Reductive reactivity of iron(III) oxides in the east china sea sediments: characterization by selective extraction and kinetic dissolution.

Reactive Fe(III) oxides in gravity-core sediments collected from the East China Sea inner shelf were quantified by using three selective extractions (acidic hydroxylamine, acidic oxalate, bicarbonate-citrate buffered sodium dithionite). Also the reactivity of Fe(III) oxides in the sediments was characterized by kinetic dissolution using ascorbic acid as reductant at pH 3.0 and 7.5 in combination with the reactive continuum model. Three parameters derived from the kinetic method: m 0 (theoretical initial amount of ascorbate-reducible Fe(III) oxides), k' (rate constant) and γ (heterogeneity of reactivity), enable a quantitative characterization of Fe(III) oxide reactivity in a standardized way. Amorphous Fe(III) oxides quantified by acidic hydroxylamine extraction were quickly consumed in the uppermost layer during early diagenesis but were not depleted over the upper 100 cm depth. The total amounts of amorphous and poorly crystalline Fe(III) oxides are highly available for efficient buffering of dissolved sulfide. As indicated by the m 0, k' and γ, the surface sediments always have the maximum content, reactivity and heterogeneity of reactive Fe(III) oxides, while the three parameters simultaneously downcore decrease, much more quickly in the upper layer than at depth. Albeit being within a small range (within one order of magnitude) of the initial rates among sediments at different depths, incongruent dissolution could result in huge discrepancies of the later dissolution rates due to differentiating heterogeneity, which cannot be revealed by selective extraction. A strong linear correlation of the m 0 at pH 3.0 with the dithionite-extractable Fe(III) suggests that the m 0 may represent Fe(III) oxide assemblages spanning amorphous and crystalline Fe(III) oxides. Maximum microbially available Fe(III) predicted by the m 0 at pH 7.5 may include both amorphous and a fraction of other less reactive Fe(III) phases.

[Comparison of amiodarone plus irbesartan regimen versus amiodarone alone on maintaining sinus rhythm in rheumatic heart disease patients with persistent atrial fibrillation post valve replacement and cardioversion].

OBJECTIVE: To compare the efficacy of combined amiodarone and irbesartan use versus amiodarone alone on maintaining sinus rhythm in rheumatic heart disease patients with persistent atrial fibrillation (AF) post valve replacement and cardioversion. METHODS: Patients were randomly divided into amiodarone group (A, n = 31) and amiodarone plus irbesartan group (AI, n = 32) and all patients received Warfarin (INR 2.0 - 3.0). For patients in group A, intravenous amiodarone (600 mg/d) was applied for 10 days and oral amiodarone (200 mg, b.i.d.) was given on the 7th day for 3 days. For patients in group AI, irbesartan (150 mg/d) was added on top of amiodarone at the study begin. Electric cardioversion was performed for patients still with AF on day 10. Amiodarone (200 mg, b.i.d. for 1 week, then 200 mg, q.d. till study end) with or without irbesartan (150 mg/d) was continued thereafter. Patients were followed up for 12 months after sinus rhythm recovery. The primary end points are first recurrence of symptomatic and asymptomatic AF. RESULTS: Twelve months post therapy, number of patients on sinus rhythm was significantly higher (68.7% vs. 41.9%, P<0.05) and left atrium diameter (LAD) was significantly smaller [(48.6 +/- 4.6) mm vs. (51.5 +/- 4.2) mm, P<0.05] in group AI than those in group A. LAD (OR 1.242) and use of irbesartan (OR 0.226) are associated with the AF recurrence. CONCLUSION: Combined amiodarone and irbesartan use is superior to amiodarone alone for maintaining sinus rhythm in rheumatic heart disease patients with persistent AF post valve replacement and cardioversion.