Wandel der Altersstrukturen: Widersprüche und Zukunftsszenarien

'In den letzten 20 Jahren ist über den Alterungsprozess der Bevölkerungen in den Industriestaaten so intensiv wie nie zuvor diskutiert worden. Ein nicht unerheblicher Teil dieser Diskussion legt den Schluss nahe, dass eine ständig wachsende Gruppe von Menschen - die Älteren - als eine Belastung oder gar als ein Risiko für die Zukunft angesehen wird. Hier sind differenzierte Analysen nötig. In der Debatte über den Alterungsprozess dominieren Perspektiven, die auf steigende Belastungen für die Gesellschaft durch eine alternde Bevölkerung ausgerichtet sind und die den Beitrag älterer Menschen für die gesellschaftliche Entwicklung problematisieren. Diesen Sichtweisen wird mit Argumenten begegnet, die auf Basis von Forschungsbefunden eine Relativierung der heute gängigen Altersbilder ermöglichen. In diesem Zusammenhang werden Überlegungen zur 'Produktivität' des Alters und Szenarien für die Zukunft des Alters formuliert.' (Autorenreferat)'Public discussions about ageing have gained unprecedented importance during the last two decades. A continuously growing group in society, the elderly, are being regarded as a burden and as a collective risk for the future. However, more careful analyses are necessary. Whereas the public discussion focuses on the erosion of generational relations and the financial burden of elderly people, thus questioning their contributions for society, a research-based approach is more inclined to criticize these images of old age. In this context, ideas about the 'productivity' of age as well as scenarios about the future of age are being formulated.' (author's abstract)

A modeling-based evaluation of isothermal rebreathing for breath gas analyses of highly soluble volatile organic compounds

Isothermal rebreathing has been proposed as an experimental technique for estimating the alveolar levels of hydrophilic volatile organic compounds (VOCs) in exhaled breath. Using the prototypic test compound acetone we demonstrate that the end-tidal breath profiles of such substances during isothermal rebreathing show characteristics that contradict the conventional pulmonary inert gas elimination theory due to Farhi. On the other hand, these profiles can reliably be captured by virtue of a previously developed mathematical model for the general exhalation kinetics of highly soluble, blood-borne VOCs, which explicitly takes into account airway gas exchange as major determinant of the observable breath output. This model allows for a mechanistic analysis of various rebreathing protocols suggested in the literature. In particular, it clarifies the discrepancies between in vitro and in vivo blood-breath ratios of hydrophilic VOCs and yields further quantitative insights into the physiological components of isothermal rebreathing.Comment: 21 page

Potential of volatile organic compounds as markers of entrapped humans for use in urban search-and-rescue operations

Volatile organic compounds emitted by a human body form a chemical signature capable of providing invaluable information on the physiological status of an individual and, thereby, could serve as signs-of-life for detecting victims after natural or man-made disasters. In this review a database of potential biomarkers of human presence was created on the basis of existing literature reports on volatiles in human breath, skin emanation, blood, and urine. Approximate fluxes of these species from the human body were estimated and used to predict their concentrations in the vicinity of victims. The proposed markers were classified into groups of different potential for victim detection. The major classification discriminants were the capability of detection by portable, real-time analytical instruments and background levels in urban environment. The data summarized in this review are intended to assist studies on the detection of humans via chemical analysis and accelerate investigations in this area of knowledge.Comment: 38 page

Modeling-based determination of physiological parameters of systemic VOCs by breath gas analysis: a pilot study

In this paper we develop a simple two compartment model which extends the Farhi equation to the case when the inhaled concentration of a volatile organic compound (VOC) is not zero. The model connects the exhaled breath concentration of systemic VOCs with physiological parameters such as endogenous production rates and metabolic rates. Its validity is tested with data obtained for isoprene and inhaled deuterated isoprene-D5.Comment: 16 page

The relationship between twitch depression and twitch fade during neuromuscular block produced by vecuronium: correlation with the release of acetylcholine

<p>Abstract</p> <p>Background</p> <p>Train-of-four stimulation pattern following the administration of non-depolarizing neuromuscular blocking drugs reveals fade on successive contractions. Fade is caused by the release of fewer acetylcholine molecules by the fourth (A₄) than by the first stimulus (A₁). The current study was conducted to define the relationship between the clinically observed fade and the simulated decline in acetylcholine release (A₄/A₁) that would be necessary to produce it.</p> <p>Methods</p> <p>The T₄/T₁ratios produced by different doses of vecuronium (15–80 μg·kg^-1) were plotted as a function of the concomitant T₁. Separately in a model of neuromuscular transmission, T₁, T₄, and T₄/T₁were estimated using simulations in the presence and in the absence of a neuromuscular blocking drug and a stepwise decrease in A₄, but constant A₁.</p> <p>Results</p> <p>Vecuronium induced neuromuscular block was associated with larger T₄/T₁ratios (less fade) during the onset than during the offset of the block. All doses caused similar fade during offset. Simulations revealed that the smallest T₄/T₁was associated with the nadir of A₄/A₁and occurred at the beginning of T₁recovery. The nadir of A₄/A₁was only marginally affected by the dose of vecuronium: 15 μg·kg^-1producing the minimum A₄/A₁of 0.8 and 80 μg·kg^-1the minimum A₄/A₁of 0.7.</p> <p>Conclusion</p> <p>The hysteresis in the fade between onset and offset appears to be caused by a delayed decrease of A₄/A₁as compared with the decrease in T₁. Tentative estimates of the decrease in A₄/A₁during fade produced by vecuronium are offered. However, the validity of these estimates is dependent on the validity of the assumptions made in simulations.</p

Physiological modeling of isoprene dynamics in exhaled breath

Human breath contains a myriad of endogenous volatile organic compounds (VOCs) which are reflective of ongoing metabolic or physiological processes. While research into the diagnostic potential and general medical relevance of these trace gases is conducted on a considerable scale, little focus has been given so far to a sound analysis of the quantitative relationships between breath levels and the underlying systemic concentrations. This paper is devoted to a thorough modeling study of the end-tidal breath dynamics associated with isoprene, which serves as a paradigmatic example for the class of low-soluble, blood-borne VOCs. Real-time measurements of exhaled breath under an ergometer challenge reveal characteristic changes of isoprene output in response to variations in ventilation and perfusion. Here, a valid compartmental description of these profiles is developed. By comparison with experimental data it is inferred that the major part of breath isoprene variability during exercise conditions can be attributed to an increased fractional perfusion of potential storage and production sites, leading to higher levels of mixed venous blood concentrations at the onset of physical activity. In this context, various lines of supportive evidence for an extrahepatic tissue source of isoprene are presented. Our model is a first step towards new guidelines for the breath gas analysis of isoprene and is expected to aid further investigations regarding the exhalation, storage, transport and biotransformation processes associated with this important compound.Comment: 14 page

Volume of the effect compartment in simulations of neuromuscular block

BACKGROUND: The study examines the role of the volume of the effect compartment in simulations of neuromuscular block (NMB) produced by nondepolarizing muscle relaxants. METHODS: The molar amount of the postsynaptic receptors at the motor end plates in muscle was assumed constant; the apparent receptor concentration in the effect compartment is the ratio of this amount and the volume arbitrarily assigned to the effect compartment. The muscle relaxants were postulated to diffuse between the central and the effect compartment and to bind to the postsynaptic receptors. NMB was calculated from the free concentration of the muscle relaxant in the effect compartment. RESULTS: The simulations suggest that the time profiles of NMB and the derived pharmacokinetic and pharmacodynamic variables are dependent on the apparent receptor concentration in the effect compartment. For small, but not for large, volumes, times to peak submaximal NMB are projected to depend on the magnitude of NMB and on the binding affinities. CONCLUSION: An experimental design to estimate the volume of the effect compartment is suggested