Positive effects of aggressive vasodilator treatment of well-treated essential hypertensive patients.

Increased systemic vascular resistance and coronary microvascular dysfunction are well-documented in essential hypertension (EH). We investigated the effect of additional vasodilating treatment on coronary and peripheral resistance circulation in EH patients with high systemic vascular resistance index (SVRI) despite well-treated blood pressure (BP). We enroled patients on stable antihypertensive treatment that were given intensified vasodilating therapy (ACE inhibitor, angiotensin II receptor blocker or calcium channel blocker). Before and following 6 months of intensified therapy, coronary resting and maximal artery flow were measured by transthoracic Doppler echocardiography to calculate coronary flow reserve (CFR) and minimum vascular resistance (C-Rmin). Cardiac output was estimated by inert gas rebreathing to calculate SVRI. Maximal forearm blood flow was determined by venous occlusion plethysmography to calculate minimum vascular resistance (F-Rmin). Patients were assigned into two groups: high-SVRI and low-SVRI subgroups, based on a median split at baseline. Following additional treatment SVRI decreased more in the high-SVRI group than in the low-SVRI group (14.4 vs -2.2%: P=0.003), despite similar baseline ambulatory BP (132/81 mm Hg) and BP reduction (6.5 and 4.6%: P=0.19). F-Rmin remained unchanged (6.5 vs -2.0%: P=0.30), while C-Rmin decreased by 22 and 24% (P=0.80) and CFR increased by 23 and 17% (P=0.16). Thus, intensified vasodilating therapy improved SVRI more in patients with high SVRI than in those with low SVRI. Regardless of SVRI status, the treatment improved cardiac but not forearm dilatation capacity. The substantial improvement of the hypertensive cardiac microvascular dysfunction was not related to the reduction in SVRI.

Experimental evidence for the formation of divalent ytterbium in the photodarkening process of Yb-doped fiber lasers.

In this work we present experimental evidence that the valence instability of the ytterbium ion play a key role for the observed photodarkening mechanism in Yb-doped fiber lasers. Luminescence and excitation spectroscopy performed on UV irradiated Yb/Al doped silica glass preforms and near-infrared diode pumped photodarkened fibers show a concentration increase of Yb(2+) ions. A concentration decrease in Yb(3+) could also be observed for the UV irradiated preform. The findings contribute to an increased understanding of the kinetic processes related to photodarkening in Yb-doped high power fiber lasers.

Effect of cystamine on blood pressure and vascular characteristics in spontaneously hypertensive rats.

BACKGROUND: Tissue transglutaminase (t-TG) has been implicated in small artery remodelling. The aim of this study was to determine if cystamine, an inhibitor of t-TG, could reduce blood pressure in spontaneously hypertensive rats (SHR) and if so to what extent this is mediated through small arteries. METHODS: In vitro inhibition of t-TG, with cystamine, was studied in organ culture and wire myograph setups in small mesenteric arteries obtained from SHR. In vivo treatment with cystamine (80 mg/kg/day) or amlodipine (10 mg/kg/day) was performed with osmotic pumps in adult SHR, and hemodynamic parameters determined with telemetry. Plasma concentrations of cystamine were determined with a liquid chromatography setup. Small arteries were harvested following administration of cystamine, and structural as well as functional characteristics were determined. RESULTS: SHR small arteries showed inward remodelling following in vitro activation. Administration of cystamine caused attenuation of the inward remodelling induced by activation. In vivo administration of cystamine caused a 9 ± 2 mm Hg reduction in blood pressure, but with no detectable alterations in small artery structure. CONCLUSION: t-TG is potentially involved in vascular remodelling of SHR small arteries and results support a possible role for t-TG in blood pressure control.

Improved photodarkening resistivity in ytterbium-doped fiber lasers by cerium codoping.

We show that the photodarkening resistivity of ytterbium-doped fiber lasers can be greatly improved by cerium codoping. It is suggested that the coexistence of the redox couple Ce(3+)/Ce(4+) in the glass provides means for trapping both hole- and electron-related color centers that are responsible for the induced optical losses in Yb-doped fiber lasers.

Comment on "Photodarkening in Yb-doped aluminosilicate fibers induced by 488 nm irradiation".

We present some strong evidence against the assignment of an ytterbium-related oxygen deficiency center (ODC) near 230 nm in Yb-doped aluminosilicate glass in the Letter by Yoo [Opt. Lett.32, 1626 (2007)]. The strong 230 nm absorption band is actually a charge-transfer band corresponding to the transfer of an electron from nearby oxygen ligands to the ytterbium ion and not related to ODCs.

Preventing photodarkening in ytterbium-doped high power fiber lasers; correlation to the UV-transparency of the core glass.

Photodarkening experiments are performed on ytterbium-doped silicate glass samples. A strong charge-transfer (CT) absorption band near 230nm in aluminosilicate glass is found to be correlated to the mechanism of induced color center formation. Excitation into the CT-absorption band generates similar color centers as observed in ytterbium-doped fiber lasers under 915nm high power diode pumping. The position of the CT-absorption band is compositional dependent and is shifted to shorter wavelengths in ytterbium doped phosphosilicate glass. Very low levels of photodarkening is observed for the ytterbium doped phosphosilicate glass composition under 915nm high power diode pumping. Possible excitation routes to reach the CT-absorption band under 915nm pumping are discussed.

Strong UV absorption and visible luminescence in ytterbium-doped aluminosilicate glass under UV excitation.

A broad visible luminescence band and characteristic IR luminescence of Yb(3+) ions are observed under UV excitation in ytterbium-doped aluminosilicate glass. Samples made under both oxidizing and reducing conditions are analyzed. A strong charge-transfer absorption band in the UV range is observed for glass samples containing ytterbium. Additional absorption bands are observed for the sample made under reducing conditions, which are associated with f-d transitions of divalent ytterbium. The visible luminescence band is attributed to 5d-4f emission from Yb(2+) ions, and the IR luminescence is concluded to originate from a relaxed charge-transfer transition. The findings are important to explain induced optical losses (photodarkening) in high-power fiber lasers.