Transthoracic impedance to direct current discharge: effect of repeated countershocks.

The effect of repeated countershocks on transthoracic apparent impedance to direct current (dc) defibrillator discharges was studied. Repeated dc countershocks result in a progressive decrease in transthoracic apparent impedance that is dependent upon the time interval between countershocks. This decrease was significantly greater in the group of animals shocked at 3-min intervals compared to the groups shocked at 15-sec intervals (P less than 0.001) or at 1-min intervals (P less than 0.005). Since lowered impedance results in higher delivered current for the same energy setting on a defibrillator, this observation may help to explain the enhanced effectiveness of repeated countershocks in defibrillation. Plots of simultaneous current against voltage during transthoracic dc discharge revealed that the current lagged slightly behind voltage during the rising phase of the recording, but that current and voltage were nearly simultaneous during the falling phase. This effect appears to be similar to an ionization phenomenon in that the effective impedance asymptotically approaches a lower value with increasingly applied voltage. This might explain why transthoracic impedance is highest at low energy countershocks and decreases with higher energy countershock.     

A 622 Mb/s LAN/WAN gateway and experiences with wide area ATMnetworking

The use of similar technology in local and wide area networks enables geographically distributed high-performance applications. Key elements in achieving high performance are the appropriate use of traffic control and the development of efficient gateways between LANs and WANs. Even though the basic technology used on both sides of a gateway may be similar, the operational aspects of these elements are significantly different. A gateway has been developed and implemented not only to support communications between an ATM LAN and WAN at 622 Mb/s, but also to provide a platform for conducting network control and traffic research. In addition, the performance of the MAGIC WAN was evaluated, and bottlenecks were identified and analyzed. Techniques were developed and implemented, specifically ATM cell-level pacing, to eliminate these bottlenecks. Throughput performance close to the theoretical maximum was demonstrated. This article describes experiences with ATM over a WAN and how the gateway was developed, implemented, and evaluated. The results included show how high-speed LAN/WAN internetworking can be achieved and applied in many environments as appropriate control techniques and interfaces become ubiquitous     

Impedance to transthoracic direct current discharge: a model for testing interface material

An in vitro method for screening the relative impedance of gels has been developed. A nonconductive chamber was built with 1-cm-diameter electrodes placed 1 cm apart. This chamber is filled with electrode gel to be tested. The defibrillator used delivers a half-sinusoidal waveform. When the same stored energy is discharged by this defibrillator into increasing impedance, the resultant delivered current wave decreases while the voltage wave increases. Thus, with increasing impedance, the delivered volt-time interval increases. Twelve electrode gels were studied; 10 measurements were made on each gel. There is a marked variation in the impedance to direct current discharge of commercially available electrode gels. A large number of commercially available electrode gels are not suitable for use as the interface between the paddle electrodes and the chest wall during elective cardioversion and emergency defibrillation.     

Development of a state wide tobacco treatment specialist training and certification programme for Massachusetts

OBJECTIVE: To describe the research conducted to structure and develop a statewide tobacco training and certification programme for tobacco treatment specialists (TTSs) in Massachusetts. DESIGN: Qualitative research strategies were used to obtain information on certification development and opinions regarding TTS training and certification from key informants. A role definition and validation study was then conducted to determine the core competencies for TTSs. A comprehensive training programme was developed, piloted, and finalised, and a certification programme was initiated. PARTICIPANTS: Key informants included: individuals involved in the development of their professional certification programmes; tobacco treatment providers from across Massachusetts; and national tobacco treatment experts. MAIN OUTCOME MEASURES: Participants' opinions about the need for and structure of a training and certification programme for individuals specialising in the provision of moderate to intensive tobacco treatment; delineation of core competencies for TTSs, using the Agency for Health Care Policy and Research (now the Agency for Healthcare Research and Quality) clinical practice guideline as a foundation for the development of evidence based standards of practice for the treatment of nicotine dependence. RESULTS: The data support a comprehensive training and certification programme for TTSs in Massachusetts. Main concerns include the cost of obtaining certification, the potential to exclude uncertified healthcare professionals from delivering basic tobacco treatment, and the role of the TTS in the healthcare delivery system and the community. The training programme developed for Massachusetts was piloted, and the structure of a statewide training and certification programme for TTSs was finalised. CONCLUSIONS: The research provides support for the need and acceptance of a training and certification programme for TTSs in Massachusetts, and presents the challenges to be addressed. We demonstrated the feasibility of developing and implementing an evidence based training programme, and of initiating a statewide certification programme in Massachusetts. This work will add to a national dialogue on the development of a training and certification programme for tobacco treatment providers and encourage further research into the potential impact of statewide and national certification.     

The rapidly deployable radio network

The rapidly deployable radio network (RDRN) is an architecture and experimental system to develop and evaluate hardware and software components suitable for implementing mobile, rapidly deployable, and adaptive wireless communications systems. The driving application for the RDRN is the need to quickly establish a communications infrastructure following a natural disaster, during a law enforcement activity, or rapid deployment of military force. The RDRN project incorporates digitally controlled antenna beams, programmable radios, adaptive protocols at the link layer, and mobile node management. This paper describes the architecture for the RDRN and a prototype system built to evaluate key system components     

Electode catheter for transvenous defibrillation.

Development of an implantable automatic defibrillator is dependent on achieving a reduction in the energy required for defibrillation, which is related to an optimal electrode configuration. This study investigated the use of a transvenous catheter electrode utilizing the damped sinusoidal waveform; compared the defibrillation effectiveness of varying the configuration of the four electrode units and of using a catheter/subcutaneous metal plate combination; and determined the lowest energy level necessary for near consistent transvenous defibrillation.     

Response of atrial fibrillation to therapy: role of etiology and left atrial diameter

Left atrial diameter was measured by echocardiography in 107 patients in atrial fibrillation. The etiology of atrial fibrillation was rheumatic heart disease with predominant mitral valve involvement (RHD) in 51 patients and idiopathic atrial fibrillation (IAF) in 56. The left atrial diameter was correlated to the patient's response to therapy. The mean left atrial diameter was 3.4 cm in patients with paroxysmal atrial fibrillation, 3.8 cm in those requiring direct current (DC) cardioversion, and 4.4 cm in patients with persistent atrial fibrillation. However, in each of these therapeutic response groups, the left atrial diameter was signficantly smaller in patients with idiopathic atrial fibrillation. In the group with paroxysmal atrial fibrillation, the mean left atrial diameter was 4.3 +/- .7 cm in patients with RHD, compared to 3.1 +/- .6 cm in those with IAF (p less than .001). In the group requiring DC cardioversion, the left atrial diameter was 4.7 +/- .8 cm in patients with RHD compared to 3.6 +/- .5 cm in those with IAF (p less than .01). In patients with persistent atrial fibrillation, the left atrial diameter was 5.2 +/- .9 cm in patients with RHD and 4.0 +/- 1.0 cm in IAF (p less than .001). Left atrial diameter as well as the etiology of the heart disease are important in determining the response of atrial fibrillation to therapy.     

Prognostic significance of spouse we talk in couples coping with heart failure.

Recent research suggests that marital quality predicts the survival of patients with heart failure (HF), and it is hypothesized that a communal orientation to coping marked by first-person plural pronoun use (we talk) may be a factor in this. During a home interview, 57 HF patients (46 men and 16 women) and their spouses discussed how they coped with the patients' health problems. Analysis of pronoun counts from both partners revealed that we talk by the spouse, but not the patient, independently predicted positive change in the patient's HF symptoms and general health over the next 6 months and did so better than direct self-report measures of marital quality and the communal coping construct. We talk by the patient and spouse did not correlate, however, and gender had no apparent moderating effects on how pronoun use predicted health change. The results highlight the utility of automatic text analysis in couple-interaction research and provide further evidence that looking beyond the patient can improve prediction of health outcomes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Postresuscitation left ventricular systolic and diastolic dysfunction. Treatment with dobutamine

BACKGROUND: Global left ventricular dysfunction after successful resuscitation is well documented and appears to be a major contributing factor in limiting long-term survival after initial recovery from out-of-hospital sudden cardiac death. Treatment of such postresuscitation myocardial dysfunction has not been examined previously. METHODS AND RESULTS: Systolic and diastolic parameters of left ventricular function were measured in 27 swine before and after successful resuscitation from prolonged ventricular fibrillation cardiac arrest. Dobutamine infusions (10 micrograms.kg-1.min-1 in 14 animals or 5 micrograms.kg-1.min-1 in 5 animals) begun 15 minutes after resuscitation were compared with controls receiving no treatment (8 animals). The marked deterioration in systolic and diastolic left ventricular function seen in the control group after resuscitation was ameliorated in the dobutamine-treated animals. Left ventricular ejection fraction fell from a prearrest 58 +/- 3% to 25 +/- 3% at 5 hours after resuscitation in the control group but remained unchanged in the dobutamine (10 micrograms.kg-1.min-1) group (52 +/- 1% prearrest and 55 +/- 3% at 5 hours after resuscitation). Measurement of the constant of isovolumic relaxation of the left ventricle (tau) demonstrated a similar benefit of the dobutamine infusion for overcoming postresuscitation diastolic dysfunction. The tau rose in the controls from 28 +/- 1 milliseconds (ms) prearrest to 41 +/- 3 ms at 5 hours after resuscitation whereas it remained constant in the dobutamine-treated animals (31 +/- 1 ms prearrest and 31 +/- 5 ms at 5 hours after resuscitation). CONCLUSIONS: Dobutamine begun within 15 minutes of successful resuscitation can successfully overcome the global systolic and diastolic left ventricular dysfunction resulting from prolonged cardiac arrest and cardiopulmonary resuscitation.