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T Heath

Publications and source records attributed to T Heath.

At least 19 recordsLinked to original sources
PubMed2001

Stochastic dynamics in a two-dimensional oscillator near a saddle-node bifurcation.

We study the oscillator equations describing a particular class of nonlinear amplifier, exemplified in this work by a two-junction superconducting quantum interference device. This class of dynamic system is described by a potential energy function that can admit minima (corresponding to stable solutions of the dynamic equations), or "running states" wherein the system is biased so that the potential minima disappear and the solutions display spontaneous oscillations. Just beyond the onset of the spontaneous oscillations, the system is known to show significantly enhanced sensitivity to very weak magnetic signals. The global phase space structure allows us to apply a center manifold technique to approximate analytically the oscillatory behavior just past the (saddle-node) bifurcation and compute the oscillation period, which obeys standard scaling laws. In this regime, the dynamics can be represented by an "integrate-fire" model drawn from the computational neuroscience repertoire; in fact, we obtain an "interspike interval" probability density function and an associated power spectral density (computed via Renewal theory) that agree very well with the results obtained via numerical simulations. Notably, driving the system with one or more time sinusoids produces a noise-lowering injection locking effect and/or heterodyning.

Journal Article↗
PubMed1999

Hepatitis A in Australia in the 1990s: future directions in surveillance and control.

The national notification data from 1952 to 1997 was examined in order to characterise hepatitis A virus (HAV) infection in Australia in the 1990s, and to determine whether currently available surveillance data are sufficient to inform disease control strategies and vaccination policies. Hepatitis A annual notification rates declined dramatically from a high of 123 notifications per 100,000 persons in 1961, to 3 per 100,000 in 1989. During 1991-97, the hepatitis A notification rate was 12 per 100,000 persons per year, although rates varied substantially between States and Territories. The Northern Territory had the highest notification rate of 52 per 100,000 persons per year. Seventy-six per cent of cases were adults, although in most regions notification rates were significantly higher in children than adults. Nationally, the male to female ratio was 1.7:1 (p < 0.001). The Northern Territory was the only area with no significant difference in notifications between the sexes. Large outbreaks were detectable through the notification system but risk factors for transmission could only be inferred from age and sex distribution of notifications, and from previous outbreak reports. National hepatitis A surveillance would be improved by collecting basic risk factor data, which identify cases as food-borne, sporadic, related to another case, or travel related. In addition, a population based serosurvey to measure age-specific hepatitis A susceptibility would assist vaccination policy development. Serosurveillance data are also needed, in conjunction with enhancements of the notification data, to provide baseline information against which the impact of changes in vaccination policy can be assessed.

Adolescent↗
PubMed1999

Symphyseal separation, sacroiliac joint dislocation and transient lateral femoral cutaneous neuropathy associated with McRoberts' maneuver. A case report.

BACKGROUND: McRoberts' maneuver is often used prophylactically with the onset of active maternal expulsive efforts or immediately before delivery of the fetus. CASE: A 31-year-old woman, gravida 1, para 0, at 39 + 2 weeks' gestational age, was continuously maintained in an exaggerated lithotomy position while actively pushing during the second stage of labor. Immediately following spontaneous vaginal delivery of a 3,598-g infant, the patient noted left gluteal pain and left anterior thigh dysesthesia. Orthopedic evaluation revealed a 5-cm symphyseal separation, sacroiliac joint dislocation and transient lateral femoral cutaneous neuropathy. The patient underwent closed reduction of the left hemipelvis, followed by open reduction and internal fixation of the symphysis pubis two weeks later after failing conservative treatment. CONCLUSION: Although McRoberts' maneuver is generally safe, care should be exercised with use of excessive force or prolonged placement of the patient's legs in a hyperflexed position.

Adult↗
PubMed1998

Pertussis vaccines: past, present and future in Australia.

In August 1997, a workshop was convened by the National Centre for Immunisation Research and Surveillance of Vaccine Preventable Diseases to consider current issues in the use of pertussis vaccines and implications for the Australian immunisation schedule. Topics covered included the history, efficacy and reactogenicity of whole-cell and acellular vaccines and vaccine schedules. Acellular pertussis vaccine is preferred by the National Health and Medical Research Council for the primary course as well as the 18 month and 4-5 year old childhood doses. At the time of the workshop, a 3-component acellular vaccine (DTPa) had been approved (licensed) in Australia for all doses in the childhood schedule. It was the first vaccine subject to a cost-effectiveness evaluation under the new vaccine funding arrangements. Issues considered in the evaluation of the cost-effectiveness of the vaccine were discussed. These included comparative efficacy, adverse events and compliance, and the question of community as well as individual benefit from the use of the vaccine.

Australia↗
PubMed1998

Pathways of interstitial fluid and lymph flow in the liver acinus of the sheep and mouse.

In the acinus of the sheep and mouse liver, lymphatic vessels are restricted to the portal tracts. Vessels less than about 25 microm across form a network around portal venules, and are closely associated with the limiting plate of hepatocytes. The perisinusoidal space of Disse is continuous with the interstitial space of the portal tracts at the origin of the sinusoids. It seems likely that excess interstitial fluid derived from the sinusoids flows along the perisinusoidal space of Disse to enter the portal tracts near the portal venules, and then enters the small lymphatics which lie adjacent to those venules. It then enters the larger vessels, which are adjacent to hepatic arterioles and bile ductules.

Animals↗
PubMed1997

A community-wide hepatitis A outbreak in the Shoalhaven region, New South Wales.

We investigated a community-wide outbreak of hepatitis A virus infection in the Shoalhaven region of the New South Wales south coast. Epidemiological features of the outbreak suggested that transmission was predominantly person-to-person. These included: the prolonged course of the epidemic, the bimodal age-specific attack rate, the lower socioeconomic risk groups affected, and the large proportion of cases who reported prior contact with another case. Although widespread use of post-exposure immunoprophylaxis appeared to be effective in preventing symptomatic infection in individuals, it did not rapidly halt the outbreak. We review methods of mass intervention for community-wide outbreaks of hepatitis A virus infection, and define priorities for investigation of future outbreaks.

Disease Outbreaks↗
PubMed1996

Lymph pathways associated with three types of follicle structure found in gut-associated lymphoid tissue of horse ileum.

In the horse ileum, lacteals in the villi are continuous with prelymphatic intercellular channels and a plexus of lymphatic sinuses in the lamina propria that encircle the domes of the follicle/dome structures and proprial follicles. These sinuses may act as the major entry site for many of the lymphocytes migrating from gut-associated lymphoid tissue via the lymphatic system. Vessels from this plexus penetrate the muscularis mucosae and lymph flows into lymphatic vessels within the interfollicular tissue between the follicles of both follicle/dome structures and lymphoglandular complexes (LGCs). No lymphatic vessels leave the follicles, but intercellular pathways of the follicles are continuous with those in the surrounding interfollicular tissue and follicular sinuses around the base of the follicles. These pathways appear to provide the only available lymphatic route for lymphocytes leaving LGCs to enter the lymphatic system. Lymph from the interfollicular tissue enters deep submucosal lymphatic vessels, containing prominent valves, which drain into other vessels transporting lymph from the surface of the ileum.

Animals↗
PubMed1995

Lymphoid tissues of the ileum in young horses: distribution, structure, and epithelium.

Lymphoid tissues in the ileum of young horses form raised plaques that are macroscopically visible from the mucosal surface. These are termed "ileal lymphoid patches". These patches are variable in size, shape and position within the ileal wall, occasionally lying along the site of mesenteric attachment. Within lymphoid patches, follicles exist in three different morphological forms: follicle/dome structures, proprial follicles, and lymphoglandular complexes (LGCs). In follicle/dome structures, the majority of the follicle lies in the submucosa and merges with a dome in the lamina propria through a gap in the muscularis mucosae. In proprial follicles, the majority, or all, of the follicle is found in the lamina propria, and in LGCs, the follicles lie in the submucosa and communicate with the intestinal lumen via a central invagination of epithelium that extends vertically through a gap in the muscularis mucosae. Follicle-associated epithelium covers the follicle/dome structures and proprial follicles. It consists of enterocytes, cells morphologically resembling M cells, intraepithelial lymphocytes, goblet cells, and amine-precursor uptake and decarboxylation (APUD) cells. The epithelium of LGCs is mainly populated by immature enterocytes, intraepithelial lymphocytes and goblet cells. Cells with coarse, long microvilli are also present. Information regarding the presence of LGCs in the small intestine is scant, but LGCs have been well described in the large intestine of many species. Further investigation will be required to determine if factors exist that are common to both the ileum of the horse and the large intestine of other species to influence the development of LGCs at these specific sites.

Animals↗
PubMed1995

Segmented filamentous bacteria associated with lymphoid tissues in the ileum of horses.

Segmented filamentous bacteria preferentially attached to the follicle-associated epithelium overlying the lymphoid tissue in samples of the terminal ileum from seven horses examined by scanning electron microscopy. The bacteria adhered to the apical membrane of the enterocytes by a holdfast segment. Each filament tended to be of uniform diameter, but the filaments ranged from 0.7 to 1.4 microns in diameter. The bacteria were usually absent from the adjacent villous epithelium.

Animals↗
PubMed1995

Nosocomial and community-acquired Xanthomonas maltophilia infection in tropical Australia.

Xanthomonas maltophilia infection is recognized as a serious problem in association with immunosuppressive and invasive therapies, and with the use of broad-spectrum antibiotics. In Darwin Hospital in Australia's Northern Territory preliminary evidence of nosocomial transmission of X. maltophilia prompted this retrospective examination of all X. maltophilia isolates over a 30 month period. X. maltophilia was most frequently isolated in the 'wet season' corresponding to times of increased antibiotic treatment of the serious community-acquired pneumonias encountered in this tropical region. A relatively high proportion of community-acquired isolates (4/18; 22%) was documented. This study demonstrates that X. maltophilia infection is an emerging cause of morbidity in tropical regions where endemic infections require the use of broad-spectrum beta-lactams.

Adolescent↗
PubMed1994

Ileal Peyer's patches in pigs: intercellular and lymphatic pathways.

BACKGROUND: The lymphatics of Peyer's patches disseminate immunological information from the gut and thus play a key role in protection of the body against environmental pathogens. The aim of this project was to describe the lymphatic pathways of these Peyer's patches in pigs, and the mucosal intercellular spaces which lead to these lymphatics. METHODS: Ileal tissue from living or freshly killed pigs was examined by light microscopy or electron microscopy, or was injected with Mercox (CL-2B, Japan Vilene Hospital, Tokyo) for scanning electron microscopy of corrosion casts. RESULTS: Intercellular fluid between intestinal epithelial cells passes through pores in the basal lamina to mix with that in the intercellular spaces and prelymphatic intercellular channels of the lamina propria and follicle domes. From there, lymph enters lacteals in the villi, or a branching network of vessels within the lamina propria. Small lymphatics penetrate the muscularis mucosae and are continuous with (1) lymphatic vessels which pass directly to the deep submucosa between follicles, or (2) lymphatic sinuses which lie adjacent to the follicles. This differs from the situation in sheep and rabbits. Basal lymphatics beneath the follicles convey lymph to vessels which leave the surface at the serosa. CONCLUSION: The differences in the structure and arrangement of the lymphatics of Peyer's patches between pigs, sheep, and rabbits will require further investigation to determine if such variation between species has an effect on the distribution of immune products to effector sites.

Animals↗
PubMed1993

Lymphatic drainage from the distal small intestine in sheep.

Lymphatic drainage from the wall of the distal small intestine, important especially in young sheep as a major site of gut-associated lymphoid tissue, begins with a series of longitudinally oriented subserosal vessels. These vessels convey lymph to the mesenteric border of the intestinal wall and unite to form larger vessels which course through the mesentery to the mesenteric lymph nodes. These nodes lie towards the periphery of a broad, fan-shaped mesentery, adjacent to major arteries and veins. Mesenteric vessels convey lymph from the jejunum and part of the proximal ileum to the jejunal nodes. Lymph from most of the ileum is conveyed to caecal nodes. The larger mesenteric lymphatics have well formed smooth muscle and connective tissue layers surrounding the endothelium. They are often adjacent to, but rarely within, the connective tissue band anchoring the major arteries and veins to one or both lamellae of mesentery. Few anastomoses occur between vessels from opposing sides of the gut wall or the mesentery. Afferent lymphatics enter the subcapsular and trabecular sinuses of the nodes over most surfaces apart from the hilar region. Lymph flows through cortical tissue to the medulla, which occupies most of the node. In the medulla, sinuses occur within medullary cords as well as between them. Initial efferent lymphatics occur throughout medullary tissue. Efferent vessels emerge at a hilus then coalesce and drain into the jejunal or ileal trunk. The hilus of the node varies from a flat, poorly defined area on the lesser curvature, to a depression or groove. The latter commonly occurs in elongated jejunal nodes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗