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Biomedical subjects

R H Jones

Publications and source records attributed to R H Jones.

At least 181 records · Page 10Linked to original sources
PubMed1988

Beyond sensitivity, specificity and statistical independence.

Sensitivity and specificity have clear definitions when there is a single test for one disease, and the test is either positive or negative. This paper presents a unified approach for obtaining posterior probabilities (predictive values) when there are more than two test outcomes and/or more than one disease state. In these cases, sensitivity and specificity do not have clear definitions. Three examples from the literature demonstrate how this approach simplifies the presentation of Bayesian revision of prior probabilities. Use of proper care in data collection for the purpose of estimating conditional probabilities can avoid assumptions of statistical independence.

Decision Support Techniques↗
PubMed1988

Using smoothing splines to make inferences about the shape of gas-exchange curves.

Respiratory gas-exchange data from progressive exercise tests are typically interpreted by visual inspection. Attempts to objectify such interpretation have applied particular parametric models which limit the measures which can be studied and the inferences which can be made. We use a known spline-smoothing procedure which fits a continuous curve to such data, yielding confidence intervals for the curve and for its first and second derivatives. Rules can be made which use the derivatives to infer features of a curve's shape and to relate features from different curves in the same data set. In this way complex interpretations can be made objective, so that they may be adequately tested.

Algorithms↗
PubMed1988

Weather and occurrence of eclampsia.

The authors performed a population-based case-control study of the association between weather and occurrence of eclampsia in Washington State. Women who were recorded as having eclampsia on Washington birth certificates from 1980 to 1983 were compared to a random sample of all women who gave birth during those years. For each woman studied, National Oceanic and Atmospheric Administration weather data were used to determine the temperature, relative humidity, precipitation, and wind speed on the date of birth at the station nearest the hospital of birth. Categorical analysis revealed that eclampsia was not associated with low temperature, high relative humidity, precipitation, or high wind speed. These results were unchanged after adjustment for race, parity, maternal age, and late initiation of prenatal care. These results do not support an association between eclampsia and weather on the date of delivery in this population.

Birth Certificates↗
PubMed1988

Hemodynamic effects of labetalol in patients with combined hypertension and left ventricular failure.

To investigate the safety of labetalol in the treatment of hypertension in patients with heart failure, sixteen hypertensive patients with a history of congestive heart failure and an ejection fraction at rest less than 45%, had measurements of ejection fraction and cardiac output by first pass radionuclide angiography at baseline, at the end of 2 weeks maintenance with labetalol (titrated to the effective antihypertensive dose of 200-1600 mg daily), and in the post-treatment placebo period. On labetalol, heart rate and blood pressure were significantly lower than placebo at rest and the ejection fraction was higher (30 vs 25%) (p less than 0.05). At maximal exercise on labetalol the heart rate and blood pressure were lower than at placebo maximal exercise (p less than 0.05) and the ejection fraction was higher (32 vs 27%) (p less than 0.01). Exercise tolerance was not changed by labetalol. No patient was discontinued from the study because of worsening heart failure. Dizziness was reported in 5 of 16 patients usually at one visit. Dyspnea that was reported in 4 of 16 patients improved with minor adjustments in digitalis or diuretic dose. In conclusion, labetalol reduces blood pressure in hypertensive patients with left ventricular dysfunction without reducing cardiac performance.

Angiography↗
PubMed1988

Hepatic extraction of somatostatin in conscious dogs.

Fractional hepatic extraction of endogenous somatostatin immunoreactivity was examined in conscious dogs with Doppler flow probes on the portal vein and hepatic artery and catheters in the portal and hepatic veins and carotid artery before and after induction of hypoglycemia by infusion of insulin. Insulin infusion (1 and 2 mU.kg-1.min-1) decreased arterial plasma glucose from 76 +/- 4 mg/dl to a nadir of 41 +/- 2 mg/dl. Basal portal vein somatostatin was 117 +/- 11 pg/ml, which was significantly greater than the 97 +/- 12 pg/ml in the hepatic vein (P less than 0.05) and 79 +/- 8 pg/ml in the carotid artery (P less than 0.05). Hypoglycemia significantly augmented portal vein somatostatin to 206 +/- 32 pg/ml with parallel increases in the hepatic vein and carotid artery. The mean basal fractional hepatic extraction of total somatostatin immunoreactivity was 9 +/- 6% and was unchanged during hypoglycemia (14 +/- 4%). Column chromatography of the portal vein somatostatin immunoreactivity in the basal period yielded three peaks with most of the material eluting with somatostatin-14 and the void volume. Very little somatostatin-28 was detected. There was very little hepatic extraction of the void volume material while approximately 50% of somatostatin-14 was removed by that organ. After insulin-induced hypoglycemia, there was the greatest percent increase in somatostatin-28 and a doubling of somatostatin-14 and the void volume material. Most of the somatostatins-14 and -28 were removed by the liver, while extraction of the void volume material was negligible.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Computer analysis of oxygen consumption and minute ventilation for the detection of the lactate threshold.

A group of 15 normal subjects performed a maximal-exercise test on a treadmill. Arterial lactate measurements were related to oxygen consumption (VO2) in an exponential fashion (individual correlation coefficients ranged from 0.9 to 0.99). In the same subjects, minute ventilation (VE) was related to VO2 in an exponential fashion (individual correlation coefficients ranged from 0.98 to 1). There was a close correlation (r = 0.97, p less than 0.001) between the slope of the log of lactate versus VO2 and the slope of the log of VE versus VO2. A computer program for predicting the VO2 corresponding to the accumulation of arterial lactate above the resting normal value (1.3 mM), defined as the lactate threshold, is described. The program is based on the slopes of the exponential relationship between lactate and VO2 and between VE and VO2 derived in the normal subjects. The program analyses 30-second values of VO2 and VE. In 28 subjects, the reproducibility of the lactate threshold prediction was evaluated during two exercise tests 1-7 days apart. The mean predicted VO2 at the lactate threshold was 18.6 +/- 7 ml/(kg.min) during test 1 and during test 2 it was 17.9 +/- 7.3 ml/(kg.min); r = 0.91, p less than 0.001. The corresponding values for maximal VO2 were 30.4 +/- 13 ml/(kg.min) and 31 +/- 13 ml/(kg.min); r = 0.99, p less than 0.001. It is concluded that this program offers a reproducible method of determining the lactate threshold during exercise testing employing a frequently used clinical protocol.

Adult↗
PubMed1988

Seasonality comparisons among groups using incidence data.

A new test using incidence data is developed for testing whether two or more groups have the same seasonal pattern. The method fits sine waves to the data with a fundamental period of one cycle per year, and has the possibility of using higher harmonics, when necessary, to adequately model the data. The seasonal pattern can, therefore, have an arbitrary shape. The method allows for different length time intervals and different size populations at risk in the time intervals. Maximum likelihood estimation, based on the Poisson distribution, is used to determine the parameters of the model. Likelihood ratio tests and Akaike's information criterion (AIC) are used to determine the number of harmonics, and to test hypotheses. This method has been used to test for seasonal patterns in the incidence of insulin-dependent diabetes mellitus (IDDM) in Colorado among persons aged 0-17 years. Comparisons of seasonal patterns are made between males and females, and three age groups, each controlling for the other effect as in analysis of variance. Other potential applications of this approach are also discussed. A basic program is available for an IBM-PC to carry out these analyses.

Adolescent↗
PubMed1988

Changing efficacy of coronary revascularization. Implications for patient selection.

To evaluate the potential impact of patient selection for coronary artery bypass graft surgery on long-term survival, the outcomes of 5,809 consecutive patients with symptomatic coronary disease documented by angiography at Duke University Medical Center were examined. Over the entire study period (1969-1984), surgical therapy was associated with improved survival compared with medical therapy whether or not adjustment was made for imbalances in baseline prognostic factors. When patients were categorized according to coronary anatomy and left ventricular function, patients with multivessel disease and poor left ventricular function had a greater long-term survival benefit with surgery than did patients with less coronary artery disease and better left ventricular function. When 5-year survival rates were examined as a function of operative risk, a direct relation was found between estimated operative risk and the medical-surgical survival difference. For patients with an operative risk of 1%, the expected 5-year mortality with surgical therapy was 3% versus 8% with medical therapy (an absolute survival difference at 5 years of 5%). In comparison, for patients with an operative risk of 5%, the expected 5-year mortality with surgery was 10% versus 23% with medical therapy (an absolute survival difference at 5 years of 13%). Over 50% of patients with significant coronary artery disease undergoing cardiac catheterization have an estimated operative mortality risk under 2.5%. These patients would be expected to have a small survival advantage treated surgically. As operative mortality rates are subjected to increasing public scrutiny, selection of low-risk patients will reduce the overall benefit of the operation to the population.(ABSTRACT TRUNCATED AT 250 WORDS)

Coronary Artery Bypass↗
PubMed1988

A new method to determine left ventricular pressure-volume loops in the clinical setting.

Left ventricular pressure-volume (P-V) loops provide a complete definition of cardiac performance but have been difficult to obtain in the clinical setting. Accordingly, we have developed a new technique for acquiring P-V loops during and after cardiac surgical procedures using portable first-pass radionuclide angiocardiography coupled with intraventricular micromanometer catheters. Using this technique 35 serial left ventricular P-V loops were acquired in 12 patients during and after coronary artery bypass grafting. Dynamic radionuclide left ventricular volume and micromanometer pressure were acquired simultaneously to generate the P-V loops. Moreover, simultaneous measurement of both volume and pressure allowed comparison of the timing of end diastole (ED) and end systole (ES) defined by each of the two cardiac parameters. For 208 EDs and 243 ESs analyzed volume-defined ED occurred 8 +/- 27 msec (s.d.) later in the cardiac cycle than pressure-defined ED while volume-defined ES occurred 29 +/- 27 msec (s.d.) earlier than pressure-defined ES. It is concluded that measurement of cardiac P-V loops with this new technique is clinically feasible and that a close agreement has been demonstrated between the timing of cardiac events defined either by volume or pressure criteria.

Coronary Artery Bypass↗
PubMed1988

A new method for cloning Giardia lamblia, with a discussion of the statistical considerations of limiting dilution.

This report describes a method of cloning Giardia lamblia by limiting dilution which is simpler than the previously described semisolid agar technique and which may also be applied as an assay of cell viability. A discussion of the basic statistics of limiting dilution, which is applicable to any cell type, and a method of statistically comparing colony-forming efficiencies from different cell populations are included. The colony-forming efficiency (CFE) of this method, when applied to late log-phase cultures, is 72.1 +/- 10.05%. When only cells adherent to the sides of culture vials are cloned, the CFE is 87.1 +/- 9.85%.

Animals↗
PubMed1988

Comparison of cardiac function in surgically corrected and congenitally corrected transposition of the great arteries.

The capacity of the anatomic right ventricle to sustain normal function against systemic pressure long after atrial baffle procedures in patients with complete transposition of the great arteries remains unknown. Pulmonary and systemic ventricular function was measured by first-pass radionuclide studies in 11 children 7 +/- 3 years (+/- standard deviation) after baffle procedures. For comparison, similar measurements were made in eight patients with isolated congenitally corrected transposition of the great arteries and in 10 children in a control group. Exercise increased heart rate and cardiac index to similar levels in all three groups. Ventricular volumes were greater than control volumes in both groups with congenital heart disease. Exercise increased pulmonary ventricular ejection fraction in the control and congenitally corrected groups, but not in the surgically corrected group. Systemic ventricular ejection fraction increased during exercise in the control group, but remained unchanged in both transposition groups. These results show that cardiac index during exercise is maintained in patients after baffle procedures for complete transposition of the great arteries. However, pulmonary and systemic ventricular ejection fractions fail to increase with exercise, and ventricular volumes are markedly greater than normal.

Adolescent↗
PubMed1987

An examination of the role of insulin dimerisation and negative cooperativity using the biological properties of the despentapeptide and deshexapeptide insulins.

The C-terminus of the insulin B chain is essential for dimerisation and expression of negative cooperativity. In order to evaluate the possible physiological role of these phenomena, we have studied the properties in vivo and in vitro of despentapeptide insulin (B26-30 deleted), derived from beef insulin, and deshexapeptide insulin (B25-30 deleted), derived from pork insulin. These materials do not dimerise and have 15% and 0% retention of negative cooperativity respective. Lipogenesis potencies in rat adipocytes were: despentapeptide insulin 19.9 +/- 0.3%; deshexapeptide insulin 19.9 +/- 1.5%. Binding potencies in adipocytes were: despentapeptide insulin 22.6 +/- 7.8%; deshexapeptide insulin 13.2 +/- 3.3%. Metabolic clearance rates were reduced compared to insulin (insulin = 19.1 +/- 0.9; despentapeptide insulin = 9.7 +/- 0.8; deshexapeptide insulin = 6.4 +/- 0.6 ml . min-1 . kg-1 at plasma concentration 0.5 nmol/l). Hypoglycaemic potencies were reduced for both analogues (40% and 30%) when calculated on the basis of plasma concentration although both analogues and insulin were equally effective at lowering plasma glucose concentration in equimolar doses. Plasma half-disappearance time was prolonged (despentapeptide insulin = 7.3 +/- 0.5; deshexapeptide insulin = 9.1 +/- 0.2 min). Both analogues were full agonists and conformed to the general relationship between in vitro and in vivo properties seen with a wide range of modified insulins. They resemble other analogues with modifications which reduce receptor affinity without impairing dimerisation or negative cooperativity. The results do not support a physiological role for dimerisation or negative cooperativity.

Adipose Tissue↗
PubMed1987

Use of radionuclide measurements of left ventricular function for prognosis in patients with coronary artery disease.

The major clinical challenge today in the management of patients with stable coronary artery disease is identification of those patients in whom myocardial revascularization would improve or prolong life. Despite widespread use over the past decade, indications for coronary artery bypass grafting remain controversial. A definite need exists for objective measures of the magnitude of myocardial ischemia before operation and for simple assessment of the hemodynamic effects of operation. The close link between myocardial ischemia and dysfunction suggests that measurement of left ventricular function during exercise can be used to assess myocardial ischemia in individual patients. In large patient populations with coronary artery disease (CAD), a relationship has been documented between the anatomic extent of disease and the magnitude of functional alteration. However, individual variation occurs with some patients with single-vessel stenosis demonstrating greater functional impairment than other patients with involvement of three vessels. The hypothesis that patients with the greatest magnitude of exercise-induced left ventricular dysfunction would profit most from surgery was examined in 857 patients studied by radionuclide angiocardiography and coronary arteriography. These patients were followed for survival and pain relief for up to 4 years after institution of medical or surgical therapy. Patients who demonstrated the greatest amount of exercise-induced left ventricular dysfunction had the most favorable outcome to myocardial revascularization by operation as judged by survival and relief. Successful myocardial revascularization commonly caused no change in resting left ventricular function. However, most patients who underwent myocardial revascularization demonstrated a reversal of left ventricular dysfunction during exercise. Therefore, radionuclide angiocardiography during rest and exercise provides useful assessment of patients before and after coronary artery bypass grafting.

Angiocardiography↗
PubMed1987

Relation of coronary artery stenosis and pressure gradient to exercise-induced ischemia before and after coronary angioplasty.

The purpose of this investigation was to evaluate the relation of coronary artery stenosis and associated pressure gradient to the magnitude of exercise-induced left ventricular dysfunction in patients with single vessel coronary artery disease. The percent stenosis and minimal cross-sectional area were measured before and after percutaneous transluminal coronary angioplasty and compared with radionuclide measurements of left ventricular function before and after angioplasty in 41 patients with proximal left anterior descending coronary artery lesions, providing 82 points of comparison. The gradient could be measured for 75 comparisons. Forty stenoses less than 50% were associated with a mean left ventricular exercise ejection fraction of 0.66 +/- 0.08 (mean +/- SD), 25 stenoses from 50 to 75% with a mean ejection fraction of 0.59 +/- 0.12 and 17 stenoses greater than 75% with a mean ejection fraction of 0.49 +/- 0.08. Thirty-five stenoses with a gradient less than 20 mm Hg were associated with a mean ejection fraction of 0.65 +/- 0.09, 24 with a gradient from 20 to 50 mm Hg with a mean ejection fraction of 0.58 +/- 0.13 and 16 with a gradient greater than 50 mm Hg with a mean ejection fraction of 0.53 +/- 0.10. These data document a relation between the magnitude of coronary artery stenosis and associated gradient to exercise-induced left ventricular dysfunction in homogeneous patient groups. However, discordance of these variables occurs commonly in individual patients.

Adult↗
PubMed1987

Comparison of nitroglycerin patches and nifedipine.

Fifteen patients with stable angina participated in a 12-week crossover study to evaluate the efficacy of nifedipine and nitroglycerin patches. There was an initial 2-week drug washout period followed by a 2-week control period when patients received no other antianginal treatment other than sublingual nitroglycerin for relief of angina episodes. At the end of the 2-week control period, exercise performance was assessed with treadmill exercise testing and measurement of oxygen consumption during the final third of the dosing interval. Myocardial perfusion was assessed using thallium scintigraphy with the injection of thallium at 85% of the maximum oxygen consumption. Patients were then randomized to nifedipine or nitroglycerin patches, and the dosage was titrated at weekly intervals according to symptomatic response. The final dose was received for at least 2 weeks. After 4 weeks, patients received the alternate medication. Maximal exercise testing and thallium scintigraphy were repeated after each drug period. Both nifedipine (mean dose, 70 mg/day) and nitroglycerin patches (mean dose, 16 cm/day) significantly reduced the frequency of angina and the consumption of sublingual nitroglycerin. Nifedipine decreased the reversible thallium defect score (49 +/- 29 vs. 28 +/- 26 U, p less than 0.01). Both drugs reduced electrocardiographic evidence of myocardial ischemia at submaximal exercise. Maximal oxygen consumption was not significantly increased by either drug when the test was done during the latter part of the dosing interval. The clinical implications of this study are that the dosage of nifedipine and nitrate patches, based on symptomatic criteria of angina frequency reduction, may not result in objective improvement in exercise performance.

Administration, Cutaneous↗
PubMed1987

Data collection in decision-making: a study in general practice.

In a study of simulated consultations with patients suffering from dyspepsia, the amount and nature of information required by 20 general practitioners to make management decisions about these simulated patients were analysed. The number of items of information required to complete all eight cases ranged from 23 to 128 (median 66). Doctors who consulted more rapidly in actual surgeries required less information in the simulations (P less than 0.01). Two-way analysis of variance showed that both cases and doctors independently influenced the number of items of information collected, but that doctors were a more powerful influence (P less than 0.05). The nature of the information collected by doctors varied widely between individuals. There was no correlation between the professional experience of the doctors studied and the amount or nature of data collected; this is at odds with previous studies and requires an alternative explanation.

Data Collection↗