Solvers for the cardiac bidomain equations

The bidomain equations are widely used for the simulation of electrical activity in cardiac tissue. They are especially important for accurately modeling extracellular stimulation, as evidenced by their prediction of virtual electrode polarization before experimental verification. However, solution of the equations is computationally expensive due to the fine spatial and temporal discretization needed. This limits the size and duration of the problem which can be modeled. Regardless of the specific form into which they are cast, the computational bottleneck becomes the repeated solution of a large, linear system. The purpose of this review is to give an overview of the equations and the methods by which they have been solved. Of particular note are recent developments in multigrid methods, which have proven to be the most efficient.

Hepatitis B immunization in low birthweight infants: do they need an additional dose?

AIM

To determine the influence of gestation and weight on the development of protective anti-HB levels and geometric mean titres after three doses of HBV vaccine and to ascertain the need for a fourth dose in low birthweight infants.

METHODS

Hepatitis B vaccine (Enivac HB, Panacea Biotec Ltd., India) was given to 82 preterm (PT) and 60 term intrauterine growth-retarded (T-IUGR) infants at birth and at 6, 10 and 14wk of life.

RESULTS

Protective anti-HB levels (>10 mIU/ml) were reached in 86.6% (71/82) of PT infants and 96.7% (58/60) of T-IUGR infants after three doses of HBV vaccine (p = 0.044). The odds of having a protective response after the third dose of HBV vaccine was 1.25 (95% CI 1.02-1.53) with every one-week increase in gestation (p = 0.032). Birthweight was not associated with the development of a protective immune response. After the third dose, only 66.7% (8/12) of the PT infants whose mothers had anti-HB antibodies, developed protective anti-HB levels compared with 90% (63/70) of those with no maternal antibodies (p = 0.028). In PT infants after the fourth dose, there was a significant increase in the proportion of infants with protective antibody levels (8.6%, 95% CI 0.6-16.6%) among those with no maternal antibodies and 12.2% overall (95% CI 6.0-21.3) (p = 0.031 to 0.002) over that reached with the third dose. Administration of the fourth dose to T-IUGR infants did not confer such a benefit.

CONCLUSION

In HBV-endemic areas, PT infants, irrespective of their birthweights, may benefit from an additional dose of hepatitis B vaccine in a schedule starting at birth. This approach will prevent vertical transmission and bring their immune response up to par with term infants. Term intrauterine growth-retarded infants should be vaccinated as per the schedule recommended for normal term infants. However, studies in other settings with different vaccine formulations and a longer follow-up period will be required before this strategy can be practised more widely.

The selector gene cut represses a neural cell fate that is specified independently of the Achaete-Scute-Complex and atonal

The peripheral nervous system (PNS) of Drosophila offers a powerful system to precisely identify individual cells and dissect their genetic pathways of development. The mode of specification of a subset of larval PNS cells, the multiple dendritic (md) neurons (or type II neurons), is complex and still poorly understood. Within the dorsal thoracic and abdominal segments, two md neurons, dbd and dda1, apparently require the proneural gene amos but not atonal (ato) or Achaete-Scute-Complex (ASC) genes. ASC normally acts via the neural selector gene cut to specify appropriate sensory organ identities. Here, we show that dbd- and dda1-type differentiation is suppressed by cut in dorsal ASC-dependent md neurons. Thus, cut is not only required to promote an ASC-dependent mode of differentiation, but also represses an ASC- and ato-independent fate that leads to dbd and dda1 differentiation.