Optimizing the Geometry of Implantable Leads for Recording the Monophasic Action Potential with Fractally Coated Electrodes

This study investigates the influence of various lead geometry on intracardial signals like the monophasic action potential (MAP) to optimize the geometry of implantable MAP leads. The experimental results were compared with a field theoretical approach to the origin of MAP from the transmembrane potential (TAP). During the experiments several lead geometries (tip surface: 1.3 to 12 mm²; tip-ring distance: 0.8 mm to 25 cm; ring surface: 1.8mm² to 40 mm²) were investigated in endo- and epicardial positions in 12 dogs (17±9 kg). The electrodes were fixed passively (tines) or actively (screws). MAP was recorded during several interventions and correlated with MAP measured using an Ag-AgCl MAP catheter. The experimental results showed that small tips provided high MAP amplitudes with less pressure. No difference was observed using active and passive fixations. A tip-ring distance smaller than 5 mm with a ring surface smaller than the tip (<5 mm²) avoided artifacts in the repolarization course. For the theoretical approach the quasistatic, anisotropic bidomain model was calculated in smalt unity volumes V_i where the TAP φ_m was constant and represented by the current density J. Two solutions for electrode positions at and outside the heart were achieved. By superposition of each solution φ_ei the summed potential at the electrode position was calculated. The theoretical findings show in good correlation with the experimental results that a larger distance than 10 mm leads to distortions in repolarization course by signals proportional to φ_out.     

Cholestyramine treatment of type IIa hypercholesterolaemia normalizes platelet reactivity against prostacyclin

Abstract. The effect of lowering total plasma and low density lipoprotein (LDL) cholesterol in heterozygous familial hypercholesterolaemia type IIa (FH) on platelet function, thromboxane (TX) formation and platelet sensitivity against iloprost, a stable prostacyclin mimetic, was studied in platelet-rich plasma ex vivo . Seven FH patients were treated with cholestyramine (12 g day^-1) for 8–11 months and were compared with eight untreated FH patients and 11 healthy control subjects. In comparison with platelets from healthy controls, platelets from untreated FH patients exhibited a significantly increased aggregation response and TX formation, and a reduced reactivity against inhibition of platelet aggregation by prostacyclin. Treatment with cholestyramine for 8–11 months resulted in a 21% reduction in total serum and LDL-cholesterol. This was not accompanied by any change in platelet hyperreactivity or TX formation. However, cholestyramine treatment normalized the platelet reactivity of FH patients against iloprost, being no more different from healthy controls. It is concluded that reduction in plasma cholesterol by cholestyramine results in normalization of the reduced platelet sensitivity against prostacyclin. This might contribute to beneficial effects of cholestyramine treatment in preventing thrombembolic complications of atherosclerosis.     

A Fractally Coated, 1.3 mm2 High Impedance Pacing Electrode

Minimizing the geometric surface area of pacing electrodes increases impedance and reduces the current drain during stimulation, provided that voltage (pulse-width) thresholds remain unchanged. This may be feasible by coating the electrode surface to increase the capacity of the electrode tissue interface and to diminish polarization. Ten unipolar, tined leads with a surface area of 1.3 mm² and a “fractal” coating of Iridium (Biotronik SD-V137) were implanted in the ventricle, and electrogram amplitude (unfiltered), slew-rate, pacing threshold (0.5 ms), and impedance (2.5 V; 0.5 ms) were measured by the 5311 PSA (Medtronic). On days 0, 2, 5, 10, 28, 90, 180, 360 postimplant, sensing threshold (up to 7.0 mV, measuring range 1–14 mV on day 360 only) and the strength duration curve (0.5–4.0 V; 0.03–1.5 ms; steps: 0.5 V; 0.01 ms, respectively) were determined, the minimum charge delivered per pulse (charge threshold), and the impedance were taken from pacemaker telemetry (Intermedics 294–03). Data were compared with those of an earlier series of 20 unipolar, tined TIR-leads (Biotronik) with a surface area of 10 mm² and a “fractal” coating of titanium nitride. With the model SD-V137 versus TIR, intraoperative electrogram amplitudes were 15.1 ± 6.1 versus 14.4 ± 3.9 mV(NS), slew rates 3.45 ± 1.57 versus 1.94 ± 1.06 V/s (P < 0. 05), pacing thresholds 0.16 ± 0.05 versus 0.52 ± 0.15 V (P < 0.01) and impedance measurements 1,136 ±175 versus 441 ± 73 Ω (P < 0.0001), respectively. During follow-up, sensing thresholds were the same with both leads. Differences in pulse width thresholds lost its significance on day 28 but resumed on day 360 (SD-V137: 0.08 ± 0.04 ms; TIR: 0.16 ± 0.06 ms at 2.5 V; P < 0.01). With an electrode surface of 1.3 mm², charge per pulse and impedance consistently differed from control, beingO.15 ± 0.15 versus 0. 66 ± 0. 20 μC (P < 0.001) and 1,344 ± 376 versus 538 ± 79 Ω, respectively, one year after implantation (P < 0.0001). In summary, “fractally” coated small surface electrodes do not compromise sensing; by more than doubling impedance against controls they offer pacing thresholds (mainly in terms of charge) that are significantly lower than with the reference electrode.     

The determinants of airway hyperresponsiveness to hypertonic saline in atopic asthma in vivo. Relationship with sub-populations of peripheral blood leucocytes

In patients with asthma there is only a weak relationship between airway responsiveness to hypertonic saline and methacholine. We tested the hypothesis that airway responsiveness to hypertonic saline in asthma is related to the presence and activity of inflammatory cells in the peripheral blood. Nineteen atopic asthmatic adults (19–28 yr; PC₂₀ 0.06–12.4 mg/ml), not receiving steroid treatment, entered a methacholine and hypertonic saline period in random order. Dose-response curves to doubling doses of inhaled methacholine (0.03–256 mg/ml) or hypertonic saline (0.9–14.4% NaCl) were obtained twice in each period, 7 days apart. The response was measured by FEV₁ Methacholine responsiveness was measured by PC₂₀ METH of FEV₁ and responsiveness to hypertonic saline was expressed as the percentage fall in FEV, after 14.4% NaCl (HYP14.4%). Peripheral blood was collected before the second challenge test of each period. Apart from leucocyte counts and serum eosinophilic cationic protein (ECP) level, sub-sets of lymphocytes (CD4 ⁺/CD3 ⁺, CD8 ⁺/CD3 ⁺, CD25 ⁺/CD4 ⁺ and VLA-1 ⁺/CD4 ⁺) were determined using flowcytornetry. HYP_14.4% was positively correlated to basophil, eosinophil and monocyte counts (r = 0.64, 0.54 and 0.44, respectively; P< 0.05). The basophil count remained positively related to HYP 14.4% when PC₂₀ METH or FEV₁%pred were entered in multiple linear regression analyses (r = 0.66 and 0.75, respectively; P 0.05). There were no significant relationships between HYP₁₄.₄% or PC₂₀ METH on one side and ECP level or T-lymphocyte subsets on the other (P> 0.05). We conclude that airway responsiveness to hypertonic saline is positively related to the number of peripheral blood basophils, eosinophils and monocytes. Basophil count is an independent correlate of responsiveness to hypertonic saline, after correction for mcthacholine responsiveness and baseline lung function. This fits in with active involvement of basophils in airway narrowing to hypertonic saline in vivo.     

环状痔切除术后发现直肠早期黑色素瘤1例

患者　女 ,40岁。因间隙性大便少量带血 ,偶伴疼痛 ,近 1个月入院。体查 :心肺及腹部均未见阳性体征。肛门外观无异常。肛门直肠镜检查见直肠轻度充血、水肿 ,未见溃疡及肿块。齿状线上下 3点6点、8点、9点、11点、12点均可见大小不等暗红色凸起 ,未见有活动性出血。诊断 :混合痔Ⅱ期。骶麻下行混合痔环形切除术。术中发现于截石位 8点齿线上下可见一凸起 ,与其它病灶不同 ,外观呈葡萄状 ,颜色略深 ,直径约 0 8ｃｍ ,质稍硬 ,触及易出血。将该病灶连同其它病灶均送病理检查。病理报告 :直肠黑色素瘤Ｉ期。首次术后 5ｄ行Ｍｉｌｅｓ术 ,术中…     

Neutral-Red Uptake and Expression of Monocytic Antigens in Amniotic-Fluid Mononuclear Phagocytes: Evaluation of a Novel Approach for Prenatal Diagnosis of Neural-Tube Defects

ABSTRACT: In cases of fetal neural-tube defects macrophages are present in the amniotic fluid. We found that these viable phagocytic cells take up neutral-red and are easily identified as “red cells” by microscopic examination. This method is suitable for the rapid identification and counting of amniotic-fluid macrophages in suspension. We have studied 298 amniotic fluid samples. In the 226 normal cases studied, 0 to 1,200 macrophages per milliliter amniotic fluid have been found. In contrast, we found 1,250 to 99,000 macrophages per milliliter amniotic fluid in our 70 open neural tube defect (ONTD) cases. Statistical evaluation was performed to estimate the normal and pathologic ranges. Specificity and sensitivity of the neutral-red test and predictive value of positive and negative results have been calculated and presented in comparison with alpha-fetopro-tein (AFP) determinations and ultrasonic methods. In 5 cases of anencephaly and 7 normal cases amniotic fluid cells were studied by immunocytochemistry: mononuclear cells present in the abnormal cases showed intense immunoreactivity for the Mo1 and Mo2 surface antigens of the phagocytic cell lineage.     

Masticatory features,EMG activity and muscle effort of subjects with different facial patterns

Summary It has been suggested that craniofacial morphology plays an important role in masticatory function, however, there are controversies and unsolved questions that still require elucidation. The aims of this study were to evaluate masticatory performance, mandibular movement, electromyographic (EMG) activity and muscle effort of masseter and anterior temporal muscles during mastication. Seventy‐eight dentate subjects were selected and divided into three groups according to vertical facial pattern: brachyfacial, mesofacial and dolichofacial. Silicon‐based material was used for chewing tests. Masticatory performance was determined by a 10‐sieve method, and masticatory movements during mastication were assessed using a 3D mandibular tracking device. Electromyographic activities of masseter and anterior temporal muscles were evaluated during mastication, and muscle effort was calculated by the percentage of activity required for mastication based on maximum muscle effort. Data were analysed using anova and anova on‐ranks tests. Dolichofacial subjects presented significantly poorer masticatory performance (6·64 ± 2·04; 4·33 ± 0·70 and 3·67 ± 0·63), slower rate of chewing (1·34 ± 0·27, 1·18 ± 0·22 and 1·21 ± 0·20 cycles per second) and larger posterior displacement during mastication (6·22 ± 2·18; 5·18 ± 1·87 and 5·13 ± 1·89) than meso‐ and brachyfacial individuals, respectively. No statistical difference was detected among groups for the other masticatory movement parameters. There was no difference in absolute EMG amplitudes of masseter and anterior temporal muscles during mastication among groups, but the relative effort of both muscles was higher in dolichofacial, followed by meso‐ and brachyfacial subjects (masseter: 39·34 ± 2·25; 36·87 ± 4·05 and 33·33 ± 4·15; anterior temporal: 38·12 ± 1·61; 38·20 ± 8·01 and 35·75 ± 2·48). It was concluded that the vertical facial pattern influences masticatory performance, mandibular movement during mastication and the effort masticatory muscles required for chewing.     

Analysis of randomness of atrial and ventricular rhythm in atrial fibrillation

The aim of the present study was to examine the relationshipbetween randomness of atrial and ventricular rhythm during atrialfibrillation. Atrial fibrillation was induced in 10 open-chestpigs by application of metacholine on the surface of the rightatrium followed by incremental pacing. Local atrial rhythm (AAintervals) was recorded with a bipolar epicardial electrode,and episodes of atrial fibrillation corresponding to 500 ventricular(RR) intervals were selected for analysis. Randomness of thedistribution of AA and RR intervals was assessed by autocorrelation.Pearson's test was used for statistical analysis. Random AAand RR interval distribution was observed in nine pigs (P0.05).In the remaining pig, atrial fibrillation had changed to atrialtachycardia. This was associated with immediate transition ofa random to a non-random ventricular rhythm. These findingsprovide strong circumstantial evidence in support of the contentionthat randomness of ventricular rhythm during atrial fibrillationis due to randomness of atrial rhythm.     

Duplex versus Unguided Pulsed Doppler Measurements of Right Ventricular Output in Newborn Infants

ABSTRACT. Noninvasive measurement of pulmonary artery blood flow has widespread implications for management of newborn infants requiring intensive care. Using a precordial, unguided, single Doppler technique, we evaluated right ventricular output in 26 preterm and 16 term infants without cardiopulmonary problems and compared it with right ventricular output obtained by duplex Doppler scanning and left ventricular output measured by a suprasternal single Doppler approach. Weights ranged from 1120 to 3960 g and postconceptional ages from 29 to 42 weeks. Unguided measurements of left and right ventricular output and guided and unguided measurements of right ventricular output were highly correlated (r=+0.92 and +0.95 respectively, p<0.001). The precordial single Doppler technique offers a reliable noninvasive estimate of right ventricular output in preterm and term newborn infants.