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Biomedical subjects

G Howard

Publications and source records attributed to G Howard.

At least 217 records · Page 12Linked to original sources
PubMed1986

The modelling of biological systems in three dimensions using the time domain finite-difference method: II. The application and experimental evaluation of the method in hyperthermia applicator design.

The three-dimensional time domain finite-difference (TDFD) method was used to design a 433 MHz circular waveguide applicator for electromagnetic hyperthermia. This applicator has a water-filled lens at one end, providing surface cooling as well as some shaping of the emergent electromagnetic field. An experimental system for scanning the EM field in three dimensions is described. The experimental data were compared with those calculated from the TDFD program and good agreement was found. A realistic three-dimensional model based on an ultrasound scan of a surface tumour was built. Both the EM field and the specific absorption rate (SAR) within the model when irradiated by the applicator were calculated.

Humans↗
PubMed1986

Response of cerebral blood flow to changes in carbon dioxide tension during hypothermic cardiopulmonary bypass.

Changes in cerebral blood flow (CBF) in response to changes in PaCO2 were measured by intraaortic injection of 133Xe in 12 patients during hypothermic (23-30 degrees C) cardiopulmonary bypass. In each patient, CBF was determined at two randomly ordered levels of PaCO2 obtained by varying the rate of gas inflow into the pump oxygenator (Group I, n = 6) or by varying the percentage of CO2 added to the gas inflow (Group II, n = 6). Nasopharyngeal temperature, mean arterial pressure, pump-oxygenator flow, and hematocrit were maintained within a narrow range. In group I, a PaCO2 (uncorrected for body temperature) of 36 +/- 4 mmHg (mean +/- SD) was associated with a CBF of 13 +/- 5 ml X 100 g-1 X min-1, while a PaCO2 of 42 +/- 4 mmHg was associated with a CBF of 19 +/- 10 ml X 100 g-1 X min-1. In group II, a PaCO2 of 47 +/- 3 mmHg was associated with a CBF of 20 +/- 8 ml X 100 g-1 X min-1, and a PaCO2 of 53 +/- 3 mmHg was associated with a CBF of 26 +/- 9 ml X 100 g-1 X min-1. Within group I, the difference in CBF was significant (P less than 0.05); within group II, the difference in CBF was significant at the P less than 0.002 level. All CBF measurements were lower than those reported for normothermic, unanesthetized subjects of similar age.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1986

Prevalence of health-risk behavior among seventh grade students in North Carolina.

Data from 386 seventh grade students, 48% male and 65% white, were collected at two sites in North Carolina. The purpose of the study was to estimate the prevalence of alcohol and drug use among adolescents as part of a continuing study of preventive health behaviors. The data were collected anonymously from self-completed questionnaires and were analyzed by race and sex to determine knowledge of and attitudes toward alcohol and smoking, self-concept, and locus of control. Black boys had the highest prevalence of alcohol (16%) and tobacco (20%) use and at the same time had the lowest amount of knowledge about the dangers of the substances. White boys, while knowing more about the potential dangers, reported similar patterns of use. In general, girls used much less alcohol and tobacco and had higher levels of knowledge and more prudent attitudes. Boys, particularly blacks, were found to be at greater risk than girls of developing patterns of behavior that are associated with abuse of alcohol and heavy smoking. The findings suggest that health education to inform adolescents of the dangers of alcohol and smoking needs to be specific to cultural and sex groups.

Adolescent↗
PubMed1986

Effects of hypertonic saline versus lactated Ringer's solution on cerebral oxygen transport during resuscitation from hemorrhagic shock.

Hypertonic saline successfully restores systemic hemodynamics in dogs and humans with severe hemorrhagic shock and, in contrast to lactated Ringer's solution, does not increase intracranial pressure (ICP). This study compares cerebral oxygen delivery in 12 dogs subjected to hemorrhagic shock by the rapid removal of blood (mean arterial pressure of 40 mm Hg maintained for 30 minutes), and then resuscitated with lactated Ringer's solution (six dogs) or 7.5% saline solution (six dogs) to restore systolic arterial pressure. Both solutions effectively restored systemic hemodynamic stability, increasing cardiac output and systolic blood pressure while decreasing mean and diastolic arterial pressure and systemic vascular resistance. The ICP was significantly lower after resuscitation in the hypertonic saline group (p less than 0.05), but cerebral blood flow, which had decreased during shock, was not restored by either fluid, and cerebral oxygen transport fell further secondary to a hemodilutional reduction of hemoglobin. Although hypertonic saline may improve systemic hemodynamics and maintain a low ICP during resuscitation, it fails, as does Ringer's solution, to restore cerebral oxygen transport to prehemorrhagic shock levels.

Animals↗
PubMed1986

Comparison of mannitol regimens in patients with severe head injury undergoing intracranial monitoring.

Eighty patients sustaining head injuries and presenting with Glasgow Coma Scale scores of 8 or less were entered into a prospective randomized study to assess the benefit of intracranial pressure (ICP) monitoring with two regimens of mannitol administration. Group I was treated with mannitol for ICP elevations greater than 25 mm Hg, while Group II received empirical mannitol therapy irrespective of ICP readings. No statistically significant differences in mortality rate or neurological outcome were demonstrated between the two groups. These results are comparable to those of several published series of head-injured patients receiving similar treatment from 1977 to 1982. However, those series must be reassessed in light of recently published studies with treatment initiated at lower levels of ICP.

Adolescent↗
PubMed1986

Effects of starvation on rat liver mRNA translation products.

The synthesis of rat liver protein and RNA decreases with starvation. It is not yet known whether such decreases are regulated strictly at a transcriptional level, or if post-transcriptional controls are also involved. In this study we investigate the effects of 0, 2, or 4 days starvation on the levels of specific, abundant mRNAs in total and polysomal RNA populations. The mRNAs were analyzed by translation in vitro in mRNA-dependent, cell-free, protein synthesizing systems. The resulting polypeptide products were separated by gel electrophoresis and visualized with fluorography. The amount of albumin translated from both polysomal and total cellular mRNA decreased 20-40% with fasting. In contrast, a specific peptide having a molecular mass of approximately 30 kDa increased two- to three-fold in total cellular RNA with a smaller increase observed in polysomal RNA. These changes were maximal at 2 days of starvation. Since starvation is known to cause alterations in liver metabolism the 30-kDa polypeptide may be related to enzymes or other proteins involved in this homeostatic response.

Albumins↗
PubMed1986

Locus of control and smokeless tobacco use among adolescents.

Seventh-grade students from two school districts in rural North Carolina were surveyed to determine the prevalence and correlates of smokeless tobacco use. The survey was carried out as part of a larger project intended to study prevalence of "risky" behaviors, specifically alcohol and tobacco use. Data were collected from 322 students: 49% male, 36.6% nonwhite. Of those reporting use of smokeless tobacco (11.4%), virtually all were male; most reported weekly use, with a small proportion (1.3%) reporting daily use. Locus of control of "occasional" users was significantly more internal than those reporting "regular" use (p less than .05).

Adolescent↗
PubMed1985

Factors influencing return to work following cerebral infarction.

A study of 379 patients, employed before cerebral infarction and living one year afterward, was undertaken to determine what factors had influenced their returning to work. We found age, occupation, degree of disability, race, and hemisphere infarcted to be significant. Younger patients with less disability were more likely to return to work. Patients employed in professional-managerial positions were more likely to return to work than patients in blue-collar or farming positions. Although there were no racial differences following a left-hemisphere infarct, white patients were more likely to return to work following a right-hemisphere infarct. Sex, blood pressure, severity of stroke, educational level, consciousness level at admission, maximum weakness in extremities, first v repeated stroke, care by a specially trained stroke team, rehabilitation therapy, and speech did not additionally influence the probability of returning to work.

Age Factors↗
PubMed1985

The role of plasma lipids in carotid bifurcation atherosclerosis.

The severity of coronary artery atherosclerosis correlates with increased plasma concentrations of total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), and triglycerides and with decreased plasma concentrations of high-density lipoprotein cholesterol (HDL-C). The role of plasma lipoproteins in the pathogenesis of cerebral atherosclerosis, however, is less clear. Several investigators report that lipoprotein abnormalities correlate inversely with the incidence of cerebral infarction. We analyzed risk factors for carotid bifurcation atherosclerosis in 121 consecutive patients who underwent cerebral angiography. This analysis revealed a significant positive correlation between the plasma TC/HDL-C ratio and the extent of carotid bifurcation atherosclerosis (p = 0.01). The extent of atherosclerosis correlated inversely with plasma concentrations of HDL-C (p = 0.02). Triglyceride concentration correlated positively with the extent of atherosclerosis with marginal significance (p = 0.07). LDL-C and TC concentrations did not correlate with bifurcation atherosclerosis (p greater than 0.1). Only 4% of the variation in the extent of bifurcation atherosclerosis was explicable on the basis of plasma lipoprotein concentrations.

Aged↗
PubMed1985

Pulmonary artery wedge pressure may fail to reflect left ventricular end-diastolic pressure in dogs with oleic acid-induced pulmonary edema.

We investigated the accuracy with which pulmonary artery wedge pressure (WP) reflected left ventricular end-diastolic pressure (LVEDP) in dogs with oleic acid-induced pulmonary edema. We compared hemodynamic variables before and during edema, as measured from a pulmonary artery catheter placed before oleic acid (PA-1) and from a second catheter (PA-2) placed 2 h after oleic acid infusion. Oleic acid decreased arterial oxygen saturation and cardiac output and increased pulmonary vascular resistance and phasic pulmonary artery pressure. LVEDP did not change after oleic acid, although WP measured by both catheters was increased. In addition, WP measured by PA-2 (7.1 +/- 0.7 mm Hg) was greater than that measured by PA-1 (5.6 +/- 0.5 mm Hg) (p less than or equal to 0.037). Using PA-1, we found that WP increased in a linear manner with LVEDP both before and after pulmonary injury (r2 = 0.91, 0.68, respectively). There was no relationship between LVEDP and WP using PA-2 (r2 = 0.07). We conclude that oleic acid-induced pulmonary edema lessens the accuracy with which WP reflects LVEDP, and that WP from a catheter placed after edema less accurately reflects LVEDP than does WP from a catheter placed before edema.

Animals↗
PubMed1985

Cardiopulmonary effects of hypertonic saline in canine oleic acid-induced pulmonary edema.

Vasoactive drugs may increase intrapulmonary shunt in patients with permeability edema. Because 7.5% hypertonic saline solution has cardiotonic properties, we studied its hemodynamic and pulmonary effects in a canine model of oleic acid-induced lung injury. Immediately after saline infusion, there were increases in cardiac output (2.0 +/- 0.1 to 3.4 +/- 0.2 L/min; p less than .001) and intrapulmonary shunt (50.3 +/- 4.4 to 57.3 +/- 3.2%; p less than .01) without alteration in arterial or mixed venous oxygen tension. Although arterial oxygen content decreased from 16.4 +/- 1.1 to 14.4 +/- 0.9 ml/dl (p less than .001), paralleling the change in hemoglobin concentration, oxygen delivery to the tissues increased from 327 +/- 23 to 486 +/- 36 ml/min (p less than .001). These effects were transient, inasmuch as all values returned to preinfusion levels within 30 min. Tissue oxygen consumption increased proportionately with cardiac output, and the directional change in arterial oxygenation was similar to the change in mixed venous oxygen tension. We conclude that tissue oxygen delivery improves after hypertonic saline infusion despite changes in intrapulmonary shunt and oxygen consumption. However, any benefit appears to be transient.

Animals↗
PubMed1985

Effects on cerebral hemodynamics of resuscitation from endotoxic shock with hypertonic saline versus lactated Ringer's solution.

This study was carried out to determine whether 7.5% hypertonic saline (HSS) and lactated Ringer's solution restore cerebral hemodynamics comparably when used for resuscitation from endotoxic shock. Endotoxic shock was produced in 13 dogs by the iv administration of 1.5 mg/kg Escherichia coli endotoxin. After 90 min of shock, seven animals were resuscitated with lactated Ringer's solution, 60 ml/kg iv, and six with 7.5% HSS, 6 ml/kg iv. Both solutions increased cardiac output and mean arterial pressure. With HSS, intracranial pressure was lower immediately after resuscitation (p less than .001) and one hour later (p less than .01). However, cerebral blood flow was not increased by either fluid and, due to hemodilution, cerebral oxygen transport decreased during resuscitation in both groups of animals. Thus, HSS restored systemic hemodynamics and maintained a lower intracranial pressure during resuscitation from endotoxic shock, but failed, as did lactated Ringer's solution, to restore cerebral blood flow and oxygen transport.

Animals↗
PubMed1985

Immediate functional recovery and avoidance of reperfusion injury with surgical revascularization of short-term coronary occlusion.

Functional recovery with surgical revascularization of acutely ischemic myocardium has not been compared with its nonsurgical counterpart in experimental preparations of coronary occlusion. This study compares the functional and metabolic recovery of ischemic (1 hr coronary occlusion) segments revascularized either by restoration of coronary patency (simulating nonsurgical recanalization, e.g., angioplasty) or by surgical revascularization with multidose hypothermic potassium blood cardioplegic solution. Twenty-two anesthetized open-chest dogs were instrumented with Millar micromanometer-tip catheters to measure left ventricular and aortic pressures. Piezoelectric ultrasonic dimension gauges were implanted in the subendocardium supplied by the left anterior descending coronary artery to measure segmental contractile function. In five dogs, only biopsy samples were obtained for control measurements of ATP, creatine phosphate, and tissue water content. In the remaining 17 dogs, the left anterior descending artery and collaterals were ligated for 1 hr. The ligatures were removed in eight dogs and coronary perfusion continued for 2 hr, simulating nonsurgical reperfusion. The remaining nine dogs were placed on cardiopulmonary bypass and the hearts were arrested for 1 hr with multidose (every 20 min) blood cardioplegic solution enhanced with glutamate and aspartate, simulating surgical revascularization (coronary artery bypass grafting). The coronary ligatures were not released until the second cardioplegic infusion, simulating graft placement. One hour of coronary occlusion placed 39.4 +/- 2.5% of the left ventricle at risk, and converted active systolic shortening to persistent paradoxical bulging (25.2 +/- 2.2% to -5.8 +/- 1.2% systolic shortening).(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1984

Return of ovulation and fertility in women using norethisterone oenanthate.

The return of ovarian activity was studied in 20 women who had discontinued norethisterone oenanthate after using the injectable contraceptive for 6 months to 5 years. Follicular activity returned within 70 days of discontinuing in four women and within 90 days in a further seven. In only 4 women was the return of follicular activity associated with a rise in the serum progesterone level. The serum norethisterone concentration was usually less than 1 ng/ml at the time of return of ovarian activity and was lower in women in whom ovarian activity returned before day 90 than in those in whom it returned after day 90. Of 40 women who discontinued norethisterone oenanthate, pregnancy occurred in 14 women within 12 weeks of discontinuing and in 21 (52.5%) within 6 months. The findings suggest that there is no impairment of fertility in women using norethisterone oenanthate.

Adult↗