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Biomedical subjects

J D Cameron

Publications and source records attributed to J D Cameron.

At least 37 records · Page 2Linked to original sources
PubMed1999

Muscular strength training is associated with low arterial compliance and high pulse pressure.

Aerobic exercise training increases arterial compliance and reduces systolic blood pressure, but the effects of muscular strength training on arterial mechanical properties are unknown. We compared blood pressure, whole body arterial compliance, aortic impedance, aortic stiffness (measured by beta-index and carotid pulse pressure divided by normalized systolic expansion [Ep]), pulse wave velocity, and left ventricular parameters in 19 muscular strength-trained athletes (mean+/-SD age, 26+/-4 years) and 19 sedentary controls (26+/-5 years). Subjects were healthy, non-steroid-using, nonsmoking males, and athletes had been engaged in a strength-training program with no aerobic component for a minimum of 12 months. There was no difference in maximum oxygen consumption between groups, but handgrip strength (mean+/-SEM, 44+/-2 versus 56+/-2 kg; P<0.01) and left ventricular mass (168+/-8 versus 190+/-8 g; P<0.05) were greater in athletes. Arterial stiffness was higher in athletes, as evidenced by lower whole body arterial compliance (0.40+/-0.04 versus 0.54+/-0.04 arbitrary compliance units; P=0.01), higher aortic characteristic impedance (1.55+/-0.13 versus 1.18+/-0.08 mm Hg. s. cm-1; P<0.05), beta-index (4.6+/-0.2 versus 3.8+/-0.4; P<0. 05), and ln Ep (10.86+/-0.06 versus 10.60+/-0.08; P<0.01). Femoral-dorsalis pedis pulse wave velocity was also higher in the athletes, but carotid-femoral pulse wave velocity was not different. Furthermore, both carotid (56+/-3 versus 44+/-2 mm Hg; P<0.001) and brachial (60+/-3 versus 50+/-2 mm Hg; P<0.01) pulse pressures were higher in the athletes, but mean arterial pressure and resting heart rate did not differ between groups. These data indicate that both the proximal aorta and the leg arteries are stiffer in strength-trained individuals and contribute to a higher cardiac afterload.

Adult↗
PubMed1999

Isoflavones from red clover improve systemic arterial compliance but not plasma lipids in menopausal women.

The possibility that the heightened cardiovascular risk associated with the menopause can be reduced by increasing dietary isoflavone intake was tested in 17 women by measuring arterial compliance, an index of the elasticity of large arteries such as the thoracic aorta. Compliance diminishes with age and menopause. An initial 3- to 4-week run-in period and a 5-week placebo period were followed by two 5-week periods of active treatment with 40 mg and then 80 mg isoflavones derived from red clover containing genistein, daidzein, biochanin, and formononetin in 14 and 13 women, respectively, with 3 others serving as placebo controls throughout. Arterial compliance, measured by ultrasound as a pressure (carotid artery) and volume (outflow into aorta) relationship, was determined after each period; plasma lipids were measured twice during each period. Urinary output of isoflavones was also determined. Arterial compliance rose by 23% relative to that during the placebo period with the 80-mg isoflavone dose and slightly less with the 40-mg dose (mean +/- SEM: placebo, .197 +/- .015; 40 mg, .237 +/- 0.007; 80 mg, .244 +/- .014). In the three women receiving continuous placebo, compliance was .16 +/- .022, similar to that during the run-in period for the remaining subjects (.17 +/- .021) [corrected]. ANOVA showed a significant (P = < 0.001) difference between treatments; by Bonferroni multiple comparisons and by paired t test, differences were significant between placebo and 40- and 80-mg isoflavone doses (by paired t test: P = 0.039 for placebo vs. 40 mg; P = 0.018 for placebo vs. 80 mg). Plasma lipids were not significantly affected. An important cardiovascular risk factor, arterial compliance, which diminishes with menopause, was significantly improved with red clover isoflavones. As diminished compliance leads to systolic hypertension and may increase left ventricular work, the findings indicate a potential new therapeutic approach for improved cardiovascular function after menopause.

Adult↗
PubMed1998

Laser-cured fibrinogen glue to repair bleb leaks in rabbits.

OBJECTIVE: To determine whether laser-cured fibrinogen glue can close bleb leaks in rabbits. METHODS: Full-thickness filtration surgery with intraoperative mitomycin and a sutured limbus-based conjunctival flap was performed in 1 eye each of 19 New Zealand albino rabbits. On the second postoperative day, a 2- to 3-mm hole was made in the bleb. In 9 rabbits, the hole was glued using fibrinogen glue with indocyanine green dye added. The glue was "cured" with a diode laser. Eyes that had been glued and developed a subsequent leak had the glue reapplied on the day the leak was detected. RESULTS: The glue remained on the conjunctiva for an average (mean+/-SD) of 1.9+/-1.8 days (range, 0-5 days). The last day of bleb leak for the rabbits with glued eyes was 1.6+/-2.4 days; for the control rabbits, it was 8.0+/-4.4 days (P=.001, Mann-Whitney U test). CONCLUSION: Laser-cured fibrinogen glue is effective in closing bleb leaks in rabbits.

Animals↗
PubMed1998

Use of radial artery applanation tonometry and a generalized transfer function to determine aortic pressure augmentation in subjects with treated hypertension.

OBJECTIVES: The purposes of this study were to investigate the use of radial artery applanation tonometry and a generalized transfer function for the assessment of central aortic pressure augmentation in subjects taking commonly used antihypertensive agents (angiotensin-converting enzyme inhibitors, beta-adrenergic blockers, Ca2+ antagonists, diuretic therapy). BACKGROUND: Applanation tonometry of the radial artery with a generalized transfer function has been proposed as a means of assessing central aortic blood pressure. Recently, a commercial apparatus based on this technique has become available; we therefore examined the effect of a generalized transfer function on derived central aortic pressure compared with measured brachial blood pressures and also investigated the potential of this technique to assess the influence of differing drug therapy. METHODS: Two hundred and sixty-two hypertensive patients on stable medication were studied using the PWV Medical Blood Pressure Analysis System (version 2, DAT-1). RESULTS: In univariate analysis, augmentation index showed association with age, sex, height and heart rate. In multivariate analysis, diastolic blood pressure and age (positively), height and heart rate (negatively) and sex were significantly associated. After adjustment for these variables, pressure augmentation was not associated with any antihypertensive treatment investigated. Linear relationships were demonstrated between brachial blood pressures and corresponding central pressures derived by transfer function methods. CONCLUSIONS: Our findings suggest that if adjustment for central-peripheral pressure difference is necessary, simple linear relationships may be sufficient. Age, heart rate and height but not the class of antihypertensive medication affected the degree of pressure augmentation observed using this technique.

Adrenergic beta-Antagonists↗
PubMed1998

Neonatal asteroid hyalosis.

Asteroid hyalosis, noted in 0.83% of routine eye examinations, is uncommon in younger patients and is more frequently seen in patients more than 60 years old. It has been considered to be related to an aging process, and when it occurs in younger patients, ocular disease is typically associated. We report a 4-week-old patient with Down syndrome and bilateral congenital cataracts who had unilateral asteroid hyalosis.

Calcinosis↗
PubMed1998

Non-invasive measurements of arterial structure and function: repeatability, interrelationships and trial sample size.

1. Repeatability of measurements of arterial compliance and flow-mediated dilation of the brachial artery has been infrequently reported, despite increasing use in interventional and risk-factor modification studies. Furthermore, little is known about the interrelationships of the various indices. The purposes of this study were to determine the repeatability and interrelationships of a range of arterial indices.2. Fifty healthy volunteers, 20 men and 30 women, aged 20-70 (mean 46.5) years, were studied on two occasions, using an identical protocol, at a mean interval of 2.5 weeks. Tonometry, ultrasound and Doppler technique were used to measure the following: carotid wall intima-media thickness (IMT), total systemic artery compliance (SAC), arterial pulse wave velocity [PWV aorto-femoral (A-F), and femoral-dorsalis pedis (F-D)], carotid distensibility coefficient (DC) and carotid augmentation index (AI). Brachial flow-mediated dilation was measured in 30 subjects with analysis of diameter change for 4 min post ischaemia.3. There were no systematic differences over the observed range of measurements for any of the reported parameters. Coefficients of variation were as follows: IMT 2.8%, SAC 9.2%, PWV(A-F) 3.2%, PWV(F-D) 5.0%, DC 10.0%, AI 1.3%. Brachial flow-mediated dilation curves were not different between visits; changes were maximum 60-s post ischaemia. All indices of arterial compliance were significantly correlated with age. The three different indices of central arterial compliance [SAC, PWV(A-F) and AI] were significantly correlated with carotid intima-media thickness.4. Under controlled experimental conditions there was good repeatability of measurements of indices between sessions of both intrinsic and functional arterial mechanical properties (central and carotid arterial compliance, intima-media thickness and brachial flow-mediated dilation). Sample size tables for clinical trials using these indices are presented.

Adult↗
PubMed1998

Age-related deterioration in arterial structure and function in postmenopausal women: impact of hormone replacement therapy.

Epidemiological evidence suggests that hormone replacement therapy (HRT) reduces morbidity and mortality from cardiovascular diseases in postmenopausal women. In this study, indices of arterial function [total systemic arterial compliance (SAC) and carotid arterial distensibility coefficient (DC)], structure [carotid intima-media thickness (IMT)], and lipid profiles were compared in postmenopausal women on long-term HRT and aged-matched controls. One hundred nine women aged 44 to 77 years taking HRT and an age-matched group of 108 female controls were entered into the study. The two groups were similar for body mass index, smoking status, exercise level, alcohol intake, and blood pressure. Fasting cholesterol, low density lipoprotein, and lipoprotein(a) were reduced and high density lipoprotein increased in the HRT group. IMT increased with age; SAC and DC were reduced with age in both groups. The HRT group had a higher mean SAC (0.42+/-0.02 versus 0.34+/-0.02 U/mm Hg, P=0.0001) and a lower mean IMT (0.67+/-0.01 versus 0.74+/-0.02 mm, P=0.006) than did controls. Subgroup analysis for estrogen versus estrogen plus progestin revealed no differences for SAC and IMT; DC, however, was greater in estrogen-only users. Smokers on HRT had a higher mean SAC (0.41+/-0.02 versus 0.31+/-0.01 U/mm Hg, P=0.008) and a lower IMT (0.65+/-0.02 versus 0.75+/-0.03 mm, P=0.002) than did smokers not taking such therapy. A protective effect of long-term estrogen therapy on age-related changes in arterial structure and function in postmenopausal women was evident in smokers and nonsmokers alike. Progestin appeared to counteract the effects of estrogen on carotid compliance only. Long-term controlled trials are needed to determine the significance of these findings.

Adult↗
PubMed1998

Relation between coronary artery disease, aortic stiffness, and left ventricular structure in a population sample.

To elucidate the relationship between coronary artery disease (CAD), aortic stiffness, and left ventricular structure, we recruited 55 subjects (33 men; average age, 63+/-1 years) with previously unknown CAD from a healthy general population sample, as well as 55 control subjects matched for gender, age, and serum cholesterol level. We measured arterial blood pressure and the systolic expansion of the transverse aorta and left ventricular structure by echocardiography. Aortic stiffness was higher in CAD patients than in controls, with a brachial pulse pressure of 59+/-3 versus 52+/-2 mm Hg and stiffness indices of Ep=212+/-26 versus 123+/-13 kN/m2 and beat=16+/-2 versus 9+/-1 (all P<0.01). Mean arterial pressure was similar in both groups during the measurements (95+/-2 versus 93+/-2 mm Hg, P=NS). Most CAD patients (61%) were in the highest stiffness quartile defined by the normal control values (P<0.05 versus control). Left ventricular mass index was also higher in CAD patients than in matched controls (139+/-5 versus 123+/-4 g/m2, P<0.05). We conclude that aortic stiffness and left ventricular mass are increased in subjects newly diagnosed as having CAD. This might explain previously reported associations of an increased mortality, particularly from CAD, found among subjects with elevated pulse pressures.

Aged↗
PubMed1998

A new model of proliferative vitreoretinopathy.

PURPOSE: To design a new model of proliferative vitreoretinopathy (PVR) that would not rely on the addition of exogenous cells. The release of endogenous cells from surrounding attachments seems to be an early event in the pathogenesis of PVR. Because the proteolytic enzyme dispase dissociates tissues, the hypothesis was that an intraocular injection of dispase could trigger events that would cause PVR. The requirement for a surgical retinal break at the time of dispase injection was also examined. METHODS: One eye of Dutch Belted rabbits was injected with 0.003 U to 1.0 U dispase in the subretinal space or vitreous cavity. Control rabbits received a saline injection. An intentional retinal tear was created in animals in some groups. Observations were made for at least 10 weeks after surgery. RESULTS: Proliferative vitreoretinopathy developed in response to subretinal or intravitreal dispase, with or without creation of a controlled retinal break. Increased severity of PVR correlated with increasing doses of dispase. Evidence of PVR included preretinal membranes, distortion of myelin wings and retinal vessels, fixed retinal folds, and traction retinal detachment. Proliferative vitreoretinopathy did not develop in saline-treated control animals. CONCLUSIONS: Dispase initiated the development of PVR without the addition of exogenous cells, growth factors, or cytokines typically found in PVR membranes. A cascade of events was probably triggered by dispase, causing native cells and factors to produce PVR. The dispase model of PVR was technically easy to perform, permitted a clear view of the retina, and had a high success rate in development of PVR.

Animals↗
PubMed1998

In vivo efficacy of silver-coated (Silzone) infection-resistant polyester fabric against a biofilm-producing bacteria, Staphylococcus epidermidis.

BACKGROUND AND AIMS OF THE STUDY: Prosthetic valve endocarditis (PVE) is an infrequent but serious complication of cardiac valve replacement. PVE is a foreign body infection predominantly based in the sewing cuff of a prosthetic heart valve leading to thromboembolism, ring abscess, paravalvular leakage, and eventual invasion of the myocardium. Mortality rates as high as 75% have been reported. A silver-coated sewing cuff is now available (St. Jude Medical mechanical heart valve SJMR Masters Series with Silzone coating) intended to inhibit the colonization and attachment to the sewing cuff of those microorganisms commonly associated with PVE. Silzone is a dense layer of metallic silver deposited on individual fiber surfaces of the valve cuff. Previously, Silzone coating was shown in vitro to decrease attachment and colonization of microorganisms with no adverse affect on biocompatibility. The present study was designed to assess the efficacy of Silzone-coated polyester fabric in vivo in a direct-contamination model. The organism chosen was a pathogenic strain of Staphylococcus epidermidis capable of producing biofilm. METHODS: Infection resistance of uncoated polyester and Silzone-coated polyester fabric was assessed by the acute inflammatory response in a guinea pig subdermal model. Fabric samples were implanted sterile or inoculated with S. epidermidis. The ability of the strain to produce biofilm was verified in vitro. Samples were explanted at one and two days postoperatively. Verification of the infecting bacteria was by colony morphology and Gram-staining properties of bacteria from the explanted samples. Inflammation was assessed histopathologically. Percent necrotic tissue within the fabric was determined by computer-assisted image analysis. RESULTS: Histopathology and image analysis of necrotic tissue showed significantly less inflammation within the Silzone-coated fabric than within uncoated polyester fabric. CONCLUSIONS: The Silzone coating reduced inflammation in this direct-contamination model using a strain of S. epidermidis that is capable of producing biofilm. This indicates a concentration of silver ions sufficient for bacteriostatic or bactericidal activity within the fabric in vivo.

Animals↗
PubMed1998

Evaluation of a novel bioprosthetic heart valve incorporating anticalcification and antimicrobial technology in a sheep model.

BACKGROUND AND AIM OF THE STUDY: The St. Jude Medical (SJM) Epic valve has been designed to diminish the risk of prosthetic valve endocarditis by the use of silver-coated polyester fabric, and to inhibit dystrophic calcification by the use of ethanol pretreatment. METHODS: A 20-week juvenile sheep mitral valve implant model was used to determine safety and efficacy of the device, as well as the rate of silver release and degree of dystrophic calcification. The SJM Epic valves were compared with SJM Biocor porcine valves (not ethanol-pretreated, not silver-modified polyester fabric) and Baxter Carpentier-EdwardsR standard valves. RESULTS: Blood concentrations of silver reached a maximum of 40 p.p.b. within 10 days of SJM Epic valve implantation, and were well below toxic levels (300 p.p.b.). Blood silver concentrations returned to baseline within 30 days after surgery. Maximal silver accumulation occurred in the liver (16.75 mg/g dry weight); concentrations in the brain, spleen, kidney and lung were similar to those reported for other silver-modified prosthetic valves. No statistically significant difference was found in calcium content between SJM Epic and Biocor valves. The fibrous response to the sewing cuff was similar among the three valve types. CONCLUSIONS: At all times tested, silver release from the SJM Epic valve led to blood concentrations well below toxic levels. Although calcification in the two SJM valve groups was extremely low, the 20-week sheep model may be insufficiently sensitive to detect differences in calcium accumulation in modern bioprosthetic valves.

Animals↗
PubMed1997

Intraocular molluscum contagiosum after a corneoscleral laceration.

PURPOSE: To report molluscum contagiosum as a cause of severe posttraumatic intraocular inflammation. METHODS: A 9-year-old girl developed severe intraocular inflammation in the right eye after a corneoscleral laceration. She underwent vitrectomy, and bacterial and fungal cultures of intraocular fluids were negative. A pedunculated white-tan mass removed from her right optic nerve head was sent for histologic evaluation. RESULT: Histologic examination of the tissue showed stratified keratinizing squamous epithelium with intracytoplasmic inclusions consistent with molluscum contagiosum. CONCLUSIONS: It is likely that infected epithelial cells were implanted at the time of injury. Vitrectomy as debridement was curative.

Child↗
PubMed1997

Hormonal therapy increases arterial compliance in postmenopausal women.

OBJECTIVES: This study investigated the effects of hormonal therapy on large arterial properties. BACKGROUND: Arterial stiffness is an emerging risk marker for coronary heart disease and is potentially modifiable. Postmenopausal use of hormonal therapy is associated with a lower risk of coronary heart disease. METHODS: Total systemic arterial compliance (SAC) and pulse wave velocity (PWV) were determined in 26 premenopausal and 52 postmenopausal women, 26 of whom were taking hormonal therapy. RESULTS: Arterial compliance was greater in the premenopausal group (mean +/- SEM 0.57 +/- 0.04 arbitrary compliance units [ACU]) than in the postmenopausal group not taking hormonal therapy (0.26 +/- 0.02 ACU, p = 0.001). Postmenopausal women taking hormonal therapy had a significantly increased total SAC compared with women not taking hormonal therapy (0.43 +/- 0.02 vs. 0.26 +/- 0.02 ACU, p = 0.001). PWV in the aortofemoral region in the premenopausal women was 6.0 +/- 0.2 vs. 8.9 +/- 0.3 m/s (p < 0.001) in untreated postmenopausal women. However, postmenopausal women taking hormonal therapy had a significantly lower PWV than those not taking hormonal therapy (7.9 +/- 0.2 vs. 8.9 +/- 0.3 m/s, p = 0.01). Eleven postmenopausal women had their hormone replacement therapy withdrawn for 4 weeks, resulting in a significant decrease in SAC and a significant increase in aortofemoral PWV. CONCLUSIONS: The increased SAC and decreased PWV in women receiving hormonal therapy suggest that such therapy may decrease stiffness of the aorta and large arteries in postmenopausal women, with potential benefit for age-related cardiovascular disorders. The reduction of arterial compliance with age appears to be altered with hormonal therapy.

Adolescent↗
PubMed1997

Effects of oestrogen and progesterone on age-related changes in arteries of postmenopausal women.

1. Hormone replacement therapy (HRT) with oestrogen or oestrogen plus progestin may have different effects on arterial structure and function. To examine this question, carotid artery intima-medial thickness (IMT) and indices of systemic and carotid arterial compliance were measured in groups of older men, postmenopausal women not on HRT (non-HRT) and those women on long-term HRT with oestrogen alone (HRT-E) or oestrogen plus progestin (HRT-EP). 2. Sixty men, 90 postmenopausal women taking HRT and 91 not taking HRT participated in the study. The groups were similar for age, body mass index, numbers of smokers, physical activity, alcohol intake and blood pressure. 3. Plasma total cholesterol was reduced and high-density lipoprotein-cholesterol was increased in the HRT group compared with the non-HRT group; low-density lipoprotein-cholesterol, triglyceride and lipoprotein (a) values were similar in these two groups. Results for HRT-E and HRT-EP subgroups were similar. 4. Carotid IMT was significantly reduced in the HRT group compared with men and non-HRT groups. Results for HRT-E and HRT-EP subgroups were similar. 5. Mean systemic arterial compliance (SAC) was significantly greater in men than in women and was related to age; SAC was higher in both HRT-E and HRT-EP groups compared with the non-HRT group. Indices of carotid stiffness were similar in men and in non-HRT groups. The HRT-EP group showed increased carotid stiffness compared with the HRT-E group. 6. There is an apparent protective effect of long-term oestrogen therapy on carotid IMT and age-related changes in arterial stiffness. Progestin does not alter the IMT effects but may adversely influence arterial stiffness.

Aged↗
PubMed1997

A self-administered questionnaire for detection of unrecognised coronary heart disease.

On an individual and a population basis, an increased incidence of coronary heart disease is associated with classical cardiovascular risk factors, but many cases occur in people not identified as at high risk. Conversely, many people at high statistical risk do not develop coronary disease. We used a questionnaire to identify unrecognised coronary heart disease in people attending large-scale health survey centres. Participants were required to report the presence and characteristics of any chest pain. Those returning responses consistent with myocardial ischaemia were offered treadmill exercise ECG tests. Over 18 months, 4070 questionnaires were returned. Of 475 respondents offered testing, 229 (198 male, 131 female) accepted. Thirty-two subjects (15 male, 17 female: a detection rate of 13.9 per cent of those assessed as likely on questionnaire, or 0.8 per cent of all respondents) had results consistent with significant coronary heart disease. Follow-up was available in 30 cases. There was no difference in classical risk-factor distribution (including multivariate risk percentiles: 42.4 (male) and 46.7 (female)) between those newly diagnosed with coronary heart disease and their community counterparts. More women than men were identified as suffering from unrecognised coronary heart disease, with a preponderance of younger women. Cost per case identified was A$1220. Screening by self-administered questionnaire is a useful and relatively cost-effective means of identifying unrecognised coronary heart disease.

Aged↗
PubMed1997

Reduced systemic arterial compliance is associated with left ventricular hypertrophy and diastolic dysfunction in older people.

OBJECTIVES: To study the relationship between left ventricular diastolic function and systemic arterial compliance in the older population. DESIGN: Cross-sectional survey. PARTICIPANTS: A total of 67 older volunteer participants (aged 67 +/- 5.4 years). MEASUREMENTS: Systemic arterial compliance (SAC) was measured using applanation tonometry and aortic velocimetry, and diastolic function was assessed using Doppler filling. Left ventricular mass was determined echocardiographically. RESULTS: There were significant univariate correlations between diastolic filling, as measured by E/A ratio, systemic arterial compliance (0.34, P < .01), and left ventricular mass (-0.41, P < .001). In multiple regression analysis, using diastolic filling as the dependent variable and heart rate, age, left ventricular mass corrected for body surface area, systolic and diastolic blood pressures, and arterial compliance as independent variables, the major determinants of diastolic filling were heart rate, left ventricular mass, and diastolic blood pressure. Arterial compliance did not make a significant independent contribution. CONCLUSION: This study demonstrates a positive relationship between diastolic filling and arterial compliance in the older population. However, in multiple regression analysis, heart rate, diastolic blood pressure, and left ventricular mass were the independent predictors of diastolic filling (E/A), whereas arterial compliance was not. These findings imply that therapeutic modulation of aortic stiffness would not, of itself, contribute to improvement in diastolic function.

Arteries↗