Does periconceptional multivitamin use reduce the risk of neural tube defects associated with other birth defects? Data from two population-based case-control studies

The role of periconceptional folic acid in the prevention of neural tube defects (NTDs) is well established. However, it is not clear whether a protective effect exists for the subset of nonsyndromic NTD with other “unrelated” major structural birth defects (NTD-multiples). This question is important to investigate because of shared pathogenetic mechanisms between NTD and other types of birth defects, and because of the epidemiologic differences that have been shown between NTD-multiples and NTD-singles. We analyzed data from two population-based case-control studies of NTDs, Atlanta 1968–1980, and California 1989–1991, to assess whether periconceptional multivitamin use reduces the risk of NTD-multiples. Maternal vitamin histories were assessed for 47 and 65 NTD-multiples cases and 3,029 and 539 control babies in Atlanta, and California, respectively. There was a substantial risk reduction associated with periconceptional multivitamin use (−3 to +3 months) for NTD-multiples (pooled odds ratio = 0.36, 95% C.I. 0.18–0.72) that persisted after adjustment for maternal race/ethnicity and education. Also, no specific types of NTDs or NTDs with specific defects explained the risk reduction with vitamin use. These data suggest that multivitamins reduce the risk of nonsyndromic NTD cases associated with other major birth defects. The implication of this finding for the role of vitamins in the prevention of non-NTD birth defects should be further explored. © 1996 Wiley-Liss, Inc.     

Influence of Diabetes Mellitus and Glycaemic Control on the Characteristics and Outcome of Common Infections

The aim of the present study was to elucidate the effect of diabetes and metabolic control on the presentation, sources, pathogens and outcome of common infections. Of 515 patients admitted to three departments of internal medicine because of a suspected acute infection, 132 (26 %) had diabetes mellitus. Osteomyelitis was diagnosed in 3 % of the diabetic patients and in 1 % of patients without diabetes, and infection of the extremities in 7 % and 0 %, respectively (p = 0.003). Klebsiella sp. caused 24 % of urinary tract infections in diabetic patients, versus 13 % in patients without diabetes (p = 0.1). The percentage of Staphylococcus aureus infections in diabetic patients was 10 % versus 5 % in non-diabetic patients (p = 0.06). The gross mortality rate in the diabetic patients was 10 %, and in patients without diabetes, 12 %. In patients without fatal underlying disorders, mortality in the diabetic patients was 10 % (2 % in patients with glycosylated haemoglobin (GHb) lower than median, and 17 % in patients with GHb higher than median) and in the non-diabetic patients 4 % (p = 0.04). Five factors were independently and significantly related to mortality in diabetic patients: acute respiratory distress (very large odds-ratio [OR]), coma (OR 3.8, 95 % confidence interval [CI] 1.0–14.3), GHb above the median (OR 3.3, 95 % CI 1.8–6.2), the interaction between GHb and absence of a severe underlying disorder (OR 12.0, 95 % CI 2.9–50.7) and duration of diabetes (OR of 1.072 for 1-year increment, and 1.42 for a 5-year increment). Choice of empiric antibiotic treatment in diabetic patients with suspected bacterial infection should take into account the preponderance of Klebsiella sp. and Staphylococcus aureus infections. The present results favour an association between poor glycaemic control and a fatal outcome of infectious diseases in diabetic patients.     

基于络病理论运用络虚通补法治疗糖尿病骨质疏松

糖尿病骨质疏松(DOP)作为糖尿病(DM)主要慢性并发症,起病隐匿,发病机制复杂,与高血糖状态、氧化应激、相关细胞因子、激素水平变化、降糖药物的使用等多种因素综合作用有关,病情缠绵难愈,严重影响患者生命质量。中医学认为DOP病位在骨,与肾脾肝脏腑功能失常,进而导致气虚血瘀密切相关,治疗多立足于调补脏腑、行气化瘀,使骨得其养从而改善症状。本文基于络病理论,针对DOP骨络脏腑亏虚、邪瘀阻络的主要病机,探讨络虚通补法在防治糖尿病骨质疏松DOP中的应用,以期为临床防治DOP提供更多思路与理论参考。     

Rank-ordered regulation of motor units

Myoelectric signals were detected from the tibialis anterior muscle of 5 subjects with a quadrifilar needle electrode while the subjects generated isometric forces that increased linearly with time (10% of maximal voluntary contraction/s) up to maximal voluntary level. Motor unit firing rates were studied as a function of force throughout the full range of muscle force output. The relationship between force and firing rate was found to contain three distinct regions. At recruitment and near maximal force levels, firing rates increased more rapidly with force than in the intermediate region. Furthermore, in the regions with rapid increases, the rate of change of firing rate was correlated to the recruitment threshold, with higher recruitment threshold motor units displaying greater rates of change. In the intermediate region, all motor units had similar rates of change of firing rate. A weak positive correlation was found between initial firing rate and recruitment threshold. Firing rates of motor units at any instant were found to be ordered according to the recruitment order: at any given time in the contraction motor units with lower recruitment thresholds had higher firing rates than units with higher recruitment thresholds. Firing rates of all motor units were observed to converge to the same value at maximal forces. Mechanisms underlying motor unit recruitment and firing rate modulation are discussed in the context of a conceptual model. © 1996 John Wiley & Sons, Inc.     

Motor control after spinal cord injury: Assessment using surface EMG

The brain motor control assessment (BMCA) protocol is a comprehensive multichannel surface EMG recording used to characterize motor control features in persons with upper motor neuron dysfunction. Key information is contained in the overall temporal pattern of motor unit activity, observed in the EMG (RMS) envelope. In paralysis, a rudimentary form of suprasegmental control of tonic and phasic reflexes can be demonstrated. EMG patterns evoked by voluntary and passive maneuvers and by volitional modulation of reflex responses reveal features of motor control not apparent in the clinical examination. Such subclinical findings may explain paradoxically different responses in apparently similar SCI subjects, and may be used to monitor spontaneous or induced changes. The recording protocol, examples of EMG patterns, and their prevalence in 40 spinal cord injured (SCI) subjects are presented, and compared with 5 healthy subjects. © 1996 John Wiley & Sons, Inc.     

A non-linear optimal greenhouse control problem with heating and ventilation

A simplified non-linear dynamic model of greenhouse crop growth with constraints on the state and the control signal is considered. The weather is assumed to be known. The optimization criterion is to minimize the heating and ventilation cost. In this paper a novel solution is presented for the case when both the heating cost and the ventilation cost are included in the criterion. Important properties of the optimal solutions are clarified. It is found that neighbouring maxima and minima of a particular function of the outside temperature, the solar radiation and the heat transfer coefficient decide whether heating or ventilation has to be applied. A numerical example is given.     

Linear quadratic optimal model-following control of a helicopter in hover

Presented are results of a study of the application of linear quadratic optimal model-following control applied to a Bell 205 helicopter in hover. The primary objective of good in-flight stability robustness and performance was accomplished via singular value analysis using perturbed systems. Nominal aircraft models were compared with experimental data and discrepancies quantified in a robustness criterion. Current military handling quality requirements were specified as a target model to be followed. The linear quadratic optimal control and command feedforward was found suitable for these requirements. Design analyses enabled consideration of the tuning process, where effects of variations in selected tuning parameters demonstrated their sensitivity to the design.     

Pollution control and the dynamics of the firm: The effects of market-based instruments on optimal firm investments

This contribution belongs to a category of papers that attempts to determine the effects of environmental regulation on the growth of an individual firm. It extends the existing literature in at least two ways. First, our pollution function explicitly deals with the fact that it is more difficult to reduce pollution by abatement activities when pollution is already low. Second, according to our knowledge it is for the first time that marketable pollution permits are incorporated in a dynamic model of the firm. In the paper we establish the effects of a pollution tax and marketable permits on the behaviour of the firm. For the tax model as well as the marketable permits model we prove that the steady state is stable and approached monotonically and we derive formulae for optimal investment policies. Owing to non-zero cross-effects in the pollution function, comparative statics analysis shows that an increase in the pollution tax rate or an increase in the permit price does not necessarily lead to a decrease in pollution. Furthermore, a condition is obtained under which long-run firm behaviour is the same when either a tax or marketable permits are imposed.     

Rotational speed tracking for hydraulic-motor-driven machine-tools

The objective of this work is to design and compare control strategies for tracking certain velocity time functions prescribed for the speed variation of a hydraulic motor axis. Continuous velocity reference trajectories with finitely many acceleration discontinuities are treated. The model for the dynamics of the coupled motor—work-table model is non-linear and linearization has proven to be inadequate for describing the qualitative behaviour of the system. We show that the use of non-linear models increases the stability and accuracy of the control. Exact and approximate techniques are developed, applied and compared whenever possible. The approximate approach leads to a bilinear-quadratic optimal control problem whose solution, obtained through a power series expansion, provides, explicit formulae for general non-linear optimal tracking approximation.