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At least 1,279 records · Page 71Linked to original sources

PubMed2001

Extension of generator longevity by use of high impedance ventricular leads.

The resistance of a pacing lead negatively correlates to current consumption. A prospective, randomized trial was conducted to evaluate the effect of a high impedance ventricular lead (CapSure Z) on generator longevity compared to a conventional lead (CapSure SP) eighty-nine patients were included in the study (51 male, 37 female, age 70.0+/-10.3 years). Forty-six patients received a CapSure SP lead (5024 bipolar), and 43 patients received a CapSure Z lead (5034 bipolar) in a randomized fashion. Follow-up data collected at 5 days, 3, 6, and 12 months postimplant included: lead impedance, pacing and sensing thresholds, impulse energy, and estimated time to replacement. All parameters were collected via pacemaker telemetry; the time to replacement was calculated automatically by a programmed algorithm of the pacemaker. There was no difference in the performance of the atrial lead when a dual chamber device was indicated. The CapSure Z leads displayed statistically significant higher impedance values than the CapSure SP lead in all follow-up periods. There was no significant difference in lead related complications. No significant differences were observed between pacing and sensing thresholds in both groups. The CapSure Z leads provided a significant reduction in current drain, resulting in a reduction of mean energy consumption at the 12-month follow-up from 10.4+/-5.0 microJ in the CapSure SP group to 6.6+/-1.4 microJ in the CapSure Z group (median from 9.9 microJ to 6.9 microJ, respectively), providing an estimated increase in mean longevity of more than 1 year from 81.1+/-23.5 months in the CapSure SP group to 94.5+/-13.4 months in the CapSure Z group (median: 76.5 months to 95.0 months, respectively). The use of a high resistance lead for ventricular pacing appears to result in a clinically relevant extension of generator longevity.

Aged↗

PubMed2001

The Heartmate II: design and development of a fully sealed axial flow left ventricular assist system.

Our group is developing the control and power transmission components required to implement a permanent and fully sealed left ventricular assist system (LVAS). Starting with the percutaneously powered HeartMate II blood pump, our development efforts are focused in the following areas: a complete redesign of the transcutaneous energy transmission system (TETS) to include a rectification network and autonomous voltage regulation within the secondary coil, a hermetically sealed electronics package containing a miniaturized implementation of the existing redundant drive and control electronics with several power-input options, an implanted rechargeable lithium ion battery pack capable of providing up to 1 h of untethered operation, implantable electrical connectors that allow components to be connected after placement in the body or to be replaced if needed, and a radio telemetry subsystem to transmit diagnostic information and to permit remote adjustment of selected parameters.

Electric Power Supplies↗

PubMed2003

Electronic visual prosthesis.

Retinitis pigmentosa (RP) and age-related macular degeneration (AMD) are incurable diseases that result in profound vision loss due to degeneration of the light sensing photoreceptors. However, the discovery that direct electrical stimulation of the retinal neurons creates visual sensation has inspired prosthetic devices aimed to restore useful vision in RP/AMD patients. The approach to one such electronic visual prosthesis is described in this article. The prosthesis consists of an external unit and an internal unit. The communication link has three components--power and data transfer from the external to the internal unit, and data transfer from the internal to the external unit. A novel method of integrating power transfer and back telemetry is described here. The goal is to design a stimulator chip with a small area with low power consumption. This chip, capable of stimulating 60 dedicated electrodes, is fabricated using AMI 1.2 microm process technology and the results are presented. Improvements in the design to increase the number of outputs to 1,000 have been discussed. The new circuit is aimed at increasing the circuit density, reducing power per stimulus, and meeting the requirements more closely than the previous designs. The results of the designed chip are presented.

Artificial Organs↗

PubMed2001

Hippocampal volume and glucose metabolism in temporal lobe epileptic foci.

PURPOSE: Reports conflict on the relation of glucose metabolism to hippocampal volume in temporal lobe foci. Previous studies usually have used side-side ratios rather than regional metabolic rates. METHODS: We measured hippocampal volume and glucose metabolism in 37 patients with temporal epileptogenic zones identified by ictal video-EEG telemetry. Metabolic rates were normalized to global brain mean. RESULTS: Both 18-fluoro-2-deoxyglucose-PET and volumetric MRI lateralized the epileptic focus determined by ictal video-EEG. There were significant correlations between left-right metabolic asymmetry and hippocampal formation volume left-right ratios. Comparisons between normalized metabolism and hippocampal formation volume, ignoring the side of the epileptic focus, showed significant relations between left hippocampal volume and left inferior lateral temporal metabolism, right hippocampus and right inferior mesial temporal, and left hippocampus and left inferior mesial temporal metabolism. In contrast, when normalized metabolism was compared with hippocampal volume in the epileptic focus, no relation was found. CONCLUSIONS: Our study suggests that the relation between hippocampal volume and glucose metabolism breaks down in epileptic foci and that hypometabolism is not dependent on neuronal loss. It is consistent with data suggesting that hypometabolism is an independent predictor of surgical outcome.

Brain↗

PubMed2002

The spectrum of nonepileptic events in children.

Nonepileptic events (NEE) are common in children, and can be difficult to distinguish from epileptic events. Several strategies can assist in differentiation. The first is an age-based approach to the differential of commonly presenting EEs in neonates, infants, and adolescents. The next strategy is to identify key elements of the patient's history to narrow the possibilities, and third is a rational approach to ancillary testing. There are additional challenges to the diagnosis and evaluation of NEEs in patients with cognitive impairments or mental retardation (MR). Twenty to 25% of neurologically normal patients (34), and up to 60% of children with MR (35) referred for an evaluation of seizures, have NEE. In most instances, the clinical history leads to the diagnosis, and ancillary testing serves as confirmation. But in certain populations, neonates, children with concurrent epilepsy, children in whom pseudoseizures are suspected, and children with MR, early use of video-EEG telemetry is indicated to establish the diagnosis and avoid overtreatment with antiepileptic drugs (AEDs).

Adolescent↗

PubMed2002

Epilepsy surgery in childhood.

Epilepsy surgery in childhood can now be more readily considered as a result of enhanced presurgical investigative techniques and safer neurosurgical practice. As in adults, surgery available may be resective (focal resection or hemispherectomy) or functional. The most common procedures are temporal lobectomy and hemispherectomy, with malformative lesions and developmental tumours the next common pathology. The timing of surgery requires careful consideration, and the definition of drug resistance given specific thought in the young child. Presurgical evaluation should be noninvasive where possible, and should include optimised MRI, including 3D data set and video EEG telemetry to document seizures. Detection of temporal lobe abnormalities in temporal lobe epilepsy with MR may be enhanced using quantitative and semiquantitative techniques. Ictal and interictal SPECT may be useful in providing information about the seizure onset zone, if reviewed in conjunction with MR data and video-EEG. Interictal PET is more likely to demonstrate abnormalities relating to structural defects, but may be particularly useful in infants where incomplete myelination may restrict structural information provided by MRI. Neuropsychology testing plays a major role by the determination of verbal and nonverbal function in older children, and in the determination of cerebral dominance. Functional MRI for determination of language or motor cortex may enhance such evaluation, although it is limited to older unsedated children at present. Although the aims of the presurgical evaluation remain similar to adult practice, the range of children presenting is wide, and the aims and likely outcome of surgery require careful evaluation with the family. This aside, the benefits of seizure elimination or reduction in drug-resistant focal epilepsy prior to adolescence, as well as in certain early catastrophic epilepsies of childhood, remain self apparent.

Age Factors↗

PubMed2004

Interaction of implantable defibrillator therapy with angiotensin-converting enzyme deletion/insertion polymorphism.

INTRODUCTION: The angiotensin-converting enzyme deletion allele (ACE D) decreases survival in patients with advanced heart failure. Whether the adverse impact on survival reflects an increased risk of pump failure or arrhythmic sudden death remains uncertain. If the ACE D genotype increases the risk of sudden death, implantable cardioverter defibrillator (ICD) therapy should diminish its negative impact. We sought to evaluate the effect of ICD therapy on ACE D genetic risk. METHODS AND RESULTS: The Genetic Risk Assessment of Cardiac Events (GRACE) study enrolled 479 patients at the University of Pittsburgh between 1996 and 2001. Blood was genotyped for the ACE D/I (deletion/insertion) polymorphism. Of the 479 patients, 82 (77% male, 84% Caucasian, age 56 +/- 11 years, 60% ischemic, left ventricular ejection fraction 0.23 +/- 0.08) received an ICD and were selected for outcomes analysis (mean follow-up 871 +/- 538 days). Transplant-free survival and survival alone were compared in ACE DD patients (n = 24, 29%) versus ACE DI/II patients (n = 58, 71%). Survival was significantly improved in ACE DI/II patients compared to those without an ICD (1 year: 93% vs 87%; 2 year: 89% vs 77%; P = 0.02) but not in ACE DD patients. Transplant-free survival among patients with an ICD was significantly worse in ACE DD versus ACE DI/II (1 year: 67% vs 88%, 2 year: 55% vs 80%, P = 0.03). Analysis of survival as a single endpoint revealed a similar result (1 year = 78% vs 94%; 2 year: 72% vs 88%; P = 0.05). ICD telemetry data showed a nonsignificant trend toward fewer individuals with arrhythmias in the ACE-DD group (46% vs 65%, P = 0.22) CONCLUSION: ICDs do not diminish the adverse influence of the ACE DD genotype on survival. This finding suggests that mortality in this high-risk genetic subset of patients is due to progression of heart failure rather than arrhythmic sudden death.

Alleles↗

PubMed1975

[The effect of prindolol on the blood-pressure profile of hypertensives (with special consideration of response to exercise and plasma-renin activity) (author's transl)].

Using microcatheter blood pressure telemetry, the pressure-lowering effect of prindolol (Visken), a beta-blocking drug, was tested at a dose of 10 mg three time daily by mouth in eight patients with essential hypertension (WHO stage II) and low to normal plasma-renin activities. After about ten days of treatment, the hypertensive reaction to everyday physical exercise (walking, climbing stairs, bicycle ergometry) was especially favourably affected. The average blood-pressure reduction at rest was 18.6/12.1 (systolic/diastolic), on stair climbing 41.5/17.2 mm Hg.

Adult↗

PubMedDate not supplied

Gelastic fits in a two years old boy with a complex cerebral malformation.

We report the case of a two years old boy showing gelastic fits as the leading clinical symptom of a rare complex cerebral malformation with closed-lip schizencephaly, an arachnoid cyst and a partial agenesis of the corpus callosum. After 5 uneventful interictal electroencephalograms the patient underwent 24 h EEG with telemetry while finally presenting two laughing fits with associated spike-wave discharges in the right-centroparietal region. Medical treatment with carbamacepine was initiated and the seizure frequency decreased significantly. This is the first cited case of gelastic fits occurring in schizencephaly. In contrast to previously cited cases with laughing fits we observed a good response to anticonvulsive treatment. Moreover our patient presented a surprisingly favourable psycho-mental and motor development during an 8 months observation period.

Agenesis of Corpus Callosum↗

PubMed1993

Validity and reliability of the Cosmed K2 instrument.

The purpose of this study was to measure the validity and reliability of a portable telemetry system (Cosmed K2) for measurement of oxygen consumption (VO2) during a laboratory exercise test at submaximum and maximum intensities. Twenty subjects performed three testing sessions on a treadmill on three consecutive days. Each testing session consisted of a submaximal and a maximal exercise test. On one day, VO2 was determined with the conventional Douglas bag method, and on the other two days, VO2 was determined using the Cosmed K2 system. Utilization of the Douglas bag method or the Cosmed K2 was randomly assigned. The results indicated that the Cosmed K2 instrument is reliable and valid (p > 0.05) for measurement of VO2 (l.min-1) during laboratory exercise testing at submaximum and maximum intensities. The assumption made by the K2 apparatus of a constant respiratory gas exchange ratio (R) of 1.00 did not have a significant influence on VO2 measurements.

Adult↗

PubMed1998

Field test for mechanical efficiency evaluation in matching volleyball players.

Field tests were performed in 10 volleyball (VB) players (4 females and 6 males) in order to obtain an index of mechanical work efficiency (mu' = Wmec/Woxy) while athletes played a game. Wmec was the mechanical work output, obtained by means of home made video image analysis software, by summing potential, kinetic translational and kinetic rotational energies of running and jumping athletes. Woxy was the oxidative energy consumption obtained from O2 consumption (VO2) by a telemetry device (Cosmed K2) that also gave values of pulmonary ventilation (VE) and heart rate (HR). VB were studied at rest before a game (R), during attacking phases (A) and during defensive phases (D). At R were found: VE = 11 +/- 1 l x min(-1), HR = 78 +/- 7b x min(-1), VO2 = 3.71 +/- 1.1 ml x kg(-1) x min(-1), Woxy = 75.1 +/- 22.3 J x kg(-1) x min(-1). During A all variables increased: VE = 49 +/- 6l x min(-1), HR = 149 +/- 15 b x min(-1), VO2 = 23.1 +/- 3.3ml x kg(-1) x min(-1), Woxy = 482.8 +/- 69.0 J x kg(-1) x min(-1), and Wmec 275.5 +/- 57.0 J x kg(-1) x min(-1) with mu'=0.57 +/- 0.09. In D HR (-9%), VE, VO2 and Woxy (-18%) were reduced when compared to A, decreasing mu' to 0.21 +/- 0.05. On the other hand mu' was found higher than 0.25 during A indicating an anaerobic contribution to energy expenditure; in D the mu' lower than 0.25 indicated a restoration of anaerobic energy sources. It might be proposed that a greater difference in mu' values between A and D also means a higher anaerobic energy contribution to the volleyball game.

Adult↗

PubMed1989

[Skin boot versus knee joint--a sports medicine, orthopedic and biomechanical problem].

In contrast to the drop in the incidence of fractures of the lower leg, or tibia, that has been observed in recent years, the incidence of knee injuries has not decreased in skiing and there has been a relative increase in the frequency of severe knee lesions and of the isolated rupture of the cruciate ligament, prompting us to conduct a comprehensive study of the causes of these phenomena. It was found necessary to develop a innovative method of measurement to analyse the patterns of movement and stress to which the knee injuries were attributed. By combining and synchronizing movement analysis, measurement of pressure distribution and measurement of force it became possible to perform a detailed analysis of the forward/backward movement in the ski boot in the laboratory and also on the course by telemetry (part 1). The first two studies were devoted to the forward lean in the ski boot (part 2). Basing on movement analysis and simultaneous determination of pressure distribution along the lower leg, the influence of different ski boot models on the Vorlage, or forward lean, movement of beginners and very experienced skiers was studied. An important result of the laboratory experiment was that whereas a ski boot can be moved without difficulty into a strong forward lean position of the skier by an experienced sportsman, a beginner can only assume a forward lean with 20% less inclination (this being a significant difference). In other words: the range of the freedom of movement in such a boot is markedly limited. The assumption that in ski amateurs such a ski boot would promote skiing in backward lean position, was confirmed by studies on the course (part 3). The pupils became definitely less adept at learning if they were required to wear a stiff ski boot; analysis of movement showed that the forward lean angles were clearly smaller and that the skiers adopted a skiing style in backward lean position that exercised an undue strain on the knees. The other two studies, therefore, focussed mainly on the backward movement in the ski boot. Specifically, the fixed rear spoilers of the modern ski boots are accused of contributing to the rupture of the anterior cruciate ligament if the skier lands on the tail ends of the skis after a jump or fall in backward lean position ('big bump, flat landing' syndrome).(ABSTRACT TRUNCATED AT 400 WORDS)

Biomechanical Phenomena↗

PubMed2006

Renin enhancer is critical for control of renin gene expression and cardiovascular function.

The important cardiovascular regulator renin contains a strong in vitro enhancer 2.7 kb upstream of its gene. Here we tested the in vivo role of the mouse Ren-1c enhancer. In renin-expressing As4.1 cells stably transfected with Ren-1c promoter with or without enhancer, expression of linked beta-geo reporter, stable expression, and colony formation were dependent on the presence of the enhancer. We then generated mice carrying a targeted deletion of the enhancer (REKO mice) and found marked depletion of renin in renal juxtaglomerular and submandibular ductal cells, as well as hyperplasia of macula densa cells. Plasma creatinine was increased, but electrolytes were normal. Male REKO mice implanted with telemetry devices had 9 +/- 1 mm Hg lower mean arterial pressure (p < 0.001), which was partly normalized by a high NaCl diet. Locomotor activity was lower, and baroreflex sensitivity was normal. Markedly reduced mean arterial pressure variability in the midfrequency band indicated a contribution of reduced sympathetic vasomotor tone to the hypotension. In conclusion, the renin enhancer is critical for renin gene expression and physiological sequelae, including response to alteration in salt intake. The REKO mouse may be useful as a low renin expression model.

Animals↗

PubMed2004

Objective measurements of auditory nerve recovery function in nucleus CI 24 implantees in relation to subjective preference of stimulation rate.

OBJECTIVE: Setting the optimal rate of stimulation for individual cochlear implant recipients is critical to the successful functional outcome of cochlear implantation. In the absence of an objective methodology, cochlear implants are currently fitted by means of a time-consuming (and therefore expensive) trial-and-error process of limited accuracy. The aim of this study was to evaluate a possible relationship between the patient's subjectively preferred stimulation rate and an objective measurement of auditory nerve recovery time. MATERIAL AND METHODS: Eleven recipients of Nucleus CI 24 implants initially fitted with a speech processor using the advanced combination encoders speech-coding strategy at a rate of 900 Hz were introduced to 2 other stimulation rate options, 1200 and 1800 Hz, at 2 different fitting sessions and were asked to choose their preferred rate. Preferences were compared with objective measurements of auditory nerve recovery time obtained with the refractory recovery function of neural response telemetry. RESULTS: The auditory nerve recovery time for individuals with a subjective preference for a slow stimulation rate was longer than that for individuals who preferred a fast stimulation rate, with significant differences between the 2 groups for 3 of the tested electrodes (Nos. 7, 11 and 15): p = 0.024, 0.009 and 0.03, respectively (Mann-Whitney test). CONCLUSIONS: The association observed between subjective stimulation rate preference and measurements of auditory nerve recovery time indicates that the measured auditory nerve recovery time can be used as a reliable predictor for setting up a basic stimulation rate of a particular individual's map, thus reducing the cost of the technology and significantly increasing its effectiveness.

Acoustic Stimulation↗

PubMed1983

The effect of body temperature on the growth rate of broilers.

The effect of body temperature (Tb) on the growth rate of male broilers was studied. Two pens (5 m2 each), one (A) near air inlets and one (B) near air outlets, were erected in a 12.5 m wide cross-ventilated, environmentally-controlled poultry house. Of 100 birds of both sexes in each pen, 18 males were marked and weighed weekly, and in three of these in each pen body temperature was measured by telemetry over 24 h at 50, 54, 55, 58, and 62 d of age. At 62 d group B birds weighed 250 g less than A; implanted birds weighed less than their group means, but relative growth rates were similar. Mean lowest (08.00 to 09.00 h) and highest Tb (11.00 to 17.00 h) in group A were 41.35 degrees C and 42.13 degrees C, and in group B 41.48 degrees C and 42.86 degrees C, respectively. The regression of G (percentage gain in body weight/d) on noon maximum Tb (Tbn) was G = 46.25 - 1.024 Tbn. This study suggests that an air temperature above 32 degrees C depresses body-weight gain of broilers by about 10% between 5 and 9 weeks of age. Therefore, house temperature should not be allowed to increase above 28 degrees C, except if relative humidity also increases to 0.70 or more.

Animals↗

PubMed2004

Influence of stimulus frequency on NRT recordings.

Research in neural response telemetry (NRT) with the Cochlear 'Nucleus' CI24M Implant began a few years ago, using the first NRT software version (2.04). It has been demonstrated that NRT offers possibilities for fitting the implant speech processor. NRT sessions, however, remain lengthy for the patients, especially for children, and NRT research is seeking to reduce session time. The new version of the NRT software (3.0) allows implant stimulation up to 400 Hz, whereas the previous version stimulated only up to 80 Hz. The time gained is very significant. The goal of the present study was to observe and assess the modifications in NRT produced by these higher stimulus frequencies. Growth functions were measured in six adult patients for electrodes 5-10-15-20 at frequencies of 20, 80, 150, 250 and 365 Hz to determine NRT thresholds (NRT-T). Subjective detection thresholds (T) were also measured for the same electrodes and frequencies. The results showed that the number of valid responses, like the quality and amplitude of the NRT response, quickly decreased at these higher rates. Consequently, the number of measurement points used for the growth function decreased with frequency. Moreover, when frequency increased, the T value decreased while NRT-T increased: the gap between the two thresholds increased with frequency in a linear manner common to all patients. The growth function slopes did not change significantly with frequency.

Auditory Perception↗

PubMed2004

Circadian and short-term regulation of blood pressure and heart rate in transgenic mice with cardiac overexpression of the beta1-adrenoceptor.

Congestive heart failure is associated with a loss of circadian and short-term variability in blood pressure and heart rate. In order to assess the contribution of elevated cardiac sympathetic activity to the disturbed cardiovascular regulation, we monitored blood pressure and heart rate in mice with cardiac overexpression of the beta1-adrenoceptor prior to the development of overt heart failure. Telemetry transmitters for continuous monitoring of blood pressure and heart rate were implanted in 8 to 9-week-old wildtype and transgenic mice, derived from crosses of heterozygous transgenic (line beta1TG4) and wildtype mice. Cardiovascular circadian patterns were analyzed under baseline conditions and during treatment with propranolol (500mg/L in drinking water). Short-term variability was assessed by spectral analysis of beat-to-beat data sampled for 30min at four circadian times. Transgenic beta1TG4 mice showed an increase in 24h heart rate, while blood pressure was not different from wildtype controls. Circadian patterns in blood pressure and heart were preserved in beta1TG4 mice. Addition of propranolol to the animals' drinking water led to a reduction in heart rate and its 24 h variation in both strains of mice. Short-term variability in blood pressure was not different between wildtype and beta1TG4 mice, but heart rate variability in the transgenic animals showed a rightward shift of the high-frequency component in the nocturnal activity period, suggesting an increase in respiratory frequency. In conclusion, the present study shows that both the circadian and the short-term regulation of blood pressure and heart rate are largely preserved in young, nonfailing beta1-transgenic mice. This finding suggests that the loss of blood pressure and heart rate variability observed in human congestive heart failure cannot be attributed solely to sympathetic overactivity but reflects the loss of adrenergic responsiveness to changes in the activity of the autonomic nervous system.

Adrenergic beta-Antagonists↗

PubMed1999

FDTD analysis of close-coupled 418 MHz radiating devices for human biotelemetry.

This paper describes the finite-difference time-domain (FDTD) analysis of antenna-body interaction effects occurring when chest-mounted 418 MHz radio transmitters are used for medical telemetry applications. Whole-body software models (homogeneous, layered and tissue-segmented) were developed for an adult male subject. Using an electrically small (300 mm2) planar loop antenna, calculated radiation efficiencies ranged between 33.5% and 39.2% for a whole-body model, and between 60.7% and 66.1% for a torso; radiation patterns were found to be largely independent of model composition. The computed radiation efficiency for a 21.5 kg phantom representing a six-year-old female was within 1.1 dB of measured results (actual body mass 28 kg) and well-correlated azimuthal radiation patterns were noted.

Adult↗