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.     

Lysis of pathogenic and nonpathogenic Entamoeba histolytica by human complement: methodological analysis

The effect of nonimmune human serum on Entamoeba histolytica trophozoites was studied: (a) using whole serum in the presence of Ca and Mg ions allowing complement activation via both the alternative and classical pathways or in the presence of MgEGTA permitting alternative pathway activation only; (b) using different E. histolytica isolates; (c) varying serum and trophozoite concentrations and the time of incubation; and (d) using three different methods to quantify lysis, i.e., microscopic inspection, flow cytometry and 111In release. All three methods yielded similar results, with flow cytometry being most sensitive in identifying membrane damage and 111In release being most valid in determining cell death. Microscopic analysis was reliable only when a chamber was used to calculate the number of complement treated cells in relation to the initial cell count. E. histolytica isolates were classified into three groups according to their susceptibility to lysis by complement: (i) pathogenic isolates after long term cultivation in vitro were susceptible; (ii) pathogenic isolates after recent in vivo passage were less susceptible; and (iii) nonpathogenic isolates were nearly unaffected by exposure to the alternative pathway alone. The extent of lysis of the various isolates correlated with the degree of complement consumption in the serum samples, suggesting that unlysed isolates did not activate complement under the conditions employed. In general, lysis of susceptible trophozoites increased with the serum concentration and with the time of incubation. However, when the trophozoite concentration was 10(6)/ml or higher, lysis no longer reflected complement susceptibility because of exhaustion of the complement supply.     

Quantitative Tissue Doppler Echocardiography: Physiological Nonuniformity of Left Ventricular Transmural Myocardial Wall-Motion Velocities and Gradients

Tissue Doppler echocardiography (TDE) is a new method by which transmural myocardial function can be studied noninvasively. In order to investigate physiology and reproducibility, 24 young, healthy volunteers were examined by M-mode TDE. Nonuniformity of transmural tissue layer velocities became apparent: Subendocardial and subepicardial velocities of the anteroseptal myocardial wall (AW) were 3.5 ± 0.7 and 1.3 ± 0.5 cm/sec (P < 0.0001 , t- test), whereas in the posterolateral wall (PW) values of 3.6 ± 0.6 and 1.2 ± 0.4 cm/sec (P < 0.0001 , t- test ), respectively, were revealed. The ratios, termed "myocardial velocity gradients" as a new indicator of left ventricular performance, were 3.1 ± 1.0 and 3.4 ± 1.1, respectively. AW and PW did not differ (N.S.). Tolerance borders did not overlap, and intraobserver variability did not reach intersubject variability (P < 0.0001, F-ratio test). TDE provides new and more sophisticated insights into left ventricular performance. It seems to be accurate and reliable and therefore worth introducing into the clinical arena.     

Bowenoid lesions, Bowen''s disease and keratoacanthomas in long-term PUVA-treated patients

Four patients are described, two with histologically proven multiple foci of bowenoid lesions, one patient with bowenoid lesions and Bowen's disease, and one patient with two keratoacanthomas, most of the lesions occurring in non sun-exposed but photochemically treated areas of the body. These patients had received long-term PUVA treatment for their psoriasis. Two patients had a history of arsenic intake. The possible relationship of these epidermal lesions to light treatment is discussed.     

Long-term changes in the perception of comfortable mandibular occlusal positions

The aim of this study was to disclose, whether use of a screw jack device to set the distance between the jaws, would contribute towards a stabilization of the magnitude and position of a comfortable zone of mandibular positions or even eliminate it. Thirteen subjects participated in each of fifteen experimental sessions distributed over a 3-week period. Throughout the investigation the zone prevailed at an average width of 1.3 mm. The gap shrank 0.08 mm on average per experimental session. Although this latter value was found to be significant statistically, it can hardly be of clinical importance, considering the time needed for a total contraction of 0.8 mm to develop.     

Horizontal stabilization of upper and lower borders of the comfortable zone

Using a screw jack device the upper and lower borders of the comfortable zone were recorded in a two step procedure designed to counteract bias inherent in previous measurements. In these measurements, successively increasing and decreasing values of zonal borders were recorded corresponding to a fully closed or fully opened starting position of the screw. Both of these positions are outside the comfortable zone. The two step procedure used a starting position which was supposed to lie inside the comfortable zone. However, the procedure did not achieve its aim fully. It succeeded only in stabilizing the lower border values. In the discussion hypothetical considerations are made concerning theneurophysiological mechanism underlying recordings of the borders of the comfortable zone, which might explain the differential behaviour of the zonal borders.     

Age changes in the two-point discrimination threshold in skin innervated by the trigeminal nerve

Fifty young and fifty elderly subjects were tested by a two-point discrimination method. An aesthesiometer was applied to the facial skin in three different areas innervated exclusively by the ophthalmic, maxillary or mandibular branch of the trigeminal nerve. Two characteristic age differences were disclosed: (1) higher threshold values were found in older subjects, and (2) a greater range of variation in these values was present also among the older subjects. Wales.     

The fallacy of facial measurements of occlusal height in edentulous subjects

A controlled trial was made using fifteen subjects and making 120 measurements with a caliper gauge between marks disposed on the upper lip and the point of the chin when maxillo-mandibular relationships were altered vertically by known amounts within a range of 6 mm. It was found that mean facial measurements could account for only half of the skeletal movement involved. The variability of soft tissue translation in relation to skeletal movement led to the conclusion that such facial measurements are inappropriate to clinical practice.