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Biomedical subjects

R D Baker

Publications and source records attributed to R D Baker.

At least 19 recordsLinked to original sources
PubMed1992

Modelling trypanosomiasis prevalence and periodic epidemics and epizootics.

Existing mathematical models of trypanosomiasis epidemiology and epizootiology are extended by including some relevant biology of the disease vector, the tsetse fly. Rickettsia-like organisms, or RLO, are a vertically transmitted symbiont of tsetse, which confer an increased susceptibility to trypanosomiasis infection. Tsetse populations are also limited by density-dependent starvation. Modelling leads to the prediction of a stable dimorphism with a fraction of tsetse possessing RLO. The equilibrium prevalence of trypanosomiasis in the vertebrate hosts is no longer in RLO models determined simply by such traditional parameters as vectorial capacity. Only the RLO-positive tsetse carry infection, and their number is itself regulated by trypanosomiasis prevalence. The result of a naive model is that controlling tsetse numbers does not decrease prevalence until all tsetse are RLO-positive. However, under the density-dependent starvation model derived in this paper, the relative mortality of RLO-positive flies is greater at lower tsetse numbers. This tips the balance towards lower equilibrium prevalence of trypanosomiasis as tsetse numbers are decreased. The presence of RLO also gives rise to long-term oscillations in trypanosomiasis prevalence in humans and animals. However, when another mechanism that can also cause periodic epizootics (of shorter periodicity) is included, namely host immunity, the two epizootic processes combine to produce periodic epizootics (and therefore epidemics) at a single frequency. There are two decaying modes, one in which the tsetse population size quickly reaches equilibrium in a few weeks, and a second very slowly decaying mode in which host immunity and RLO effects interact. The equilibrium reached is shown to be asymptotically stable. In view of the seeming importance of RLO in trypanosomiasis epidemiology, it is important that field biologists enable RLO models to be validated by measuring the proportion of tsetse with RLO, in conjunction with vector density and trypanosomiasis prevalence and incidence in tsetse and vertebrate hosts.

Animals↗
PubMed1992

A double blind placebo controlled trial of recombinant tissue plasminogen activator in the treatment of digital ischemia in systemic sclerosis.

The treatment of digital ischemia in systemic sclerosis remains inadequate. We report a double blind, placebo controlled trial of recombinant tissue plasminogen activator (rtPA), a potent thrombolytic agent. Ten patients received rtPA. A potent, acute fibrinolytic effect was observed. During the infusion of rtPA, improvements in skin blood flow were seen. These improvements were shortlived.

Adolescent↗
PubMed1991

A randomized cross-over study of the effects of proinsulin on lipid metabolism in type 2 diabetes.

The effects of human proinsulin and insulin on lipid metabolism in Type 2 diabetes were examined in a randomized cross-over study in 15 patients. Blood glucose control was indistinguishable at the end of the two treatment periods, but fasting levels of triglycerides appeared somewhat lower after proinsulin (1.17(SE 0.16) vs 1.39(0.21) mmol I-1; p less than 0.07), and the maximal postprandial triglyceride response (2.19 (0.25) vs 2.87(0.28) mmol I-1, p less than 0.001) and triglyceride area under the curve (p less than 0.01) were significantly reduced. In five hyperlipidaemic patients postprandial triglyceridaemia was reduced with proinsulin (2.89(0.60) vs 3.68(0.56); p less than 0.001), but in addition fasting serum triglycerides (1.20(0.30) vs 1.96(0.30) mmol I-1, p less than 0.04) and possibly VLDL-cholesterol (0.49(0.15) vs 0.60(0.20) mmol I-1; p less than 0.10) were lower and fasting LDL-cholesterol levels higher (4.82(0.42) vs 3.92(0.57) mmol I-1, p less than 0.03) after proinsulin therapy. Proinsulin appears to preferentially suppress the production of triglyceride-rich lipoproteins in Type 2 diabetes, particularly postprandially, and may enhance their clearance and conversion to LDL, especially in hyperlipidaemic Type 2 diabetes.

Adult↗
PubMed1990

The possible role of Rickettsia-like organisms in trypanosomiasis epidemiology.

A simple model of human and animal trypanosomiasis is proposed in which the Ross equation for disease transmission is supplemented by a differential equation describing the inheritance of susceptibility in the vector. The model predicts an equilibrium state of balanced polymorphism for the fraction, theta, of susceptible tsetse and the occurrence of periodic epidemics at roughly the observed intervals. A loss of infectivity to tsetse of mechanically transmitted strains of trypanosome would seem to be a good evolutionary strategy for the trypanosome. The main implication for disease control is that measures initially reducing trypanosomiasis incidence could trigger off subsequent epidemics. Since theta leads incidence, monitoring theta could give several years advance warning of major epidemics. The model leads to oscillations in prevalence which are only lightly damped. Other mechanisms producing periodic epidemics would interact with this mechanism, and result in only one sequence of recurrent epidemics. With typical random variation of tsetse numbers about the seasonal norm the model shows the behaviour of a narrow-band system excited by broad-band noise, i.e. predicted trypanosomiasis incidence exhibits an undamped series of oscillations of variable amplitude and phase, similar to what is actually observed.

Animals↗
PubMed1990

Acute phase proteins in neonatal rabbits: diminished C-reactive protein response.

Acute phase protein response accompanies tissue injury, inflammation, or infection. During the acute phase, serum levels of C-reactive protein (CRP) can increase as much as 1,000-fold. We found that in response to an intramuscular injection of turpentine, neonatal rabbit CRP-specific RNA and serum CRP rose minimally. In contrast, adult serum levels of CRP increased 20-fold and mRNA for CRP in adults increased commensurately. However, during neonatal acute phase reactions, changes in the synthesis of the third component of complement (C3) and albumin were induced, implying a dysynchronous development of the response of various acute phase proteins.

Acute-Phase Reaction↗
PubMed1990

Growth of the early bovine fetus.

Testing for bovine hereditary syndactyly used artificial insemination, superovulation, and embryo transfer. Thirty-two suspect bulls and 9 suspect cows were mated with 10 syndactyly cows and two syndactylous bulls, respectively. 209 embryos were recovered and one, two, or three embryos was/were transfered into each recipient cow and 56 to 77 days after transfer, 174 fetuses were recovered. There was a significant relationship between amniotic fluid weights from the left uterine horn, fetal weights from right and left uterine horns, and fetal sex, side of corpus luteum, and number of embryo implants. Fetal membrane weights, amniotic fluid weights, fetal weights, and crown-rump lengths increased significantly with fetal age, but recipient cow weight had no significant effect. Survival data from single, double, and triple embryo implants indicated that it was most profitable under these test conditions to implant two embryos per recipient cow, one in each uterine horn.

Animals↗
PubMed1990

Platelet and plasma vasoactive amines in type 1 (insulin-dependent) diabetes mellitus with and without vascular disease.

Platelet and plasma vasoactive amine concentrations were measured in healthy controls and in type 1 (insulin-dependent) diabetic patients with or without vascular disease. Platelet concentrations of serotonin and noradrenaline were similar in all groups and were unrelated to age or gender, or to duration of diabetes, blood pressure, glycaemia or renal function in the diabetic subjects. Plasma concentrations of serotonin in the diabetic groups were comparable (118 +/- 16 (mean +/- SEM) and 127 +/- 21 pmol/mL), and were significantly higher in comparison to the healthy controls (66 +/- 12 pmol/mL, P = 0.002).

Adolescent↗
PubMed1990

The management of patients with an intrinsic supratentorial brain tumour.

The management of patients presenting with supratentorial glioma between 1978 and 1986 is reviewed. Complete follow-up in 517 cases was obtained. One hundred and fifty eight patients were not submitted to any form of surgery, 299 patients were biopsied and 60 patients underwent craniotomy and internal decompression. The no surgery group contained a higher proportion of patients with poor prognostic indicators than either the biopsy or craniotomy groups. The craniotomy group consisted of patients with better prognostic indicators than the biopsy group, in particular, younger age and more favourable site, type and grade of tumour. This was reflected in the difference in outcome between the groups. Median survival was 14 months in the craniotomy group, four months in the biopsy group and 2.2 months in the no surgery group. The outcome in patients with histologically proven malignant gliomas was best in those patients who received radiotherapy. The craniotomy group had a median survival of 18.5 months, a two year survival of 48% and a five year survival of 9%. The median survival following radiotherapy of those patients with proven malignant gliomas who had a biopsy was 9.5 months with a two year survival of 16% and a five year survival of 2%. These results compare favourably with studies which have adopted a more aggressive approach, suggesting that outcome is determined as much by patient selection using favourable prognostic indicators as by the treatment itself. The need for prospective trials of the management of unselected consecutive glioma patients randomizing them to conservative and radical treatment groups in order to define the role of both conventional therapy and radical therapy is discussed.

Adolescent↗
PubMed1990

Short-term malnutrition in neonatal rabbits: effect on function and synthesis of free radical metabolizing enzymes in the gastrointestinal tract.

Oxygen-derived free radicals are an important component of gastrointestinal injury in necrotizing enterocolitis (NEC). To assess the effect of a 72-h fast on the ability of neonatal small bowel to metabolize free radicals, the activity of superoxide dismutase (SOD), catalase, and the glutathione cycle were quantitated in mucosal scrapings from proximal and distal small bowel of fed and fasted neonatal rabbits. Hexose monophosphate shunt activity, quantitated in enterocytes from fed and fasted neonatal rabbits, was significantly less, p less than 0.01, in fasted animals. SOD activity was lower in distal small bowel from fasted animals than fed. The two mechanisms available to metabolize H2O2, catalase and the glutathione cycle, were significantly lower in both proximal and distal small bowel from fasted animals than in those from fed animals. To determine if fasting caused decreased enzyme activity at the level of gene expression, gastrointestinal tract DNA, RNA and protein, and specific mRNA levels for catalase, glutathione peroxidase (GPx), and SOD were quantitated. DNA, total RNA, and mRNA for SOD were lower in mucosal scrapings from fasted animals. However, mRNA for catalase, and GPx were not lower in fasted animals. Thus, a 72-h fast in neonatal rabbits causes a regional-specific decrease in SOD activity, which may be explained by decreased transcription. Changes in transcription do not completely account for regulation of catalase and glutathione cycle enzymes.

Animals↗
PubMed1989

Dose-response curves for suxamethonium in neonates, infants and children.

Single dose-response curves were determined for suxamethonium in neonates, infants and children during thiopentone-fentanyl-nitrous oxide anaesthesia. During onset of neuromuscular block, suxamethonium produced an increase in muscle tone which was greatest in neonates and infants. The dose-response curves for the three groups were parallel. The effective doses producing 90% depression of twitch height were significantly greater in neonates and infants compared with children (517 and 608 v. 352 micrograms kg-1). These values were greater than those obtained in a comparable study in adults. In view of their higher ED values compared with adults and a marked individual variability in response to small doses of suxamethonium, we recommend an intubating dose of 3 mg kg-1 for neonates and infants and 2 mg kg-1 for children. These doses are 50-100% greater than those previously recommended for paediatric patients.

Anesthesia↗
PubMed1989

Skin blood flow and limited joint mobility in insulin-dependent diabetes mellitus.

Hand skin blood flow in 32 insulin-dependent (IDDM) diabetics was compared with 13 healthy controls at room temperature and after immersion of the hands in warm and cold water. Subjects were examined for limited joint mobility (LJM) to analyse the association between this and blood flow. Digital arteries remained patent in IDDM compared to controls after cold challenge (p = 0.0001), and the difference persisted to a lesser degree 15 min (p = 0.009) and 30 min (p = 0.03) after recovery. Capillary blood flow was reduced in IDDM at room temperature at the finger nailbeds (p less than 0.02) and the palms (p = 0.004) and remained so after warm water immersion in the palms (p = 0.002), where further vasoconstriction was observed immediately after cold water immersion (p less than 0.001) and 15 and 30 min into recovery (p = 0.07 and p = 0.009 respectively). Thermographic analysis confirmed a pattern of predominantly distal rewarming after cold challenge in IDDM with a greater mean index finger temperature than the controls. Together, these features suggested enhanced arteriovenous anastomotic blood flow. All IDDM and IDDM males with LJM had reduced palm capillary flow immediately after cold challenge (p less than 0.05). After warm water (p less than 0.03) and 30 min after cold challenge (p less than 0.05) IDDM males with LJM had reduced palm capillary flow compared to those IDDM without. A microvascular aetiology for LJM is proposed by virtue of reduced nutritional blood flow and evidence of enhanced arteriovenous shunting in the hands of insulin-dependent diabetics.

Adolescent↗
PubMed1989

Conceptual model for the use of aerial color infrared photography by mosquito control districts as a survey technique for Psorophora columbiae oviposition habitats in Texas ricelands.

Two photographic missions per year are recommended to provide information on land-use and mosquito oviposition habitats. A winter mission, following a rain, will-provide a view of low areas within fields which may be obscured by summer vegetation. A summer mission will provide current land-use and crop distribution information and may show plant stress conditions due to excessive soil moisture. An aerial color infrared photographic survey with directed ground verification should result in a substantial savings in cost and increased efficiency in surveillance of mosquito producing habitats over ground survey techniques currently employed by mosquito control districts.

Animals↗
PubMed1989

Anaesthetic induction in children: the effects of maternal presence on mood and subsequent behaviour.

Forty-nine children, aged from 1 to 9 years, undergoing elective surgery under general anaesthesia, were studied in two groups. In one group, each child's mother was present during induction of anaesthesia, whereas in the other group no parent was present. Children's moods and cooperation during waiting and induction periods did not differ significantly between the groups, neither was the incidence of technical difficulties with anaesthetic induction different. Induction took longer (P = 0.005) if the mother was present. Mothers, when present, were calm and supportive to their children, with one exception. No mother was critical or interfering. Each child's behaviour was assessed by questionnaire pre-operatively and 4 weeks post-operatively. There was a significant overall improvement in behaviour scores post-operatively. There were no significant differences in direction or magnitude of behaviour changes between the two groups.

Affect↗
PubMed1989

Calculating the basic reproductive rate Ro when there are 2 or more pathogens.

Some reasons why observed prevalences of the 3 major trypanosomes in cattle and livestock animals might not be independent are discussed. Apart from genuine interactions between the infections, averaging over heterogeneous populations produces an apparent correlation between pathogens. More subtly, chemotherapy and mortality both induce a positive correlation between pathogens. The calculation of the basic reproductive rate Ro for one pathogen in the endemic presence of another is explained, and illustrated by a simple calculation. Although multi-pathogen calculations are difficult, the calculation of Ro is both useful and feasible.

Africa↗