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Biomedical subjects

M J Davis

Publications and source records attributed to M J Davis.

At least 73 records · Page 4Linked to original sources
PubMed1995

Longitudinal study of hand bone densitometry in rheumatoid arthritis.

OBJECTIVE: To measure hand bone mineral content (BMC) by dual x-ray absorptiometry and to seek clinical correlates in patients with rheumatoid arthritis (RA), in a prospective, longitudinal study. METHODS: Eighty-one patients with non-steroid-treated RA were assessed at baseline and at month 12, for hand BMC and for disease activity and severity. Hand BMC in patients was compared with that in a control group of 95 normal volunteers, and rate of loss was compared with that in 37 controls. RESULTS: At the initial assessment, male and female patients with RA had lower hand BMC than controls, after correction for age, height, and weight (mean reduction 7.5% in men [P = 0.003] and 7.8% in women [P = 0.01]). After 1 year, there was a further loss of hand BMC in patients (median loss 3.25% in men [P = 0.001] and 1.46% in women [P = 0.05]), but normal controls did not have significant changes in their hand BMC. In patients with disease duration of < 2 years at study entry, the parameters of disease activity improved over 1 year, but they lost significant amounts of hand BMC. Hand BMC loss correlated with baseline C-reactive protein levels. In those with RA of > 2 years duration at entry, the Health Assessment Questionnaire scores and Larsen scores had worsened after 1 year, but there was no significant loss of hand BMC. CONCLUSION: Patients with RA had low hand BMC compared with normal controls, even within 2 years of disease onset. The rate of loss was highest in patients with early disease and correlated with measures of initial disease activity. This loss continued despite clinical improvement.

Absorptiometry, Photon↗
PubMed1995

Combined ultrasound and fluorescence spectroscopy for physico-chemical imaging of atherosclerosis.

This paper describes a combined ultrasonic and spectroscopic system for remotely obtaining physico-chemical images of normal arterial tissue and atherosclerotic plaque. Despite variations in detector-tissue separation, R, fluorescence powers corresponding to pixels in the image are converted to the same set of calibrated units using distance estimations from A-mode ultrasound reflection times. An empirical model, validated by Monte Carlo simulations of light propagation in tissue, is used to describe changes in fluorescence power as a function of R. Fluorescence spectra of normal and atherosclerotic human aorta obtained with this system are presented as a function of R. To compensate for changes in fluorescence power with R, the empirical model was used in each case to calculate the fluorescence power at a constant reference value of R(Rref = 1.67 mm). Prior to compensation, tissue fluorescence power decreased more than a factor of two as R was increased from 2.5 to 5 mm. Following compensation, the fluorescence power varied less than +/- 10% of the average compensated peak. The chemical composition of each sample was determined by fitting its fluorescence spectrum (in calibrated units) to a model of tissue fluorescence incorporating structural protein and ceroid fluorescence, as well as structural protein and hemoglobin attenuation. Parameters of the fit were used to classify tissue type. Without compensation for distance variation, classification of tissue type was frequently incorrect; however, with compensation, predictive value was high. A 1-D chemical image of a section of human aorta containing both normal and atherosclerotic regions obtained with this system is also presented. After compensation for detector-sample separation, tissue classifications along the cross-section closely resemble those obtained from histology. Regions of elevated ceroid concentration and intimal thickening are clearly observable in the resultant chemical image. The potential value of this type of system in the diagnosis and treatment of coronary artery disease is discussed.

Aorta↗
PubMed1995

Radiofrequency catheter ablation of atrial tachycardia.

BACKGROUND: Atrial tachycardia is a relatively uncommon arrhythmia which usually responds poorly to antiarrhythmic drug therapy. Transcatheter radiofrequency (RF) ablation is a new therapeutic modality for patients with atrial tachycardia. AIM: This study analyses our early experience with the treatment of atrial tachycardia by this technique. METHODS: Thirteen consecutive patients (age 13-63 years) with 15 drug-refractory atrial tachycardia foci were treated with RF catheter ablation. Atrial tachycardia was mapped by seeking the earliest atrial activation in the right atrium in eight patients and in the left atrium in five. RESULTS: Tachycardias were abolished in nine (69%) patients, including two sinoatrial re-entrant tachycardias and seven automatic atrial tachycardias, after 9 +/- 10 (range, one to 28) pulses of RF current. Six of these ablated atrial tachycardia foci were right sided and three were on the left. One patient had three separate right atrial tachycardia foci; one was eliminated. Tachycardia recurred after two weeks in one patient with apparently successful ablation of sinoatrial re-entrant tachycardia. One patient with successful ablation of a right atrial tachycardia developed cardiac tamponade requiring surgical intervention. CONCLUSION: This study demonstrates that atrial tachycardia arising from diverse sites can be eliminated by RF catheter ablation.

Adolescent↗
PubMed1995

The impact of the implantable cardioverter defibrillator on quality-of-life.

The implantable cardioverter defibrillator (ICD) is an established treatment for patients with life-threatening ventricular arrhythmias. While it clearly reduces the incidence of death from recurrent arrhythmia, little is known about the impact on patients' quality-of-life. In this prospective study, quality-of-life was assessed by questionnaire before and after ICD implantation. The "Sickness Impact Profile" (SIP), which evaluates physical, psychosocial, and other activities, as well as functions of daily life, was used. Employment and rehospitalization rates were also examined. Twenty-one of 23 consecutive patients, aged 58 +/- 11 years, undergoing ICD implantation at Royal Perth Hospital were studied. During the 14 +/- 8 month follow-up, 4 patients died. Functional capacity was unchanged in all but one of the survivors in whom it improved from New York Heart Association Class III to II. Four of 8 survivors employed before implant have since retired. Six patients required rehospitalization on 13 occasions, problems related to arrhythmias or the ICD. Overall SIP scores preimplant (11.2 +/- 9.3; P < 0.05) were significantly worse at 6-month follow-up (21.7 +/- 18.2), but returned to preimplant levels by 12-month follow-up (8.8 +/- 10.8; NS). This was primarily due to transient problems in the areas of emotional behavior, alertness, and social interaction. SIP psychosocial dimension scores: preimplant: 7.2 +/- 9.0; 6-month: 17.8 +/- 18.1 (P < 0.05); and 12-month: 8.6 +/- 10.3 (NS). Early retirement and hospitalizations due to arrhythmias may still be expected even after implantation of an ICD; however, quality-of-life appears only to temporarily decline.

Arrhythmias, Cardiac↗
PubMed1995

Substance P-induced calcium entry in endothelial cells is secondary to depletion of intracellular stores.

Substance P (SP) induces an elevation in cytosolic Ca2+ concentration ([Ca2+]i) in porcine coronary artery endothelial cells by way of Ca2+ influx and release from intracellular stores. We tested the hypothesis that SP-induced Ca2+ influx occurs due to activation of a Ca(2+)-permeable influx pathway coupled to depletion of intracellular stores. With the use of the perforated patch technique and fura 2 microfluorimetry, a fivefold greater increase in [Ca2+]i per unit decrease in membrane potential was obtained in the presence of SP (10 nM) compared with resting state, implying that SP increased Ca2+ conductance. When K+ channels were blocked, SP activated a net inward current with a reversal potential (2.5 +/- 1 mV) not significantly different from that (2 +/- 1 mV) for inward current recorded in response to store depletion by (2,5-di-tert-butylhydroquinone) (BHQ, 10 microM). Increasing bath [Ca2+] induced a similar shift in reversal potential for SP- and BHQ-induced currents. Inositol 1,4,5-trisphosphate (20 microM), applied through the patch pipette, activated an inward current with Ca2+ selectivity similar to SP- and BHQ-activated currents. Dialysis of cells with heparin (5 mg/ml) completely blocked SP-induced inward current but not BHQ-induced current. These results suggest that the SP-induced increase in Ca2+ conductance can be completely explained by activation of a Ca(2+)-permeable influx pathway coupled to depletion of intracellular stores.

Animals↗
PubMed1994

Combination therapy for rheumatoid arthritis and drug-induced systemic lupus erythematosus.

Development of drug-induced systemic lupus erythematosus (SLE) is an uncommon complication of the use of D-penicillamine and sulphasalazine. We report two cases of patients with rheumatoid arthritis (RA) who developed symptoms and signs of SLE and suggest that increasing use of these two agents as combination therapy in RA may cause an additive risk to the occurrence of this complication.

Adult↗
PubMed1994

Predictors of early and late recurrence of atrioventricular accessory pathway conduction after apparently successful radiofrequency catheter ablation.

The correlation between electrophysiologic parameters and recurrence in 239 patients who underwent successful catheter ablation for an accessory pathway mediated tachycardia was analysed. Pathway conduction recurred in 15 patients (6.3%) after a mean follow-up of 7.3 months. Recurrence was most common in patients with right free wall pathways (17.1%). Accessory pathway conduction resumed in 18.9% of patients with decremental ventriculo-atrial (VA) conduction post-ablation compared with those patients without VA conduction (3.4%) (P < 0.001). Recurrence was common also in patients with repeated return of accessory pathway conduction during the ablation procedure (40% vs. 1.3%, P < 0.01). The patients in whom these observations are made should be monitored closely for recurrence of accessory pathway conduction post-ablation.

Adult↗
PubMed1994

The cost-effectiveness of treatment of supraventricular arrhythmias related to an accessory atrioventricular pathway: comparison of catheter ablation, surgical division and medical treatment.

BACKGROUND: Treatment alternatives for patients with incapacitating supraventricular arrhythmias related to an accessory atrioventricular pathway include transcatheter radiofrequency (RF) ablation, surgical division and long-term antiarrhythmic therapy (medical). AIM: The aim of this study was to compare in terms of cost and efficacy, transcatheter, surgical and medical treatment of patients with incapacitating supraventricular arrhythmias resulting from an accessory pathway. METHODS: The study population consisted of 52 patients who underwent transcatheter RF ablation (20 consecutive patients), surgical treatment (20) and medical treatment (12). Two types of economic analysis were used. In all groups, a resource based costing method was used and in the medical and surgical treatment groups, a diagnostic related group (DRG) based costing method was used. RESULTS: Eighteen out of 20 (90%) patients who underwent catheter ablation remained asymptomatic during 8.4 +/- 1.6 months of follow-up. All surgically treated patients remained asymptomatic during 54 +/- 15 months of follow-up. Only one of the 12 patients in the medical treatment group remained completely free of symptoms during the mean 58 +/- 23 month follow-up period. The mean cost (1992 Australian dollars) per patient, calculated on the basis of actual resources used (with a DRG based costing given in brackets), was $2746 +/- $800 for catheter ablation, $12141 +/- $4465 ($12880 +/- $3998) for surgical treatment and $1713 +/- $748 ($1967 +/- $33) for medical treatment. The total cost of management over 20 years is estimated to be: $2911 for catheter ablation, $17467 for surgery and $4959 for medical treatment. CONCLUSIONS: In the long term transcatheter RF ablation is the most cost-effective treatment strategy for patients with incapacitating supraventricular arrhythmias related to an accessory pathway.

Adolescent↗
PubMed1994

Measurement of hand bone mineral content by dual energy x-ray absorptiometry: development of the method, and its application in normal volunteers and in patients with rheumatoid arthritis.

OBJECTIVES--To develop a method of measuring hand bone mineral content (BMC) by dual energy x ray absorptiometry (DXA); to apply this method of measuring hand BMC to normal volunteers to ascertain causes of variability; and to measure hand BMC in patients with rheumatoid arthritis (RA) of varying duration and severity. METHODS--The x ray beam of the Hologic QDR 1000 dual energy x ray absorptiometer was hardened by introducing a perspex-aluminium plate and the analysis software altered to allow for the small tissue bulk of the hand compared with the torso. Ninety five volunteers (46 men age 24-81 and 49 women age 20-83) had scans of both hands. Eight volunteers were assessed repeatedly to establish reproducibility and effect of hand position. Fifty six patients (22 men, 34 women, age range 25-86 years) with RA of differing duration and severity, had hand BMC measurement by DXA. RESULTS--The precision of BMC measurement was 2.3% with no additional variation due to hand position. Hand dominance had no significant effect on BMC. In men, hand BMC correlated with height (r = 0.57, p < 0.0001), weight (r = 0.58, p < 0.0001), forearm span (r = 0.5, p = 0.0006) and hand volume (r = 0.66, p < 0.0001). In women hand BMC correlated with height (r = 0.66, p < 0.0001), weight (r = 0.4, p = 0.003), forearm span (r = 0.3, p = 0.03) and hand volume (r = 0.49, p = 0.0008). After correcting for all these variables, male volunteers had significantly higher hand BMC than female volunteers (p = 0.01) and patients with RA had lower hand BMC than normal volunteers (total hand BMC in male volunteers 90.9 gms, 95% CI 86.9-95, in male patients 81.7 gms, 95% CI 73.7-89.6, p < 0.004, total hand BMC in female volunteers 62.2 gms 95% CI 59.8-64.5, female patients 52.3 gms, 95% CI 48.1-56.5, p < 0.005). In patients with RA, the hand BMC showed an inverse correlation with age (r = -0.44, p = 0.01), disease duration (r = -0.62, p = 0.0003), Larsen's grades (r = -0.62, p = 0.0002) and modified Sharp's method score (r = -0.69, p < 0.0001) in female patients only. CONCLUSIONS--A new, sensitive and reproducible technique of measurement of hand bone mineral content by DXA, has been developed and this method has been applied to normal volunteers and patients with RA. Hand dominance had no significant effect on hand BMC. After correcting for physical size, men have higher hand BMC than women. Hand BMC inversely correlates in women patients with disease duration and other validated methods of assessing radiological outcome in RA. Longitudinal studies are needed to establish its role in monitoring disease progression.

Absorptiometry, Photon↗
PubMed1994

Mechanism of substance P-induced hyperpolarization of porcine coronary artery endothelial cells.

Substance P (SP) is a potent endothelium-dependent vasodilator, and in porcine coronary arterioles the vasodilatory action of SP appears to be mediated entirely by nitric oxide. We tested the hypothesis that SP induces hyperpolarization in porcine coronary artery endothelial cells (PCAECs) by activating Ca(2+)-activated K+ (KCa) channels. With a bath Ca2+ concentration ([Ca2+]) of 1 mM, 10 nM SP elicited an increase in cytosolic [Ca2+] ([Ca2+]i) from a baseline of 25 +/- 4 nM to a peak of 808 +/- 120 nM, followed by a slowly declining plateau phase, which was absent in Ca(2+)-free bath and was abolished by addition of extracellular lanthanum or nickel. Whole cell current-clamp recordings revealed that the time course of SP-induced [Ca2+]i increases correlated closely with membrane hyperpolarization from an average resting potential of -42 +/- 2 to a peak of -79 +/- 2 mV. Under voltage clamp, SP stimulated whole cell currents with reversal potentials strongly dependent on extracellular K+ concentration. In 62% of patches tested, single-channel recordings revealed an intermediate-conductance K+ channel with activation highly correlated with the SP-induced [Ca2+]i increase. These results suggest that, in PCAECs, SP induces Ca2+ release from stores along with Ca2+ influx which activate a KCa channel leading to hyperpolarization. This may increase the driving force for Ca2+ entry and thus modulate endothelium-derived nitric oxide release.

Animals↗
PubMed1994

Chloride and cation currents activated by bradykinin in coronary venular endothelial cells.

Bradykinin (BK) is known to activate several types of ion channels in endothelial cells, including a K+ channel and a nonselective cation channel. The predominant BK-activated current in most endothelial cells appears to be an outward, Ca(2+)-activated K+ current. We consistently recorded a rapidly activated, spontaneously inactivated inward current stimulated by BK in bovine coronary venular endothelial cells (CVECs). With the use of a whole cell, perforated patch recording mode, the average magnitude of the current was -293 +/- 38 pA. Simultaneous measurements of current and intracellular Ca2+ concentration ([Ca2+]i) showed that the inward current correlated closely with transient increases in [Ca2+]i due to Ca2+ release from intracellular stores. The current could be blocked by 4,4'-diisothiocyanatostilbene-2, 2'-disulfonic acid (DIDS) but not by La3+, and it persisted in Ca(2+)-free/Na(+)-free solution. When intra- and/or extracellular Cl- concentrations were altered, the reversal potential of the current shifted according to the calculated Cl- -equilibrium potential, indicating that the current was carried primarily by Cl-. Another inward current was also activated by BK. This current was slower to activate, could be blocked by La3+, but was not blocked by DIDS. The time course of the slowly activated current correlated with the plateau phase of the BK-stimulated [Ca2+]i increase, which was similar to the behavior of a nonselective cation current reported previously. We propose that these two currents may contribute to the depolarizations and net inward currents induced by BK in this cell line.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1994

Whole-cell and single-channel calcium currents in guinea pig basal forebrain neurons.

1. Whole-cell and single-channel patch-clamp recordings of calcium (Ca2+) currents were made in acutely dissociated neurons from the medial septum (MS) and nucleus of the diagonal band (nDB) of adult guinea pig. Barium (Ba2+) was used as the charge carrier across the Ca2+ channel and multiple channel types were identified in different cell types. 2. Both low-voltage-activated (LVA) and high-voltage-activated (HVA) currents were distinguished on the basis of steady-state voltage dependence, activation and inactivation properties, and pharmacological sensitivity. HVA currents had activation thresholds approximately 20 mV more positive than LVA currents. Steady-state inactivation of HVA currents was approximately 50% when the holding potential was shifted from -80 to -40 mV. 3. The dihydropyridines had consistent effects on HVA currents. The amplitude was increased and the activation threshold shifted by 10 mV in the hyperpolarizing direction in the presence of the agonist Bay K 8644 (2-5 microM). The antagonist nifedipine (10 microM) produced approximately 50% inhibition of HVA currents from a holding potential of -80 mV. 4. A second component of the HVA current was blocked by omega-conotoxin (omega-CTX) (300-700 nM). At a holding potential of -80 mV, omega-CTX inhibited 45% of the HVA current. 5. LVA currents were activated near -70 mV and displayed time-dependent inactivation during a 200- to 300-ms voltage step. Voltage-dependent inactivation of LVA currents was also observed and could be described by a single Boltzman relationship with a half-inactivation potential of -84 mV. LVA currents were not significantly changed by Bay K 8644 and were not blocked by low concentrations of nifedipine or omega-CTX. 6. Single voltage-gated Ca2+ channels were investigated using cell-attached patches. In these experiments, 100 mM Ba2+ was used in the patch pipette and the membrane potential was zeroed with isotonic potassium (K+)-aspartate. A low-conductance channel was activated at negative potentials and inactivated rapidly during a 200- to 300-ms voltage step. Unitary amplitudes were determined at different membrane potentials with single-channel conductances calculated to be 7.8 +/- 1.2 (SD) pS. These channels were not blocked by nifedipine (10 microM) and appeared similar to T channels previously reported in both peripheral and central neurons. Ensemble averages from cell-attached patches of T channels resembled LVA currents recorded in the whole-cell configuration.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

Transcatheter radiofrequency ablation. Early experience with supraventricular tachyarrhythmias related to accessory atrioventricular and dual atrioventricular nodal pathways.

OBJECTIVE: To describe our initial experience with transcatheter radiofrequency ablation, a useful new treatment for supraventricular tachyarrhythmias related to the presence of an accessory atrioventricular (AV) pathway or dual atrioventricular nodal pathways. PATIENTS AND METHODS: One hundred and ten patients, including 77 with accessory pathways, 32 with dual atrioventricular (AV) nodal pathways and one with both, underwent electrophysiological studies and were treated with transcatheter radiofrequency ablation in a large metropolitan teaching hospital. RESULTS: Ninety-five patients (86%) were without evidence of accessory pathway conduction or inducible supraventricular tachycardia and were free of symptoms after a mean follow-up of 13 months (range, 3.0-51 months). Sixty-six of 79 accessory pathways (83.5%) were ablated including 42 of 46 left-sided (91%), 14 of 21 posteroseptal (66%), six of seven anteroseptal (86%), three of four right-sided and one of one midseptal pathways. Thirty-one patients with AV nodal reentry were successfully treated by ablation of either the slow (12 patients) or fast (19 patients) conducting AV nodal pathway. There was a progressive improvement in the success rate of the first procedure from 17% to 64% with the use of large-tip catheters and from 64% to 91% when a purpose-built radiofrequency generator was employed. Complications occurred in nine patients: cardiac tamponade (two patients); mild mitral regurgitation (four); subclavian vein thrombosis (one); transient cerebral ischaemic attack (one); and non-thrombocytic purpuric rash (one). These occurred predominantly during the early experience and were without long-term sequelae. Late in our experience, one patient developed complete atrioventricular block requiring permanent pacemaker implantation. CONCLUSIONS: In this institution, radiofrequency catheter ablation has been a safe and effective treatment strategy for patients with life-threatening or highly symptomatic supraventricular arrhythmias.

Adolescent↗
PubMed1993

An index of disease activity in rheumatoid arthritis.

This paper describes the Stoke Index which has been designed to give a global measure of disease activity in rheumatoid arthritis. The index is based on two objective laboratory measurements, one subjective and two semi-objective clinical measurements, chosen from 13 measurements using clinical judgement. Variable selection routines in principal components analysis are used to demonstrate that the index measures clinically defined disease activity. Its sensitivity and reversibility are also considered. A comparison is carried out with another index (Mallya-Mace) and a modification is suggested.

Adult↗
PubMed1993

Distribution and control of coronary microvascular resistance.

Coronary blood flow depends upon the vascular resistance distributed non-uniformly within the coronary microcirculation. Coronary microvascular resistance is governed by metabolic, myogenic, endothelial and neurohumoral influences. A number of these control mechanisms interact locally within a microvascular segment. In addition, these control mechanisms occupy differing longitudinal response gradients, a feature which maximizes their potential for the synergistic control of flow.

Animals↗