Search

The growth potential of a tumour can significantly depend on host features such as age, cell proliferation rates and caloric intake. Although this is widely known, existing mathematical models for tumour growth do not account for it. We therefore developed a new model for tumour growth, starting from a mathematical framework that describes the host's physiology. The resulting tumour-in-host model allowed us to study the implications of various specific interactions between the energetics of tumour and host. The model accounts for the influence of both age and feeding regimen of the host organism on the behaviour of a tumour. Concerning the effects of a tumour on its host, it explains why tumour-mediated body-weight loss is often more dramatic than expected from the energy demands of the tumour. We also show how the model can be applied to study enhanced body-weight loss in presence of cachectic factors. Our tumour-in-host model thus appears a proper tool to unite a wide range of phenomena in tumour-host interactions. [ABSTRACT FROM AUTHOR]

Background: Educational programs targeted towards youth to prevent HIV transmission are based on a model that increased knowledge equals reduced risk behaviour. This study explored HIV knowledge among a cohort of young drug users, and their perceptions of HIV risk acquisition. Methods: Between September 2005 and August 2009, youth who used illegal drugs were recruited into a prospective cohort known as the at-risk youth study (ARYS) in Vancouver, Canada. Participants completed an 18 item HIV Knowledge Questionnaire (HIV-KQ-18) and responses were scored dichotomously (i.e., ≥ 15 indicating high knowledge and <15 indicating low knowledge). We compared high- and low-scoring youth using Pearson's chisquare test and logistic regression. We also examined youths' perceptions of risk for acquiring HIV compared to their peers. Results: Of 589 youth recruited into ARYS, the mean age was 22 (interquartile range [IQR]: 20-24), 186 (31.6%) were female, and 143 (24.3%) were of Aboriginal ancestry. The median score on the HW-KQ- 18 was 15 (IQR: 12-16). Internal reliability was high (Cronbach's α=0.82). The analyses demonstrated that youth with higher HW knowledge were more likely to be older (adjusted odds ratio [AOR] = 1.08, per year older p = 0.031), completed high school (AOR=1.42, p=0.0S4), and engage in unprotected intercourse (AOR 1.73, p = 0.023). The majority of respondents (77.6%) perceived themselves to be at lower risk for acquiring HIV in comparison to their peers. Conclusions: HIV knowledge scores of participants were surprisingly low for an urban Canadian setting as was their HIV risk perception. Higher HIV knowledge was not associated with reduced sexual risk behaviour. Results demonstrate that education programs are not reaching or impacting this high-risk population. Given the complex forces that promote HIV risk behaviour, prevention programs should be fully evaluated and must recognize the unique characteristics of drug-using youth and factors that drive risk among this population. [ABSTRACT FROM AUTHOR]

Background: People who use unregulated drugs (PWUD) often face significant barriers to-and thereby avoid seeking-health care. In Vancouver, Canada, a neighborhood-wide health care system reform began in 2016 to improve health care delivery and quality. In the wake of this reform, we sought to determine the prevalence of health care avoidance and its association with emergency department use among PWUD in this setting and examine patient-reported nonmedical qualities of health care ("responsiveness")., Methods: The study derived data from two prospective cohort studies of community-recruited PWUD in Vancouver in 2017-18. Responsiveness was ascertained by the World Health Organizations' standardized measurements and we evaluated seven domains of responsiveness (dignity, autonomy, communication, confidentiality, prompt attention, choice of provider, and quality of basic amenities). The study used Pearson chi-squared test to examine differences in responsiveness between those who did and did not avoid care. The study team used multivariable logistic regression to determine the relationship between care avoidance due to past mistreatment and emergency department use, adjusting for potential confounders., Results: Among 889 participants, 520 (58.5%) were male, 204 (22.9%) reported avoiding health care, most commonly for chronic pain (47.4%). Overall, 6.6% to 36.2% reported suboptimal levels (i.e., not always meeting the expected quality) across all seven measured domain of responsiveness. Proportions reporting suboptimal qualities were significantly higher among those who avoided care than those who did not across all domains, including care as soon as wanted (51.0% vs. 31.8%), listened to carefully (44.1% vs. 20.4%), and involved in health care decision-making (27.9% vs. 12.7%) (all p < 0.05). In multivariable analyses, avoidance of health care was independently associated with self-reported emergency department use (adjusted odds ratio = 1.49; 95% confidence interval:1.01-2.19)., Conclusion: We found that almost a quarter of our sample of PWUD avoided seeking health care due to past mistreatment, and all seven measured domains of responsiveness were suboptimal and linked with avoidance. Individuals who reported avoidance of health care were significantly more likely to report emergency department use. Multi-level interventions are needed to remedy the suboptimal qualities of health care and thereby reduce care avoidance., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Background: Aerosolization of exogenous surfactant remains a challenge. This study is aimed to evaluate the efficacy of atomized poractant alfa (Curosurf) administered with a novel atomizer in preterm lambs with respiratory distress syndrome., Methods: Twenty anaesthetized lambs, 127 ± 1 d gestational age, (mean ± SD) were instrumented before birth and randomized to receive either (i) positive pressure ventilation without surfactant (Control group), (ii) 200 mg/kg of bolus instilled surfactant (Bolus group) at 10 min of life or (iii) 200 mg/kg of atomized surfactant (Atomizer group) over 60 min from 10 min of life. All lambs were ventilated for 180 min with a standardized protocol. Lung mechanics, regional lung compliance (electrical impedance tomography), and carotid blood flow (CBF) were measured with arterial blood gas analysis., Results: Dynamic compliance and oxygenation responses were similar in the Bolus and Atomizer groups, and both better than Control by 180 min (all P < 0.05; two-way ANOVA). Both surfactant groups demonstrated more homogeneous regional lung compliance throughout the study period. There were no differences in CBFConclusion:In a preterm lamb model, atomized surfactant resulted in similar gas exchange and mechanics as bolus administration. This study suggests evaluation of supraglottic atomization with this system when noninvasive support is warranted.

Normative data are needed to create a reference that indicates optimal development of weight in relation to height and age, particularly in the face of the unfolding obesity epidemic. The body-mass index (BMI) has some serious limitations: it is a relatively poor predictor of current and future fatness. Currently, however, there are few available alternatives, with the possible exception of waist circumference or skinfolds. The use of cross-sectional references to construct a BMI-reference curve is problematic when there are period and cohort effects. Ideally, a reference would be based on longitudinal data in populations with little underweight, overweight, and obesity. In the meantime cross-sectional data in appropriate populations could be used to construct BMI percentiles linking BMI values at age 5 to those at age 18 (or 21) that would correspond with adult BMI values reflecting optimal health (e.g., that would correspond to adult BMI values between 21 and 23 kg/m2).

Standardized long-term carcinogenicity tests aim to reveal the relationship between exposure to a chemical and occurrence of a carcinogenic response. The analysis of such tests may be facilitated by the use of mathematical models. To what extent current models actually achieve this purpose is difficult to evaluate. Various aspects of chemically induced carcinogenesis are treated by different modeling approaches, which proceed very much in isolation of each other. With this paper we aim to provide for the non-mathematician a comprehensive and critical overview of models dealing with processes involved in chemical carcinogenesis. We cover the entire process of carcinogenesis, from exposure to effect. We succinctly summarize the biology underlying the models and emphasize the relationship between model assumptions and model formulations. The use of mathematics is restricted as far as possible with some additional information relegated to boxes.

In this article, I analyse how photoadaption affects the photosynthesis-irradiance curve in phytoplankton. Four parameters are presumably affected by photoadaption: (1) the size of a photosynthetic unit; (2) the number of photosynthetic units per cell; (3) the average turnover time of a photosynthetic unit; and (4) the chlorophyll-specific absorption cross-section. Prezelin's well-known conceptual model of photoadaption deals with variation in size and number of photosynthetic units, but not with the other two parameters. Prezelin's model predicts that the photosynthesis-irradiance curve is differentially affected by variations in size or number of photosynthetic units. By contrast, my analysis shows that if photoadaptional variation in the turnover time is also accounted for, only the cellular chlorophyll concentration is relevant; variation in the size vs. number of photosynthetic units is immaterial. The photoadaptional response of the chlorophyll-specific absorption cross-section allows a simple description consistent with experimental data. I use this description to derive a single expression for the rate of photosynthesis as dependent on irradiance and the cellular chlorophyll concentration. This model for the photosynthesis-irradiance-curve accounts for the photoadaptional alterations of all four parameters. Copyright 1997 Academic Press Limited

Current models on protandry in butterflies assume that females are mated instantaneously upon eclosion. However, for most butterfly species this assumption is not realistic. In this paper a model is formulated in which the mating rate depends on both male and female density. Given the female presence curve, protandry is an evolutionarily stable strategy (ESS) for males. The evolutionarily stable amount of protandry decreases with increasing death rate and decreasing encounter rate. Given the male presence curve, protandry also is an ESS for females. However, male and female ESS are not identical; moreover, in the present model a simultaneous ESS does not exist. Protandry critically depends on the assumption that females mate only once, whereas males are capable of multiple mating. If females too are capable of multiple mating, absence of protandry is the ESS for males as well as females. The model predicts that protandry depends on population density: protandry should be more pronounced in populations with high density than in populations with low density. Protandry also depends on sex ratio. It becomes more pronounced when the proportion of males among emerging adults increases.