Optimization of Tetrapolar Impedance Electrodes in Microfluidic Devices for Point of Care Diagnostics using Finite Element Modeling

Electrophoresis is widely applied in the field of biochemistry and molecular biology. Tetrapolar electrical impedance sensing (TEIS) has been shown capable of replacing the conventional detection technology in order to develop a point of care electrophoretic analyzer. Besides the advantages of reduced influence of electrode polarization, TEIS is affected by sensitivity distribution depending on the electrode design. A well reported practice outside of electrophoresis, systematic investigation of the effects of sensitivity distribution on the TEIS in microfluidic devices has not been conducted. Here we utilize finite element modeling, backed by experimental results, to optimize the sensor design within an electrophoretic separation device. Numerous sensor designs were validated regarding detectability, sensitivity and spatial resolution. The results show, that minimizing the distance between the central/pick-up electrodes increases sensitivity and spatial resolution whereas the distance between the central electrodes and the outer electrode do not influence sensitivity and spatial resolution.

Ventricular arrhythmias and antioxidative medication: experimental study

INTRODUCTION

Reperfusion arrhythmias could be due to free radicals, while contraction excitation feedback is the cause of arrhythmias generated by blood pressure elevation (BPE). The aim of this study was to test the antiarrhythmic effects of an antioxidant (vitamin C [vit C], 1.5 g), an iron-binding agent (deferoxamine [Def], 1 g), and their combination in an experimental model of arrhythmia based on these 2 mechanisms.

METHODS

Thirty anaesthetised sheep were divided into 4 groups, depending on the infused agent: saline (8 sheep), combination of vit C and Def (8), Def (6), and vit C (8). Induction of ventricular arrhythmias was attempted in all animals using both ischaemia-reperfusion (phase I) and a combination of ischaemia and BPE (phase II). In all cases ischaemia was caused by ligating the left anterior descending coronary artery distally to the origin of the 1st diagonal artery, while reperfusion was achieved by releasing the ligation 45 min later. BPE was achieved by obstructing the ascending aorta or by administering intravenous metaraminol. All agents were infused intravenously for 15 min and their administration was started 30 min after the first ligation. Phases I and II lasted 50 and 20 min, respectively.

RESULTS

Ventricular tachycardia/fibrillation (VT/VF) was induced in all animals in the control group (8/8) and in the Def group (6/6). VT/VF appeared in 6/8 of the animals in the vit C group (75%) and in only 3/8 of the animals in the combination therapy group (37.5%). The difference between the combination and control groups was statistically significant (p < 0.03).

CONCLUSIONS

The intravenous administration of vit C and Def in combination protects against VT/VF induced by ischaemia-reperfusion and/or BPE. Administration of Def alone does not appear to help, while the action of vit C alone is not clear.

Focusing of macromolecules using equilibrium between centrifugal and electric force

A focusing separation model for macromolecules has been theoretically investigated. The method involves an ultracentrifugation device, which however, deploys an electric field gradient oriented longitudinally along the radial direction. When a macromolecular sample solution is centrifuged, the molecules which have different density to the surrounding solvent and a non-zero electric charge, experience a combination of centrifugal and electric forces. This forces the molecules to move to the equilibrium positions along the radius of the rotor, which are characterised by the charge over mass ratio of the molecules. Therefore a molecular sample will be separated into its constituents and bands will form, akin to electrophoresis. The bands are, however, focused at their equilibrium position. An example configuration has been examined whereby four proteins with masses between 20 and 100 kDa can be separated within a radial distance of 20 cm, for a rotor spinning at approximately 130,000 rpm and with a varying electric field between 0 and 100 V/cm.

An arrhythmia classification system based on the RR-interval signal

OBJECTIVE

This paper proposes a knowledge-based method for arrhythmic beat classification and arrhythmic episode detection and classification using only the RR-interval signal extracted from ECG recordings.

METHODOLOGY

A three RR-interval sliding window is used in arrhythmic beat classification algorithm. Classification is performed for four categories of beats: normal, premature ventricular contractions, ventricular flutter/fibrillation and 2 degrees heart block. The beat classification is used as input of a knowledge-based deterministic automaton to achieve arrhythmic episode detection and classification. Six rhythm types are classified: ventricular bigeminy, ventricular trigeminy, ventricular couplet, ventricular tachycardia, ventricular flutter/fibrillation and 2 degrees heart block.

RESULTS

The method is evaluated by using the MIT-BIH arrhythmia database. The achieved scores indicate high performance: 98% accuracy for arrhythmic beat classification and 94% accuracy for arrhythmic episode detection and classification.

CONCLUSION

The proposed method is advantageous because it uses only the RR-interval signal for arrhythmia beat and episode classification and the results compare well with more complex methods.

Mapping the binding domains of the alpha(IIb) subunit. A study performed on the activated form of the platelet integrin alpha(IIb)beta(3)

alpha(IIb)beta(3), a member of the integrin family of adhesive protein receptors, is the most abundant glycoprotein on platelet plasma-membranes and binds to adhesive proteins via the recognition of short amino acid sequences, for example the ubiquitous RGD motif. However, elucidation of the ligand-binding domains of the receptor remains controversial, mainly owing to the fact that integrins are conformationally labile during purification and storage. In this study, a detailed mapping of the extracellular region of the alpha(IIb) subunit is presented, using overlapping 20-peptides, in order to identify the binding sites of alpha(IIb) potentially involved in the platelet-aggregation event. Regions alpha(IIb) 313-332, alpha(IIb) 265-284 and alpha(IIb) 57-64 of alpha(IIb)beta(3) were identified as putative fibrinogen-binding domains because the corresponding peptides inhibited platelet aggregation and antagonized fibrinogen association, possibly by interacting with this ligand. The latter is further supported by the finding that the above peptides did not interfere with the binding of PAC-1 to the activated form of alpha(IIb)beta(3). Furthermore, alpha(IIb) 313-332 was found to bind to fibrinogen in a solid-phase binding assay. It should be emphasized that all the experiments in this study were carried out on activated platelets and consequently on the activated form of this integrin receptor. We hypothesize that RAD and RAE adhesive motifs, encompassed in alpha(IIb) 313-332, 265-284 and 57-64, are capable of recognizing complementary domains of fibrinogen, thus inhibiting the binding of this ligand to platelets.

Aortic dissection with aorto-left atrial fistula formation soon after aortic valve replacement: A lethal complication diagnosed by transthoracic and transesophageal echocardiography

Fistulas between the aorta and left atrium are a rare manifestation of aortic dissection and are infrequently diagnosed premortem. We report the case of a 70-year-old man who exhibited this condition soon after aortic valve replacement and eventually died from rapidly developing refractory congestive heart failure. The diagnosis was indicated by transthoracic echocardiography and was ultimately made with transesophageal echocardiography and color flow Doppler imaging. Transesophageal echocardiography is the procedure of choice for establishing the correct diagnosis and leading to prompt surgical repair of this lethal condition.

Sudden death due to an unrecognized cardiac hydatid cyst

Echinococcosis is an endemic disease, most common in sheep-raising communities, usually caused by the larval or cyst stage of the tapeworm Echinococcus granulosus. Isolated cardiac hydatid cyst is uncommon at any age, occurs through the coronary circulation, and accounts for less than 3% of all hydatid disease. We describe a case of an 1%-year-old female, who died suddenly. The post-mortem examination revealed an isolated cyst in the left ventricle of the heart with intact wall. The cytologic examination of the cyst fluid demonstrated the presence of the characteristic scolices and hooklets and established the diagnosis of cardiac hydatid cyst. The present case is of special interest because of the rare primary localization and the onset of sudden death in a young person as the initial manifestation of the disease.

Outcome of patients with congestive heart failure treated with standard versus high doses of enalapril: a multicenter study. High Enalapril Dose Study Group

OBJECTIVES

We sought to prospectively and randomly compare survival with clinical and hemodynamic variables in patients with congestive heart failure (CHF) treated with standard versus high doses of enalapril.

BACKGROUND

Angiotensin-converting enzyme (ACE) inhibitors produce hemodynamic and symptomatic benefits in patients with CHF, but there is still controversy about the optimal dose in this clinical setting.

METHODS

Two hundred and forty-eight patients with advanced CHF (age 56.3+/-12 years) were randomized to receive a maximal tolerated dose of enalapril, up to 20 mg/day in group 1 (mean dose achieved 17.9+/-4.3 mg/day, n = 122) and 60 mg/day in group 2 (mean dose achieved 42+/-19.3 mg/day, n = 126).

RESULTS

At enrollment, patients in group 1 were in New York Heart Association (NYHA) functional class 2.6+/-0.7 and had a mean systolic blood pressure (SBP) of 117+/-18 mm Hg, a mean heart rate (HR) of 85+/-16 beats/min and a left ventricular ejection fraction (LVEF) of 20.0+/-9.8%. In group 2, patients were in NYHA class 2.6+/-0.7; their SBP was 118+/-17 mm Hg, HR 83+/-15 beats/min and LVEF 18.8+/-8.1%. There were no significant differences in these characteristics between the two groups of patients at enrollment. After 12 months of follow-up, 22 (18%) of 122 patients in group 1 and 23 (18%) of 126 patients in group 2 had died (p = 0.995, with 80% power of the study to detect a delta difference of 13%). The NYHA class was the same (1.9+/-0.7) in both groups; SBP was 111+/-16 and 111+/-17 mm Hg, HR 77+/-12 and 79+/-13 beats/min and LVEF 31+/-19% and 30+/-12% in groups 1 and 2, respectively. These differences were not statistically significant. The study had a power of 80% to detect (p = 0.05) the following changes: 13% in death rate, 0.25 units in NYHA class, 6 mm Hg in SBP, 5 beats/min in HR and 6% in LVEF.

CONCLUSIONS

No significant differences were found in survival and clinical and hemodynamic variables between patients receiving standard and those receiving high doses of enalapril.

Pain intensity in nondiabetic patients with myocardial infarction or unstable angina. Its association with clinical and psychological features

Sixty nondiabetic coronary artery disease (CAD) patients submitted to coronary angiography were asked to rate (score 0 to 20) pain intensity (RPI) during their last major anginal episode having occurred prior to coronary angiography. This parameter was examined in relation to other variables of CAD and to psychological features. Stepwise regression analysis revealed that RPI was not related to New York Heart Association (NYHA) classification of angina or to angiographic variables. Yet, RPI was found to be significantly affected by psychological features: higher RPI scores were reported by low state anxiety patients (P=0.008), by Type A coronary-prone behavior patients (P=0.02) and by patients with high depression (P=0.03).

Clinical characteristics and follow-up of patients with chest pain and normal coronary arteries

The authors identified 160 men and women from all 3,700 patients with anginal pain between 1990 and 1994 who were subsequently found to have normal coronary arteries at diagnostic cardiac catheterization with follow-up to the present (mean follow-up 2.5 years). The group comprised 50 women and 110 men. Mean age was significantly greater in women (53.1 +/- 7.7 vs 47.2 +/- 9.2 years, p<0.001). Forty percent of the women but only 10% of the men had a positive exercise test. At follow-up, a larger proportion of patients continue to experience chest pain (95 patients, 59%) of whom 65 patients (41%) continue antianginal therapy. Furthermore one patient suffered a sudden cardiac death and two patients had a nonfatal myocardial infarction. Of patients referred with chest pain, women were more likely to have normal coronary arteries, compared with men. All patients have an excellent prognosis. A large proportion of women had a positive exercise test in the absence of coronary artery disease. On the other hand, morbidity remains high in these patients, despite the reassurance of a normal-appearing coronary arteriogram.

Lipid profile in patients with microvascular angina

Lipid, lipoprotein and apolipoprotein levels, as well as the susceptibility of low-density lipoprotein (LDL) to oxidation, were studied in patients with micro-vascular angina in comparison with patients with coronary artery disease (CAD) and normal subjects. Total cholesterol, LDL-cholesterol and apolipoprotein B levels in microvascular angina patients (235 +/- 46 mg dL-1, 135 +/- 33 mg dL-1 and 146 +/- 32 mg dL-1 respectively) were significantly higher than in control subjects (204 +/- 40 mg dL-1, 116 +/- 35 mg dL-1 and 129 +/- 29 mg dL-1 respectively, P < 0.01). These parameters were also significantly higher in CAD patients than in control subjects. By contrast, high-density lipoprotein (HDL)-cholesterol levels in microvascular angina patients were no different from those in control subjects, although both were significantly higher than in the CAD patients (48 +/- 16 mg dL-1 and 45 +/- 12 mg dL-1 compared with 40 +/- 10 mg dL-1, P < 0.01 and P < 0.05 respectively). Similar results were obtained for the apolipoprotein AI levels. Furthermore, the atherogenic risk ratio, LDL-cholesterol/HDL-cholesterol, in microvascular angina patients was significantly lower than in the CAD patients (3.4 +/- 1.2 vs. 4.1 +/- 1.5 respectively, P < 0.01). Median (range) serum lipoprotein (a) [Lp(a)] levels in microvascular angina patients and CAD patients [13 mg dL-1 (0.8-92) and 16 mg dL-1 (0.8-96) respectively] were significantly higher than in control subjects [7 mg-dL-1 (0.8-44)], P < 0.01 and P < 0.005 respectively. Sigmoidal curves and electrophoretic mobility of the Cu(2+)-oxidized LDL in both microvascular angina and CAD patients were not significantly different from those of control subjects. Finally, no significant differences were found between groups in total triglyceride levels or in very low-density lipoprotein (VLDL), LDL and HDL triglyceride levels. Our results show that the microvascular angina patients exhibit lipid abnormalities similar to those observed in CAD patients, with the important exception of the HDL-cholesterol and apolipoprotein AI levels, which are significantly higher in microvascular angina patients. We suggest that the abnormal cholesterol and Lp(a) levels may be involved in the pathophysiology of microvascular angina by affecting endothelial function and endothelium-mediated vasodilator responses, whereas the higher HDL levels may be a factor contributing to the absence of angiographically documented CAD in microvascular angina patients.

PAF-acetylhydrolase activity of Lp(a) before and during Cu(2+)-induced oxidative modification in vitro

In human plasma with no detectable lipoprotein (a) (Lp(a)) levels, platelet-activating factor acetylhydrolase (PAF-AH) is associated with low density lipoprotein (LDL) and high density lipoprotein (HDL) with a distribution of 70 and 30%, respectively. We used a density gradient ultracentrifugation procedure to study the distribution of PAF-AH among lipoproteins in plasma containing Lp(a). Lp(a) was migrated as a broad band in the density region of d = 1.050-1.100 g/ml, independently of its isoform size. In plasma with Lp(a) levels 30-40 mg/dl or 80-100 mg/dl the PAF-AH activity migrated in this density region was 4 or 9% higher as compared to plasma having Lp(a) levels < 8 mg/dl (P < 0.05 or P < 0.02, respectively). Enrichment of plasma with the dense LDL5 subfraction, significantly increased the enzyme activity distributed in this density region. The physicochemical properties of the Lp(a)-associated PAF-AH activity were similar to those reported for the LDL-associated enzyme. However, the kinetic constants in small Lp(a) isoforms were significantly higher compared to large ones. Isoform F had apparent Km = 117 +/- 9 mumol/l and Vmax = 94 +/- 5 nmol/mg protein per min, and isoform S2/S3 had apparent Km = 36 +/- 9 mumol/l and Vmax = 25 +/- 5 nmol/mg protein per min. Removal of apolipoprotein (a) (apo(a)) from Lp(a) by reductive cleavage with dithiothreitol, slightly affected the amount of PAF-AH existing on Lp(a) since, only 15 +/- 5% of the total enzyme activity dissociated from its particle after density gradient ultracentrifugation. During Cu(2+)-induced Lp(a) oxidation, the PAF-AH activity decreased from 10.90 +/- 2.30 nmol/mg per min to 2.57 +/- 0.56 nmol/mg per min 4 h after the initiation of the oxidation (P < 0.001). The apparent Km of the enzyme remained essentially unchanged during oxidation, whereas Vmax was significantly decreased from 58.6 +/- 7.8 nmol/mg protein per min to 38.2 +/- 8.7 nmol/mg protein per min (P < 0.03). An extensive hydrolysis of the endogenous phosphatidylcholine (PC) to lysophosphatidylcholine (lyso-PC) was observed during Lp(a) oxidation, since the Lyso-PC/sphingomyelin molar ratio at the end of oxidation (0.55 +/- 0.09) was significantly higher than that before oxidation (0.19 +/- 0.01, P < 0.001). Our results show that the existence of Lp(a) in plasma alters the distribution of PAF-AH among the other lipoproteins. Apo(a) seems to affect the association of the enzyme with Lp(a) but does not bind itself to PAF-AH. During Lp(a) oxidation, the PAF-AH activity decreases whereas an extensive hydrolysis of the endogenous PC to Lyso-PC is observed which is possibly due to the PAF-AH activity.

Isolated corrected transposition of great arteries and double left anterior descending artery originating from the left and right coronary artery. A rate combination of coronary artery anomaly and congenital heart disease

A case of double left anterior descending coronary artery in a patient with isolated corrected transposition of great arteries is presented. The double artery originated from the left main stem and the right coronary artery. There were no stenoses on these two arteries. This anomaly seems to be very rare.

Platelet aggregability to platelet activating factor at rest and after exercise in patients with coronary artery disease

The platelet response to the aggregatory effect of platelet-activating factor (PAF) in relation to blood PAF levels, serum PAF-acetylhydrolase (PAF-AH) activity and to their lipidaemic profile, was studied in 44 patients with coronary artery disease undergoing exercise tests. The PAF EC50 values in 21 patients with positive exercise test results were found to be significantly decreased at rest compared with 21 normal subjects (12.6 +/- 3.9 nM and 24.9 +/- 11.7 nM respectively) (P<0.0001). Moreover, the maximal percentage of aggregation to 50 nM PAF was found to be significantly increased (20.0 +/- 4.3% vs 13.5 +/- 3.6%, respectively) (P<0.0001). By contrast, the PAF EC50 values and the maximal percentage of aggregation in 23 patients with negative exercise test results were not statistically significantly different from the control group (25.2 +/- 11.4 nM and 14.1 +/- 4.7%, respectively). At the end of exercise, the PAF EC50 values and the maximal percentage of aggregation did not change in any group, and there were no significant differences in the whole-blood PAF levels either at rest or at the end of exercise. In patients with positive exercise test results, the PAF-AH activity at rest was significantly higher compared with the control group (37.2 +/- 8.0 nmol.ml(-1).min(-1) vs 32.4 nmol.ml(-1).min(-1), (P<0.03), whereas the enzyme activity did not differ in patients with negative exercise test results compared to controls (33.6 +/- 6.1 nmol.ml(-1).min(-1)). There was no change in PAF-AH activity during exercise in any group. The enzyme activity was positively correlated to the serum total and low density lipoprotein (LDL) cholesterol levels in the control group and in patients with negative exercise test results, whereas no correlation was found between PAF-AH activity and total or LDL cholesterol levels in patients with positive exercise test results.

Cardiac performance in collagen diseases estimated by non-invasive methods

The myocardial performance was studied in 3 collagen diseases, i.e. rheumatoid arthritis (RA), systemic lupus erythematosus (SLE) and progressive systemic sclerosis (PSS). Sixteen patients with SLE, 12 with RA and 11 with PSS were examined, measuring the systolic time intervals from the first derivative of the carotid pulse in all cases. The ejection fraction (EF), was evaluated in 33 patients using radionuclide left ventricular angiography. The systolic time intervals were compared to those of 103 normal persons and the EF to that of 22 normal controls. In the SLE group the pre-ejection period was significantly shorter, while the ejection period was longer than normally expected. In the same group, the EF was significantly higher that the EF of the control group. These differences could not be related to age, blood pressure, disease duration, coronary risk factors, heart rate or blood values. Most findings in the RA group tended to be opposite to those of SLE. It is concluded that in SLE before any direct involvement of the heart the systolic time intervals and the EF present features similar to those of increased cardiac performance.

24-hour blood pressure differences in hypertension and normotension in bed-confined subjects

This study investigates whether the degree of hypertension may be evaluated by information derived from the 24-h blood pressure (BP) curve unrelated to the pressure height. We performed 24-h BP intra-arterial monitoring in 52 bed-confined subjects (10 normotensives, 10 borderlines, and 32 hypertensives on WHO criteria). Computer analysis of 1152 BP values per subject per 24-h revealed the following: During the night hours, the percentage of the 1152 systolic BP values greater than or equal to 160 (in mmHg) increased (or did not change if 100%) in all subjects with mean 24-h systolic BP (24-h BP) greater than 170 and it decreased (or did not change if 0%) in all subjects with 24-h BP less than 150. The change in the percentage of the 1152 diastolic BP values greater than or equal to 95 during the night hours did not correlate to either the mean 24-h diastolic or systolic BP. The higher the mean 24-h systolic BP, the lower the skewness of the distribution of the 1152 systolic BP values (p less than 0.01). No such correlation existed between the skewness of the distribution of the 1152 diastolic BP values and either the mean 24-h diastolic or systolic BP. It is concluded that both the change in systolic BP during the night hours and the skewness of its distribution during the 24-h monitoring period are correlated to the severity of hypertension.