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At least 955 records · Page 53Linked to original sources
PubMed1988

[Experimental simulation study on EC-IC bypass--Part 1: Optimum conditions for bypass on the basis of hydraulic and theoretical models with autoregulation mechanism].

There have been several reports about unexpected occlusive change of stenotic lesion in the internal carotid artery (ICA) or middle cerebral artery (MCA) following bypass surgery, rupture or formation of an aneurysm after carotid ligation and ICA EC-IC bypass for the treatment of inaccessible ICA aneurysm. These suggest that operation for one vessel causes hemodynamic changes in others, not only near the operation site but in remote sites. Although complete hemodynamic analysis in the brain and quantitative speculation of the possible effect of a cerebrovascular operation are essential to prevent these complications, these measures are usually very difficult to carry out because multiple factors are related mutually in complex fashion in a living body. One effective means to simulate these changes would be the use of a vascular model. A hydraulic model of unilateral ICA stenosis (resistance of stenosis: R) with EC-IC bypass (resistance of bypass: Rby) has been manufactured with silicone and glass tubes. Peripheral vascular resistance (Rp) is adjusted to obtain an arterial flow of 180 ml/min at poststenotic pressures of 60, 70, 80, 90, and 100 mmHg. To simulate the autoregulation mechanism, appropriate Rp is selected for each combination of R and Rby so as to make, as far as possible, a hemispheric flow (sum of stenosis flow and bypass flow) of 180 ml/min. The Rp with the lowest value (60/180 mmHg/ml/min) is to be chosen in flow conditions of lower than 180 ml/min, where autoregulation is no longer functioning. Twelve kinds of stenosis segments with an inner diameter from 0.37 to 2.59 mm are prepared and used in the models.(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebral Revascularization↗
PubMedDate not supplied

Theoretical model testing to identify personality variables effecting preventive behaviors.

To test the preventive behavior model, the impact of perceived barriers and benefits and health value orientations on two health care activities (smoking and exercise) was examined. Data from 76 subjects who had taken part in a health screening program were analyzed using regression analysis. A reduced empirical model for exercise resulted, explaining 46% of the variance. However, only one variable that accounted for 7% of the variance was significant in explaining smoking behavior. Significant personality variables in the exercise model provide clues toward understanding psychological factors that may be operating to influence an individual's participation in health care activities.

Adolescent↗
PubMedDate not supplied

Theoretical modeling to predict physiological indicants of cardiac preventive behaviors.

The Preventive Behavior Model was tested and expanded to explore the influence of perceived barriers, benefits, health value orientations, and certain health care activities on physiological outcomes. Data from 41 subjects from a health screening program were analyzed. Four empirical models resulted, explaining 39%, 45%, 66%, and 47% of the variance in cholesterol, high density lipoprotein, systolic blood pressure, and diastolic blood pressure, respectively. Significant variables in the four models provide important clues for understanding factors that influence physiological outcomes of risk factor reduction.

Adult↗
PubMed1986

Carboxylate groups in bovine somatotropin involved in growth promoting activity. Theoretical models based upon individual kinetic constants to interpret the activity decay after chemical modification.

Modification of approximately one fifth of the carboxylate groups in bovine somatotropin with a water soluble carbodiimide caused loss of growth promoting potency pointing to the existence of residues related to the hormonal activity among those belonging to a fast reacting set. A sigmoidal curve was obtained whether the inactivation process was referred to reaction time or degree of modification. Isoelectrofocusing of derivatives released the native hormone from responsibility for the biological potency exerted by preparations with 1.5-2.6 modified carboxylate groups. Examination of the individual reaction kinetics of the 11 fast reacting residues, in turn, excluded the possibility of the sigmoidal character of the inactivation curve being caused by a nonexponential disappearance of essential residues, as a possible consequence of the chemical modification of others. According to synthetic models, the experimental curve may be the consequence of the effect of cumulative modification of 2 or 3 out of a set of 3 to 8 relevant residues.

Carboxypeptidases↗
PubMedDate not supplied

[Theoretical model of the B-Z transition in DNA with an arbitrary sequence].

A statistical-mechanical model is suggested that makes it possible to describe the B-Z transition in DNA with an arbitrary sequence of nucleotides. The key point consists in allowance for the fact that each base pair can assume one of the two states with different energies. One of these states corresponds to the standard Z-form with purines in the syn conformation and pyrimidines in the anti conformation. However, in natural DNA sequences such standard base-pair conformations should be interrupted by energetically unfavorable conformations (syn for pyrimidines and anti for purines). Open regions and cruciform structures are also allowed for in the model. The probabilities of formation of the Z-form stretches, open regions and cruciform structures have been calculated for different values of parameters for pBR322 and pAO3 DNA.

Base Sequence↗