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Biomedical subjects

John B Chambers

Publications and source records attributed to John B Chambers.

6 recordsLinked to original sources
PubMed2006

Aldosterone and left ventricular hypertrophy in Afro-Caribbean subjects with low renin hypertension.

BACKGROUND: Activity of the renin-angiotensin-aldosterone system is thought to play a major role in determining blood pressure (BP) and target organ damage such as left ventricular hypertrophy. In Afro-Caribbean subjects, however, hypertension tends to be more severe despite lower plasma renin activity. We investigated whether this might be due to a different relation between aldosterone and renin in Afro-Caribbean compared to white subjects. METHODS: Plasma aldosterone and renin activity were assessed in the morning after 15 min seated in 383 hypertensive subjects of Afro-Caribbean or white ethnicity (61% Afro-Caribbean, 83% on treatment) attending a hypertension clinic in London, UK. Left ventricular mass index (LVMI) was assessed by echocardiography in 276 subjects. RESULTS: Plasma renin activity was lower in Afro-Caribbean compared to white subjects (0.4 [0.3-1.0] v 1.4 [0.5-3.4] ng/mL/h, medians [interquartile range], P < .0001). Despite this, aldosterone was higher in Afro-Caribbean compared to white subjects (8.0 [6.1-12.6] v 7.4 [2.3-17.1] ng/dL, medians [interquartile range], P < .01). The LVMI corrected for sex and BP was higher in Afro-Caribbean than in white subjects. In Afro-Caribbean but not in white subjects LVMI was independently correlated with plasma aldosterone (standardized regression coefficient, beta= 0.25, P < .001). CONCLUSIONS: In Afro-Caribbean hypertensive subjects in London, plasma aldosterone is elevated despite lower renin and may contribute to increased severity of hypertension and left ventricular hypertrophy in Afro-Caribbean compared to white subjects.

Adult↗
PubMed2006

The subcoronary Toronto stentless versus supra-annular Perimount stented replacement aortic valve: early clinical and hemodynamic results of a randomized comparison in 160 patients.

BACKGROUND: A stentless valve is expected to be hemodynamically superior to a stented valve. The aim of this study was to compare early postoperative hemodynamic function and clinical events in a randomized, prospective series of 160 stentless and stented biological replacement aortic valves. METHODS: We randomized 160 consecutive patients on 1 surgeon's list to receive either a Toronto stentless porcine valve (St Jude Medical, Inc, St Paul, Minn) or a Perimount stented bovine pericardial valve (Edwards Lifesciences, Irvine, Calif). Echocardiography was performed at discharge, between 3 and 6 months, and at 1 year after surgery. Statistical analysis was performed by both intention to treat and actual valves implanted. RESULTS: The mean labeled size of both designs of valve was 24.7. There were no statistically significant differences in results at any time interval or whether analysis was performed by actual valves implanted or intention to treat. At 3 to 6 months for the Toronto versus the Perimount valve, the effective orifice area was 1.58 versus 1.66 cm2, the mean pressure difference was 7.54 versus 7.42 mm Hg, and the peak velocity was 2.07 versus 2.0.1 m/s. There was no difference in mortality, regression of left ventricular hypertrophy, or complications other than paraprosthetic regurgitation at 12 months or on follow-up for a proportion of the sample to 8 years. The incidence of regurgitation through the valves was similar for Toronto (10%) and Perimount (13.8%) at 1 year, but mild paraprosthetic regurgitation was found in 5 patients with the Perimount valve and none with Toronto valves. CONCLUSIONS: There were no significant differences in hemodynamic function or clinical events between the stented and stentless biological valves chosen for comparison in the early postoperative period or in preliminary follow-up to 5 years.

Aged↗
PubMed2003

Nominal size in six bileaflet mechanical aortic valves: a comparison of orifice size and biologic equivalence.

OBJECTIVES: Nominal size remains the standard by which valves are compared, but its relationship with orifice area and the patient tissue annulus diameter may differ according to valve design. The aims of this study were to measure the orifice size and compare biologic equivalence in six bileaflet mechanical heart valve designs. METHODS: The inflow aspect of each of 29 valves was photographed then digitized, and the maximum internal diameter and orifice area were calculated. Biologic equivalence was assessed with a series of machined polypropylene blocks. RESULTS: The orifice area ranged between 159 and 222 mm(2) for the six size 19 valves. The internal diameter ranged from 1.6 to 4.6 mm less than the manufacturer's nominal size. Biologic equivalence assessed from an estimate of tissue annulus diameter with machined blocks ranged from 1.0 and 3.5 mm larger than nominal size for the intra-annular valves. This diameter ranged from 3.5 mm smaller to 1.5 mm larger than nominal size for the supra-annular valves. CONCLUSION: There are major differences between nominal size and biologic equivalence. This may lead to confusion when attempting to make comparisons between different valve designs with the same nominal size. A clearer sizing nomenclature is required and could be based on in vitro assessment of tissue annulus diameter or an alphanumeric code.

Aortic Valve↗
PubMed2002

Prosthesis-related complications: first-year annual rates.

The rates of valve-related complications determine the clinical performance of biological and mechanical heart valve prostheses by valve position. The crude rates of valve-related complications within the first year after implantation have not been previously reported. The Food and Drug Administration (FDA) of the United States guidance document for the performance of new heart valve prostheses uses objective performance criteria (OPC) as target values for valve-related complications. The FDA requirement for each valve-related complication is that the rate cannot be greater than twice the OPC. This report provides the first-year rates of valve-related complications from a university database of over 7,000 implants, followed longitudinally between 1982 and 1999, of currently marketed biological and mechanical heart valve prostheses. The aim of this report was to provide an additional method for consideration by regulatory authorities in determination of the standards of performance for pre-market approval of new prosthetic valves for heart valve replacement surgery.

Aortic Valve↗
PubMed2002

Treatment of left-sided prosthetic valve thrombosis: thrombolysis or surgery?

Although, traditionally, surgery has been the treatment of choice for left-sided prosthetic valve thrombosis (PVT), there are significant risks associated with re-do surgery. Thrombolysis is an alternative to surgery and has a success rate in excess of 80%, but is associated with an -10% risk of systemic embolism and a 7% mortality rate. Guidelines for the use of thrombolytic therapy for PVT were produced using data acquired from older valves, and largely without the use of transesophageal echocardiography (TEE). Data from more recent studies suggest that thrombolysis should be regarded as first-line therapy for PVT in all NYHA classes. The use of TEE is recommended to visualize thrombus in suspected cases.

Echocardiography, Transesophageal↗