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Biomedical subjects

A Murray

Publications and source records attributed to A Murray.

At least 253 records · Page 14Linked to original sources
PubMed1994

Simplified body-surface electrocardiographic maps with depolarization magnitude and direction.

A new technique is presented for extracting the magnitude and direction of ventricular depolarization at the body surface from surface electrocardiographic (ECG) map data. Bipolar electrocardiograms were obtained from 36 sites on the chest surface in five normal subjects. The direction and magnitude of depolarization as seen from the chest surface were calculated for 18 body-surface areas centred between electrode positions V1 and V6. Each area was bounded by three electrodes with an electrode spacing of 5 cm. A major depolarization component could be calculated for all triangular areas, with 48% of areas having a smaller second component. The area with the greatest magnitude in each subject had a depolarization vector pointing downwards and to the left, with an average angle to the horizontal of 55 degrees. This was consistent with an average angle of 51 degrees obtained from the subjects' 12-lead electrocardiograms. There was more variability in vector angle between adjacent areas on the right-hand side. At the V5/V6 areas, close to the cardiac apex, the vector component had an upwards orientation in all subjects, opposing the overall downward component of ventricular depolarization. The technique was able to determine local depolarization directions which were in agreement with the normal cardiac vector derived from standard electrocardiography. Reversal of the vector direction close to the cardiac apex and the collision of depolarization components from different directions could be detected. This simple form of body-surface mapping can reduce the essential features of depolarization to a single map, and provide information not directly available from a 12-lead electrocardiogram.

Adult↗
PubMed1994

Changes in the surface electrocardiogram during the onset of spontaneous ventricular fibrillation in man.

The aim of this study was to quantify electrocardiographic changes during the onset and early stages of ventricular fibrillation. Thirty recordings of ventricular fibrillation (mean duration 57 s, range 24-160 s) were obtained from 23 Coronary Care Unit patients. Each recording was investigated using frequency analysis on 1 s epochs of data. A significant rise in the mean dominant frequency of ventricular fibrillation from 3.9 Hz (SD 0.8 Hz) to 5.9 Hz (SD 1.0 Hz) was observed between 1 s and 30 s (P < 0.0001). At the same time, the width of the dominant peak decreased significantly (P < 0.001) and the height of higher frequency harmonics fell (P < 0.01). There was no significant change in peak height as ventricular fibrillation evolved. This study shows that the electrocardiogram retains periodic characteristics during the first 30 s of ventricular fibrillation and that these periodic characteristics become concentrated in a progressively narrower band of frequencies. These findings would suggest that during the early stages of ventricular fibrillation myocardial activation is both accelerating and coherent, rather than incoherent as has been traditionally believed.

Electric Countershock↗
PubMed1994

Errors in manual measurement of QT intervals.

OBJECTIVE: To quantify the errors associated with manual measurement of QT intervals and to determine the source of the errors. DESIGN: A randomised study of QT measurement by four cardiologists of electrocardiograms plotted on paper in presentations with different noise levels, paper speeds, amplifier gains, and with and without a second QRST complex to indicate the RR interval. SUBJECTS: Four electrocardiograph leads (I, aVR, V1, V5) recorded in eight healthy people relaxing in a semirecumbent position. MAIN OUTCOME MEASURES: Manual measurement of QT interval in 512 electrocardiograms (eight subjects x four leads x eight presentations x two repeats) by each of four cardiologists. RESULTS: QT intervals measured were significantly longer with greater amplifier gain: by 8 ms for a doubling of gain (p < 0.005), equivalent to a doubling of T wave height. QT intervals measured were significantly longer at slower paper speeds: by 11 ms when paper speed was reduced from 100 to 50 mm/s (p < 0.001) and by 16 ms when speed was further reduced from 50 to 25 mm/s (p < 0.001). Neither the presence of noise nor the presence of a second QRST complex altered the mean QT measurements. There were consistent differences in the measurements between cardiologists, amounting to a maximum mean difference of 20 ms. CONCLUSIONS: Manual measurement of QT interval is significantly affected by the paper speed used to plot the electrocardiogram and by electrocardiogram gain, and hence also T wave amplitude. Manual QT measurement also differed consistently with different cardiologists.

Diagnostic Errors↗
PubMed1994

Comparison of body sway analysis techniques. Assessment with subjects standing on a stable surface.

Different analysis methods for the objective measurements of body sway were examined to establish the most sensitive method for identifying changes in stability. Changes between stability with eyes open and eyes closed were used to assess the techniques. Body sway was measured in a group of normal subjects standing on a stable surface using "sway magnetometry," which measures hip movement in the sagittal and coronal planes by magnetic field detectors worn at the waist. The following analysis methods were studied; path length, mean distance from the centre, the area enclosed by the path of movement, and the areas of a convex hull, an ellipse and a circle enclosing the sampled points. The results showed that the path length technique had the smallest inter-subject variability, both with eyes open and eyes closed, and was the only technique whose mean Romberg Coefficient (Eyes Open/Eyes Closed) was more than two standard derivations from 1.0 (0.74 +/- 0.11, mean +/- S.D.), indicating that this technique showed greatest sensitivity for detecting changes in body sway.

Adult↗
PubMed1993

Self-terminating ventricular tachyarrhythmias--a diagnostic dilemma?

Ventricular fibrillation is generally regarded as being lethal unless promptly halted. There have been reports of self-terminating ventricular fibrillation, but similar events are described by some cardiologists as polymorphic ventricular tachycardia or even torsade de pointes. To examine how experienced cardiologists would diagnose such tachyarrhythmias, electrocardiograms of self-terminating ventricular tachyarrhythmias compatible with accepted definitions of ventricular fibrillation (rate > 300/min) were sent to 22 cardiologists. During the study period of 19 months, 2462 patients treated in a 10-bed coronary-care unit were monitored by use of a single bipolar chest lead. 45 (2%) had episodes of ventricular fibrillation that were terminated by direct current (DC) shock. 12 self-terminating tachyarrhythmias (duration 5.2-49.5 s) were recorded from 8 patients, 3 of whom also had sustained ventricular fibrillation terminated by DC shock. The cardiologists offered 264 diagnoses for the self-terminating events; 42 (15.9%) ventricular fibrillation, 99 (37.5%) polymorphic ventricular tachycardia, 98 (37.1%) torsade de pointes, and 25 (9.5%) "other". The cardiologists differed (p < 0.01) in their response patterns. The findings show that rapid self-terminating ventricular tachyarrhythmias are not uncommon in coronary-care unit patients, and that the diagnostic categorisation of these important events is highly subjective and inconsistent.

Cardiology↗
PubMed1993

Comparison of balance assessment by sway magnetometry and force platforms.

Sway magnetometry, which monitors body movement at the hips, was compared with two commercial force platforms to determine its sensitivity in identifying differences in stability between eyes opened and eyes closed. Sway path length and area were examined. All devices showed an ability to distinguish between stability with eyes opened and eyes closed on repeated testing. The magnetometry system using path length analysis was most sensitive and was able to detect an increase in sway with eyes closed compared with eyes open for individual tests with 97% confidence (mean [+/- SD] path length Romberg Coefficient, .76 +/- .13). Standing on a rubber base caused destabilization of posture. Sway magnetometry is seen as a potentially useful tool in quantification of body sway to aid the clinician in assessment of balance in the dizzy patient.

Adult↗
PubMed1993

Comparison of four techniques for recognition of ventricular fibrillation from the surface ECG.

Four ventricular fibrillation (VF) detection techniques were assessed using recordings of VF to evaluate sensitivity and VF-like recordings to evaluate specificity. The recordings were obtained from Coronary Care Unit patients. The techniques were: threshold crossing intervals (TCI); peaks in the autocorrelation function (ACF); signal content outside the mean frequency (VF-filter); and signal spectrum shape (spectrum). Using 70 extracts, each 4 s long, from VF recordings, the VF filter achieved a sensitivity of 77 per cent; the ACF, TCI and spectrum algorithms had sensitivities of 67, 53 and 46 per cent, respectively. Susceptibility to false alarms was assessed using 40 extracts from VF-like recordings. The TCI algorithm was the most specific (93 per cent), while the spectrum, VF filter and ACF algorithms had specificities of 72, 55 and 38 per cent, respectively. The TCI algorithm achieved overall sensitivity of 93 per cent and specificity of 60 per cent. The spectrum, VF filter and ACF algorithms had overall sensitivities of 80, 93 and 87 per cent, and overall specificities of 60, 20 and 0 per cent, respectively.

Algorithms↗
PubMed1993

Repeatability of subject/bed interface pressure measurements.

The repeatability of a technique for measuring interface pressures has been assessed. Pressure was measured using a Talley SA500 Pressure Evaluator under six anatomical sites (occiput, scapula, elbow, sacrum, buttock, and heel) of six healthy subjects lying supine on a Clinifloat mattress (trademark, SSI). For each site of each subject, four repeat readings were taken per day on four separate days. Mean pressures varied significantly between subjects (p < 0.02), though differences in mean pressures between sites were greater. Pressure was not significantly related to subject mass. The overall repeatability of the technique was +/- 0.77 kPa (+/- 5.8 mm Hg) which was much smaller than the range of pressures found under different sites (2.72 kPa or 20.4 mm Hg at the sacrum to 9.00 kPa or 67.5 mm Hg at the heel). Repeatability varied from site to site, from +/- 0.47 kPa (+/- 3.5 mm Hg) at the buttocks to +/- 1.20 kPa (+/- 9.0 mm Hg) at the heel. Measurements were found to vary significantly more between days than between repeats on the same day (p < 0.02).

Adult↗
PubMed1993

Accuracy of interface pressure measurement systems.

Interface pressure measurement is needed to assess beds designed to prevent pressure sores, so it is therefore important to establish the accuracy of interface pressure measuring systems. In this study, the Talley SA500 pressure evaluator (with 28 mm and 100 mm sensor pads), the DIPE (with 100 mm sensor pad), and a water-filled bladder system (with 0.1 ml and 0.3 ml water) were assessed. Measurement errors were evaluated using a loading system with pressures up to 7.4 kPa (55 mm Hg) in steps of 0.9 kPa (6.9 mm Hg). All systems tested over-measured interface pressure, the error being approximately linearly proportional to the loading pressure. The repeatability for a given system was approximately constant. The mean error (+/- SD) (%) and repeatability (kPa) for the systems were: 28 mm Talley 12 +/- 1%, +/- 0.07 kPa; 100 mm Talley 15 +/- 1%, +/- 0.07 kPa; DIPE 27 +/- 3%, +/- 0.12 kPa; 0.1 ml water bladder 17 +/- 1%, +/- 0.13 kPa; 0.3 ml water bladder 26 +/- 3%, +/- 0.07 kPa. Different interfaces affected accuracy markedly, and repeatability was affected when an inhomogeneous interface was used. The study shows that the errors associated with interface pressure measurement systems can be substantial, and can vary from one system to another.

Beds↗
PubMed1993

Molecular characterization of a dense granule antigen (Gra 2) associated with the network of the parasitophorous vacuole in Toxoplasma gondii.

The monoclonal antibody (mAb) TG17.179 recognizes an excreted-secreted antigen (ESA) of 28.5 kDa named Gra 2, which is stored in the dense granules of Toxoplasma cells and secreted into the parasitophorous vacuole after host cell invasion. Screening of an expression cDNA library with TG17.179 led to the isolation of several clones, the longest one (clone L) being of 1030 bp. Clone L cDNA was found to be homologous to a previously described composite cDNA encoding a P28 protein of Toxoplasma gondii. Characterization of one genomic clone indicates that the complete GRA 2 gene is about 1.3 kb in length, including an intron of 241 bp. Northern blot and primer extension analyses confirmed the size of the mature messenger (1.1 kb). Amino acid partial sequencing of the native antigen purified by HPLC and metabolic radiolabelings of ESAs perfectly matched the primary amino acid structure deduced from the clone L cDNA. This primary translation product consists of an 185 amino acid polypeptide (19.8 kDa) including a 23 amino acid signal sequence. The presence of many serine and threonine residues may indicate an O-glycosylation. The predicted mature polypeptide shows an internal helical domain with 2 amphipathic alpha-helices. These might be involved in the association of Gra 2 with the membranous network within the parasitophorous vacuole.

Amino Acid Sequence↗
PubMed1993

Clinical thermoluminescence dosimetry: how do expectations and results compare?

Thermoluminescence dosimetry (TLD) for radiotherapy treatment verification is performed in the Prince of Wales Hospital in Sydney for a wide range of applications: (A) to determine the dose in difficult treatment geometries, (B) to record the dose to critical organs, and (C) to monitor special treatments such as total body irradiation (TBI). TLD measurements were performed with the aim to investigate cases where dose prediction is difficult and not as part of a routine verification procedure. We reviewed 1058 reports of TLD performed during the treatment of 502 patients between 1986 and 1991 to evaluate how the TLD results compare with the dose determined by the treatment plan. Reasons for possible discrepancies should be identified. In 19% of all investigated cases a discrepancy of more than 10% was found between expected and measured doses. The discrepancies could be divided into three groups: (1) errors made in the TLD determination or evaluation, such as placement errors of the TLD chips (21% of all discrepancies); (2) mistakes made during the patient set-up, such as insufficient shielding or inadequate patient immobilisation (30%); (3) inadequate treatment planning and dose calculation procedure, such as wrong inverse square law corrections or errors due to limitations of the two-dimensional treatment planning system used (41% of all). In 8% of all discrepancies the reason remained unclear. A number of changes to treatment plans and modalities (e.g. changed scrotal shield, modified bolus) were introduced due to TLD results. The increasing number of TLD requests per year attests to the value of TLD as a treatment verification method in clinical practice.

Electrons↗
PubMed1993

Rapid HLA-DR oligotyping by an enzyme-linked immunosorbent assay performed in microtiter trays.

A simple, sensitive ELISA that is performed in 96-well microtiter plates and that requires less than 90 minutes to complete was developed for HLA-DRB oligotyping. The second exon of HLA-DRB1 was amplified using an unlabeled forward primer and a biotinylated reverse primer and the PCR product was immobilized in avidin-coated wells. Subsequent treatment included exposure to 0.4 N NaOH to remove the nonbiotinylated sense strand, addition of a fluorescein-labeled oligonucleotide probe, one or more 5-minute stringency washes, addition of an alkaline-phosphatase-labeled anti-FL FAB, and then alkaline-phosphatase substrate and amplifier. An intense red-violet color developed within 15 minutes in positive wells and could be quantitated by OD readings at 490-495 nm. To control for stringency and to establish threshold OD values for positive reactions, biotin-labeled antisense oligos that were complementary to the probe or that differed by one or more bases were immobilized in wells in place of PCR products. The assay was sensitive to < 0.05 pmol (approximately 4 ng)/well and required only standard incubators and waterbaths and an optional microplate reader. All reagents were commercially available. The method should facilitate oligotyping of both class I and class II alleles and is adaptable for analysis of other polymorphic gene products.

Base Sequence↗
PubMed1993

Oral immunization with recombinant BCG induces cellular and humoral immune responses against the foreign antigen.

It has been shown recently that BCG can be used as a live recombinant vaccine to stimulate immune responses. Proliferative or cytotoxic T-cell responses against several viral proteins such as HIV Gag, Env or Nef were obtained after parenteral immunization with BCG expressing these proteins. Antibody responses were also obtained after immunization of mice with recombinant BCG strain which expressed lac Z under the control of a promoter sequence isolated from Mycobacterium paratuberculosis. We have used this recombinant vaccine in guinea-pigs to investigate the influence of various routes of immunization on the immunogenicity of a foreign antigen expressed by recombinant BCG. Guinea-pigs were immunized by oral, respiratory or intradermal routes and proliferative responses, delayed-type hypersensitivity and antibody responses specific for beta-galactosidase were followed for 16 weeks. Results demonstrated that humoral and cellular immune responses specific for beta-galactosidase can be produced in all groups of guinea-pigs. However, the respiratory and especially the oral route of administration induced higher local and systemic immune responses than the intradermal route of immunization. Moreover, the oral immunization of mice with this recombinant BCG induced IgA responses which could be detected in both sera and intestinal secretions. Therefore, this study demonstrates for the first time that oral immunization with recombinant BCG can induce strong cellular and humoral immune responses.

Administration, Inhalation↗
PubMed1993

Comparative assessment of the ventricular fibrillation detection algorithms in five semi-automatic or advisory defibrillators.

The sensitivity and specificity of ventricular fibrillation (VF) detection in three semi-automatic defibrillators (Laerdal Heartstart 3000, Spacelabs First Medic 610, Physio-Control Lifepak 300) and two advisory defibrillators (S&W DMS940, Marquette Responder 1500) were assessed with 25 ECG recordings, each of length 40 s. Of the 25 ECG recordings, 12 contained VF requiring defibrillation, three contained a tachyarrhythmia with a waveform similar to VF but which self-terminated, and 10 were selected from abnormal rhythms and artefacts which contained some features similar to VF. Sensitivity was assessed from the VF data. Specificity was assessed from both the rhythm preceding VF or the tachyarrhythmias, and from the VF-like data. The response to a changing rhythm was assessed from the self-terminating tachyarrhythmias. Each recording was replayed to the defibrillators at three signal amplitudes (normal, half and double). For each defibrillator, requests to check the patient and advice to shock were noted separately. The sensitivity for recommending a shock when a shock was required varied from 81 to 97%. The sensitivity for drawing attention to VF, either through requesting the patient to be checked or advising a shock, varied from 92% to 100%. There were no false detections in the rhythms preceding VF or the tachyarrhythmias (specificity with good quality signals 100%). The specificity with the VF-like data ranged from 63 to 90% for recommending a shock, and from 63% to 70% for requesting the patient be checked or shocked. There was no difference between the defibrillators for VF detection, but there was a significant difference between the semi-automatic and advisory defibrillators (P < 0.05) for the specificity of the final recommendation.

Algorithms↗
PubMed1993

Development of a neural network screening aid for diagnosing lower limb peripheral vascular disease from photoelectric plethysmography pulse waveforms.

An artificial neural network (ANN) was trained to classify photoelectric plethysmographic (PPG) pulse waveforms for the diagnosis of lower limb peripheral vascular disease (PVD). PPG pulses from the lower limbs, and pre- and post-exercise Doppler ultrasound ankle to brachial systolic blood pressure ratio measurements were obtained from patients referred to a vascular investigation laboratory. A single PPG pulse from the big toe of each leg was processed and normalized, and used as input data to the ANN. The ANN outputs represented the diagnostic classifications (normal, significant PVD and major PVD) and the ANN was trained with the ankle to brachial pressure indices (ABPI). The ANN structure consisted of an input layer (50 neuron units from the PPG pulse input), a single hidden layer (15 neurons) and an output layer (3 neurons for the PVD diagnoses). The back-propagation learning algorithm was used to train the ANN for 500 epochs with a PPG training set of pulses from 100 legs. Test data for network assessment comprised pulses from a further 50 legs (20 normal and 30 PVD, of which 15 were categorized as having major disease). A network sensitivity of 93% and specificity of 85% was achieved with respect to the Doppler ABPI standard, giving a diagnostic accuracy of 90%. The results of this study indicate that a neural network can be trained to distinguish between PPG pulses from normal and diseased lower limb arteries. The simplicity of PPG measurement and neural network classification holds promise for the screening of lower limb arterial PVD.

Humans↗
PubMed1993

Review of seven cardiac electrophysiology stimulators.

Seven cardiac electrophysiology stimulators from four manufacturers (Biotronik, Bloom, Digitimer and Medtronic) in common current use are reviewed. The stimulators differ in the features provided and the design adopted to achieve these features. The number of output channels ranges from one to four, the number of extra-stimuli available ranges from two to six, and these can be delivered as a variety of sequences. Some of the stimulators (Digitimer and Bloom) are modular while others (Biotronik and Medtronic 532 series) are of an integrated design comprising a single physical unit. The design of the Medtronic EP-2 has both integrated and modular characteristics. The features of the stimulators associated with input, output, control and the user interface are specifically reviewed. The features are also compared against the published recommendations of the American Heart Association. In addition, a summary of stimulator user comments from a number of electrophysiology centres is presented. All of the stimulators fulfil, or are close to fulfilling, basic electrophysiological requirements, but some provide more complex facilities such as would be required by specialist centres.

Electric Stimulation↗