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Biomedical subjects

A M Walker

Publications and source records attributed to A M Walker.

At least 289 records · Page 16Linked to original sources
PubMed1983

Increased arterial pressure variability after arterial baroreceptor denervation in fetal lambs.

Baroreceptor reflexes can be demonstrated during fetal life, but whether baroreceptors normally regulate fetal arterial pressure is unknown. This problem was addressed directly by measuring arterial pressure and analyzing its variation in eight unanesthetized fetal lambs throughout the last third of gestation, and comparing these data with similar measurements made in seven fetal lambs with denervated arterial baroreceptors. Measurements were made at 5-minute intervals over 24 hours in a total of thirty-three experiments. The coefficient of variation of mean arterial pressure (standard deviation of mean arterial pressure/mean value of mean arterial pressure) expressed as a percentage was used as an index of blood pressure variability. Coefficients averaged 7.0% in intact lambs and 12.1% in barodenervated lambs (P less than 0.001), signifying considerably increased variability of mean arterial pressure after barodenervation. Mean arterial pressure averaged over 24 hours was not different between the two groups prior to 120 days (0.8) of gestation. Between 120 days and term, mean pressure was significantly greater in the denervated fetuses (65 cm H2O) than in the sham-operated controls (60 cm H2O, P less than 0.025). These data demonstrate that a baroreceptor-blood pressure reflex functions during late gestational development in lambs and signify an important role of arterial baroreceptors in regulating fetal arterial pressure. Failure to regulate arterial pressure in the barodenervated fetus could result in significant alterations in placental perfusion and exchange, and in the regional delivery of oxygen and substrates to developing organs in these animals.

Animals↗
PubMed1983

Ultrastructure of the myocardium during development from early fetal life to adult life in sheep.

The ultrastructure of the developing fetal lamb myocardium was studied in a series of animals spanning 29 days of gestation to term, and compared with newborn and adult animals. All major ultrastructural features which characterise the adult myocyte were found in early fetal life, although with considerably different degrees of development of specific features. Notably, myofibrils at 29 days of gestation are sparse and show little organisation. With advancing gestation there is an increasing number of myofibrils and the development of well defined striations. Thus, at term, the fetal tissue is not substantially different from the adult myofibril in the appearance of sarcomere structure. The observation of contractile tissue paucity and disorder in early fetal lamb myocardium is difficult to reconcile with available physiological data, which show an extraordinary pumping performance of the heart in vivo, and requires further investigation.

Animals↗
PubMed1983

Projections of asbestos-related disease 1980-2009.

Approximately 19,000 cases of mesothelioma and 55,000 cases of lung cancer will arise in U.S. men with histories of nontrivial occupational exposure to asbestos. There are approximately 65,000 U.S. men now alive with clinically diagnosable asbestosis. These estimates are based, in the case of the cancer, on estimates of the effective number of asbestos-exposed workers required to produce the current national incidence of mesothelioma. The asbestosis estimates are based on a number of rough measures relating the prevalence of asbestosis to the incidence of mesothelioma, the incidence of compensable asbestosis in other countries, the prevalence of and mortality from pneumoconioses generally, and the number of workers heavily exposed to asbestos.

Asbestos↗
PubMed1982

Risk factors for rate of progression of glaucomatous visual field loss: a computer-based analysis.

Factors affecting the progression of visual field loss were examined in 57 patients with bilateral open angle glaucoma. patients who already had marked visual field loss experienced further field loss at a greatly accelerated rate. Family history of glaucoma, sex, and initial registration intraocular pressure were also important prognostic factors for progressive visual field loss, whereas age and systemic blood pressure were not found to affect rate of visual field loss. Follow-up data from these patients were drawn from a computer-based clinic record system that may serve as a prototype for the collection of information on the natural history of ophthalmic diseases.

Age Factors↗
PubMed1982

Models of varying parametric form in case-referent studies.

The analysis of case-referent data can be based on a consideration of case and referent counts in various exposure categories as the realization of a set of binomial processes. After appropriate modeling of the binomial parameters, a joint likelihood function can be formed and maximized to obtain estimates of the parameters constituting the model elements. The procedure has been applied to the problem of additive and multiplicative models of disease incidence rates, as encountered in case-referent studies. Likelihood ratios can be used to compare models with equal numbers of parameters. These ratios do not lead to significance tests, but to estimate of the relative degree of corroboration of different hypotheses by the data at hand.

Body Weight↗
PubMed1982

An independent analysis of the National Cancer Institute study on non-nutritive sweeteners and bladder cancer.

We evaluated the possible relation between use of non-nutritive sweeteners and bladder cancer using data obtained from the National Cancer Institute Bladder Cancer Study under the Freedom of Information Act. In the general study group, there was no evidence for an association between non-nutritive sweeteners and bladder cancer. Control for a variety of factors through multivariate techniques diminished the plausibility of earlier interpretations of these data, which had raised the possibility that certain subgroups of users or non-nutritive sweeteners might be at an increased risk for bladder cancer. We found that the putative effects of non-nutritive sweeteners were not consistent among subgroups with similar baseline risk, did not display consistent dose-response trends, and were subject to considerable sampling error. We concluded that the data provided little evidence that non-nutritive sweeteners increase risk for bladder cancer among subgroups of users, and that definitive evidence on this question is beyond the reach of conventional research.

Adult↗
PubMed1982

The influence of behavioural state on the cardiovascular system of newborn lambs.

The influence of behavioural state, as defined by clinical observation and EEG recording, on cardiac output, heart rate, stroke volume and blood pressure was investigated in eight newborn lambs during the first 2 weeks of life. Cardiac output was measured using the technique of thermodilution. Highest mean value (mean +/- SEM) of cardiac output was found in the very alert awake state in week 1, 271 +/- 16 ml/min per kg. Other values were significantly lower; quiet sleep, 173 +/- 4 ml/min per kg; rapid-eye-movement sleep, 191 +/- 7 ml/min per kg; quiet awake, 174 +/- 3 ml/min per kg; alert awake, 180 +/- 5 ml/min per kg. Similar values were found in week 2. These values of cardiac output were lower than those previously reported for newborn lambs except in the very alert awake state. Heart rate was significantly lower during sleep than in the awake states in week 1. The heart rate was found to be significantly higher in all states except the very alert awake state in week 2 compared with week 1. Stroke volume was significantly higher in rapid-eye-movement sleep, 1.08 +/- 0.06 ml/kg, and in the very alert awake state, 1.16 +/- 0.09 ml/kg, compared with the other states in week 1, but only in the very alert awake state in week 2. Blood pressure was highest in the very alert awake state in both weeks. These findings demonstrate that behavioural state has a very significant influence on the cardiovascular system during newborn life in lambs, particularly on cardiac output values, which in the very alert awake and rapid-eye-movement sleep states significantly exceed values in the other states.

Animals↗
PubMed1982

Anamorphic analysis: sampling and estimation for covariate effects when both exposure and disease are known.

When study subjects are obtained through sampling procedures based on the level of known characteristics, covariate data can be used to adjust effect estimates. This principle, which is well-understood for both exposure-based sampling (cohort studies) and disease-based sampling (case-control studies), can also be applied to cross-classifications of the source population. An opportunity for exposure--disease-based sampling arises whenever data on exposure and disease are both available on a group of subjects who are incompletely characterized in terms of other covariates. This is a common intermediate stage in epidemiologic studies of many kinds.

Dyspnea↗
PubMed1981

Hospitalization rates in vasectomized men.

Six thousand ninety-two men who had undergone vasectomy were observed for 20,491 person-years of observation in a prepaid group practice. The incidences of first-time hospitalizations for a variety of diagnoses were examined as a proxy for disease incidence rates and compared with similarly derived rates in the remaining male membership of the practice. Vasectomized men had comparatively high rates of hospitalization for a variety of diseases of the genitourinary system during the early postvasectomy period. Apart from these, there were no important, statistically convincing elevations in the new hospitalization rates among vasectomized men, as compared with those of the nonvasectomized comparison group.

Adult↗
PubMed1981

Vaginal spermicides and congenital disorders.

Among 763 liveborn infants of white women who had obtained a vaginal spermicide in the ten months before conception, the prevalence of certain major congenital anomalies was 2.2%. The prevalence of such anomalies in a comparison group of 3,902 infants was 1.0%. The difference between these groups was due to an excess of limb-reduction deformities, neoplasms, syndromes associated with chromosomal abnormalities, and hypospadias in the infants whose mothers are presumed to have used vaginal spermicides. Pregnancies in women who had used vaginal spermicides ended in spontaneous abortion requiring hospitalization 1.8 times more commonly than did pregnancies in those who had not. Since a well-defined syndrome among babies with congenital disorders whose mothers used spermicides was not present, these results should be considered tentative until confirmed by other data.

Abnormalities, Drug-Induced↗
PubMed1981

Vasectomy and non-fatal myocardial infarction.

The incidence of non-fatal myocardial infarction among 4830 vasectomised men was 0.9 cases per 1000 man-years during 24 420 man-years of observation. This was slightly lower than the rate in 24 150 non-vasectomised men, matched with a vasectomised man for calendar year of birth and duration of observation. Review of medical records for a matched sample of study subjects indicated no measurable confounding by important cardiac risk factors.

Adult↗
PubMed1981

The etiology of multiple sclerosis: temporal-spatial clustering indicating two environmental exposures before onset.

Studies in the Orkney and Shetland Islands have demonstrated the highest rates of multiple sclerosis (MS) recorded. Accumulated evidence suggests that an environmental factor is paramount in etiology. The role of an environmental exposure (infectious or toxic) is confirmed in this study by the demonstration in Orkney of clustering of cases in time and space. Lifetime data showed temporal-spatial clustering of MS patients (1) at least 21 years prior to onset, and (2) just prior to onset. Each of the two time clusters occurred on three separate islands. No clustering was seen at birth, by chronological age, or by schooling. Clustering was not demonstrated in Shetland. Previous efforts to demonstrate clustering may have failed because of lack of specificity of the data or inappropriate methodology. These data indicate that not one but two environmental factors play a role in the etiology of MS, representing exposures to two different environmental insults, or exposure twice to the same insult, prior to onset of MS.

Epidemiologic Methods↗
PubMed1980

Predictors of bleeding during heparin therapy.

Among 2,656 patients receiving heparin sodium therapy, bleeding was a dose-related phenomenon that occurred most commonly among women, severely ill patients, and patients who received asprin during heparin therapy. Except for dose, factors that predisposed patients to bleeding were more strongly associated with major bleeding than with minor bleeding. Heavy alcohol drinkers were at particularly high risk for major bleeding episodes during heparinization. The seven-day cumulative risk for any bleeding was 9.1%. Risk was greatest on the third day of heparin administration.

Adult↗