Total Serum Zinc (TSZn) and albumin were determined, and low molecular weight serum Zn measured by radiochemical UltraFiltration (UFSZn) in healthy Dutch infants and children, and in samples obtained from those with diseases that are expected to alter TSZn. Our control TSZn values, 10.2 +/- 3.5 mumol/L, were low compared to those reported in the literature. Variation in serum albumin could not explain this: No correlation of TSZn with serum albumin was found (p > 0.5). Likely explanations are the nonfasting state and the stress owing to hospital surroundings at the time of sampling. A range of other influences not registered may be active and are discussed. No significant age-dependence was found (p < 0.8). Boys over 9 yr of age showed higher TSZn compared with girls of the same age (p < 0.08). In a separate experiment a 17% decrease in TSZn was demonstrated by food intake (eggs). These results support the opinion that TSZn is of little value to measure Zn status. There was no discrimination in TSZn between healthy subjects and patients. Our UFSZn values, 0.28 +/- 0.13 mumol/L in the controls as well as in the patients, were correlated with TSZn and therefore not a suitable alternative for the measurement of TSZn as parameter to determine the Zn status. The UFSZn was not correlated with serum albumin (p < 0.7). UFSZn values were higher in infants (p < 0.01), no sex dependence was found. We conclude that TSZn as well as UFSZn are of limited clinical relevance.

Optimal control simulations have shown that both musculoskeletal dynamics and physiological noise are important determinants of movement. However, due to the limited efficiency of available computational tools, deterministic simulations of movement focus on accurately modelling the musculoskeletal system while neglecting physiological noise, and stochastic simulations account for noise while simplifying the dynamics. We took advantage of recent approaches where stochastic optimal control problems are approximated using deterministic optimal control problems, which can be solved efficiently using direct collocation. We were thus able to extend predictions of stochastic optimal control as a theory of motor coordination to include muscle coordination and movement patterns emerging from non-linear musculoskeletal dynamics. In stochastic optimal control simulations of human standing balance, we demonstrated that the inclusion of muscle dynamics can predict muscle co-contraction as minimal effort strategy that complements sensorimotor feedback control in the presence of sensory noise. In simulations of reaching, we demonstrated that nonlinear multi-segment musculoskeletal dynamics enables complex perturbed and unperturbed reach trajectories under a variety of task conditions to be predicted. In both behaviors, we demonstrated how interactions between task constraint, sensory noise, and the intrinsic properties of muscle influence optimal muscle coordination patterns, including muscle co-contraction, and the resulting movement trajectories. Our approach enables a true minimum effort solution to be identified as task constraints, such as movement accuracy, can be explicitly imposed, rather than being approximated using penalty terms in the cost function. Our approximate stochastic optimal control framework predicts complex features, not captured by previous simulation approaches, providing a generalizable and valuable tool to study how musculoskeletal dynamics and physiological noise may alter neural control of movement in both healthy and pathological movements.

ABSTRACT. To establish a parameter for zinc status that is independent of the occurrence of infection, we studied the effects of low dietary zinc and endotoxin in weaning rats 21 d after 65Zn intubation. We monitored aspects of zinc status (tissue zinc content, 65Zn distribution, and specific 6sZn activity in tissue) and 65Zn metabolism (absorption, excretion, and biologic half-life), as well as weight gain, feed conversion, and dietary zinc use. The low zinc diet induced classical deficiency with losses of bone zinc, resulting in lower content (7.4 versus 19.6 pmol) and higher spec act (17 versus 8 kBqlpmo1). Other tissue-specific and plasma-specific activities were also higher (overall, 20 versus 8 kBq/pmol; plasma, 8 versus 4 kBq/pmol). Endotoxin caused lower total-plasma zinc (0.04 versus 0.05 pmol) but did not affect spec act (4 kBq/pmol); combined endotoxin and low-zinc diet caused low total-plasma zinc (0.01 pmol) and high spec act, as did the low-zinc diet alone (12 kBq/pmol). We conclude that plasma-spec act (or stable isotope enrichment) can serve as an index for nutritional zinc status during recurrent infection. (Pediatr Res 28: 332-335,1990) Groups of children suffering from recurrent upper respiratory tract infection were found to have low hair zinc (1) and high urinary zinc values, as well as lower SD scores of height for age (2). However, these parameters are considered poor indicators of the zinc status of individual patients (3). Moreover, the relationship between zinc status and the health of a child is ambiguous: deficiency either predisposes to recurrent infection (4) or is induced by it (5). In this study involving young male rats, we monitored the zinc status as affected by low dietary zinc and repeated endotoxin exposure. Weight gain, efficiency of feed conversion, and dietary zinc use were measured. Zinc status was characterized by tissue zinc contents, tissue 65Zn distribution, and specific 65Zn activities (65Zn activity per mol zinc). Regulation of the zinc status was measured by whole-body 65Zn absorption, excretion, and turnover. On the basis of these results, we evaluated the suitability of the parameters studied to discriminate between low zinc intake, endotoxin exposure, and their combination.