Application of light-emitting diodes (LEDs) in cultivation of phototrophic microalgae: current state and perspectives.

The quality and regulation of the incident light is crucial in microalgae cultivation processes. Depending on wavelength, spectrum, and intensity, growth characteristics and biochemical composition of these organisms vary. With mainly fluorescent lamps (FL) used previously for illumination, such variabilities could not be studied adequately due to their broad emission spectrum. In contrast, light-emitting diodes (LEDs) emit a very narrow wavelength band and enable flexible photobioreactor designs due to their small size. This review provides a condensed overview on the application of LEDs in microalgal cultivation processes. It summarizes the current availability and applicability of LED technologies as an illumination source for research-focused photobioreactor systems. A particular focus is the use of narrow-wavelength LEDs to address fundamental as well as applied aspects of light color on algae biomass and value-added compound formation. In this respect, the application of internal and external illumination systems is reviewed together with trends in the industrial use of LED systems to intensify algae process efficiency.

A system for automatic feedback control of plasma potassium concentration.

A system is described for automatic feedback control of plasma potassium concentration in experimental animals. Plasma potassium was monitored continuously and the signal compared with the desired plasma potassium concentration. The resulting error signal controlled the infusion rates of a concentrated potassium chloride solution (50 or 200 mmol litre-1) and a solution of 50% glucose with insulin 200 u litre-1. Plasma potassium was increased or decreased to the desired concentration at various rates, dictated by the controller constants. Increases were achieved significantly faster than reductions. The system may prove useful for elucidating the fate of infused potassium and for determining the optimum rate of insulin infusion in hyperkalaemia. If adapted for clinical use, it may find applications in the management of various abnormalities of potassium homeostasis.

Heparinization of samples for plasma ionized calcium measurement.

Maintenance of normal plasma ionized calcium concentration forms part of the management of the critically ill patient; it is, therefore, important to measure accurately plasma ionized calcium. We have compared the ionized calcium concentration of blood samples heparinized with a carefully measured amount of heparin with that of blood samples heparinized in the conventional fashion. The amount of heparin in the deadspace of a syringe was demonstrated to artifactually lower the plasma ionized calcium concentration. Samples for plasma ionized calcium measurement should be heparinized with a measured quantity of heparin, since the conventional technique introduces an unknown and probably excessive quantity of heparin into the syringe deadspace.

Anaesthesia for surgical occlusion of the basilar artery. A technique involving intra-operative awakening to allow neurological assessment.

A case is described of a giant fusiform aneurysm of the basilar artery which was treated successfully by proximal surgical occlusion of the artery. The anaesthetic management involved the intra-operative awakening of the patient in order to assess neurological function immediately after application of the clip. The difficulties involved in this type of surgery are discussed.

Computer applications in intravenous anaesthetic administration.

The place of computerization in intravenous anaesthesia delivery: Although total intravenous anaesthesia may have advantages over inhalational anaesthesia in certain circumstances, it has drawbacks from the point of view of feedback control. The ideal agent is not available, although di-isopropylphenol holds promise. There is an undefinable end-point. Inadequate dosage produces the extremely unpleasant phenomenon of intra-operative awareness. Future developments, it seems, should include the development of suitable intravenous agents and transducers of anaesthetic depth, rather than increasingly complicated control systems. It is extremely unlikely that a computer will replace the anaesthetist in the foreseeable future. The anaesthetist is still required for, amongst other things, specifying the desired depth of anaesthesia and varying it during the operation, and for responding to unforeseen crises. It may be hoped that, by liberating the anaesthetist from those tasks which can be automated, more time can be devoted to patient monitoring and other aspects of anaesthetic care, thereby improving patient safety. There is an undoubted place for computerized delivery of anaesthesia in teaching (particularly teaching pharmacokinetic principles) and in research (for standardization of anaesthetic depth).

Plasma ionized calcium during open-heart surgery.

Plasma ionized calcium has been measured in eighteen patients undergoing open heart surgery. No change in ionized calcium concentration was found during the period of cardiopulmonary bypass. In the early postbypass period, a wide range of ionized calcium concentrations was found, but this did not obviously affect myocardial performance. Factors influencing the ionized calcium concentration under these circumstances are discussed.

Choice of calcium salt. A comparison of the effects of calcium chloride and gluconate on plasma ionized calcium.

Equimolar quantities of calcium chloride and calcium gluconate produced similar changes in plasma ionised calcium concentration when injected intravenously into anaesthetised ferrets or when added to human blood in vitro. In vivo changes were followed with a calcium electrode positioned in the animal's aorta, and this showed that the ionisation of calcium gluconate on its first pass through the circulation is as great as that of calcium chloride. This does not support the common suggestion that calcium chloride is preferable to calcium gluconate because of its greater ionisation.

The effect of temperature on plasma ionized calcium measured in whole blood in vitro.

Plasma calcium ion concentration (cCa2+) in samples from 50 healthy volunteers was measured at four temperatures (21, 26, 31 and 37 degrees C) using a calcium electrode based on a neutral carrier ligand. A small negative correlation was found between temperature and cCa2+, the coefficient being -0.0017 mmol . l-1 . degrees C-1 (P less than 0.001). The significance of this in clinical, physiological and instrumentation fields is discussed. The effect on measured cCa2+ of overnight storage at 4 degrees C was slight, but did increase the variance of the results. It is suggested that the most accurate results of cCa2+ will be obtained from fresh samples measured at body temperature.

Hypotension following cimetidine administration during cardiopulmonary bypass.

Intravenous administration of cimetidine may occasionally cause profound hypotension. Cimetidine 200 mg was administered as a bolus injection to patients whilst on cardiopulmonary bypass and subsequent changes in systemic arterial pressure were recorded. A statistically significant fall in arterial pressure was observed (p less than 0.001), which was attributable to a fall in systemic vascular resistance.