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Biomedical subjects

C Walton

Publications and source records attributed to C Walton.

At least 91 records · Page 5Linked to original sources
PubMed1990

Depression, episodic behavioral dyscontrol, and polydipsia following right temporal lobe damage.

A patient referred to the authors for evaluation and treatment of depression, behavioral dyscontrol syndrome, and polydipsia is described. The authors reviewed his medical status and, finding damage to his right temporal lobe, conceptualized his symptom constellation as representing interictal syndrome and treated him with carbamazepine. His affective symptoms, but not the polydipsia, improved following treatment with carbamazepine.

Adult↗
PubMed1990

Increased urinary excretion of transferrin in children with type 1 diabetes mellitus.

Urinary transferrin excretion was measured by radioimmunoassay in 74 children with Type 1 diabetes mellitus and in 40 normal children, and compared with urinary excretion of albumin, alpha-1-microglobulin, and N-acetyl-beta-D-glucosaminidase. Urinary transferrin excretion was significantly elevated in diabetic (median (range) 186 (18-1671) mg mol-creatinine-1) compared with normal (85 (27-668) mg mol-creatinine-1) children (p less than 0.001). Seventeen diabetic children had transferrin excretion above the 95th centile for normal children. In contrast there was no significant increase in urinary albumin excretion in the diabetic children although 8 had urinary albumin excretion which exceeded the 95th centile for normal children (6 of these 8 patients having coexistent urinary hyperexcretion of transferrin). Urinary transferrin excretion correlated significantly with urinary albumin excretion in both normal (rs = 0.62, p less than 0.001) and diabetic (rs = 0.61, p less than 0.001) children. The indices of proximal renal tubular function (urinary excretion of alpha-1-microglobulin and N-acetyl-beta-D-glucosaminidase) correlated significantly with transferrin excretion in both diabetic (rs = 0.43 and rs = 0.41, p less than 0.001) and normal (rs = 0.40, p less than 0.02 and rs = 0.53, p less than 0.001) children, but not with albumin excretion (rs = 0.20, p greater than 0.05 and rs = 0.22, p greater than 0.05). In addition urinary transferrin excretion significantly correlated with urinary glucose concentration (rs = 0.34, p less than 0.007) in Type 1 diabetic children. The discrepancy in urinary excretion of transferrin and albumin may reflect impaired proximal renal tubular reabsorption of transferrin and/or altered glomerular basement membrane selectivity for the two proteins.

Acetylglucosaminidase↗
PubMed1990

Microproteinuria in type 2 diabetes mellitus from diagnosis.

Glomerular and tubular microproteinuria precede the development of overt nephropathy in Type 1 diabetes mellitus. However, in Type 2 diabetes urinary protein excretion and its relationship to diabetic nephropathy has not been clearly characterized. Twenty consecutive, newly diagnosed patients with Type 2 diabetes, whose urine was Albustix-negative and sterile on culture, were studied. Two timed overnight urine samples were collected at diagnosis, and after 2 months and 2 years, and excretion rates of albumin, alpha-1-microglobulin and N-acetyl-beta-D-glucosaminidase were calculated. HbA1c fell from 12.1 +/- 2.4% at diagnosis to 9.5 +/- 1.5% at 2 months and 9.6 +/- 2.2% at 2 years. Albumin excretion rate fell marginally from 6.5 (2.1-242.5) micrograms min-1 at diagnosis to 5.5 (1.7-274.0) micrograms min-1 at 2 months (p less than 0.05) rising again to 6.1 (1.9-201.7) micrograms min-1 at 2 years. alpha-1-Microglobulin excretion rate fell from 13.5 (3.6-59.9) micrograms min-1 at diagnosis to 8.4 (2.9-16.1) micrograms min-1 at 2 months and 8.8 (1.8-54.1) micrograms min-1 at 2 years (both p less than 0.05). Albumin excretion rate was found to correlate significantly with creatinine clearance at diagnosis (rs = 0.61, p less than 0.005), though not subsequently. In contrast, excretion rates of alpha-1-microglobulin and N-acetyl-beta-D-glucosaminidase correlated with HbA1c (rs = 0.68 and 0.66, respectively, p less than 0.005 at diagnosis and rs = 0.57 and 0.53, p less than 0.05 subsequently in both cases).(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylglucosaminidase↗
PubMed1989

An animal model for the chronic study of ventricular repolarisation and refractory period.

We have developed a simple model permitting stable, chronic measurements of ventricular repolarisation and refractory period to be made in conscious, unsedated, unrestrained animals. The model utilises the ventricular paced evoked response, recorded from permanent pacemaker electrodes implanted into the right ventricle of New Zealand White rabbits. After a "bedding in" period of 18-21 d, measured variables are stable for long periods; the stimulus to T wave interval of the evoked response remains stable up to at least 150 d after electrode insertion. The principal advantage of the model lies in the control of heart rate by pacing, eliminating the requirement for unreliable methods of correction of repolarisation data for sinus rate. Surgical techniques are straightforward. The model can also be used for studies involving recordings of the intrinsic (non-paced) intracardiac electrogram, as the quality of the signal obtained is consistently superior to standard methods of recording the electrocardiogram in animals. The stimulus-T interval of the paced evoked response has been found to correlate significantly (r = 0.96) with action potential duration measured by transmembrane microelectrode recordings in the isolated, arterially perfused interventricular septum.

Action Potentials↗
PubMed1989

Determination of myocardial depolarization and repolarization times using the unipolar ventricular evoked potential: contrasting effects of stimulus interval and isoprenaline in the isolated perfused rabbit heart.

The effects of changes in stimulus interval and the infusion of isoprenaline upon myocardial depolarization and repolarization times have been determined using the unipolar ventricular evoked potential. An isolated perfused rabbit heart was the experimental vehicle and the stimulus-to-R wave (St-R) and R wave-to-end (R-E) of complex time intervals were used as measures of depolarization and repolarization times, respectively. Variation in the stimulus interval was shown to have highly statistically significant effects upon both of the parameters of the unipolar paced evoked potential that were investigated. Myocardial repolarization time is increased at longer intervals, while activation time is reduced. Isoprenaline was found to reduce the duration of the R-E interval of the unipolar ventricular evoked potential when infused at a constant rate at a fixed stimulus interval. At the maximum concentration of the drug, when stimulus interval was just shorter than the intrinsic RR interval, it was estimated that one third of the total change in the R-E interval was due purely to the effects of decreased stimulus interval. It proved impossible to identify any effect of isoprenaline infusion upon the St-R interval. The absence of any effect of isoprenaline on the St-R interval of the evoked potential suggests that it may serve as a monitor of purely stimulus interval dependent variations of the signal.

Animals↗
PubMed1988

The ventricular intracardiac unipolar paced-evoked potential in an isolated animal heart.

The endocardial unipolar paced evoked response has excited a great deal of interest due to its possible use in the measurement of the metabolic state of the body and other pacer-related areas. Although rate-responsive pacing utilizing this signal has been clinically evaluated, little is known regarding the behavior of the components of this waveform under normal physiological conditions. We have developed an electronic circuit which allows the recording of the evoked response within a few milliseconds of a pacing stimulus of 5 V and 0.5 ms duration being applied using a single unipolar, smooth platinum electrode of 14 mm2 surface area. The paced evoked response was measured using a total of 20 isolated rabbit heart preparations. Five were run for 8 hours and the remaining fifteen were run for 5 hours. Our results indicate that the waveform components of the evoked response remain stable while the preparation is viable, but that two of the time-related measurements change with loss of viability. A significant lengthening of the stimulus-R interval was seen together with a dramatic shortening of the R-T period. The net result of these changes was an overall reduction of 17% in the complex duration. In addition, we found the R-T shortening to be a sensitive measure of myocardial integrity. We conclude that the combination of our interface charge elimination circuit and the isolated heart preparation has proved a useful system for the investigation of the paced evoked potential. Furthermore, the loss of myocardial viability has a complex action on this response.

Animals↗
PubMed1988

In vitro estimation of the electrical performance of bipolar pacing electrode systems.

With the current interest in bipolar stimulation, there is a need for greater understanding of the electrical contributions of the two electrodes in this type of pacing. This has been investigated using a specially designed cell in which an electrode under test was immersed in a buffered saline solution (pH 7.42) at 37-38 degrees C. Four electrode types were studied: a single stimulating electrode (6 mm2 dish tip, Pt-black coated) and three indifferent electrodes. The indifferent electrodes were a 41 mm2 polished Pt ring, a Pt-black coated version of the same electrode, and a titanium pacemaker enclosure which was included to allow comparison with the unipolar situation. These electrodes were tested individually against a chlorided silver reference electrode of negligible (1-2 omega) impedance, the results being processed in such a way as to allow estimation of the properties of the stimulating electrode taken in combination with each of the indifferents. Constant current pulses (1-10 mA amplitude, 0.5 and 1.0 ms duration) were applied and measurements made from the resulting voltage waveforms. These were v1 and v2, the potential at the leading and trailing edge of the pulse, and v3, the post-pulse potential at 20 ms following the trailing edge. The potential v2--v1 is electrode dependent and allows the determination of the energy loss due to polarization to be calculated. Sinusoidal AC signals (0.1 Hz-10 kHz, 20 microA maximum amplitude) were also employed, allowing determination of sensing impedance. Under all conditions, the calculated performance of the stimulating electrode with the coated ring was nearly equivalent to that with the pacemaker enclosure.(ABSTRACT TRUNCATED AT 250 WORDS)

Electric Conductivity↗
PubMed1988

Tubular dysfunction and microalbuminuria in insulin dependent diabetes.

The nature of microproteinuria in the early years of insulin-dependent diabetes was investigated in a cross sectional study of 80 children with insulin-dependent diabetes and 40 normal children. Urinary excretion of three low molecular weight proteins: alpha-1-microglobulin, beta-2-microglobulin and kappa light chains was used as an index of proximal renal tubular function. The first urine samples of the morning were collected and excretion of proteins measured was expressed as ratio of protein to creatinine. There was a strong correlation between excretion of alpha-1-microglobulin and chi light chains and their excretion was significantly higher in diabetic children indicating decreased proximal tubular reabsorbtion. The excretion of beta-2-microglobulin was found to be an unsatisfactory index of proximal tubular function. Urinary albumin excretion was not significantly raised in diabetic children and did not correlate with urinary alpha-1-microglobulin or chi light chain excretion. Glycaemic control might influence proximal tubular function as both urinary glucose concentration and glycosylated haemoglobin showed correlations with urinary alpha-1-microglobulin excretion and with urinary chi light chain excretion.

Adolescent↗
PubMed1987

Platinum pacemaker electrodes: origins and effects of the electrode-tissue interface impedance.

Investigation of the unipolar properties of the paced-evoked response requires special measures to eliminate the post-stimulus potential, and this in turn requires a knowledge of the properties of the electrode-tissue interface which is not supplied by any single source in the literature. We have therefore drawn together published information and some of our own experimental results. The behavior of a particular type of pacemaker electrode was investigated in vitro under a range of conditions. The application of DC potentials revealed an extremely nonlinear voltage-current characteristic with conduction thresholds at about +1 V and -1 V. Small signal AC response to applied voltages well within these values (20 mV pk-pk) was found to be linear when a nonpolarizable counterelectrode was used. Nonlinearities were introduced by the use of a stainless steel counterelectrode. The response of an in vitro model of a paced patient to voltage pulses (amplitude 5 V, duration 0.5 ms) was also investigated. We have made extensive use of previously published work to demonstrate the mechanisms underlying these results and also their relationship to each other. We have concluded with some theoretical comments upon the design requirements for a device to eliminate the post-stimulus afterpotential in order to detect the paced-evoked response.

Electric Conductivity↗
PubMed1986

Personalized versus usual care of previously uncontrolled hypertensive patients: an exploratory analysis.

This study was conducted to explore whether the quality of provider care may contribute to blood pressure reduction and whether other factors related to the treatment of hypertension may explain decline in blood pressure. In the study, 46 uncontrolled (greater than or equal to 140/90 mm Hg), medically treated hypertensive patients who received more personalized care differed significantly in the magnitude of blood pressure reduction from 36 usual-care patients (10/7 vs 2/2 mm Hg means for systolic and diastolic blood pressure reduction, respectively). About twice as many experimental patients as controls were reclassified as having "controlled" blood pressure, and this difference reached statistical significance. A multiple regression analysis for personalized-care subjects showed that no dynamic variables were related to blood pressure changes. It was postulated that more personalized care may have accounted for the significant difference between groups in blood pressure reduction. Similar personalized monitoring services might be important additions to usual medical care in order to control blood pressure more fully in high-risk hypertensive patients.

Biofeedback, Psychology↗
PubMed1984

HLA antigens and risk factors for nephropathy in type 1 (insulin-dependent) diabetes mellitus.

This study of risk factors for diabetic nephropathy in juvenile Type 1 (insulin-dependent) diabetes mellitus compares two carefully characterised groups of patients, one with proteinuria (n = 23), the other a control group (n = 24) with no evidence of nephropathy despite more than 25 years of diabetic life. No significant difference was observed between the groups in any HLA-A, -B or -DR antigen of Bf allotype. DR3 was present in 87% of patients with proteinuria and 75% of the diabetic control group; DR4 was present in 48% of patients with proteinuria and 63% of diabetic controls; BfFl was present in 17% of patients with nephropathy and 9% of the diabetic control group. Compared with the control group, patients with proteinuria had significantly higher mean diabetic-clinic blood glucose concentrations before the diagnosis of microvascular disease, a significantly earlier age at diagnosis of diabetes, and had more often been treated with once-daily as opposed to twice-daily insulin regimens. Susceptibility to nephropathy in Type 1 diabetes appears to be determined by the quality of metabolic control and age of onset of diabetes; although the number of subjects studied was relatively small no evidence was found of any influence of HLA or Bf phenotype.

Adolescent↗
PubMed1983

The potential use of Health Care Financing Administration data sets for health care services research.

Administrative Record Systems may be an overlooked source of data for health services researchers. Through its administration of the Medicare and Medicaid Programs, the Health Care Financing Administration (HCFA) routinely receives data on items such as its beneficiary population, providers certified to deliver care to its beneficiary population, providers certified to deliver care to the beneficiaries, the use of services and reimbursements to providers. the most important data bases that are useful for research, their relative strengths and weaknesses and the extent to which they are available to outside users.

Centers for Medicare and Medicaid Services, U.S.↗
PubMed1983

Endocrine abnormalities in idiopathic haemochromatosis.

Anterior pituitary functions and sex steroid levels were measured in 12 patients with idiopathic haemochromatosis (eight males, four postmenopausal females) and age-matched controls, 12 with diabetes mellitus and five with hepatic cirrhosis. In idiopathic haemochromatosis gonadotrophin deficiency was present in seven of 12 patients including six of seven patients who had clinical evidence of hypogonadism. Basal prolactin levels were significantly lower in the patients with idiopathic haemochromatosis compared with either of the control groups (p less than 0.02). Nine patients with idiopathic haemochromatosis exhibited subnormal prolactin responses to thyrotrophin releasing hormone. Thyroid and adrenocortical functions were normal in all patients with idiopathic haemochromatosis. Testosterone values were subnormal in five of eight males with idiopathic haemochromatosis; females with idiopathic haemochromatosis had significantly lower testosterone values compared with the diabetic females (p less than 0.05). Oestradiol values in both sexes and sex hormone binding globulin values in the males were not significantly different in patients with idiopathic haemochromatosis compared with the controls. Sex hormone binding globulin levels were significantly higher in females with idiopathic haemochromatosis compared with either diabetic or cirrhotic females (p less than 0.05). Impairment of anterior pituitary function occurs in idiopathic haemochromatosis but is selective; gonadotrophin and prolactin deficiencies are common. Clinical hypogonadism is usually hypogonadotrophic in origin.

Aged↗