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Biomedical subjects

P Vaughan

Publications and source records attributed to P Vaughan.

At least 55 records · Page 3Linked to original sources
PubMed1980

Cavitational bio-effects of 1.5 MHz.

The effects of continuous wave ultrasound on three different classes of biosystems have been investigated at a frequency of 1.5 MHz. The criteria for cavitation are given, and these are applied to experimentally observed growth retardation of plant roots, cell death and DNA degradation in bacteria and pyknosis of human lymphocytes. An attempt is being made to find common physical mechanisms for all these biological responses, and cavitation processes in particular are examined here. A description is given of the techniques used to monitor the presence of cavitation, and indirect evidence, drawn from pulsed field and elevated pressure experiments, is presented to show that other-non-linear processes are also operative.

Acoustics↗
PubMed1976

Inhibition of Neisseria gonorrhoeae by a bacteriocin from Pseudomonas aeruginosa.

Supernatants from broth-grown cultures of Pseudomonas aeruginosa PA 103 exhibited bactericidal activity against Neisseria gonorrhoeae. The concentration of the bactericidal substance increased significantly after induction by mitomycin C. Purification was effected by salt fractionation, chromatography on diethylaminoethyl-cellulose, and sedimentation by centrifugation at 100,000 x g for 90 min. Electron microscopy of this purified preparation revealed structures resembling R-type pyocins in both the contracted and uncontracted state. Pyocins in the contracted state were observed in association with the gonococcal cell surface. No loss of bactericidal activity was observed after treatment with proteolytic enzymes. Standard pyocin typing procedures identified the pyocin pattern as 611 131. The bactericidal activity of this pyocin was examined on various species of Neisseria. Out of 56 strains of N. gonorrhoeae from disseminated and nondisseminated infections, all were susceptible to pyocin 611 131. However, only 3 of 20 strains of N. meningitidis and 5 of 16 strains of N. lactamica were susceptible. The bactericidal activity that pyocin 611 131 has for N. gonorrhoeae and other species of Neisseria is significant because it departs from the expected specificity that heretofore has distinguished bacteriocins from most "classical" antibiotics.

Bacteriocins↗
PubMed1968

The effect of calcium depletion upon the tension-independent component of cardiac heat production.

Rabbit papillary muscle has been exposed to calcium concentrations ranging from 2.5 mM to zero. Its mechanical and electrical activity has been monitored and its heat production measured using a myothermic technique. Calcium depletion decreased the magnitude of the tension-independent heat per contraction from a mean of 0.45 mcal/g muscle to 0.31 mcal/g muscle at room temperature (18 degrees to 22 degrees C). Calcium-chelating agents did not abolish action potential conduction under the experimental conditions used but they further reduced the magnitude of the tension-independent heat. Raising the temperature from room level to 32 degrees C decreased the tension-independent heat from a mean of 0.52 to a mean of 0.24 mcal/g muscle. Calcium depletion at 32 degrees C further decreased this heat and it was calculated that the energy now liberated in activating the muscle was about 2% of the total energy normally liberated in the working heart. The results are interpreted in terms of current biochemical and myothermic data.

Action Potentials↗
PubMed1968

Histological and electrophysiological investigation of lizard skeletal muscle.

1. The patterns of innervation and electrical properties of muscle fibres in a skeletal muscle of the blue tongue lizard Tiliqua nigrolutea have been investigated.2. Gold impregnation of nerve terminals and staining of muscle fibre junctional areas for cholinesterase showed that there are two histological types of muscle fibre in scalenus muscles of the lizard: (a) those usually receiving single en plaque innervation, and (b) those that receive multiple en grappe terminations.3. In normal solution and in solutions to which small doses of curare were added, two types of subthreshold post-junctional response were recorded following nerve stimulation, (a) potentials with rapid rates of rise and a half-decay time of less than 10 msec and (b) responses with fast rise times and long half-decay times (50 msec or more).4. Fast time course subthreshold responses often gave rise to propagated action potentials. In curarized preparations ((+)-tubocurarine 0.4-1.0 mug/ml.) action potentials failed, giving way to junction potentials of decreasing amplitude, when stimulation was maintained at rates of 5/sec or more. The decay phases of fast time course potentials were closely approximated by error functions.5. Slow time course responses summated during repetitive stimulation, but action potentials were never produced. The decays of slow junction potentials were well fitted by exponentials. It is suggested that fibres in which they were recorded received distributed, en grappe innervation.6. Fibres in which fast time course junction potentials were recorded were excited by direct stimulation via an intracellular micro-electrode. They had apparent membrane resistance and capacity of about 4000 Omega. cm(2) and 7 muF/cm(2).7. Fibres exhibiting slow junction potentials could not be excited directly, even when depolarizing pulses were preceded by hyperpolarizations of 50 mV or more for more than 20 msec. Such fibres had an apparent membrane resistance of 31 x 10(3) Omega.cm(2) (mean) and a capacity of less than 3 muF/cm(2) (eight fibres).8. Curarized muscles developed tension in response to nerve stimulation at frequencies of 5/sec or more. The tension profile was smooth at even the lowest frequencies at which a response was elicited. Normal fusion frequency was around 50/sec.9. It is suggested that fibres exhibiting slow junction potentials were functionally similar to amphibian tonic fibres.10. Some fibres were found in which action potentials could be elicited by stimulation of one or more axons. Their subthreshold responses and passive properties were not determined and it remains uncertain to which of the two structural types they belong.

Action Potentials↗
PubMed1967

The dawn of state medicine in Britain.

Dr R M S McConaghey traces the development of State control in the provision of medical services and also describes the rise in status of the general practitioner, from the early apothecary-surgeons.Mr Paul Vaughan describes the history of the British Medical Association and its development from the Provincial Medical and Surgical Association, founded by Sir Charles Hastings. He considers the relationship between the BMA and the Government, both in the past and present.

Family Practice↗