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Biomedical subjects

D A Thomson

Publications and source records attributed to D A Thomson.

30 records · Page 2Linked to original sources
PubMed1986

Control of end-tidal halothane concentration. Part A: Anaesthesia breathing system and feedback control of gas delivery.

Conventional anaesthetic breathing systems are not designed to control end-tidal gas concentrations, nor can they be used to measure accurately the uptake of oxygen or of anaesthetic agent. We built and tested a leak-tight closed-loop anaesthetic breathing system with low solubility to volatile anaesthetic agents and with efficient gas mixing. The system included a water-sealed spirometer, a small carbon dioxide absorber, a coaxial tube to the patient, a circulating pump and feedback controllers for system volume and anaesthetic concentration. Feedback control was implemented to adjust and control automatically the end-tidal anaesthetic concentration and the volume of the system with oxygen supplied through a mass flow controller and with halothane supplied by a titrating syringe. Controller gains, as a function of body weight, were found using a nine-compartment tissue uptake model. Stability was maintained with +/- 50% changes in alveolar ventilation and cardiac output. During subsequent investigations in an animal model, arterial, mixed venous and cerebral venous blood halothane concentrations were measured to show that the feedback-controlled halothane induction was optimized. We conclude that feedback control appears to be clinically applicable for adjusting the end-tidal halothane concentration and system volume to provide a rapid and optimized induction of anaesthesia.

Anesthesia, Inhalation↗
PubMed1986

Control of end-tidal halothane concentration. Part B: Verification in dogs.

Conventional anaesthetic techniques do not allow for the automatic control of end-tidal halothane concentration and, therefore, brain concentration cannot be predicted. In this study, eight dogs were ventilated with halothane in oxygen using a new closed-loop anaesthetic breathing system which provided a constant end-tidal concentration. During the first 60 min the end-tidal concentration was maintained at 0.87 vol% (1 MAC). Then followed 60 min of halothane wash-out and a further 120-min period of halothane at 1.74 vol% (2 MAC). Halothane concentrations were measured in the inspired and expired air, and in the arterial, cerebral venous and mixed venous blood. Haemodynamic and respiratory variables were measured. The system reached 95% of the target end-tidal concentration within 6 min without over-shooting. After 2 h of wash-in, significant gradients still persisted between end-tidal, arterial and cerebral venous blood concentrations. Measured uptake differed from theoretically calculated uptake by 18.3-57.6%, depending on the model used. Measured arterial and cerebral venous concentrations differed from theoretically calculated values by 7% and 17.5%, respectively. It was shown that the required end-tidal concentrations can be obtained rapidly and accurately, and that brain tissue concentrations can be predicted within certain limits.

Anesthesia, Inhalation↗
PubMed1986

Meckel's cartilage in Xenopus laevis during metamorphosis: a light and electron microscope study.

Meckel's cartilage, in Xenopus laevis prior to metamorphosis, is a tissue exhibiting very large lacunae, separated by thin rims of matrix, presenting a net-like appearance, similar to that of cartilage in invertebrates. The cells on the periphery of the tissue are rather more flattened, and more closely packed. On the lateral aspects of the cartilage distinct columns of apparently dividing cells are evident. During metamorphic climax, the amount of matrix separating the lacunae increases, with an associated decrease in lacunar size, and some of the deeper cells develop cilia, which are not seen either before or after climax. By the end of metamorphic climax there is a considerable increase in the amount of matrix present in the tissue, while many cells at all depths in the cartilage show the presence of lysosome-like structures, possibly associated with the changing shape of the cartilage. Intramembranous ossification is proceeding around Meckel's cartilage, but there is no evidence of endochondral ossification up to the end of metamorphosis.

Animals↗
PubMed1985

Determination of the partial pressure of halothane (or isoflurane) in blood.

A gas chromatographic method is described for the direct quantitative determination of the partial pressure of halothane (or isoflurane) in blood as well as the blood-gas partition coefficient. A head space technique and a flame ionization detector were used. Standard blood was obtained by equilibrating patients' blood with known gas concentrations in a tonometer. Using an infra-red analyser to measure the halothane gas concentration in the tonometer and within the anaesthetic system allowed for the direct comparison of the partial pressure in blood to the partial pressure in the inspired gas. Technical problems associated with this procedure, and with comparable methods, are discussed.

Chromatography, Gas↗
PubMed1975

Influence of oestrogen on experimental pyelonephritis caused by Escherichia coli.

Strains of Escherichia coli isolated from patients with suspected pyelonephritis had a strong predilection for growth in kidney tissue. Viable bacterial counts in experimentally infected mice showed that after 96 hours approximately 98% of the total-body count was found in the kidney. Strains of E. coli isolated from cases of gastroenteritis in man and animals had little or no tendency to grow in the kidney. Treatment of male and female mice with oestrogen significantly enhanced the growth of "pyelonephritic" strains in the kidney, but had no effect of any kind on the growth of "gastroenteritis" strains. These preliminary results suggest that oestrogen may predispose to the development of kidney infection in the female and that there is an important link with the virulence of the E. coli concerned. Only those strains that have a natural predilection for growth in the kidney are likely to be influenced by oestrogen.

Animals↗
PubMedDate not supplied

Anesthesia and the immune system.

While the direct effects of anesthesia on immunological competence have not yet been fully elucidated, it is clear that the use of certain anesthetics and anesthetic procedures contributes to reduced immune function, as demonstrated by such clinical markers as increased infection and tumor growth. This review evaluates evidence of the participation of anesthesia in suppression or activation of the immune system, and discusses the implications of these changes to patient care and outcome.

Acquired Immunodeficiency Syndrome↗