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Biomedical subjects

H Morgan

Publications and source records attributed to H Morgan.

At least 73 records · Page 4Linked to original sources
PubMed1996

Consistency of microvascular and autonomic abnormalities in diabetes.

The progression of early measures of microvascular disease and autonomic neuropathy were studied in a group of 81 children with insulin dependent diabetes mellitus over a mean interval of 4.2 years. Repeated measurements were made of blood pressure, albumin excretion, joint mobility, and pupillary dilatation in darkness. Over the years between the first and the second study, systolic and diastolic blood pressure showed positive tracking correlations (r = 0.38 and r = 0.32) with a small but significant deviation from normality; albumin/creatinine ratio was significantly increased (0.79 v 0.55); a greater number of children were identified in the second study as having limitation of mobility of the fifth metacarpophalangeal joint; and pupillary dilatation in darkness significantly decreased (61.5% v 62.9%); 62% of the children with one or more abnormal measurements in the first study were found to have measurements outside the normal ranges in the second study, indicating a consistency in observations over time. It remains to be seen with what accuracy these measurements predict adult onset clinical disease.

Adolescent↗
PubMed1995

Patterning and regeneration of surfaces with antibodies.

We describe the application of a new technique for the site-specific immobilization of six different proteins within an area of 200 microns x 50 microns. The procedure involves coating the surface with deglycosylated avidin, which binds a photoactive biotin analogue, so providing a light-addressable surface onto which proteins can be immobilized. This is the first time that consecutive patterning of a number of different proteins has been described, and we demonstrate this with the fabrication of an immunospot for the qualitative visualization of the binding of multiple antigens. We also show that such a structured surface can be readily regenerated and subsequently repatterned.

Antibodies↗
PubMed1995

Photo-patterning of sensor surfaces with biomolecular structures: characterisation using AFM and fluorescence microscopy.

The miniaturisation of biosensors has resulted in the need to develop techniques for the high resolution patterning of different biological molecules onto surfaces. In this paper, we describe a procedure for the selective deposition of antibodies using biological self-assembly with photo-activation of a bound ligand, and we will detail methods which may subsequently be used to characterise the resultant biomolecular constructs.

Antibodies, Monoclonal↗
PubMed1995

Physiological identification of the auditory nerve during surgery for acoustic neuroma.

We report the design and clinical use of an electrode which can locate the acoustic nerve fibres in the normal eighth nerve and also in eighth nerves deformed by acoustic neuromas. The improvement in facial nerve preservation during acoustic neuroma surgery is partly due to the use of a facial nerve stimulator to anatomically locate the fibres. Our new acoustic nerve detector has the capability of anatomical location of cochlear fibres which may help to improve hearing preservation in selected cases of acoustic neuroma. The device functions by detecting the compound action potential evoked by no frequency auditory simulation at 500 Hz. The 500 Hz compound action potential is detected with a bipolar probe and then amplified and filtered. This results in a 500 Hz tone when the probe contacts the auditory nerve. Detection is virtually instantaneous. The acoustic nerve detector (AND) is demonstrated in a normal eighth nerve complex and its use is then described in the total removal of an acoustic neuroma with a 1 cm extracanalicular extension in which useful hearing was saved post-operatively. The present prototype may not be sensitive enough to detect the very low signals that may result when cochlear fibres are widely distorted around a large tumour or in cases where slight contusion of the nerve occurs during dissection. In all other cases the real time anatomical information is extremely helpful in guiding acoustic nerve dissection and also in monitoring the effects of petrous bone drilling.

Amplifiers, Electronic↗
PubMed1994

The lack of evidence for ELF magnetic-field effects on bilayer membranes and reconstituted membrane channels.

The effects of low-frequency (10-500 Hz) magnetic fields on the electrical properties of channel-free bilayer membranes, and on the single-channel conductance and macroscopic gating characteristics of porin channels incorporated into membranes, have been studied for field strengths in the range 10-100 microT. The field conditions that could in theory give rise to 'cyclotron resonance' effects were also studied. No evidence has been found to support the concept that cyclotron resonance and membrane ion channel effects are involved in the reported biological effects of ELF magnetic fields.

Dose-Response Relationship, Radiation↗
PubMed1994

Facial and acoustic nerve preservation during excision of extracanalicular acoustic neuromas using the suboccipital approach.

The results are presented from a consecutive operative series of 62 acoustic neuromas in 60 patients following the introduction of improved neurophysiological monitoring techniques. Twenty-two patients had usable preoperative hearing. Thirty tumours were less than 2.5 cm diameter and 32 greater in size. Operation was via a 3-4-cm diameter retromastoid craniectomy. The internal auditory meatus was opened by an ENT surgeon (RM) using a drill and the facial nerve identified by stimulation. The tumour was then centrally evacuated by a neurosurgeon (MT/HC) using an ultrasonic aspirator, and the thin exterior part of the tumour carefully dissected off the nerves in or around the capsule with constant stimulation and monitoring of facial EMG, BSAEP and electrocochleography. A new type of stimulation probe has been designed and coupled to a stimulator/integrator/tone burst generator (SB) so that continuous immediate direct feedback to the surgeon is possible. A variable amplitude discriminator rejects baseline EMG (> 50 microV) and a gating circuit prevents stimulus artefact (during monopolar stimulation) from causing interference. By these means the VII nerve could be identified even when translucent and undefinable as a nerve bundle. Anatomical preservation was possible in 98% of VII nerves. Full facial function was present in 20 cases immediately postoperatively. Full delayed recovery occurred in 23 cases giving an eventual total in House Grade I of 69%. Seven other cases recovered to House Grade II. There was therefore 81% satisfactory facial nerve function. This percentage is exactly the same for larger and for smaller tumours. Anatomical preservation of the VIII nerve was achieved in 24/62 (39%) of the whole series and 11/16 (69%) of those with a hearing loss of < 50 dB. Functional preservation of hearing described as usable by the patient (< 65 dB) was achieved in 7/22 cases (32%), 3/13 (23%) in tumours < 2.5 cm and 4/9 (44%) in those > 2.5 cm diameter. Hearing preservation of < 50 dB in patients with preoperative hearing threshold < 50 dB and tumours of < 2.5 cm was 3/11 (27%). Monitoring by BSAEP and ECochG was technically unsatisfactory because the responses were affected by drilling and stimulation. Acoustic nerve preservation should be attempted in all cases with measurable hearing, regardless of tumour size.

Ear Neoplasms↗
PubMed1993

The Costello syndrome.

In 1971 and again in 1977, Costello reported on two unrelated children with multiple congenital malformations associated with growth and developmental retardation and nasal papillomata (Costello, NZ Med J 74:397, 1971; Costello, Aust Paediatr J 13:114-118, 1977). Subsequently, two similar cases were described (Der Kaloustian et al., Am J Med Genet 41:69-73, 1991; Martin and Jones, Am J Med Genet 41:346-349, 1991). Costello syndrome is now a distinct entity. We describe another patient who additionally had hitherto unreported malformations, such as hydrocephalus, seizures, atrial fibrillation, and flutter with atrial septal defect. Although no nasal lesions were found he had laryngeal papillomata associated with a congenital web. A skin biopsy showed no evidence of lipid or mucopolysaccharide storage disease and muscle biopsy was normal by gross and electron microscopic examination.

Abnormalities, Multiple↗
PubMed1993

Time-domain dielectric spectroscopy applied to cell suspensions.

A precision difference time-domain reflectometry (TDR) technique is described for the investigation of the dielectric properties of cell suspensions. The dielectric spectra obtained for erythrocytes using TDR are comparable with those reported in previous dielectric studies employing frequency-domain technique.

Animals↗
PubMed1992

A surface plasmon resonance immunosensor based on the streptavidin-biotin complex.

It is shown that a streptavidin monolayer immobilized onto an evaporated gold film with biotin forms the basis of a highly specific sensing element. As an example, we show that by immobilizing the biotinylated antibody sex hormone binding globulin (alpha-SHBG) to the bound streptavidin monolayer a specific sensor for the antigen SHBG is readily fabricated. The interaction between immobilized antibody and corresponding antigen is monitored by surface plasmon resonance spectroscopy and is shown to follow a classic Langmuir isotherm. Detection of SHBG at nanomolar concentrations is demonstrated.

Antigens↗
PubMed1991

Proton transport at the monolayer-water interface.

It is shown that when monolayers of stearic acid, palmitic acid, DPPC, or DPPS are compressed above some critical area Ac a lateral conduction mechanism is initiated at the monolayer/water interface. The interfacial conductance increases on further increasing the molecular packing density in the monolayer. All compounds also show major changes in surface potential at Ac the potential becoming more positive in all cases. It is argued that this is a consequence of structural reorganisation at the headgroup/water interface causing a significant reduction in the local permittivity. The critical area, Ac, is approximately double the molecular areas estimated from the pressure-area isotherm, and experiments with stearic acid monolayers show that Ac decreases significantly when the chaotropic ion SCN-, which is known to disrupt the molecular structure of water, is added to the subphase. It is likely, therefore, that the structural changes occurring at Ac involve the formation of a hydrogen bonded network between monolayer headgroups and adjacent water molecules at the monolayer/water interface. It is suggested that the conduction mechanism initiated at Ac arises from proton hopping along this hydrogen-bond network.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1990

Polarity-dependent voltage-gated porin channels from Escherichia coli in lipid bilayer membranes.

A porin preparation from Escherichia coli 0111:B4 consisting of Omp F and Omp C (with Omp F in excess) was purified by salt extraction procedures and investigated in bilayer lipid membranes formed according to the Montal-Mueller technique. The porin preparation was added to the KCl electrolyte compartment of the Montal-Mueller cell which was connected to the voltage source. As the porin incorporated into the membrane, asymmetric, voltage-gated ion channels were formed. Transmembrane voltages greater than +50 mV (measured with respect to the side of porin addition) caused channel closing, while negative voltages, on the other hand, had no effect on channel behaviour but did increase the rate of porin incorporation at higher voltages. With porin added to both compartments voltage gating no longer occurred. Single-channel conductances corresponded to effective pore diameters of 1.5 nm for opening events and 1.18 nm for channel closing events. The number of charges involved in gating was approximately 2.

Bacterial Outer Membrane Proteins↗