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Biomedical subjects

S Bentley

Publications and source records attributed to S Bentley.

At least 19 recordsLinked to original sources
PubMed2006

Cerebral critical closing pressure estimation from Finapres and arterial blood pressure measurements in the aorta.

Estimates of cerebral critical closing pressure (CrCP) and resistance-area product (RAP) are often derived using noninvasive measurements of arterial blood pressure (ABP) in the finger, but the errors introduced by this approach, in relation to intra-vascular measurements of ABP, are not known. Continuous recordings of ABP (Finapres and solid-state catheter-tip transducer in the ascending aorta), cerebral blood flow velocity (CBFV, bilateral Doppler), ECG and transcutaneous CO(2) were performed following coronary catheterization. CrCP and RAP were calculated for each of 12,784 cardiac cycles from 27 subjects using the classical linear regression (LR) of the instantaneous CBFV-ABP relationship and also the first harmonic (H(1)) of the Fourier transform. There was a better agreement between LR and H(1) for the aortic measurements than for the Finapres (p < 0.000,01). For LR there were no significant differences for either CrCP or RAP due to the source of ABP measurement, but for H(1) the differences were highly significant (p < 0.000,03). The coherence functions between either CrCP or RAP values calculated with aortic pressure (input) or the Finapres (output) were significantly higher for H(1) than for LR for most harmonics below 0.2 Hz. When using the Finapres to estimate CrCP and RAP values, the LR method produces similar results to intra-arterial measurements of ABP for time-averaged values, but H(1) should be preferred in applications analysing beat-to-beat changes in these parameters.

Airway Obstruction↗
PubMed1996

Exercise-induced muscle cramp. Proposed mechanisms and management.

Muscle cramp is a common, painful, physiological disturbance of skeletal muscle. Many athletes are regularly frustrated by exercise-induced muscle cramp yet the pathogenesis remains speculative with little scientific research on the subject. This has resulted in a perpetuation of myths as to the cause and treatment of it. There is a need for scientifically based protocols for the management of athletes who suffer exercise-related muscle cramp. This article reviews the literature and neurophysiology of muscle cramp occurring during exercise. Disturbances at various levels of the central and peripheral nervous system and skeletal muscle are likely to be involved in the mechanism of cramp and may explain the diverse range of conditions in which cramp occurs. The activity of the motor neuron is subject to a multitude of influences including peripheral receptor sensory input, spinal reflexes, inhibitory interneurons in the spinal cord, synaptic and neurotransmitter modulation and descending CNS input. The muscle spindle and golgi tendon organ proprioceptors are fundamental to the control of muscle length and tone and the maintenance of posture. Disturbance in the activity of these receptors may occur through faulty posture, shortened muscle length, intense exercise and exercise to fatigue, resulting in increased motor neuron activity and motor unit recruitment. The relaxation phase of muscle contraction is prolonged in a fatigued muscle, raising the likelihood of fused summation of action potentials if motor neuron activity delivers a sustained high firing frequency. Treatment of cramp is directed at reducing muscle spindle and motor neuron activity by reflex inhibition and afferent stimulation. There are no proven strategies for the prevention of exercise-induced muscle cramp but regular muscle stretching using post-isometric relaxation techniques, correction of muscle balance and posture, adequate conditioning for the activity, mental preparation for competition and avoiding provocative drugs may be beneficial. Other strategies such as incorporating plyometrics or eccentric muscle strengthening into training programmes, maintaining adequate carbohydrate reserves during competition or treating myofascial trigger points are speculative and require investigation.

Central Nervous System↗
PubMed1995

Smoking in hotels: prevalence, and opinions about restrictions.

Exposure to high levels of environmental tobacco smoke can occur in hotels. Controversy exists about smoking regulation on licensed premises. This survey of 138 people attending one of three Newcastle hotels during 1993 found that 57 per cent of respondents were nonsmokers. Fifty-eight per cent (95 per cent confidence interval (CI) 50 to 66 per cent) of respondents in these hotels believed their health was being adversely affected by other people's smoke in the hotel. Seventy per cent (CI 62 to 78 per cent), including half the smokers, were in favour of restriction of smoking in the hotels. Most preferred the establishment of smoke-free areas to the introduction of total smoking bans in hotels. The failure of hotels to regulate smoking suggests that a legislative approach is required. The case for legislation would be strengthened by a larger study elsewhere in Australia.

Adult↗
PubMed1995

Underutilization of isoniazid chemoprophylaxis in tuberculosis contacts 50 years of age and older. A prospective analysis.

STUDY OBJECTIVES: To examine the utilization of chemoprophylaxis for tuberculosis in certain high-risk groups, ie, infected contacts 50 years and older, and to study the safety of isoniazid (INH) preventive therapy in such persons. DESIGN: From 1987 to 1992, two-part questionnaires were sent to each of the regional health offices within the 95 counties of Tennessee to document cases of purified protein derivative skin test conversion or reaction among close contacts of new patients with active tuberculosis. Infected contacts 50 years and older were included in the study. METHODS: Data collected from these questionnaires were grouped according to age, sex, race, liver functions test (LFT), and whether chemotherapy was completed. Reasons for early discontinuation were also recorded. High values of LFTs were classified in the various groups as either twofold elevation or greater than threefold elevation. RESULTS: Of the 829 responses for persons fitting the criteria for INH chemoprophylaxis, 415 began treatment; 249 (60%) of those completed the full course (9 months) and 166 stopped prematurely. Of the 414 persons (50%) who did not start preventive therapy, 233 (56.5%) respondents listed age as the reason. No patients started on a regimen of therapy developed hepatitis. Of those completing therapy, 6.9% had a rise in liver enzyme values but remained asymptomatic for hepatitis. Liver enzyme level elevation was significantly higher among patients who discontinued therapy, particularly white women, than those who completed the full course. Asymptomatic liver enzyme level elevation (> or = 3 times normal value), private practitioners' preferences, and patients arbitrarily stopping therapy were the leading reasons for incomplete INH preventive therapy. CONCLUSION: We conclude that 30% of tuberculosis-infected contacts deserving chemoprophylaxis were actually provided the full benefit of INH preventive therapy, indicating underutilization of this prevention strategy, particularly in contacts older than 50 years.

Age Distribution↗
PubMed1995

A clinical and pharmacokinetic study of high-dose carboplatin, paclitaxel, granulocyte colony-stimulating factor, and peripheral blood stem cells in patients with unresectable or metastatic cancer.

We have developed a regimen incorporating multiple cycles of high-dose carboplatin and fixed-dose paclitaxel (Taxol; Bristol-Myers Squibb Company, Princeton, NJ) with granulocyte colony-stimulating factor and peripheral blood stem cell support given every 21 days for up to four cycles. Our phase I study of this regimen has treated 26 patients with good performance status and histologically documented unresectable or metastatic carcinoma, sarcoma, or melanoma, 21 of whom received all planned courses every 21 days. Paclitaxel 250 mg/m2 was infused over 24 hours, followed by a 1-hour carboplatin infusion, with doses escalated between area under the concentration-time curve (AUC) targets of 8 and 20. Considering the carboplatin doses administered (two to three times those generally achieved with growth factor support), toxicity has been relatively modest. The median duration of grade 4 neutropenia and thrombocytopenia was not significantly different between the AUCs of 8 and 18, which proved to be the maximum tolerated carboplatin dose. Twelve courses were associated with hospitalization for neutropenic fever or catheter-related thrombophlebitis. One treatment-related death occurred, and severe toxicity caused withdrawal of two patients treated at the AUC of 20. Peripheral neuropathy was the most common serious nonhematologic complication. Pharmacokinetic analysis showed significantly lower measured versus predicted AUC values. Among 25 evaluable patients, preliminary results show one complete response (ovarian cancer) and 11 partial responses, including four in patients with non-small cell lung cancer. Additional issues to be addressed include the effect of a shorter (or longer) paclitaxel infusion on the carboplatin AUC (and the incidence of toxicity) and whether the discrepancy between actual and predicted AUCs (greater in our study than reported elsewhere) is due to the variability of creatinine clearance-determined glomerular filtration rate or to altered carboplatin pharmacokinetics when a short high-dose infusion follows paclitaxel. Additional patients are being accrued at the AUC of 18.

Adult↗
PubMed1993

Measurement of inspiratory muscle performance with incremental threshold loading: a comparison of two techniques.

BACKGROUND: Incremental threshold loading (ITL) is a test of inspiratory muscle performance which is usually performed by breathing through a weighted inspiratory plunger, the load on the inspiratory muscles being increased by externally adding weights to the intake valve. This is not a true threshold device and may be inaccurate. This method was compared with a true threshold device consisting of a solenoid valve which only opens to supply air at a predetermined negative mouth pressure. METHODS: Six naive, normal subjects (three men and three women) aged 22-24 years underwent three tests using each system. The inspiratory loads were increased every minute by equivalent amounts, -10 cm H2O with the solenoid valve and by 50 g with the weighted plunger, until the subjects could not inspire or sustain inspiration for a full minute. Six experienced subjects (four men and two women) aged 23-41 years were subsequently randomised to perform ITL with the solenoid valve, twice with the breathing pattern fixed and twice free. RESULTS: The solenoid valve generated a more accurate mouth pressure response and was less variable at higher loads than the weighted plunger. The work performed (expressed as the pressure-time product) was less with the solenoid valve but was more reproducible. ITL with the solenoid valve was not influenced by controlling the breathing pattern of the subjects. CONCLUSIONS: The solenoid valve has several features that make it superior to the weighted plunger as a device for ITL. It generates a more accurate mouth pressure response which is less variable at higher loads. Increases in load are smoother and quicker to introduce. ITL with the solenoid valve is not influenced by varying breathing patterns and does not require any external regulation.

Adult↗
PubMed1992

Effect of methacholine induced bronchoconstriction on the spectral characteristics of breath sounds in asthma.

BACKGROUND: Analysis of breath sounds by digital techniques offers an attractive non-invasive method of monitoring changes in airway calibre. Asthmatic breath sounds have been analysed and related to changes in forced expiratory volume in one second (FEV1). METHODS: Bronchoconstriction was induced with methacholine in six asthmatic subjects on two occasions and changes in FEV1 and breath sound spectra were measured. RESULTS: Audible wheeze appeared after a mean (SE) fall in FEV1 of 35% (6.3%) but the level was not reproducible within patients. The mean and median frequency of the spectra of breath sounds correlated with the percentage of predicted FEV1 (r = -0.5 and -0.6 respectively; p < 0.001). Inclusion of the quartile frequencies in a stepwise multiple regression reduced the residual variance by a further 9%. CONCLUSION: Detecting changes in airway calibre by this method of sound analysis so far produces qualitative data only and will not yield quantitative data in individual patients.

Asthma↗
PubMed1991

The management of impotence in diabetic men by vacuum tumescence therapy.

The treatment of impotence in diabetic men with vacuum tumescence therapy was studied in a specialist clinic. Of 54 diabetic men referred with impotence, seven declined treatment, three chose self-injection with papaverine, and 44 chose vacuum therapy. Patients underwent autonomic function testing (heart rate response to respiration), measurement of penile blood flow (duplex Doppler scanning), and estimation of serum prolactin and testosterone levels. After 2 months, 33 men (75%) were able to have satisfactory intercourse using vacuum therapy. Three others could produce a satisfactory erection with vacuum therapy but their partners found it unacceptable. Eight men (18%) were unable to have satisfactory intercourse; six of these were later treated by self-injection. The median frequency of use of vacuum therapy was 5.5 (1-26) times a month. Outcome was independent of penile blood flow, autonomic function or endocrine status. Impotent diabetic men should be given counselling and offered a choice of the available treatments. Vacuum tumescence therapy is an effective and simple treatment which requires little investigation.

Diabetes Mellitus↗
PubMed1990

99mTc radioimmunoscintigraphy of colorectal cancer.

The monoclonal antibody PR1A3 against a normal colonic columnar cell surface antigen has been labelled with 99mTc and used for imaging colorectal cancer. High uptake in undifferentiated cancer is seen. The tumour to mucosa ratio was up to 63:1 and the percentage of the injected activity in the tumour up to 1.7 X 10(-2%)g-1. As 99mTc is continuously available in a Nuclear Medicine Department, on receipt of a request the study may be completed within 24 h enabling radioimmunoscintigraphy to be used routinely in the management of patients with colorectal cancer.

Adenocarcinoma↗
PubMed1987

Modification of deoxyribonucleic acid-thyroid hormone receptor interaction by histones.

The effects of histones on receptor-DNA interaction were examined using an in vitro DNA-cellulose-binding assay of [125I]T3 receptor. H1 histones bound to DNA-cellulose strongly inhibited binding of receptor to DNA-cellulose. DNA-cellulose column chromatography showed that 80% of T3-binding activity attached to DNA-cellulose could be eluted using 1 mg H1 histone/ml at low ionic strength. The potent inhibitory activity of H1 histones on receptor-DNA binding was reversed by removal of H1 histones from DNA-cellulose or by removal of H1 histones from receptor. The interaction was specific for the DNA-binding activity of receptor, since H1 histones inhibit neither T3-binding activity nor core histone-binding activity of receptor. In contrast, low concentrations of core histones enhanced binding of T3 receptor to DNA-cellulose. This effect was also seen when DNA-cellulose was treated with core histones and then deprived of free core histones. The enhancement was reversed by removal of core histones bound to DNA-cellulose. A tryptic fragment of the receptor, which lost DNA-binding activity but retained hormone and core histone-binding activities, was capable of binding to DNA-cellulose in the presence of core histones. These data suggest that enhanced binding of receptor to DNA-cellulose by core histones is mediated through the core histone-binding activity of receptor. A heat-labile protein factor in nuclear extracts (possibly receptor itself) also enhanced receptor binding to DNA-cellulose. Our data suggest important roles of histones in the organization of nuclear thyroid hormone receptors in chromatin. Since H1 histone participates in condensation of chromatin and is enriched in transcriptionally inactive chromatin, inhibition of DNA-binding activity of receptor by H1 histone bound to DNA could explain the preferential binding of nuclear thyroid hormone receptor to transcriptionally active chromatin.

Animals↗
PubMed1986

Some failings of pulsatility index and damping factor.

Pulsatility index (PI) is a commonly used method of objective assessment of the Doppler waveform. PI falls with increasing proximal stenosis and is raised by increasing peripheral resistance. Damping factor (DF) for an arterial segment is calculated by dividing the proximal by the distal PI. DF rises with increasing severity of disease of the arterial segment. DF is not, however, sufficiently accurate to be used alone but is usually combined with transit time measurements to provide information of diagnostic use. Both PI and DF have been examined in a canine model of combined segment disease. With increasing stenosis, distal PI falls as expected but so also does proximal PI. Such a stenosis is, in effect, a flow-throttling resistance so that although the characteristics of blood flow are altered by its presence, similar changes are observed both above and below the stenosis. The reduction of PI by a stenosis distal to the insonation site may result in the false interpretation of a low PI as indicating disease proximal to the insonation site. The observed similarity between PI proximal and distal to a stenosis reduces the usefulness of pulsatility index damping factor, particularly in the assessment of the femoro-popliteal segment in combined segment disease.

Animals↗
PubMed1985

A technique for the long term measurement of intra-compartmental pressure in the lower leg.

The early diagnosis of an acute compartmental pressure syndrome is often difficult, but can be facilitated by long term, up to several days, measurement of intra-compartmental pressures. A measuring system has been developed, together with its associated surgical and operational procedures, which may be applied in a variety of situations, including an immobile patient or a patient mobilized following surgery. If the technique is adopted as soon as the patient enters hospital, or immediately postoperatively, an acute compartmental syndrome may be recognized early and measures taken to alleviate its consequences.

Biomedical Engineering↗
PubMed1984

Haemodynamics of the adjunctive arteriovenous fistula in femorodistal bypass grafting: an experimental study.

The results of femorotibial bypass for limb salvage vary a great deal. One of the reasons for this might be the discrepancy between potential inflow and run-off into the foot. An arteriovenous fistula at the distal graft anastomosis may improve results but the best anatomical arrangement for the fistula is unknown. Ileofemoral grafts were performed in dogs after the hind limb was rendered ischaemic. The distal end of the graft was anastomosed proximal to, superimposed upon, or distal to an arteriovenous fistula between the femoral artery and its accompanying femoral vein. The effect of the fistula on graft/run-off haemodynamics was then measured. The adjunctive arteriovenous fistula increased inflow by a mean of 900 per cent and reduced systemic pressure by 10 per cent. Peripheral resistance was reduced by 85 per cent. Distal arterial run-off was maximized with respect to total graft flow when the graft was placed distal to the fistula (P less than 0.05). The venous steal of flow and perfusion pressure produced by the fistula was minimized with the same configuration compared to the two other arrangements (P less than 0.01 and P less than 0.05). Placement of the graft distal to the adjunctive arteriovenous fistula maximized distal arterial flow and pressure, and significantly increased graft flow.

Animals↗
PubMed1982

Clinical trials of the efficacy and duration of antibacterial cover for elective resection in inflammatory bowel disease.

A prospective double-blind placebo controlled trial was performed to test the values of 24-h cover with metronidazole and gentamicin in 57 patients requiring elective resections for inflammatory bowel disease (phase 1). The short term antimicrobial cover was not associated with a reduction in the incidence of postoperative sepsis. A further group of 30 patients who received metronidazole and gentamicin cover for 5 days (phase 2) was therefore studied and the results were compared with phase 1. There was a significant reduction in the incidence of sepsis in the patients receiving 5-day postoperative antibiotic cover compared with the placebo group.

Adult↗