A novel optical system was used to map the inspiratory movement of the anterior chest wall in patients anaesthetized with isoflurane and nitrous oxide. Flow in the airway, and pressures in the airway, oesophagus and stomach were also measured, during mechanical ventilation and spontaneous ventilation, with and without the effects of opioid. In addition, breathing was stimulated with carbon dioxide. Both normal breathing, and occlusion of either inspiration or expiration for single breath cycles were studied. In some patients, electromyograms of diaphragm and external oblique muscles were recorded, to test whether inspiratory or expiratory occlusion affected either the timing of the respiratory cycle, or the activation of these muscles. The effects of airway occlusion on timing and muscle activity, compared with an unoccluded breath, were small. Occlusion decreased the amplitude of the EMG activity by 7.5%. During carbon dioxide stimulation, diaphragm activity was prolonged. There were no discernible effects on the external oblique activity. Passive inflation inflated the ribcage more than the abdomen, as shown by previous investigators. However during spontaneous ventilation, expansion during inspiration was predominantly abdominal. Stimulation with carbon dioxide increased the movement, and opioid reversal increased ventilation, but neither affected the pattern of movement, which was always closely proportional to the overall amplitude. Airway occlusion pressure indicated that expiration was active, and the movement during occlusion of expiration was inversely proportional to inspiratory movement.

The use of spinal anaesthesia has increased in recent years, probably because of the steadily accumulating evidence of its beneficial effects in certain specific situations. However, opinions vary on the relative importance of the various factors which affect the spread of local anaesthetic solutions in the subarachnoid space. Many authorities have based their opinions on clinical impressions rather than on the results of controlled trials. Despite the large number of local anaesthetic agents which have been administered intrathecally, few are suitable for use today. Neither of the agents currently available in this country is ideal and there is a need for another agent. Bupivacaine has been widely used intrathecally in an isobaric solution but little is known about its properties when administered in hyperbaric solution. Clinical studies have been carried out on 140 patients to assess the effects of varying the baricity of the solution used, the dose and volume administered, the addition of vasoconstrictors and the rate of injection. A solution of 0.5% bupivacaine in 8% dextrose is a suitable hyperbaric solution for intrathecal use and consistently produces good spinal nerve block. The use of 0.75% bupivacaine in 8% dextrose does not confer any advantage, the addition of vasoconstrictors cannot be relied upon to produce a significant increase in duration in individual cases and varying the rate of injection does not appear to have any significant effect. 0.5% bupivacaine in 8% dextrose would be a valuable addition to those agents currently available for intrathecal use in this country. Clinical studies with it have demonstrated that some of the opinions on the factors which affect the spread of local anaesthetic solutions in the subarachnoid space and the pattern of the resulting sensory loss are incorrect.

In each experiment an adult male albino mouse was placed in an apparatus consisting of two narrow semi-circular tunnels joined together to form a complete circle. The apparatus was either mounted in a pressure vessel or a glass vessel. The tunnels were kept at different temperatures (usually 21.6 and 27.5 <SUP>o</SUP>C) and behavioural, thermoregulation was monitored by measuring the length of time spent in each tunnel. It was found that general anaesthetics (N<SUB>2</SUB>O, CHCIF<SUB>2</SUB>, CHCI<SUB>3</SUB>, N<SUB>2</SUB> and Ar) induced changes in behaviour directed at lowering deep body temperature. The following occurred: a) Dose related falls in rectal temperature. Tr was maintained at temperatures above the ambient temperature. b) Effects of anaesthetics on behavioural thermoregulation were reversible. c) Effects of different anaesthetics on behavioural thermoregulation were additive. d) At pressures above 11.33 atm the effects of N<SUB>2</SUB> and Ar are greater than predicted. This response is a two component response; "anaesthetic" and "pressure" component. e) Effects of anaesthetics were not pressure reversed, but showed an additive effect. f) Pressure induces a change in behaviour directed at lowering deep body temperature at pressures of either Ne or He greater than 11.33 atm. In conclusion it was thought general anaesthetics induced changes in the optimal "set-point", which down regulated deep body temperature. The sites of action of pressure and anaesthetic are different, but as yet unknown. Further mechanistic experiments are required to uncover those anatomical sites affected.