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At least 55 records · Page 3Linked to original sources
PubMed1988

Activated carbon as a biological model: comparison between activated carbon adsorption and oil-water partition coefficient for drug activity correlation.

Octanol-water partition coefficients have been used as a principal parameter for the analysis of quantitative structure-activity relationships (QSAR). With ionized drugs, however, the correlation is not impressive. Although clinical local anesthetics exist mainly in the ionized form at physiological pH, the nerve-blocking potency is correlated with the oil-water partition coefficients of the un-ionized species. In the present report, the adsorption of 18 local anesthetics onto activated carbon surfaces was compared with oil-water partition coefficients for correlation with the minimum nerve-blocking (MBC) potency. The log octanol-water partition coefficients showed large differences between the charged and uncharged species (lidocaine: 0.49 and 1.82, procaine: -0.56 and 1.74, respectively), whereas the log carbon surface adsorbabilities showed much smaller differences (lidocaine: 3.00 and 3.04, and procaine 2.95 and 3.00, respectively). An excellent correlation was found between the log carbon surface adsorption and the log MBC values in both ionized and un-ionized drugs.

Adsorption↗
PubMed1979

A biologic model of parasystole.

The electrotonic interactions of a parasystolic pacemaker with ventricular responses to the normal pacemaker across an area of depressed excitability were simulated in a model consisting of strands of canine Purkinje fibers mounted in a sucrose gap preparation. Experiments were conducted to study the patterns of ectopic activity that result from entrainment of the "ectopic" pacemaker (EP) on one side of the sucrose gap by evoked responses (sn) on the other side of the gap. When one-way conduction ("entrance block") was established, manipulations of the SN frequency and of the impedance between the two outer chambers resulted in periods of silence, concealed or manifest bigeminy, trigeminy and quadrigeminy, and periods of more complex patterns of group beating as the entrainment ratios changed. The results confirm the predictions of the previously described mathematical model that these patterns depend on the magnitude of the electrotonic influence of SN on the EP cycle length and also on the ratio of the intrinsic frequencies. These studies should help to distinguish between reentrant and parasystolic mechanisms in clinical arrhythmias.

Animals↗
PubMed1982

Sensitivity analysis of biological models.

An inhomogenous linear model of the lung mechanics system was selected for the demonstration of one of the methods of sensitivity analysis. Given the values of state variables, the sensitivity of the model makes possible a safe adjustment of coefficients, without leading to large errors of solution with even a small deviation in adjustment. Any mathematical model only represents a picture of basic and substantial dynamic properties and relations of a real object. By means of sensitivity analysis it is possible to obtain a faithful description of the real object's behavior by computing the simplest model solution, with knowing at the same time, by sensitivity analysis, the range of errors introduced by simplifications and approximations.

Computers↗
PubMed1998

Uterine artery blood flow velocity waveforms in pregnant women with müllerian duct anomaly: a biologic model for uteroplacental insufficiency.

OBJECTIVE: The purpose of this study was to determine whether there are demonstrable alterations in uterine artery blood flow in pregnant women with müllerian duct anomaly. STUDY DESIGN: Flow velocity waveforms obtained from the placental and nonplacental uterine arteries were studied at 18 to 24 weeks' gestational age in 15 pregnant women with müllerian duct anomaly and in 30 controls. The systolic/diastolic ratios were compared and correlated with the degree of placental laterality and perinatal outcome. RESULTS: Systolic/diastolic ratio in the uterine artery was abnormal in 80% of the cases and in 10% of controls (p < 0.0001). A completely lateral placenta was found in 10 of 15 women of the study group and only in 1 of the 30 controls (p < 0.0001). Women with müllerian duct anomaly had higher systolic/diastolic ratios in the nonplacental uterine artery than those with a normal uterus (median 4.3, range 2.0 to 7.4 vs median 2.8, range 2.0 to 4.0; p < 0.001). Twelve of 15 women of the study group had poor perinatal outcome compared with 4 of the 30 controls (p < 0.001). Among those women with poor perinatal outcome, 11 of 12 (92%) in the study group and only 1 of the 4 (25%) in the control group had an abnormal systolic/diastolic ratio in the uterine arteries (p < 0.05). CONCLUSION: There is a clear association between placental laterality and high systolic/diastolic ratio in the nonplacental uterine artery in pregnant women with müllerian duct anomaly who had poor perinatal outcome. This finding suggests that unilateral placental implantation could lead to functional exclusion of one uterine artery from the uteroplacental circulation and could explain pregnancy complications in women with developmental fusion defects of the uterus.

Abortion, Spontaneous↗