A computationally efficient electrophysiological model of human ventricular cells.

Recent experimental and theoretical results have stressed the importance of modeling studies of reentrant arrhythmias in cardiac tissue and at the whole heart level. We introduce a six-variable model obtained by a reformulation of the Priebe-Beuckelmann model of a single human ventricular cell. The reformulated model is 4.9 times faster for numerical computations and it is more stable than the original model. It retains the action potential shape at various frequencies, restitution of action potential duration, and restitution of conduction velocity. We were able to reproduce the main properties of epicardial, endocardial, and M cells by modifying selected ionic currents. We performed a simulation study of spiral wave behavior in a two-dimensional sheet of human ventricular tissue and showed that spiral waves have a frequency of 3.3 Hz and a linear core of approximately 50-mm diameter that rotates with an average frequency of 0.62 rad/s. Simulation results agreed with experimental data. In conclusion, the proposed model is suitable for efficient and accurate studies of reentrant phenomena in human ventricular tissue.

Wave propagation in an excitable medium with a negatively sloped restitution curve.

Recent experimental studies show that the restitution curve of cardiac tissue can have a negative slope. We study how the negative slope of the restitution curve can influence basic processes in excitable media, such as periodic forcing of an excitable cell, circulation of a pulse in a ring, and spiral wave rotation in two dimensions. We show that negatively sloped restitution curve can result in instabilities if the slope of the restitution curve is steeper than -1 and report different manifestations of this instability. (c) 2002 American Institute of Physics.

Spiral waves in excitable media with negative restitution.

We study numerically the dynamics of spiral waves in an excitable medium with negative restitution. For our study we use two models of the excitable medium: a cellular automaton and a reaction-diffusion model. There are no significant effects of negative restitution as long as the slope of the restitution curve is less steep than -1. In media with slopes steeper than -1, the dynamics of spiral waves can change significantly: (1) the average restitution time jumps to a value where the slope of the restitution curve is about -1; (2) spiral waves can break up into turbulent patterns. We discuss a possible connection between such instabilities and fibrillation in atrial tissue.

The diversity of rearranged immunoglobulin heavy chain variable region genes in peripheral blood B cells of preterm infants is restricted by short third complementarity-determining regions but not by limited gene segment usage.

The immunoglobulin diversity is restricted in fetal liver B cells. This study examined whether peripheral blood B cells of extremely preterm infants show similar restrictions (overrepresentation of some gene segments, short third complementarity-determining regions [CDR3]). DNA of rearranged immunoglobulin heavy chain genes was amplified by polymerase chain reaction, cloned, and sequenced. A total of 417 sequences were analyzed from 6 preterm infants (25-28 weeks of gestation), 6 term infants, and 6 adults. Gene segments from the entire V(H) and D(H) gene locus were rearranged in preterm infants, even though the D(H)7-27 segment was overrepresented (17% of rearrangements) compared to term infants (7%) and adults (2%). CDR3 was shorter in preterm infants (40 +/- 10 nucleotides) than in term infants (44 +/- 12) and adults (48 +/- 14) (P <.001) due to shorter N regions. Somatic mutations were exclusively found in term neonates and adults (mutational frequency 0.8% and 1.8%). We conclude that preterm infants have no limitations in gene segment usage, whereas the diversity of CDR3 is restricted throughout gestation.

[Functional behavior patterns of the pylorus in duodeno-gastric reflux]. / Funktionelle Verhaltensformen des Pylorus bei duodeno-gastralem Reflux.

There are relations between function of the pylorus and the appearance of duodeno-gastric reflux. However, much speaks for the fact that the pylorus alone is not able to prevent duodeno-gastric reflux. In the problem of the causes of reflux also the motoric behaviour of the upper duodenum must be taken into consideration.

[Post-cholecystectomy condition: duodeno-gastric reflux and bile acid concentration in the gastric juice]. / Zustand nach Cholezystektomiel duodenogbastraler Reflux und Gallensäurekonzentrationen im Magensaft.

In cholecystectomized patients highly significantly more frequently a duodenogastric reflux was found than in a group of patients with a healthy abdomen and a group of patients with cholelithiasis. The average concentration of bile acid in the gastric juice was after the removal of the gall-bladder manifoldly higher than in the control groups. The number of patients with concentrated reflux was also highly significantly larger than in patients with cholelithiasis not operated on and in patients with a healthy abdomen. Despite the high reflux rate and the high concentration of the bile acids influencing on the mucous membrane of the stomach the number of patients with ulcera ventriculi was not significantly larger than in a group of not cholecystectomized persons. These observations plead for the fact that the bile acids in the duodenogastric reflux alone are not to be regarded as an ulcerogenic agent, but that perhaps other components of the duodenal juice have to be considered as causes of lesions of the gastric mucous membrane.

[Mitral valve disorders and bile duct diseases]. / Mitralvitien und Gallenwegserkrankungen

In a number of cases of post-mortem examinations of patients with mitral valve defects a morbidity rate of cholelithiasis of 41.3 per cent was found, above all by the larger morbidity rate in younger women. Up to the 50th year it was 37.1 per cent at an average death age of 40.7 years. Is was conspicuous that more women who had not been delivered suffered from cholelithiasis than those ones who had been delivered (68.9 per cent of the nulliparae). Before the 50th year 55.6 per cent of the women who had not been delivered suffered from such a disease at an average death age of 39.3 years. Probably in these women the heart disease was so severe that there did not develop a gravidity.