantified the associated skin damage using a scoring protocol developed for this study. In contrast to previous studies, histological examinations demonstrated second-degree skin burns following defibrillation. The new electrode design, however, induced 44-46% less skin damage than two of the traditional uniform-impedance electrodes.

Quantitative and qualitative analysis of in vivo Doppler signal enhancement of FS-069.

RATIONALE AND OBJECTIVES: In vivo lifetime of ultrasound (US) contrast agents is still limited and thus a cause for ongoing investigations of new substances. The purpose of this study was to determine the time intensity changes of the Doppler signals obtained within the femoral vein after two different doses of a new microsphere-based ultrasound contrast agent. METHODS: Twenty-four healthy male volunteers (mean age, 29; average weight, 76 kg) were included in this study. All underwent a triplex Doppler US examination after an intravenous bolus injection of 0.3 mL and 1.0 mL Optison. To examine the signal enhancement characteristics of this contrast agent the audio signal of the pulsed-wave spectral Doppler US was measured quantitatively using an audio analyzer, whereas velocity-encoded color Doppler examinations were scored qualitatively (score 0-3). RESULTS: The mean maximal enhancement of the audio signal at a dose of 1.0 mL FS-069 was significantly higher than with a bolus of 0.3 mL FS-069 (29 +/- 2 dB vs. 26 dB +/- 2 dB, P < 0.001). The time-intensity curves after each bolus injection yielded an early peak (one minute after the injection) followed by constantly decreasing signal intensities. The scoring of the velocity-encoded color Doppler US revealed an optimal enhancement (score 2) for 3 minutes and 20 seconds (0.3 mL Optison) and for 6 minutes (1.0 mL Optison), respectively. CONCLUSIONS: This study showed the capability of triplex Doppler ultrasound signal enhancement after Optison. 1.0 mL Optison proved to be the more appropriate dose for an optimal signal enhancement than 0.3 mL Optison.

Developing a code of ethics for human cloning.

Under what conditions might the cloning of human beings constitute an ethical practice? A tendency exists to analyze human cloning merely as a technical procedure. As with all revolutionary technological developments, however, human cloning potentially exists in a broad social context that will both shape and be shaped by the biological techniques. Although human cloning must be subjected to technical analysis that addresses fundamental ethical questions such as its safety and efficacy, questions exist that focus our attention on broader issues. Asserting that cloning inevitably leads to undesirable consequences commits the fallacy of technological determinism and untenably separates technological and ethical evaluation. Drawing from the Report of the National Bioethics Advisory Committee and Aldous Huxley's Brave New World, we offer a draft "Code of Ethics for Human Cloning" in order to stimulate discussion about the ethics of the broader ramifications of human cloning as well as its particular technological properties.

Electrophysiological control of ventricular rate during atrial fibrillation.

Thirteen anesthetized canine subjects (17-29 kg) were used to demonstrate that mild cervical left vagal stimulation could control ventricular rate effectively during atrial fibrillation (AF). Two studies are presented. The first study used six subjects to demonstrate the inverse relationship between (manually applied) left vagal stimulation and ventricular excitation (R wave) rate during AF. As left vagal stimulation frequency was increased, ventricular excitation rate decreased. In these studies, a left vagal stimulus frequency of 0-10 per second reduced the ventricular excitation rate from > 200/min to < 50/min. The decreasing ventricular excitation rate with increasing left vagal stimulation frequency was universal, occurring in all 26 trials with the six subjects. This fundamental principle was used to construct an automatic controller for use in the second study, in which seven subjects were used to demonstrate that ventricular rate can be brought to and maintained within a targeted range with the use of an automatic (closed-loop) controller. A 45-minute record of automatic ventricular rate control is presented. Similar records were obtained in all seven subjects.

An adaptive noise reduction stethoscope for auscultation in high noise environments.

Auscultation of lung sounds in patient transport vehicles such as an ambulance or aircraft is unachievable because of high ambient noise levels. Aircraft noise levels of 90-100 dB SPL are common, while lung sounds have been measured in the 22-30 dB SPL range in free space and 65-70 dB SPL within a stethoscope coupler. Also, the bandwidth of lung sounds and vehicle noise typically has significant overlap, limiting the utility of traditional band-pass filtering. In this study, a passively shielded stethoscope coupler that contains one microphone to measure the (noise-corrupted) lung sound and another to measure the ambient noise was constructed. Lung sound measurements were made on a healthy subject in a simulated USAF C-130 aircraft environment within an acoustic chamber at noise levels ranging from 80 to 100 dB SPL. Adaptive filtering schemes using a least-mean-squares (LMS) and a normalized least-mean-squares (NLMS) approach were employed to extract the lung sounds from the noise-corrupted signal. Approximately 15 dB of noise reduction over the 100-600 Hz frequency range was achieved with the LMS algorithm, with the more complex NLMS algorithm providing faster convergence and up to 5 dB of additional noise reduction. These findings indicate that a combination of active and passive noise reduction can be used to measure lung sounds in high noise environments.

Skin-temperature distribution under a new type of defibrillating electrode.

The temperature rises under a new type of x-ray-transparent, improved current-density-distribution defibrillation electrode applied to pig skin were measured at four sites with fiberoptic thermal probes. Three anesthetized pigs, ranging in weight from 79 to 92 lb, were used. Temperature-time curves were obtained and the maximum temperature was identified. For 17 measurements at each site, the maximum temperature rise for a 360-joule shock was 317.3 +/- 53.0 millidegrees Celsius.

Retention force changes in implant-supported titanium telescope crowns over long-term use in vitro.

Titanium is used to fabricate spherical and bar attachments for overdentures on osseointegrated implants. This in vitro study investigated the long-term effects of commercially pure titanium on the retention force of telescope crowns with conical interface. Combinations of various materials for the inner and outer crowns were tested. Telescope crowns of pure titanium showed retention force characteristics comparable to telescope crowns fabricated conventionally in a precious alloy.

The effect of elevated intracranial pressure on the vibrational response of the ovine head.

Although potentially fatal increases in intracranial pressure (ICP) can occur in a number of pathological conditions, there is no reliable and noninvasive procedure to detect ICP elevation and quantitatively monitor changes over time. In this experimental study, the relationships between ICP elevation and the vibrational response of the head were determined. An ovine animal model was employed in which incremental increases in ICP were elicited and directly measured through intraventricular cannulae. At each ICP increment, a vibration source elicited a flexural response of the animal's head that was measured at four locations on the skull using accelerometers. Spectral analysis of the responses showed changes in proportion to ICP change up to roughly 20 cm H2O (15 mm Hg) above normal; a clinically significant range. Both magnitude and phase changes at frequencies between 4 and 7 kHz correlated well (gamma > 0.92) with ICP across the study group. These findings suggest that the vibrational response of the head can be used to monitor changes in ICP noninvasively.

A new concept of overdentures with telescope crowns on osseointegrated implants.

Primary splinting of fixtures with bar attachments has proven to be clinically effective for overdentures on osseointegrated implants in the edentulous mandible. However, in vitro investigations indicate that a more favorable force transfer to the individual fixtures can be attained by secondary splinting of four implants with tapered telescope crowns, compared to primary splinting with rigid or jointed bar attachments. Moreover, in contrast to jointed attachments, the telescope crowns ensure a stable denture position. These results underscore the need to clinically test telescope crowns as anchors for overdentures on osseointegrated implants. Telescope crowns on four implants allow an optimal restorative concept of overdentures with the bridgelike design of the removable suprastructure.

Allocation of critical care resources: entitlements, responsibilities, and benefits.

Determination of allocation of limited critical care resources appears to be an inevitable development. Criteria proposed to assign such limited resources among patients are not defined. It has been argued that allocation of critical care resources could be based on the principals of patient entitlements to health care, responsibilities of the physician to the critically ill patient, and beneficence. However, based on an analysis of the philosophical tenants of the Hippocratic Oath, there is little to support the concept of "sin" taxes or patient triage on the basis of judgment on the moral merit of the patient.

The evaluation of five specialized support surfaces by use of a pressure-sensitive mat.

This study used two full-size pressure-sensitive mats to evaluate five patient support surfaces. The mats, containing 1,536 and 2,340 pressure measurement sites, respectively, made it possible to quantify the entire interface pressure distribution of each support surface. Measurements for groups of 64 and 32 subjects were obtained in supine positions of 0 degree, 30 degrees, at maximal head elevations (50 degrees-60 degrees), and at lateral recumbency. Several statistical descriptors were calculated to characterize the interface pressure distributions. The support surfaces tested included: a powered-air overlay (ACUCAIR Continuous-Air-flow System), a low-airloss bed (FLEXICAIR MC3 Low-Airloss Therapy), a continuous lateral-rotation low-airloss bed (RESTCUE Dynamic Air Therapy), an air-fluidized bed (CLINITRON II Air-Fluidized Therapy), and an integrated bed (prototype Advance 2000 Bed). An analysis of variance revealed that the interface pressure was significantly lower and weight-bearing area was significantly higher on the five surfaces, when compared to the standard hospital mattress.

Closed-chest cardiac stimulation with a pulsed magnetic field.

Magnetic stimulators, used medically, generate intense rapidly changing magnetic fields, capable of stimulating nerves. Advanced magnetic resonance imaging systems employ stronger and more rapidly changing gradient fields than those used previously. The risk of provoking cardiac arrhythmias by these new devices is of concern. In the paper, the threshold for cardiac stimulation by an externally-applied magnetic field is determined for 11 anaesthetised dogs. Two coplanar coils provide the pulsed magnetic field. An average energy of approximately 12 kJ is required to achieve closed-chest magnetically induced ectopic beats in the 17-26 kg dogs. The mean peak induced electric field for threshold stimulation is 213 V m-1 for a 571 microseconds damped sine wave pulse. Accounting for waveform efficacy and extrapolating to long-duration pulses, a threshold induced electric field strength of approximately 30 V m-1 for the rectangular pulse is predicted. It is now possible to establish the margin of safety for devices that use pulsed magnetic fields and to design therapeutic devices employing magnetic fields to stimulate the heart.

[Hybrid prosthetic implant supported suprastructures in edentulous mandible. Conus crowns and shell-pin-systems on HA-Ti-implants. 2. Prosthetic construction principles]. / Hybridprothetische implantatgetragene Suprastrukturen im zahnlosen Unterkiefer. Konuskronen und Hülsen-Stift-Systeme auf Ha-Ti-Implantaten. Teil II: Prothetische Konstruktionsprinzipien.

Dental literature covers a wide range of implant-based denture supports. Based on static/dynamic as well as preventive periodontal considerations, rigidly anchoring the removable superconstruction of hybrid dentures using secondary splinting of four implants with telescope crowns or readymade cap-andpost systems, is generally appropriate in cases where the lower jaw is toothless. This makes possible an impeccable bridge-shaped design for the main part of the dentures, with wide-open inter-implant rincing areas. Clinical experience has shown that, in comparison to bridge dentures or rigid bridgework, secondary splinting in reconstructions greatly simplifies oral hygiene, particulary for elderly patients.

[Hybrid prosthesis implant-supported superstructures in edentulous jaw. 1. Case planning]. / Hybridprothetische implantatgetragene Suprastrukturen im zahnlosen Unterkiefer. Teil 1: Fallplanung.

Dental literature covers a wide range of implant-based denture supports. Based on static/dynamic as well as preventive periodontal considerations, rigidly anchoring the removable superconstruction of hybrid dentures using secondary splinting of four implants with telescope crowns or readymade cap-andpost systems, is generally appropriate in cases where the lower jaw is toothless. This makes possible an impeccable bridgeshaped design for the main part of the dentures, with wide-open inter-implant rincing areas. Clinical experience has shown that, in comparison to bridge dentures or rigid bridgework, secondary splinting in reconstructions greatly simplifies oral hygiene, particularly for elderly patients.

A pressure-sensitive mat for measuring contact pressure distributions of patients lying on hospital beds.

The authors describe a novel system for sensing and displaying the distribution of contact pressure caused by a patient's lying on a hospital bed. The system includes a flexible, pressure-sensitive mat, electronics to activate the mat, a small computer to process data, and a color video display. The present prototypes can sense pressure at 1,536 discrete locations in a rectangular grid of 24 x 64 nodes, each node representing an area of 4 cm2. The computer receives data from each node and displays the results as a false-color map, refreshable every 5 seconds. The pressure-sensitive mat itself includes two orthogonal arrays of ribbon-like conductors, composed of silver-coated nylon fabric, which are separated by insulating open-cell foam rubber. The system monitors the electrical capacitance between selected pairs of horizontal and vertical conductors on opposite sides of the foam. The crossing points form pressure-sensitive nodes. Increased contact pressure compresses the foam, thereby decreasing the distance between the conductors and increasing the capacitance. Node capacitance is determined by measuring the current through it from a voltage source. The outputs of the various nodes are scanned, normalized, and converted to pressures using the known compressive stress-strain relationship for the foam, and the data are then displayed as a false-color image of the pressure distribution.