Multi-population model of a microbial electrolysis cell.

This work presents a multi-population dynamic model of a microbial electrolysis cell (MEC). The model describes the growth and metabolic activity of fermentative, electricigenic, methanogenic acetoclastic, and methanogenic hydrogenophilic microorganisms and is capable of simulating hydrogen production in a MEC fed with complex organic matter, such as wastewater. The model parameters were estimated with the experimental results obtained in continuous flow MECs fed with acetate or synthetic wastewater. Following successful model validation with an independent data set, the model was used to analyze and discuss the influence of applied voltage and organic load on hydrogen production and COD removal.

The effect of real-time external resistance optimization on microbial fuel cell performance.

This work evaluates the impact of the external resistance (electrical load) on the long-term performance of a microbial fuel cell (MFC) and demonstrates the real-time optimization of the external resistance. For this purpose, acetate-fed MFCs were operated at external resistances, which were above, below, or equal to the internal resistance of a corresponding MFC. A perturbation/observation algorithm was used for the real-time optimal selection of the external resistance. MFC operation at the optimal external resistance resulted in increased power output, improved Coulombic efficiency, and low methane production. Furthermore, the efficiency of the perturbation/observation algorithm for maximizing long-term MFC performance was confirmed by operating an MFC fed with synthetic wastewater for over 40 days. In this test an average Coulombic efficiency of 29% was achieved.

A two-population bio-electrochemical model of a microbial fuel cell.

This work presents a two-population model describing the competition of anodophilic and methanogenic microbial populations for a common substrate in a microbial fuel cell (MFC). Fast numerical solution of the model is provided by using ordinary differential equations to describe biomass growth and retention in the anodic compartment. The model parameters are estimated and validated using experimental results obtained in four continuous-flow air-cathode MFCs operated at various external resistances and organic loads. Model analysis demonstrates the influence of operating conditions on MFC performance and suggests ways to maximize MFC power output. The model is suitable both for process optimization and on-line control applications.

QRS changes during percutaneous transluminal coronary angioplasty and their possible mechanisms.

OBJECTIVES: The purpose of the study was to describe the configuration, and investigate the mechanisms, of QRS changes occurring during percutaneous transluminal coronary angioplasty (PTCA). BACKGROUND: QRS changes during PTCA have been attributed to both a passive ST segment shift and conduction disturbances (peri-ischemic block). The direct relation between ST segment shift and QRS changes, however, has not been established, and the definition of conduction disturbances remains to be clarified. METHODS: Twelve-lead electrocardiograms (ECGs) were recorded before PTCA, at the end of 2 min of PTCA and after return to baseline values in 29 patients (left anterior descending coronary artery [LAD] in 13 patients, right coronary artery [RCA] in 14 and left circumflex coronary artery in 2). Electrocardiographic complexes before and during PTCA were superimposed to determine the amplitudes of initial, terminal and total QRS deflection; the relations of QRS changes to baseline (TP segment) and ST segment shift; and the duration of QRS and corrected QT intervals. RESULTS. 1) The direction of the initial QRS deflection was unchanged, but changes of its amplitude occurred. 2) Terminal QRS deflection changed in all patients with a ST segment shift > 17% of the R amplitude, and the correlation between the decrease in the S amplitude and ST segment shift was significant (r = 0.9, p < 0.01) in patients with LAD PTCA. Correlation between changes in total QRS amplitude and ST segment shift in patients with RCA PTCA was weaker (r = 0.54, p = 0.056). 3) Transient conduction disturbance manifested by QRS widening in selected leads occurred in 2 of 29 patients. CONCLUSIONS. 1) Changes in terminal QRS deflection during PTCA are proportional to the magnitude of the ST segment shift. 2) Conduction disturbances manifested by increased QRS duration occurred infrequently. We suggest that the term peri-ischemic block be applied only to changes in QRS configuration associated with QRS widening.

Prognosis of patients with frequent premature ventricular complexes and nonsustained ventricular tachycardia after coronary artery bypass graft surgery.

BACKGROUND: Previous studies in small groups of predominantly nongeriatric patients showed that complex ventricular arrhythmias occurring after coronary artery graft (CABG) surgery are of no prognostic significance. The purpose of this study was to compare the prognosis of patients with and without advanced grade ventricular arrhythmias (AGVA) after CABG in a large group of patients. [In this paper, AGVA is used as an abridged definition of frequent premature ventricular complexes (PVCs) and nonsustained ventricular tachycardia (NSVT) which represent advanced grade ventricular arrhythmias.] METHODS: Twenty-four hour ambulatory electrocardiographic (ECG) monitoring was performed 3 days after CABG in 185 consecutive patients with 185 closely matched control patients without AGVA. Of 185 patients with AGVA, 77 had frequent PVCs, 45 had NSVT, and 63 patients had both. The average age of both groups was 65 +/ 9.7 years. Patients were followed for 34 +/ 10 months, and in 30 patients ambulatory monitoring was repeated at the end of the follow-up. RESULTS: Fifteen AGVA and nine control patients died. In each group seven deaths were noncardiac. Six nonsudden and two sudden cardiac deaths (SCD) occurred in the AGVA group at 2-36 months after CABG and two nonsudden cardiac deaths in the control group at 3 and 35 months after CABG (p = 0.053). Both SCDs occurred 33 months after CABG after new events known to predispose to SCD. In 18 of 30 patients AGVA was no longer present when ambulatory ECG monitoring was repeated 36 +/ 11 months after CABG. CONCLUSION: AGVA after CABG was not a marker of an early sudden cardiac death. In 60% of patients not treated with antiarrhythmic drugs, AGVA was no longer present late after operation.

Cardiac myxoma: the Indiana Heart Institute experience.

Surgical resection of a cardiac myxoma was performed in 14 patients at the Indiana Heart Institute at St. Vincent Hospital and Health Care Center in Indianapolis from 1974 to 1989. Thirteen were located in the left atrium and one in the right atrium. The 10 women and four men ranged in ages from 28 to 75 years. Surgical complications included one perioperative death, one late death and one late recurrence requiring reoperation. Physicians must be highly suspicious to correctly diagnose this unusual but surgically correctable entity. Two-dimensional echocardiography is the diagnostic technique of choice for both early diagnosis of a cardiac myxoma and late follow-up after resection.

Cardiac rupture following acute myocardial infarction: a case with successful surgical treatment.

This report involves a patient who sustained an acute lateral wall myocardial infarction complicated by cardiogenic shock. Cardiac catheterization revealed diastolic equilibration of all intracardiac pressures. Cardiac angiography revealed only acute occlusion of a small branch of the left circumflex coronary artery with good left ventricular systolic function. Since these findings could not explain the degree of cardiogenic shock, an immediate echocardiogram revealed a moderate pericardial effusion with an echo-dense mass suggestive of subacute cardiac rupture. Emergency cardiac surgery confirmed the diagnosis and successful surgical correction resulted in survival of the patient.

Morphologic observations late after coronary balloon angioplasty: mechanisms of acute injury and relationship to restenosis.

Despite widespread use of coronary balloon angioplasty, advances in angioplasty technology, and improvements in operator technique, restenosis at the angioplasty site is the major problem limiting the long-term efficacy of this procedure. The article reviews morphologic-histologic observations at angioplasty restenosis sites, speculates about the connection between the acute injury patterns of balloon angioplasty and the development of restenosis, and briefly reviews the currently understood pathways to restenosis and possible approaches to its reduction or elimination.

Using videotape modeling to prepare children psychologically for surgery: influence of parents and costs versus benefits of providing preparation services.

Sixty pediatric patients having first-time elective surgery participated in this study. Surgery preparation using videotape procedures was employed. The research design included two viewing conditions (with parent present and without parent present) and three treatment procedures (adult-narrated videotape, peer-narrated videotape, and control/no-videotape condition). Results suggested that children who viewed the videotape with their parent present exhibited less preoperative arousal compared to children who did not. The patients undergoing preparation using the videotape model exhibited less arousal, less self-reported anxiety, and less behaviorally rated anxiety when compared to patients who did not view the videotape preparation. There was no difference between the patients who viewed the adult-narrated versus the peer-narrated videotape. In addition, parents who viewed the videotape or whose children viewed the videotape without them exhibited less arousal prior to the operation than parents who did not and whose children did not view the videotape preparation. Finally, a cost-benefit analysis revealed that preparation services could reduce individual and overall medical costs.

Nicotine dependence and likelihood of quitting smoking.

This study examined the hypothesis that high nicotine dependent smokers would have more difficulty with initial cessation of smoking than low dependent smokers as measured by the Fagerstrom Tolerance Questionnaire (FTQ). Two replications of a nicotine-fading smoking program were conducted at different worksites. Significantly less heavily dependent smokers quit smoking during treatment. The correlation between the FTQ and smoking rate at posttreatment remained even when the pretreatment rate of smoking was partialled out. It was concluded that the concept of nicotine dependence should be re-examined especially in the context of improving the quit rates of behavioral programs at the worksite.

Psychosocial stress and coping in smokers who relapse or quit.

Relapse remains a major problem in successful smoking cessation. This study evaluated selected responses and coping skills in male and female quitters and relapsers in four situational contexts: general social competence, smoking-specific "high-risk-for-relapse" situations, social anxiety, and relaxation. Results showed that quitters coped better than relapsers with intrapersonal (e.g., negative mood) smoking-specific situations. Quitters had lower heart rates than relapsers during relaxation and intrapersonal situations and had lower anxiety scores at the end of the procedures. Women showed more stress and less confidence in their ability to cope than did men. Groups did not differ in responses to the general social competence and social anxiety procedures. Results are discussed in the context of the importance of considering individual differences in responses and in coping skills for treatment and relapse prevention for smokers.

Use of inpatient seclusion at a community mental health center.

Little research has been done on the use of seclusion in community mental health centers. The authors studied 56 seclusion room placements for 25 inpatients at a community mental health center and found that use of seclusion may more frequently be a function of staff than of patient need. Evening and night shifts made more frequent use of seclusion than did day shifts. Shifts staffed primarily with female employees used seclusion more than shifts where male staff predominated. Shifts with both a low staff-patient ratio and a larger number of female staff tended to use seclusion the most. The authors urge other CMHCs to critically examine their seclusion practices to ensure that they are humane and appropriate.