The K-complex and slow oscillation in terms of a mean-field cortical model.

We use a mean-field macrocolumn model of the cerebral cortex to offer an interpretation of the K-complex of the electroencephalogram to complement those of more detailed neuron-by-neuron models. We interpret the K-complex as a momentary excursion of the cortex from a stable low-firing state to an unstable high-firing state, and hypothesize that the related slow oscillation can be considered as the periodic oscillation between two meta-stable solutions of the mean-field model. By incorporating a Hebbian-style learning rule that links the growth in synapse strength to fluctuations in soma potential, we demonstrate a self-organization behaviour that draws the modelled cortex close to the edge of stability of the low-firing state.

The sleep cycle modelled as a cortical phase transition.

We present a mean-field model of the cortex that attempts to describe the gross changes in brain electrical activity for the cycles of natural sleep. We incorporate within the model two major sleep modulatory effects: slow changes in both synaptic efficiency and in neuron resting voltage caused by the ∼90-min cycling in acetylcholine, together with even slower changes in resting voltage caused by gradual elimination during sleep of somnogens (fatigue agents) such as adenosine. We argue that the change from slow-wave sleep (SWS) to rapid-eye-movement (REM) sleep can be understood as a first-order phase transition from a low-firing, coherent state to a high-firing, desychronized cortical state.

Particulate contamination in plastic ampoules.

Plastic ampoules of Water for Injections, JP, and Injection Sodium Chloride, JP, were investigated to determine their particle load. Four batches were studied. The ampoules were twist-opened as they would be in the clinical setting and the total particle load, both inherent and that created in opening, was determined by reading the contents with a HIAC 420 particle counter with a CMB 60 sensor.

Particulate contamination of Australian ampoules.

Theoretical predictions and computer simulations indicate that it may be impossible to achieve values of the coefficient of variation usually found in large volume parenterals (LVP) when the intrinsic particulate contamination in small volume parenterals (SVP) is investigated. Snap-opened ampoules from Australian manufacturers containing 5, 10 or 20 ml Water for Injections or Sodium Chloride Injection had a high level of particulate contamination, although within the USP XXI SVP limits. Heat-opened ampoules had much lower levels of contamination which were generally below the official LVP limits.

Oxygen tension measurement using an automatic blood gas analyser.

Two different methods of assessing the reliability of the oxygen electrode of one model of an automatic blood gas analyser (BGA) have been studied. In the first, a single automatic BGA was assessed by using outdated bank blood which was pumped around a small extracorporeal circuit into which known gas mixtures were passed. Oxygen tension was varied between 2 and 16 kPa.