Biological boundaries and biological age

Population dynamics model for aging

The chronological age used in demography describes the linear evolution of the life of a living being. The chronological age cannot give precise information about the exact developmental stage or aging processes an organism has reached. On the contrary, the biological age (or epigenetic age) represents the true evolution of the tissues and organs of the living being. Biological age is not always linear and sometimes proceeds by discontinuous jumps. These jumps can be negative (we then speak of rejuvenation) or positive (in the event of premature aging), and they can be dependent on endogenous events such as pregnancy (negative jump) or stroke (positive jump) or exogenous ones such as surgical treatment (negative jump) or infectious disease (positive jump). The article proposes a mathematical model of the biological age by defining a valid model for the two types of jumps (positive and negative). The existence and uniqueness of the solution are solved, and its temporal dynamic is analyzed using a moments equation. We also provide some individual-based stochastic simulations.

A Model for the Lifespan Loss Due to a Viral Disease: Example of the COVID-19 Outbreak

The end of the acute phase of the COVID-19 pandemic is near in some countries as declared by World Health Organization (WHO) in January 2022 based on some studies in Europe and South Africa despite unequal distribution of vaccines to combat the disease spread globally. The heterogeneity in individual age and the reaction to biological and environmental changes that has been observed in COVID-19 dynamics in terms of different reaction to vaccination by age group, severity of infection per age group, hospitalization and Intensive Care Unit (ICU) records show different patterns, and hence, it is important to improve mathematical models for COVID-19 pandemic prediction to account for different proportions of ages in the population, which is a major factor in epidemic history. We aim in this paper to estimate, using the Usher model, the lifespan loss due to viral infection and ageing which could result in pathological events such as infectious diseases. Exploiting epidemiology and demographic data firstly from Cameroon and then from some other countries, we described the ageing in the COVID-19 outbreak in human populations and performed a graphical representation of the proportion of sensitivity of some of the model parameters which we varied. The result shows a coherence between the orders of magnitude of the calculated and observed incidence numbers during the epidemic wave, which constitutes a semi-quantitative validation of the mathematical modelling approach at the population level. To conclude, the age heterogeneity of the populations involved in the COVID-19 outbreak needs the consideration of models in age groups with specific susceptibilities to infection.

Age Dependent Epidemic Modeling of COVID-19 Outbreak in Kuwait, France, and Cameroon

Revisiting the classical model by Ross and Kermack-McKendrick, the Susceptible−Infectious−Recovered (SIR) model used to formalize the COVID-19 epidemic, requires improvements which will be the subject of this article. The heterogeneity in the age of the populations concerned leads to considering models in age groups with specific susceptibilities, which makes the prediction problem more difficult. Basically, there are three age groups of interest which are, respectively, 0−19 years, 20−64 years, and >64 years, but in this article, we only consider two (20−64 years and >64 years) age groups because the group 0−19 years is widely seen as being less infected by the virus since this age group had a low infection rate throughout the pandemic era of this study, especially the countries under consideration. In this article, we proposed a new mathematical age-dependent (Susceptible−Infectious−Goneanewsusceptible−Recovered (SIGR)) model for the COVID-19 outbreak and performed some mathematical analyses by showing the positivity, boundedness, stability, existence, and uniqueness of the solution. We performed numerical simulations of the model with parameters from Kuwait, France, and Cameroon. We discuss the role of these different parameters used in the model; namely, vaccination on the epidemic dynamics. We open a new perspective of improving an age-dependent model and its application to observed data and parameters.

Estimation of Daily Reproduction Numbers during the COVID-19 Outbreak

(1) Background: The estimation of daily reproduction numbers throughout the contagiousness period is rarely considered, and only their sum R0 is calculated to quantify the contagiousness level of an infectious disease. (2) Methods: We provide the equation of the discrete dynamics of the epidemic’s growth and obtain an estimation of the daily reproduction numbers by using a deconvolution technique on a series of new COVID-19 cases. (3) Results: We provide both simulation results and estimations for several countries and waves of the COVID-19 outbreak. (4) Discussion: We discuss the role of noise on the stability of the epidemic’s dynamics. (5) Conclusions: We consider the possibility of improving the estimation of the distribution of daily reproduction numbers during the contagiousness period by taking into account the heterogeneity due to several host age classes.

Optimal age- and sex-based management of the queue to ventilators during the Covid-19 crisis

Triage protocols for intensive care units are based on priorities assigned to presents, but ignore patients about to arrive, so a priority newcomer may not find a ventilator and its associated nursing staff available because they are occupied by a lower-priority patient who however was present at the moment of assignment. Conversely, waiting too long leads to losing elderly patients who could have been saved by ventilators. As age and sex are major determinants of mortality by Covid-19 and have the merit, in contrast to other priority criteria, of being immediately available to health professionals, the criterion is the minimization of the mean mortality rate weighted by age- and sex-specific life expectancies. The dynamics is a queuing process involving mortality and return home flows and competition between ages. The result is the determination of an optimal threshold age that can guide triage.

Biological aging and physical fitness in men aged 20-70 years from Kraków, Poland

OBJECTIVES

The increasing problem of population aging requires appropriate economic and health-related measures to mitigate its negative effects. The aim was to categorize the biological age of men between 20 and 70 years of age and assess its relationship to their physical activity and fitness.

METHODS

Data included morphological variables, total body water, the results of five Eurofit motor tests and the percentage of maximum heart rate (HR%), during a cardiovascular test of more than 1,400 20-70 year-old men living in Kraków. Biological age was estimated with regression equations.

RESULTS

There were significant and consistent differences in physical fitness profiles between the three established groups of relations between biological and chronological age (biologically younger, equal, and older). These three categories of biological age were generally consistent with the regression analysis of physical fitness results, although declared physical activity seemed to be an independent factor.

CONCLUSIONS

The selected morphological variables represent a set of characteristics useful for the determination of the biological age. The existing relationship between physical activity and biological age indicates that physical activity may contribute to the inhibition of involutional changes, even if it had only been performed regularly in the past. Am. J. Hum. Biol. 28:503-509, 2016. © 2015 Wiley Periodicals, Inc.

Postoperative Functional Outcomes in Older Adults

As the world's aging population grows, the surgical population is increasingly made up of older adults. Due to changes in physiologic function and increasing comorbidity burden, older adults are at increased risk of morbidity, mortality, and functional decline after surgery. In addition, decision to undergo surgery for the older adult may be based on the postoperative functional outcome rather than survival. Although few studies have evaluated an older adult's function as a postoperative outcome, surgeons are becoming increasingly aware of the importance of maintaining or regaining function in an older patient. Interventions to improve postoperative functional outcomes are being developed and show promising results. This review discusses existing literature on postoperative functional outcomes in older adults and recently developed interventions.

Evolution of social networks: the example of obesity

The present paper deals with the effect of the social transmission of nutrition habits in a social and biological age-dependent context on obesity, and accordingly on type II diabetes and among its complications, the neurodegenerative diseases. The evolution of social networks and inside a network the healthy weight of a person are depending on the context in which this person has contacts and exchanges concerning his alimentation, physical activity and sedentary habits, inside the dominant social network in which the person lives (e.g., scholar for young, professional for adult, home or institution for elderly people). Three successive steps of evolution will be considered for social networks (like for neural one's): initial random connectivity, destruction and consolidation of links following a new transition rule called homophilic until an asymptotic architectural organization and configuration of states. The application of such a network dynamics concerns the sequence overweight/obesity/type II diabetes and neurodegenerative diseases.

Stability, complexity and robustness in population dynamics

The problem of stability in population dynamics concerns many domains of application in demography, biology, mechanics and mathematics. The problem is highly generic and independent of the population considered (human, animals, molecules,…). We give in this paper some examples of population dynamics concerning nucleic acids interacting through direct nucleic binding with small or cyclic RNAs acting on mRNAs or tRNAs as translation factors or through protein complexes expressed by genes and linked to DNA as transcription factors. The networks made of these interactions between nucleic acids (considered respectively as edges and nodes of their interaction graph) are complex, but exhibit simple emergent asymptotic behaviours, when time tends to infinity, called attractors. We show that the quantity called attractor entropy plays a crucial role in the study of the stability and robustness of such genetic networks.

Macro- and micro-level predictors of age categorization: results from the European Social Survey

This study evaluated macro- and micro-level variables associated with individuals' perception of the ending of youth, the beginning of old age, and the length of the middle age period. The European Social Survey is a biennial multi-country, cross-sectional survey. Our analysis is based on the fourth wave, which included a rotating module on ageism. The source sample consisted of 28 countries and a total of 54,988 respondents. Whereas macro-level variability accounted for 14 % of the variance associated with the perception of the ending of youth, only 5.7 % of the variance associated with the perception of the beginning of old age was accounted for by macro-level variability. Almost 10 % of the variance associated with the perception of the middle age period was associated with macro-level variability. Different patterns of macro- and micro-level correlates emerged for the ending of youth, beginning of old age, and the period of middle age. Overall, results demonstrate that individual differences in the perception of the ending of youth, the beginning of old age, and the length of the middle age period are more pronounced than contextual differences. Results also suggest that individuals' mental maps regarding the timing of these events are not necessarily concordant.

Predictive power of "a minima" models in biology

Many apparently complex mechanisms in biology, especially in embryology and molecular biology, can be explained easily by reasoning at the level of the "efficient cause" of the observed phenomenology: the mechanism can then be explained by a simple geometrical argument or a variational principle, leading to the solution of an optimization problem, for example, via the co-existence of a minimization and a maximization problem (a min-max principle). Passing from a microscopic (or cellular) level (optimal min-max solution of the simple mechanistic system) to the macroscopic level often involves an averaging effect (linked to the repetition of a large number of such microscopic systems with possible random choice of the parameters of each of them) that gives birth to a global functional feature (e.g. at the tissue level). We will illustrate these general principles by building in four different domains of application "a minima" models and showing the main properties of their solutions: (1) extraction of a minimal RNA structure functioning as the first "peptidic machine," a kind of ancestral ribosome; (2) study of a genetic regulatory network of Drosophila centred on Engrailed gene and expressing successively two genes inside a limit cycle; (3) study of a genetic network regulating neural activity and proliferation in mammals; and (4) study of a simple geometric model of epiboly in zebrafish.

Neuraxial opioids in geriatrics: A dose reduction study of local anesthetic with addition of sufentanil in lower limb surgery for elderly patients

Background and Objectives:

Neuraxial anesthesia in the elderly is associated with exaggerated responses to conventional doses of local anesthetics, thereby increasing the incidence of hemodynamic complications. A double-blind prospective study was carried out in our institute with an aim to compare the hemodynamic stability and quality of the conventional dose of hyperbaric bupivacaine (LA) with low dose of LA and sufentanil in elderly patients scheduled for lower limb surgery, randomized to receive combined spinal epidural anesthesia.

Methods:

A total of 50 elderly patients of ASA grade I and II, divided randomly into groups I and II, of either sex undergoing lower limb surgery under combined spinal epidural anesthesia at our institute attached to a Government Medical College were enrolled for study. Group I received 2.5 ml of intrathecal hyperbaric bupivacaine (LA), while group II received 1.5 ml of intrathecal LA+0.1 ml sufentanil (5 μg). Both initial and postoperative subarachnoid block characteristics, hemodynamic and respiratory parameters, duration of analgesia, and side effects were observed and recorded. Statistical analysis was carried out using Chi-square and paired t test.

Results:

Demographic profile was comparable in both groups. Group I had a greater incidence of hypotension and, consequently, higher use of vasopressors (P<0.05). Onset of sensory analgesia, time to achieve peak sensory level, and recovery from motor blockade were significantly earlier in group II (P<0.05). Postoperative consumption of LA through epidural route was significantly higher in group I (P<0.05). The side effect profile was similar, except for a significantly higher incidence of shivering in group I (P<0.05).

Conclusions:

The study established that the dose of a local anesthetic can be safely and significantly lowered by 40%, with addition of low-dose sufentanil, thereby avoiding the hemodynamic fluctuation and providing a stable perioperative and postoperative period in the geriatric population. In addition, duration of sensory analgesia is prolonged and postoperative requirement for the epidural top-up also decreases.

Demography and diffusion in epidemics: malaria and black death spread

The classical models of epidemics dynamics by Ross and McKendrick have to be revisited in order to incorporate elements coming from the demography (fecundity, mortality and migration) both of host and vector populations and from the diffusion and mutation of infectious agents. The classical approach is indeed dealing with populations supposed to be constant during the epidemic wave, but the presently observed pandemics show duration of their spread during years imposing to take into account the host and vector population changes as well as the transient or permanent migration and diffusion of hosts (susceptible or infected), as well as vectors and infectious agents. Two examples are presented, one concerning the malaria in Mali and the other the plague at the middle-age.