Agonist-induced calcium waves in oscillatory cells: a biological example of Burgers' equation

Oscillations in cytosolic Ca2+ concentrations in living cells are often a manifestation of propagating waves of Ca2+. Numerical simulations with a realistic model of inositol 1,4,5-trisphosphate (IP3)-induced Ca2+ wave trains lead to wave speeds that increase linearly at long times when (a) IP3 levels are in the range for Ca2+ oscillations, (b) a gradient of phase is established by either an initial ramp or pulse of IP3, and (c) IP3 concentrations asymptotically become uniform. We explore this phenomenon with analytical and numerical methods using a simple two-variable reduction of the De Young-Keizer model of the IP3 receptor that includes the influence of Ca2+ buffers. For concentrations of IP3 in the oscillatory regime, numerical solution of the resulting reaction diffusion equations produces nonlinear wave trains that shows the same asymptotic growth of wave speed. Due to buffering, diffusion of Ca2+ is quite slow and, as previously noted, these waves occur without appreciable bulk movement of Ca2+. Thus, following Neu and Murray, we explore the behavior of these waves using an asymptotic expansion based on the small size of the buffered diffusion constant for Ca2+. We find that the gradient in phase of the wave obeys Burgers' equation asymptotically in time. This result is used to explain the linear increase of the wave speed observed in the simulations.     

Percutaneous transluminal angioplasty of an innominate artery occlusion

A middle-aged woman presented with recent-onset left hemiparesis and right subclavian steal syndrome. She was found to have an obstructed innominate artery. We successfully performed balloon angioplasty of the occluded innominate artery and encountered no complications during follow-up of currently 8 months.     

Biochemical basis for increased susceptibility to Cidofovir of herpes simplex viruses with altered or deficient thymidine kinase activity

It has been observed that herpes simplex virus mutants with deficient or altered thymidine kinase activity are more susceptible to Cidofovir (CDV; 1-[(S)-3-hydroxy-2-(phosphonomethoxy)propyl]cytosine dihydrate) in tissue culture than are the parental strains. During infection of cells, the elevation of the dCTP pool by thymidine kinase mutant viruses is less than that induced by the wild-type virus. The competition between CDV diphosphate and dCTP at the viral polymerase is therefore changed in favor of CDV diphosphate, enhancing its activity.     

Adverse environmental conditions in the respiratory and medical ICU settings

Sleep deprivation and fragmentation occurring in the hospital setting may have a negative impact on the respiratory system by decreasing respiratory muscle function and ventilatory response to CO2. Sleep deprivation in a patient with respiratory failure may, therefore, impair recovery and weaning from mechanical ventilation. We postulate that light, sound, and interruption levels in a weaning unit are major factors resulting in sleep disorders and possibly circadian rhythm disruption. As an initial test of this hypothesis, we sampled interruption levels and continuously monitored light and sound levels for a minimum of seven consecutive days in a medical ICU, a multiple bed respiratory care unit (RCU) room, a single-bed RCU room, and a private room. Light levels in all areas maintained a day-night rhythm, with peak levels dependent on window orientation and shading. Peak sound levels were extremely high in all areas representing values significantly higher than those recommended by the Environmental Protection Agency as acceptable for a hospital environment. The number of sound peaks greater than 80 decibels, which may result in sleep arousals, was especially high in the intensive and respiratory care areas, but did show a day-night rhythm in all settings. Patient interruptions tended to be erratic, leaving little time for condensed sleep. We conclude that the potential for environmentally induced sleep disruption is high in all areas, but especially high in the intensive and respiratory care areas where the negative consequences may be the most severe.