The effect of changing excitation frequency on parallel conductance in different sized hearts

OBJECTIVE: An important component of the ventricular volume measured using the conductance catheter technique is due to parallel conductance (Vc), which results from the extension of the electric field beyond the ventricular blood pool. Parallel conductance volume is normally estimated using the saline dilution method (Vc(saline dilution)), in which the conductivity of blood in the ventricle is transiently increased by injection of hypertonic saline. A simpler alternative has been reported by Gawne et al. [12]. Vc(dual frequency) is estimated from the difference in total conductance measured at two exciting frequencies and the method is based on the assumption that parallel conductance is mainly capacitive and hence is negligible at low frequency. The objective of this study was to determine whether the dual frequency technique could be used to substitute the saline dilution method to estimate Vc in different sized hearts. METHODS: The accuracy and linearity of a custom-built conductance catheter (CC) system was initially assessed in vitro. Subsequently, a CC and micromanometer were inserted into the left ventricle of seven 5 kg pigs (group 1) and six 50 kg pigs (group 2). Cardiac output was determined using thermodilution (group 1) and an ultrasonic flow probe (group 2) from which the slope coefficient (alpha) was determined. Steady state measurements and Vc estimated using saline dilution were performed at frequencies in the range of 5-40 kHz. All measurements were made at end-expiration. Finally, Vc was estimated from the change in end-systolic conductance between 5 kHz and 40 kHz using the dual frequency technique of Gawne et al. [12]. RESULTS: There was no change in measured volume of a simple insulated cylindrical model when the stimulating frequency was varied from 5-40 kHz. Vc(saline dilution) varied significantly with frequency in group 1 (8.63 +/- 2.74 ml at 5 kHz; 11.51 +/- 2.65 ml at 40 kHz) (p = 0.01). Similar results were obtained in group 2 (69.43 +/- 27.76 ml at 5 kHz; 101.24 +/- 15.21 ml at 40 kHz) (p < 0.001). However, the data indicate that the resistive component of the parallel conductance is substantial (Vc at 0 Hz estimated as 8.01 ml in group 1 and 62.3 ml in group 2). There was an increase in alpha with frequency in both groups but this did not reach significance. The correspondence between Vc(dual frequency) and Vc(saline dilution) methods was poor (group 1 R2 = 0.69; group 2 R2 = 0.22). CONCLUSION: At a lower excitation frequency of 5 kHz a smaller percentage of the electric current extends beyond the blood pool so parallel conductance is reduced. While parallel conductance is frequency dependent, it has a substantial resistive component. The dual frequency method is based on the assumption that parallel conductance is negligible at low frequencies and this is clearly not the case. The results of this study confirm that the dual frequency technique cannot be used to substitute the saline dilution technique.     

Myocardial contractility is not constant during spontaneous atrial fibrillation in patients

BACKGROUND: The variation in stroke volume and pulse pressure characteristic of atrial fibrillation is usually ascribed to time-dependent ventricular filling, implying a single positive relationship between end-systolic pressure and volume, which defines a single state of myocardial contractility. We tested the hypothesis that contractility also varies. METHODS AND RESULTS: We measured the left ventricular pressure and volume continuously with a conductance catheter with catheter-tip micromanometer introduced retrogradely into the left ventricle. The end-systolic pressure-volume relationship was determined in 6 patients in atrial fibrillation undergoing cardiac catheterization for diagnostic purposes and 4 control patients in sinus rhythm undergoing coronary artery bypass graft surgery. The normal positive relationship between end-systolic pressure and volume was found in the control patients, but no such positive relationship was found in any patient in atrial fibrillation. In the latter, the slopes of the linear regressions were either not significantly different from zero or significantly negative (r values <0.08), both results indicating a change in contractility from beat to beat. Significantly negative relationships were found between end-systolic volume and preceding R-R interval (-0.82相似文献   

Transfer in artificial grammar learning: A reevaluation.

This article covers methodological and theoretical issues in artificial grammar learning. Arguments that such tasks are mediated by abstract knowledge (e.g., A. S. Reber, see record 1991-00330-001) are based primarily on evidence from transfer experiments, where the surface vocabulary is changed between learning and test items. Because of a number of methodological concerns, the small magnitudes of artificial grammar learning effects generally are difficult to interpret. Possible solutions are offered here. Furthermore, even reliable transfer effects imply neither that subjects have acquired abstract knowledge of the underlying grammar nor that they are performing a process of abstract analogy from memorized whole exemplars. Models that learn only surface fragments of the training stimuli and perform abstraction at test rather than during learning are wholly consistent with transfer phenomena. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

15-lipoxygenase immunoreactivity in normal and in asthmatic airways

Products of the 15-lipoxygenase (15-LO) pathway of arachidonic acid metabolism such as the mono- and di-hydroxyeicosatetraenoic acids (HETEs) may contribute to the pathophysiology of allergic airway inflammation through the recruitment and activation of inflammatory cells and stimulation of glandular secretion. In this study we have examined the expression of 15-LO and its cellular localization in the asthmatic and normal bronchial mucosa. Bronchial mucosal biopsies were obtained by fiberoptic bronchoscopy from 10 patients with symptomatic allergic asthma and six normal control subjects and processed into glycolmethacrylate resin. Sections 2 microns thick were immunostained using a specific rabbit polyclonal antihuman 15-LO antibody. Strong immunoreactivity for 15-LO was present throughout the epithelium in both the asthmatic and the normal subjects, with no difference between the two groups. Cells expressing 15-LO immunoreactivity were also present in the submucosa of both groups, with a significantly greater number present in the asthmatic group (median, 15.3 cells/mm2) than in the normal group (median, 6.9 cells/mm2) (p = 0.01). The majority (85%) of the submucosal 15-LO+ cells were eosinophils. Patchy 15-LO immunoreactivity was also seen in the vascular endothelium in both groups. These findings demonstrated increased 15-LO expression in the bronchial submucosa of asthmatic subjects, and they suggest that 15-LO products in asthma originate from both bronchial epithelium and infiltrating eosinophils.     

Cardiopulmonary interactions in healthy children and children after simple cardiac surgery: the effects of positive and negative pressure ventilation

On the day of the disaster, 641 victims were seen at St. Luke's International Hospital. Among those, five victims arrived with cardiopulmonary or respiratory arrest with marked miosis and extremely low serum cholinesterase values; two died and three recovered completely. In addition to these five critical patients, 106 patients, including four pregnant women, were hospitalized with symptoms of mild to moderate exposure. Other victims had only mild symptoms and were released after 6 hours of observation. Major signs and symptoms in victims were miosis, headache, dyspnea, nausea, ocular pain, blurred vision, vomiting, coughing, muscle weakness, and agitation. Almost all patients showed miosis and related symptoms such as headache, blurred vision, or visual darkness. Although these physical signs and symptoms disappeared within a few weeks, psychologic problems associated with posttraumatic stress disorder persisted longer. Also, secondary contamination of the house staff occurred, with some sort of physical abnormality in more than 20%.     

Not evidence for separable controlled and automatic influences in artificial grammar learning: Comment on Higham, Vokey, and Pritchard (2000).

P. A. Higham, J. R. Vokey, and J. L. Pritchard (see record 2000-16324-006) claimed to provide evidence for separable controlled and automatic processes in artificial grammar learning. It is argued that their results are compatible with a single controlled influence: Participants might mistakenly identify more grammatical items than nongrammmatical items as belonging to the other grammar, because the grammars are very similar to each other, and the nongrammatical items are relatively highly dissimilar. Participants' knowledge may be ambiguous, rather than automatic. It is further argued that even if Higham et al's data do support automatic effects, opposition logic, in this case, cannot be said to have succeeded where dissociation logic has failed, because it is used to address the issue of whether participants have conscious control over the knowledge they acquire, rather than whether they possess conscious awareness of that knowledge. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Should atrial septal defects in adults be closed?

BACKGROUND: By assessing current surgical outcome and symptomatic relief, this study attempts to answer whether atrial septal defects in adults should be closed. METHODS: Thirty-nine adult patients aged 35.2 +/- 13.6 years underwent operation for an atrial septal defect between June 1988 and June 1994. Indications for closure were symptoms (33 patients) or a significant left-to-right atrial shunt (6 patients). Data were obtained from hospital records, and the latest status of the patients was determined by a written questionnaire. RESULTS: There were no deaths. Pulmonary embolism in 1 patient was the only complication observed. The QRS duration on the surface electrocardiogram decreased immediately (p < 0.001), and the cardiothoracic ratio on chest radiographs was significantly lower 3 to 6 months after operation (p < 0.001), both findings reflecting improved hemodynamics. No residual shunts were seen on follow-up (mean follow-up, 3.3 +/- 2.2 years). Twenty-seven (81.8%) of the 33 symptomatic patients improved clinically in terms of exercise performance, atrial arrhythmias, or both. Three (50%) of the 6 previously asymptomatic patients reported improved functional capacity post-operatively. CONCLUSIONS: Today, operation for atrial septal defects in adults can be performed with no mortality and low morbidity and results in symptomatic improvement in the majority of patients. Clinical improvement was seen even in patients who considered themselves asymptomatic preoperatively. We advocate closure of atrial septal defects in adult patients with symptoms or significant atrial shunts.