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PubMed2002

Validation of parasite transmission models: the example of onchocerciasis.

Most parasites have complex life cycles; and mathematical models can help in targeting interventions and predicting disease-control efforts. For actual applications, quantification and validation of models is a key issue. We illustrate the process of validation by presenting a (re)analysis of fly-feeding experiments carried out by the Onchocerciasis (river blindness) Control Programme (OCP/WHO) in West Africa, with the objective to validate ONCHOSIM, an onchocerciasis transmission model. In these experiments flies were fed on human patients and dissected to count the number of microfilariae they had ingested. To assess microfilarial skin densities, skin snips (biopsies) were taken and examined. Originally, the resulting curve was interpreted as showing saturation and considered the main regulating (density-dependent) mechanism of onchocerciasis transmission in the model. Taking into account measurement errors in the skin microfilarial density of human subjects (on whom the flies were fed) we now conclude that the relationship is essentially linear. This prompts us to requantify ONCHOSIM. Possible alternative density-dependent mechanisms are discussed.

Adult↗

PubMed2001

Feature mining and predictive model construction from severe trauma patient's data.

In management of severe trauma patients, trauma surgeons need to decide which patients are eligible for damage control. Such decision may be supported by utilizing models that predict the patient's outcome. The study described in this paper investigates the possibility to construct patient outcome prediction models from retrospective patient's data at the end of initial damage control surgery by using feature mining and machine learning techniques. As the data used comprises rather excessive number of features, special attention was paid to the problem of selecting only the most relevant features. We show that a small subset of features may carry enough information to construct reasonably accurate prognostic models. Furthermore, the techniques used in our study identified two factors, namely the pH value when admitted to ICU and the worst partial active thromboplastin time, to be of highest importance for prediction. This finding is pathophysiologically reasonable and represents two of three major problems with severe trauma patients, metabolic acidosis, hypothermia, and coagulopathy.

Algorithms↗

PubMed2002

Demographic and clinical correlates of homelessness among African Americans with severe mental illness.

The purpose of the present study is to compare the demographic and clinical characteristics of African Americans with and without an immediate history of homelessness upon entry into a state psychiatric hospital. Four variables made statistically significant contributions to the logit model predicting homelessness with the other variables controlled. They were never being married, lifetime comorbid substance abuse, severe paranoia, and high self-esteem. The four significant predictors from the logit model were used to assign patients to different risk groups. There was a significant dose-response relationship between the percentage of cases of homelessness and the number of these risk indicators.

Adolescent↗

PubMed2006

Model-based analysis of mechanisms responsible for sleep-induced carbon dioxide differences.

This work describes a comprehensive mathematical model of the human respiratory control system which incorporates the central mechanisms for predicting sleep-induced changes in chemical regulation of ventilation. The model integrates four individual compartments for gas storage and exchange, namely alveolar air, pulmonary blood, tissue capillary blood, body tissues, and gas transport between them. An essential mechanism in the carbon dioxide transport is its dissociation into bicarbonate and acid, where a buffering mechanism through hemoglobin is used to prevent harmfully low pH levels. In the current model, we assume high oxygen levels and consider intracellular hydrogen ion concentration as the principal respiratory control variable. The resulting system of delayed differential equations is solved numerically. With an appropriate choice of key parameters, such as velocity of blood flow and gain of a non-linear controller function, the model provides steady-state results consistent with our experimental observations measured in subjects across sleep onset. Dynamic predictions from the model give new insights into the behaviour of the system in subjects with different buffering capacities and suggest novel hypotheses for future experimental and clinical studies.

Algorithms↗

PubMed1996

Dynamic aspects of morbidity and acquired immunity in schistosomiasis control.

In schistosomiasis control, rational planning of chemotherapy programmes is complicated by the dynamic interactions between treatment and levels of acquired immunity and morbidity in the community. In this paper, mathematical models that address the development of acquired immunity and the prevalence of morbidity are incorporated within an age-structured transmission framework to explore some of the dynamic complexities of long-term chemotherapy programmes. As well as illustrating some of the potential problems inherent in predicting the consequences of control measures, the model provides insights into the dynamics of schistosomiasis transmission and the parameters that need to be measured to further improve the design of community-based control programmes.

Humans↗

PubMed1993

Effects of stressful job demands and control on physiological and attitudinal outcomes in a hospital setting.

We tested the job demands--job control model of stress with a group of 136 registered nurses. Significant interactions between subjective and objective measures of work load and a measure of perceived control predicting physiological and attitudinal outcomes indicated support for the model. In addition, objectively assessed job demands were significantly associated with blood pressure and cortisol levels. The model also predicted elevations in physiological responses after individuals left work, suggesting that potentially health-impairing reactions to jobs that have high demands and low controllability might carry over to home settings and thus pose a high risk of long-term health impairment. The results have implications for the role of personal control in occupational stress generally and for nurse-management practices specifically.

Adult↗

PubMed1981

DNA synthesis in Escherichia coli during a nutritional shift-up.

DNA synthesis in a thymine-requiring Escherichia coli K12 strain was studied by exploiting deoxyguanosine, so simulating the behaviour of Thy+ strains. DNA synthesis is inhibited during the first 24 min after a nutritional shift-up. The new DNA/mass is lower than that predicted by current models for initiation control.

Cell Division↗

PubMed2004

Psychological attributes of preoperative total joint replacement patients: implications for optimal physical outcome.

In this study, 107 primary total joint replacement (TJR) patients were assessed preoperatively using the SF-36 (Mental Component Score [MCS] and Physical Component Score [PCS]), Beck Depression Inventory (BDI), Spielberger Trait Anxiety Inventory, Interpersonal Support Evaluation List, and the Coping Strategies Questionnaire. Patients with preoperative MCS < 50 had significantly higher trait anxiety (P <.001), higher BDI scores (P <.001), and lower appraisal (P <.018) and belonging (P <.006) support when compared with patients with preoperative MCS > or = 50. Low MCS patients used more catastrophizing coping techniques (P <.001) and reported poorer pain control (P <.04). A multivariate prediction model found that adding preoperative MCS to baseline demographic and physical function (PCS) measures significantly improved the prediction of 6-month change in PCS. Further research should evaluate the role of multimodality emotional support in assuring optimal physical return after TJR.

Adaptation, Psychological↗

PubMedDate not supplied

[Short-term prediction of cases of AIDS in Catalonia (1991-1994)].

Predicting AIDS incidence is a useful strategy for health service planning and for the design of preventive and control programmes. The different predictive mathematical models of AIDS can be classified in simple and complex, according to the assumptions used. The present study presents the prediction of the minimum AIDS incidence in Catalonia for the period 1991-94 by means of three simple mathematical models. The models that have been compared are the projection method of Chin and Lwanga, the retroprojection method of Brookmeyer and Gail, and the extrapolation method of Cox and Medley. Baseline information about AIDS cases comes from the AIDS Registry of the "Generalitat" of Catalonia. In a comparable manner, the three methods point out an increase of AIDS incidence until 1994, varying from 1160 to 1733 new cases in that year depending on the method used. We conclude that it will be necessary to increase the provision of health, social and preventive resources against AIDS in Catalonia in the coming years.

Acquired Immunodeficiency Syndrome↗

PubMed2000

Vestibular, visual, and somatosensory contributions to human control of upright stance.

We investigated the changes of human posture control of upright stance which occur when vestibular cues (VEST) are absent and visual and somatosensory orientation cues (VIS, SOM) are removed. Postural responses to sinusoidal tilts of a motion platform in the sagittal plane (+/-2 degrees, f=0.05, 0.1, 0.2 and 0.4 Hz) were studied in normal subjects (Ns) and patients with bilateral vestibular loss (Ps). We found that absence of VEST (Ps, visual reference) and removal of VIS (Ns, no visual reference) had little effect on stabilization of upright body posture in space. In the absence of both VEST and VIS (Ps, no visual reference) somatosensory graviception still provided some information on body orientation in space at 0.05 and 0.1 Hz. However, at the higher frequencies Ps qualitatively changed their behavior; they then tended to actively align their bodies with respect to the motion platform. The findings confirm predictions of a novel postural control model.

Cues↗

PubMed2002

Mothers' influence on the timing of first sex among 14- and 15-year-olds.

PURPOSE: To better understand maternal influence on the timing of first sex for adolescents. METHODS: Using data from the National Longitudinal Study of Adolescent Health, Cox proportional hazard models were used to assess the association between maternal characteristics and the timing of first sex. Matched dyads of mothers and their adolescent children were used. RESULTS: Of the 2,006 adolescents aged 14 and 15 years who reported to be virgins, 95 males (10.8%) and 162 females (15.8%) indicated they had initiated sex within the follow-up period, 1 year later. For males, few variables beyond the controls used in the models were predictive of timing of first sexual intercourse. For females, mother's satisfaction with her relationship with her daughter (hazard ratio =.62), mother's strong disapproval of her daughter having sex (hazard ratio =.56), and frequency of communication with the parents of her daughter's friends were associated with later sexual debut (hazard ratio =.88). CONCLUSION: Based on the variables in the model, mothers' values and beliefs and relationship satisfaction have more influence on daughters than on sons.

Adolescent↗

PubMed2004

The presentation of irritable bowel syndrome in the context of somatization disorder.

BACKGROUND AND AIMS: Somatization disorder, a female predominant disorder, has been found with higher than expected prevalence in previous studies of irritable bowel syndrome (IBS) and might be responsible for some of the comorbidity and excessive health care resource use associated with IBS. The study's aim was to determine within a female IBS population the degree of segregation of psychiatric illness, functional disorders, and health care utilization with somatization disorder. METHODS: In a prospective, 6-month follow-up study, psychiatric disorders were assessed with the Diagnostic Interview Schedule, gastrointestinal and other symptoms with self-report questionnaires, and medically unexplained complaints by thorough chart review. The setting was a university gastroenterology clinic. The participants were a convenience sample of female clinic attendees with IBS (N = 56). RESULTS: Somatization disorder was diagnosed in 25% of patients and highly probable in another 5%. Somatization disorder was associated with significantly greater numbers of gastrointestinal and other symptoms, psychiatric disorders, physicians consulted, telephone calls to physicians, urgent care visits, medication changes, and missed work days and with benzodiazepine use. On follow-up, somatization disorder was associated with psychiatric and IBS symptoms, medication changes, and treatment dissatisfaction. Both somatization disorder and other psychiatric illnesses were associated with other functional gastrointestinal disorders; only somatization disorder remained predictive in a regression model that controlled for the presence of other psychiatric illness. CONCLUSIONS: Among female IBS patients attending a university gastroenterology clinic, many aspects of comorbidity and health care behaviors previously associated with IBS segregated with the diagnosis of somatization disorder. Recognition and appreciation of somatization disorder in IBS have important ramifications for the conduct of research and clinical practice.

Adolescent↗

PubMed2005

Pilot-scale demonstration of surfactant-enhanced PCE solubilization at the Bachman Road site. 2. System operation and evaluation.

A pilot-scale demonstration of surfactant-enhanced aquifer remediation (SEAR) was conducted during the summer of 2000 at the Bachman Road site in Oscoda, MI. Part two of this two-part paper describes results from partitioning and nonpartitioning tracer tests, SEAR operations, and post-treatment monitoring. For this field test, 68 400 L of an aqueous solution of 6% (wt) Tween 80 were injected to recover tetrachloroethene-nonaqueous phase liquid (PCE-DNAPL) from a shallow, unconfined aquifer. Results of a nonreactive tracer test, conducted prior to introducing the surfactant solution, demonstrate target zone sweep and hydraulic control, confirming design-phase model predictions. Partitioning tracer test results suggest PCE-DNAPL saturations of up to 0.74% within the pilot-scale treatment zone, consistent with soil core data collected during site characterization. Analyses of effluent samples taken from the extraction well during SEAR operations indicate that a total of 19 L of PCE and 95% of the injected surfactant were recovered. Post-treatment monitoring indicated that PCE concentrations at many locations within the treated zone were reduced by as much as 2 orders of magnitude from pre-SEAR levels and had not rebounded 450 days after SEAR operations ceased. Pilot-scale costs ($365 900) compare favorably with design-phase cost estimates, with approximately 10% of total costs attributable to the intense sampling density and frequency. Results of this pilot-scale test indicate that careful design and implementation of SEAR can result in effective DNAPL mass removal and a substantial reduction in aqueous concentrations within the treated source zone under favorable geologic conditions

Carcinogens↗

PubMed2006

The effect of the Müller-Lyer illusion on the planning and control of manual aiming movements.

Two experiments used Müller-Lyer stimuli to test the predictions of the planning-control model (S. Glover, 2002) for aiming movements. In Experiment 1, participants aimed to stimuli that either remained the same or changed upon movement initiation. Experiment 2 was identical except that the duration of visual feedback for online control was manipulated. The authors found that the figures visible during movement planning and online control had additive effects on endpoint bias, even when participants had ample time to use visual feedback to modify their movements (Experiment 2). These findings are problematic not only for the planning-control model but also for A. D. Milner and M. A. Goodale's (1995) two visual system explanation of illusory bias. Although our results are consistent with the idea that a single representation is used for perception, movement planning, and online control (e.g., V. H. Franz, 2001), other work from our laboratory and elsewhere suggests that the manner in which space is coded depends on constraints associated with the specific task, such as the visual cues available to the performer.

Adult↗

PubMed1999

Contribution of glucose transport to the control of the glycolytic flux in Trypanosoma brucei.

The rate of glucose transport across the plasma membrane of the bloodstream form of Trypanosoma brucei was modulated by titration of the hexose transporter with the inhibitor phloretin, and the effect on the glycolytic flux was measured. A rapid glucose uptake assay was developed to measure the transport activity independently of the glycolytic flux. Phloretin proved a competitive inhibitor. When the effect of the intracellular glucose concentration on the inhibition was taken into account, the flux control coefficient of the glucose transporter was between 0.3 and 0.5 at 5 mM glucose. Because the flux control coefficients of all steps in a metabolic pathway sum to 1, this result proves that glucose transport is not the rate-limiting step of trypanosome glycolysis. Under physiological conditions, transport shares the control with other steps. At glucose concentrations much lower than physiological, the glucose carrier assumed all control, in close agreement with model predictions.

Animals↗

PubMed2005

Simulating dynamic activities using a five-axis knee simulator.

This work describes the design and capabilities of the Purdue Knee Simulator: Mark II and a sagittal-plane model of the machine. This five-axis simulator was designed and constructed to simulate dynamic loading activities on either cadaveric knee specimens or total knee prostheses mounted on fixtures. The purpose of the machine was to provide a consistent, realistic loading of the knee joint, allowing the kinematics and specific loading of the structures of the knee to be determined based on condition, articular geometry, and simulated activity. The sagittal-plane model of the knee simulator was developed both to predict the loading at the knee from arbitrary inputs and to generate the necessary inputs required to duplicate specified joint loading. Measured tibio-femoral compressive force and quadriceps tension were shown to be in good agreement with the predicted loads from the model. A controlled moment about the ankle-flexion axis was also shown to change the loading on the quadriceps.

Arthroplasty, Replacement, Knee↗

PubMed2006

Neuronal basis of Hammel's model for set-point thermoregulation.

In 1965, H. T. Hammel proposed a neuronal model to explain set-point thermoregulation. His model was based on a synaptic network encompassing four different types of hypothalamic neurons: i.e., warm-sensitive and temperature-insensitive neurons and heat loss and heat production effector neurons. Although some modifications to this model are suggested, recent electrophysiological and morphological studies support many of the model's major tenets. Hypothalamic warm-sensitive neurons integrate core and peripheral thermal information. These neurons sense changes in hypothalamic temperature, and they orient their dendrites medially and laterally to receive ascending afferent input from cutaneous thermoreceptors. Temperature-insensitive neurons have a different dendritic orientation and may provide constant reference signals, which are important in determining thermoregulatory set points. In Hammel's model, temperature-sensitive and -insensitive neurons send mutually antagonistic synaptic inputs to effector neurons controlling various thermoregulatory responses. The model predicts that warm-sensitive neurons synaptically excite heat loss effector neurons and inhibit heat production effector neurons. In recent studies, one counterpart of these effector neurons may be "excitatory postsynaptic potential-driven neurons," the activity of which is dependent on synaptic excitation from nearby cells. Excitatory postsynaptic potential-driven neurons have sparse dendrites that appear to be specifically oriented, either medially or laterally, presumably to receive selective synaptic input from a discrete source. Another counterpart of effector neurons may be "silent neurons," which have extensive dendritic branches that may receive synaptic excitation from remote sources. Because some silent neurons receive synaptic inhibition from nearby warm-sensitive neurons, Hammel's model would predict that they have a role in heat production or heat retention responses.

Animals↗

PubMed1995

Motor adaptation to Coriolis force perturbations of reaching movements: endpoint but not trajectory adaptation transfers to the nonexposed arm.

1. Reaching movements made in a rotating room generate Coriolis forces that are directly proportional to the cross product of the room's angular velocity and the arm's linear velocity. Such Coriolis forces are inertial forces not involving mechanical contact with the arm. 2. We measured the trajectories of arm movements made in darkness to a visual target that was extinguished at the onset of each reach. Prerotation subjects pointed with both the right and left arms in alternating sets of eight movements. During rotation at 10 rpm, the subjects reached only with the right arm. Postrotation, the subjects pointed with the left and right arms, starting with the left, in alternating sets of eight movements. 3. The initial perrotary reaching movements of the right arm were highly deviated both in movement path and endpoint relative to the prerotation reaches of the right arm. With additional movements, subjects rapidly regained straight movement paths and accurate endpoints despite the absence of visual or tactile feedback about reaching accuracy. The initial postrotation reaches of the left arm followed straight paths to the wrong endpoint. The initial postrotation reaches of the right arm had paths with mirror image curvature to the initial perrotation reaches of the right arm but went to the correct endpoint. 4. These observations are inconsistent with current equilibrium point models of movement control. Such theories predict accurate reaches under our experimental conditions. Our observations further show independent implementation of movement and posture, as evidenced by transfer of endpoint adaptation to the nonexposed arm without transfer of path adaptation. Endpoint control may occur at a relatively central stage that represents general constraints such as gravitoinertial force background or egocentric direction relative to both arms, and control of path may occur at a more peripheral stage that represents moments of inertia and muscle dynamics unique to each limb. 5. Endpoint and path adaptation occur despite the absence both of mechanical contact cues about the perturbing force and visual or tactile cues about movement accuracy. These findings point to the importance of muscle spindle signals, monitoring of motor commands, and possibly joint and tendon receptors in a detailed trajectory monitoring process. Muscle spindle primary and secondary afferent signals may differentially influence adaptation of movement shape and endpoint, respectively.

Adaptation, Physiological↗