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Biomedical subjects

H J Moore

Publications and source records attributed to H J Moore.

13 recordsLinked to original sources
PubMed2001

Case report: spontaneous atriofascicular pathway automaticity simulating ventricular tachycardia.

Atriofascicular pathways most commonly present electrocardiographically as an antidromic reciprocating AV reentrant tachycardia. We report the case of a child who presented in infancy with a wide QRS complex tachycardia thought to be supraventricular tachycardia with aberrant conduction, associated with tachycardia-induced cardiomyopathy. Later in life the same patient represented with episodes of palpitations secondary to a wide QRS complex tachycardia, thought to be ventricular tachycardia. Electrophysiologic mapping demonstrated the origin of the wide QRS complex tachycardia was from automatic activity originating from a right anterolateral atriofascicular pathway, which also participated in a reentrant antidromic AV reciprocating tachycardia. Radiofrequency ablation of the atriofascicular pathway successfully eliminated both arrhythmias. The mechanism of the wide QRS complex tachycardia appeared to result from spontaneous automaticity of the atriofascicular pathway.

Catheter Ablation↗
PubMed2000

Case report: pulmonary vein stenosis following RF ablation of paroxysmal atrial fibrillation: successful treatment with balloon dilation.

Paroxysmal atrial fibrillation and atrial tachycardia may originate from a focal source in one or multiple pulmonary veins. A focal origin facilitates a potential cure amendable to radiofrequency ablation. Herein we report the case of a 16 year old adolescent male with a tachycardia induced cardiomyopathy who presented with very frequent paroxysmal episodes of atrial fibrillation, atrial flutter and atrial tachycardia. The origin of the arrhythmia was mapped to the secondary branches of the left lower pulmonary vein using an octapolar micro-mapping catheter. Immediately following application of three radiofrequency lesions, angiography of the left lower pulmonary vein revealed a region of focal stenosis at the site of energy application, with delayed pulmonary venous emptying. Attempts to relieve any element of spasm using direct administration of nitroglycerin were unsuccessful. Three months later repeat catheterization revealed an unchanged region of tight anatomical stenosis. Balloon dilation of two stenotic areas resulted in dramatic relief of the obstruction and improved venous drainage. Recatheterization 6 months later revealed mild restenosis that was successfully redilated. Intracardiac ultrasound demonstrated focal constriction. Care should be exercised in attempting RF ablation in distal arborization sites of the pulmonary veins in children, because of the small caliber compared to adult subjects. Radiofrequency induced focal areas of stenosis may be amenable to balloon catheter dilation.

Adolescent↗
PubMed1998

Cellular phone interference testing of implantable cardiac defibrillators in vitro.

An in vitro study was undertaken to investigate the potential for cellular telephones to interfere with representative models of presently used ICDs. Digital cellular phones (DCPs) generate strong, amplitude modulated fields with pulse repetition rates near the physiological range sensed by the ICD as an arrhythmia. DCPs with Time Division Multiple Access (TDMA) pulsed amplitude modulation caused the most pronounced effect--high voltage firing or inhibition of pacing output of the ICDs. This electromagnetic interference (EMI) occurred only when the phones were within 2.3-5.8 cm of the ICD pulse generator that was submerged 0.5 cm in 0.18% saline. ICD performance always reverted to baseline when the cellular phones were removed from the immediate proximity of the ICD. Three models of ICDs were subjected to EMI susceptibility testing using two types of digital phones and one analog cellular phone, each operating at their respective maximum output power. EMI was observed in varying degrees from all DCPs. Inhibition of pacer output occurred in one ICD, and high voltage firing occurred in the two other ICDs, when a TDMA-11 Hz DCP was placed within 2.3 cm of the ICD. For the ICD that was most sensitive to delivering unintended therapy, inhibition followed by firing occurred at distances up to 5.8 cm. When a TDMA-50 Hz phone was placed at the minimum test distance of 2.3 cm, inhibition followed by firing was observed in one of the ICDs. EMI occurred most frequently when the lower portion of the monopole antenna of the cellular phone was placed over the ICD header.

Contraindications↗
PubMed1997

Overview of the Mars Pathfinder mission and assessment of landing site predictions.

Chemical analyses returned by Mars Pathfinder indicate that some rocks may be high in silica, implying differentiated parent materials. Rounded pebbles and cobbles and a possible conglomerate suggest fluvial processes that imply liquid water in equilibrium with the atmosphere and thus a warmer and wetter past. The moment of inertia indicates a central metallic core of 1300 to 2000 kilometers in radius. Composite airborne dust particles appear magnetized by freeze-dried maghemite stain or cement that may have been leached from crustal materials by an active hydrologic cycle. Remote-sensing data at a scale of generally greater than approximately 1 kilometer and an Earth analog correctly predicted a rocky plain safe for landing and roving with a variety of rocks deposited by catastrophic floods that are relatively dust-free.

Atmosphere↗
PubMed1996

Pressure exposure unmasks differences in release properties between high and low yield excitatory synapses of a single crustacean axon.

The cellular mechanisms underlying the effect of high pressure on synaptic transmission at two types of synapses were studied in the opener muscle of the lobster walking leg. Excitatory postsynaptic currents (EPSCs) were recorded using a loose macropatch clamp technique at normal pressure and 3.5, 6.9 MPa helium pressure. Responses of the single excitatory axon could be grouped into two types: low yield (L) synapse exhibiting a small mean EPSC with a considerable number of failures, and high yield (H) synapse having a larger mean EPSC with very few failures. The change in several synaptic transmission parameters indicated that high pressure similarly reduced presynaptic evoked release in both L and H synapses. However, some differences in the kinetics and probability of release could be detected. A major difference was the spontaneous miniature EPSCs (mEPSCs) activity. Many of the mEPSC, observed only in L synapses, were 'giant' (size of 2-5 q). High pressure selectively increased the frequency of the giant mEPSCs in the L synapse but had little effect on their amplitude histogram. High pressure depressed evoked synaptic transmission in both synapses by modulating the presynaptic quantal release parameters, but concomitantly enhanced spontaneous quantal release in L synapses by an unknown mechanism.

Animals↗
PubMed1996

A second defibrillator chest patch electrode will increase implantation rates for nonthoracotomy defibrillators.

Nonthoracotomy defibrillator systems can be implanted with a lower morbidity and mortality, compared to epicardial systems. However, implantation may be unsuccessful in up to 15% of patients, using a monophasic waveform. It was the purpose of this study to prospectively examine the efficacy of a second chest patch electrode in a nonthoracotomy defibrillator system. Fourteen patients (mean age 62 +/- 11 years, ejection fraction = 0.29 +/- 0.12) with elevated defibrillation thresholds, defined as > or = 24 J, were studied. The initial lead system consisted of a right ventricular electrode (cathode), a left innominate vein, and subscapular chest patch electrode (anodes). If the initial defibrillation threshold was > or = 24 J, a second chest patch electrode was added. This was placed subcutaneously in the anterior chest (8 cases), or submuscularly in the subscapular space (6 cases). This resulted in a decrease in the system impedance at the defibrillation threshold, from 72.3 +/- 13.3 omega to 52.2 +/- 8.6 omega. Additionally, the defibrillation threshold decreased from > or = 24 J, with a single patch, to 16.6 +/- 2.8 J with two patches. These changes were associated with successful implantation of a nonthoracotomy defibrillator system in all cases. In conclusion, the addition of a second chest patch electrode (using a subscapular approach) will result in lower defibrillation thresholds in patients with high defibrillation thresholds, and will subsequently increase implantation rates for nonthoracotomy defibrillators.

Adult↗
PubMed1995

Analysis of evoked and spontaneous quantal release at high pressure in crustacean excitatory synapses.

The cellular mechanisms underlying the effect of high pressure on synaptic transmission were studied in the opener muscle of the lobster walking leg. Excitatory postsynaptic currents (EPSCs) were recorded using a loose macropatch-clamp technique at normal pressure and 3.5, 6.9 MPa helium pressure. Responses of the single excitatory axon could be grouped into two types: low-yield (L) synapses exhibiting small EPSCs with a considerable number of failures, and high-yield (H) synapses having larger EPSCs with very few failures. High pressure reduced the average EPSC amplitude in all synapses and shifted their amplitude histograms to the left by decreasing the quantal content (m) without changing their quantum current (q). A binomial distribution fit of EPSC amplitudes revealed that high pressure greatly decreased n, the number of available active zones, but the effect on p, the probability of release for each zone, was not consistent. Many of the spontaneous miniature EPSCs (mEPSCs), observed only in L-type synapses, were "giant" (size = 2-5 q). High pressure increased the frequency of the giant mEPSCs but had little effect on their amplitude histogram. High pressure depressed evoked synaptic transmission by modulating the presynaptic quantal release parameters, but concomitantly enhanced spontaneous quantal release by an unknown mechanism.

Air Pressure↗
PubMed1995

Thermistor guided radiofrequency ablation of atrial insertion sites in patients with accessory pathways.

Radiofrequency ablation has gained acceptance in the treatment of patients with symptomatic Wolff-Parkinson-White syndrome. The purpose of this study was to characterize the relation between temperature and other electroconductive parameters in patients undergoing atrial insertion accessory pathway ablation utilizing a thermistor equipped catheter. The mean temperature and power at sites of atrial insertion ablation are lower than has been previously associated with creation of radiofrequency lesions in the ventricle. While high cavitary blood flow in the atrium may result in cooling, the thinner atrial tissue may require less energy to achieve adequate heating than ventricular myocardium.

Adolescent↗
PubMed1994

Quantal analysis of presynaptic inhibition, low [Ca2+]0, and high pressure interactions at crustacean excitatory synapses.

The cellular mechanisms underlying the effects of high pressure, GABAergic presynaptic inhibition, and low [Ca2+]0 on glutamatergic excitatory synaptic transmission were studied in the opener muscle of the lobster walking leg. Excitatory postsynaptic currents (EPSCs) were recorded with or without prior stimulation of the inhibitor using a loose macropatch clamp technique at atmospheric pressure and at 6.9 MPA helium pressure. High pressure reduced the mean EPSC amplitude and variance, decreased the quantal content (m), but did not affect the quantum current (q). Pressure shifted the median of the amplitude histogram to the left by 1-2 q. Under normal pressure conditions, presynaptic inhibition and low [Ca2+]0 induced similar effects. However, quantal analysis using a binomial frequency distribution model revealed that high pressure and low [Ca2+]0 diminished n (available active zones) and slightly increased p (probability of release), but presynaptic inhibition reduced p and slightly increased n. At high pressure, presynaptic inhibition was reduced, at which time the major contributor to the inhibitory process appeared to be reduction in n and not p. The similarity of the alterations in quantal parameters of release at high pressure, low [Ca2+]0, and in some conditions of presynaptic inhibition is consistent with the hypothesis that pressure reduces Ca2+ inflow into the presynaptic nerve terminals to affect the Ca(2+)-dependent quantal release parameters n and p.

Animals↗
PubMed1992

A system for saturating in vitro preparations with high pressure O2, He, H2, and mixtures.

Saturation of a liquid with gas before perfusing a tissue or cellular preparation under pressure can be achieved by bubbling the gas through the liquid. A container for this purpose that is housed in the pressure chamber with the preparation allows saturation of the liquid under hyperbaric conditions. Sealing the container allows saturation with a gas different from the gas used to compress the pressure chamber. If the pressure within the sealed container is maintained at a slightly higher level, the bubbling gas can also provide the driving force for the liquid to flow to the preparation. Based on this concept, an apparatus was built and tested to pressures of 6.8 MPa. This paper describes the saturator and the associated circuitry used to control bubbling gas pressure relative to the pressure vessel, gas flow through the saturator, and liquid flow to the preparation. A special application in the case of hydrogen gas is described, where this system has added safety advantages.

Equipment Design↗
PubMed1985

Myasthenia gravis-associated antibodies in asymptomatic thymoma.

Serum antibodies associated with myasthenia gravis were evaluated before and after therapy in an asymptomatic patient having a malignant thymoma. The case illustrates that myasthenia-associated antibodies may also be useful as a tumor marker of thymoma in the work-up of mediastinal masses, in evaluating therapy of thymoma, and possibly in detecting recurrence of thymoma and potential for developing myasthenia gravis.

Aged↗
PubMed1982

Influence of a visual display and frequency of whole-body angular oscillation on incidence of motion sickness.

Visual search within a head-fixed display consisting of a 12 X 12 digit matrix is degraded by whole-body angular oscillation at 0.02 Hz (+/- 155 degrees/s peak velocity), and signs and symptoms of motion sickness are prominent in a number of individuals within a 5-min exposure. Exposure to 2.5 Hz (+/- 20 degrees/s peak velocity) produces equivalent degradation of the visual search task, but does not produce signs and symptoms of motion sickness within a 5-min exposure.

Acceleration↗