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Biomedical subjects

D Wagstaff

Publications and source records attributed to D Wagstaff.

11 recordsLinked to original sources
PubMed1994

Brinley plots, explained variance, and the analysis of age differences in response latencies.

Critics of Brinley plot analyses (e.g., Fisk, Fisher, & Rogers, 1992; Perfect, 1994) claim: (a) that lack of overlap between latencies on different tasks inflates r2 values; (b) that Brinley plots mask task-specific age differences; and (c) that measurement error in young adults' latencies precludes the use of regression techniques with Brinley plot data. We dispute these claims. We show that lack of overlap does not inflate r2 and that the possible presence of task-specific effects in Brinley plot data may be evaluated using standard regression techniques. These techniques are illustrated using data from the Fisk and Rogers (1991) study of visual and memory search. Analysis of their data reveals significant differences between the lexical and nonlexical domains, but not between types of search. Finally, the effect of measurement error on Brinley plot analyses is shown to be small and, if taken into account, leads to increased support for general cognitive slowing.

Adolescent↗
PubMed1992

Octreotide inhibits the meal-induced increases in the portal venous pressure of cirrhotic patients with portal hypertension: a double-blind, placebo-controlled study.

The aim of this study was to determine the effects of the long-acting somatostatin analog, octreotide, on portal venous pressure and collateral blood flow in cirrhotic patients with portal hypertension during fasting and postprandial states. In a double-blind, placebo-controlled study, we investigated the effects of octreotide on the hepatic venous pressures and azygos blood flow of 21 patients before and after a standard liquid meal containing 40 gm of protein in 250 ml. Octreotide significantly reduced azygos blood flow from a mean of 499 +/- 65 ml/min to a mean of 355 +/- 47 ml/min (p < 0.01), but it had no effect on the hepatic venous pressure gradient. The hepatic venous pressure gradient of patients in the placebo group increased significantly, from a fasting mean of 16.4 +/- 1.6 mm Hg to a mean of 20.0 +/- 1.7 mm Hg 30 min after the meal (p < 0.01). In a second protocol hepatic venous pressures were measured in 20 patients at 30-min intervals for 2 hr after ingestion of the mixed meal. Again the placebo group showed a significant increase in the hepatic venous pressure gradient 30 min after the meal (20.4 +/- 1.5 mm Hg vs. 18.2 +/- 1.2 mm Hg; p < 0.05), but the group receiving octreotide showed no significant changes during the 2 hr of observation. We conclude that octreotide significantly reduces azygos blood flow, with little effect on portal venous pressure, and that it appears to inhibit postprandial increases in portal pressure in cirrhotic patients with portal hypertension.

Blood Flow Velocity↗
PubMed1990

The effect of non-protein liquid meals on the hepatic venous pressure gradient in patients with cirrhosis.

It has been suggested that protein feeding increases portal pressure in cirrhotic patients, but that carbohydrate and fat have little effect. We examined the relationship between feeding and portal pressure, using different liquid test meals (250 or 500 ml non-protein, 250 ml protein-containing, 500 ml water), in 29 alcoholic patients with cirrhosis and portal hypertension. The mean hepatic venous pressure gradient (HVPG) increased significantly 30 min after the protein meal (10% increase; p = 0.009) and returned to basal levels at 60 min. The mean HVPG also increased significantly after the non-protein meal: after 500 ml the increase was 23% at 30 min (p = 0.046) and 17% at 60 min (p = 0.12); and after 250 ml it was 15% at 30 min (p = 0.012) and 7% at 60 min (p = 0.05). Ingestion of 500 ml water caused a small, non-significant, increase in mean HVPG. Plasma glucagon levels increased significantly at 30 and 60 min after the protein meal, but did not change significantly after the non-protein meal or water. Both protein-containing and non-protein meals significantly elevate HVPG in alcoholic patients with cirrhosis and portal hypertension.

Adult↗
PubMed1990

The information-loss model: a mathematical theory of age-related cognitive slowing.

A model of cognitive slowing is proposed with the following assumption: Information is lost during processing, processing occurs in discrete steps with step duration inversely related to the amount of information currently available, and the effect of aging is to increase the proportion of information lost per step. This model correctly predicts a positively accelerated relation between latencies of older and younger adults and provides a unified account of the effects of task complexity, practice, speed-accuracy tradeoffs, and fluctuations in individual performance. Strong support for the thesis that cognitive slowing is global, and not localized in specific age-sensitive components, is provided by the fact that the model accurately predicts the latencies of older adults on the basis of those of younger adults, without regard to the nature of the task, across a latency range of nearly 2 orders of magnitude.

Adult↗
PubMed1987

General slowing of nonverbal information processing: evidence for a power law.

Data were analyzed from studies of nonverbal information processing in which the dependent measure was the latency of pressing or releasing a response key. Positively-accelerated power functions described the relationship between the response latencies of groups of older (50 to 60 years and 65 to 75 years) and younger adults (20 to 25 years) with extreme precision (r2 = .99). The exponent of the best-fitting power function increased with the age of the older group. The form of the relationship is allometric, and is consistent with a model (Botwinick, 1984) in which response latency increases exponentially with task difficulty. The present findings suggest that this model holds across a wide variety of information-processing tasks and over a very broad range of latencies.

Adult↗
PubMed1984

Long-term beneficial effects of endralazine, a new arteriolar vasodilator at rest and during exercise capacity in chronic congestive heart failure.

Hemodynamic measurements were made at rest and during submaximal and maximal exercise in 12 patients with chronic congestive heart failure before and after oral endralazine (EN). After acute assessment, patients received endralazine, twice daily, for a mean of 2.8 months, when hemodynamic measurements were repeated. The drug was withdrawn for 3 to 4 days and subsequently reintroduced. Three patients with greatly elevated pulmonary wedge pressures were assessed after 30 mg of isosorbide dinitrate, which was also chronically administered. Resting mean cardiac and stroke volume indexes increased by 44 and 33%, respectively (p less than 0.01), with concomitant reduction of the systemic resistance. This improvement was maintained on a long-term basis in 8 of the 11 surviving patients. Withdrawal and subsequent reintroduction of EN confirmed that there was worsening of left ventricular dysfunction in the other 3 subjects. Chronic but not acute therapy produced a modest reduction in wedge pressure. At maximal exercise, cardiac and stroke volume indexes increased by 29 and 18%, respectively (p less than 0.01), after EN; the duration of exercise increased in 7 of the 10 subjects after acute therapy and this was maintained on a long-term basis. Mean creatinine clearance increased by 34% (p less than 0.01). The results confirm that EN produces acute and long-term hemodynamic and functional improvement without tolerance in congestive heart failure.

Aged↗
PubMed1983

Acute hemodynamic effects of endralazine: a new vasodilator for chronic refractory congestive heart failure.

Invasive hemodynamic measurements were made in 10 supine patients with chronic refractory congestive heart failure (CHF) due to ischemic heart disease or cardiomyopathy before and after oral administration of a new arteriolar vasodilator, endralazine. In 9 patients, a 10 mg dose of endralazine produced maximal increases in cardiac and stroke volume indexes of 56 and 41%, respectively, with a 45% reduction in total systemic resistance. After a 5 mg dose of endralazine, cardiac index increased maximally by 38% and stroke volume index by 34%, with a 31% decrease in total systemic resistance. Mean arterial pressure decreased 11 +/- 4 mm Hg (mean +/- standard error of mean) with the 5 mg dose and 17 +/- 5 mm Hg after the 10 mg dose. There were no significant changes in the right atrial, pulmonary arterial, or pulmonary capillary wedge pressures. After administration of a single dose of endralazine, statistically significant hemodynamic changes were observed from 1 to 8 hours with peak responses at 3 to 4 hours. These observations suggest that endralazine has hemodynamic properties similar to those of its structural analog, hydralazine. However, endralazine metabolism is largely independent of the patients' acetylator status, and no cases of systemic lupus erythematosus have been reported after long-term oral administration. These findings suggest that endralazine may be an efficacious drug that is potentially safer than hydralazine in the treatment of chronic CHF.

Adult↗
PubMed1980

Comparison of serial electrocardiographic and vectorcardiographic changes during recovery from status asthmaticus.

Serial electrocardiographs (ECG) and vectorcardiographs (VCG) have been performed on 10 patients admitted to hospital in status asthmaticus on 12 separate occasions. The VCG was more efficient than the ECG in the detection of right atrial and ventricular enlargement. Both investigations were equally reliable in recording changes in frontal plane P wave axis. The mean frontal plane P wave axis fell from +60 degrees (range +35 degrees to +90 degrees) on the day of admission to +43 degrees (range +30 degrees to +60 degrees) at the time of discharge. The mean FEV1 expressed as a percentage of predicted values increased from 48% (range 25% to 81%) to 87% (range 44% to 123%). In direct contrast to previous studies the presence of an abnormally vertical frontal plane P wave axis (> 60 degrees) was related to the severity of airway obstruction (p < 0.01).

Acute Disease↗
PubMed1975

Variations in mechanical sampling: their causes and effects.

Three characteristics of a sample of AutoAnalyzer Sampler II modules have been measured: eccentricity of the cam, eccentricity of the spindle driving the cam, and the lengths of the chords of the cam lobes. Imprecision in timing may make a significant contribution to analytical error.

Autoanalysis↗