Trygg Hansas Forskningsstiftelse

In two recent papers, Granger and Ding (1995a,b) considered long return series that are first differences of logarithmed price series or price indices. They established a set of temporal and distributional properties for such series and suggested that the returns are well characterized by the double exponential distribution. The present paper shows that a mixture of normal variables with zero mean can generate series with most of the properties Granger and Ding singled out. In that case, the temporal higher-order dependence observed in return series may be described by a hidden Markov model. Such a model is estimated for ten subseries of the well-known S&P 500 return series of about 17,000 daily observations. It reproduces the stylized facts of Granger and Ding quite well, but the parameter estimates of the model sometimes vary considerably from one subseries to the next. The implications of these results are discussed. © 1998 John Wiley & Sons, Ltd.

To investigate the concentrations of reduced and total glutathione in relation to the muscle free amino acid pattern in critically ill patients and matched healthy controls. Prospective case control. University hospital intensive care unit (ICU). Eleven critically ill patients in the intensive care unit were studied after a stay of at least 4 days. Eleven age- and gender-matched metabolically healthy patients undergoing elective surgical procedures served as controls. None. Reduced and total glutathione concentrations were determined in skeletal muscle, in plasma, and in whole blood, together with muscle free amino acid concentrations. In the ICU group, reduced and total glutathione values were 57% and 62%, respectively, of the values seen in the control group (p < .001). In addition, a decreased ratio between reduced and total glutathione compared with the controls was seen (0.80 as compared with 0.91, p < .001). The glutamine concentration in skeletal muscle in the ICU group was 72% lower compared with that value seen in healthy controls (p < .001). Correlations were found between the concentrations of glutamine and the total muscle glutathione (r2 = .46, p < .001), as well as between glutamine and the ratio of reduced and total glutathione (r2 = .45, p < .001) in skeletal muscle, suggesting that the redox status of glutathione and the glutamine status of the tissue are related. Critical illness is associated with alterations in muscle glutathione metabolism. The muscle-reduced glutathione concentrations decrease and, in addition, the ratio between reduced and total glutathione decreases, indicating a situation of oxidative stress in this tissue. This decrease may impair the defense of muscle against oxygen free radicals and influence amino acid transport, thus contributing to the loss of balance between protein synthesis and protein degradation that is characteristic of protein catabolism.