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Alginic acid (algine, alginate) is a viscous gum that is abundant in the cell walls of brown algae. more...

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Structure

Chemically, it is a linear copolymer with homopolymeric blocks of (1-4)-linked ß-D-mannuronate (M) and its C-5 epimer α-L-guluronate (G) residues, respectively, covalently linked together in different sequences or blocks.

The monomers can appear in homopolymeric blocks of consecutive G-residues (G-blocks), consecutive M-residues (M-blocks), alternating M and G-residues (MG-blocks) or randomly organized blocks. The relative amount of each block type varies both with the origin of the alginate. Alternating blocks form the most flexible chains and are more soluble at lower pH than the other blocks. G-blocks form stiff chain elements, and two G-blocks of more than 6 residues each form stable cross-linked junctions with divalent cations (e.g. Ca²⁺, Ba²⁺, Sr²⁺ among others) leading to a three-dimensional gel network. At low pH, protonized alginates will form acidic gels. In these gels, it is mostly the homopolymeric blocks that form the junctions, where the stability of the gel is determined by the relative content of G-blocks.

Forms

Commercial varieties of alginate are extracted from seaweed, including the giant kelp Macrocystis pyrifera, Ascophyllum Nodosum and various types of Laminaria.

Alginate absorbs water quickly, which makes it useful as an additive in dehydrated products such as slimming aids, and in the manufacture of paper and textiles. It is also used for waterproofing and fireproofing fabrics, for thickening drinks, ice cream and cosmetics, and as a detoxifier that can absorb poisonous metals from the blood. Alginate is also produced by certain bacteria, notably Azotobacter species. Attempts to produce bacterial alginate have not yet been commercially successful.

Alginate ranges from white to yellowish brown, and takes filamentous, grainy, granular, and powdered forms. It is insoluble in water and organic solvents, and dissolves slowly in basic solutions of sodium carbonate, sodium hydroxide and trisodium phosphate.

Uses

Purified forms of alginate are used in antacid preparations such as Gaviscon®, Bisodol®, Asilone®, and Boots Own® tablets. Alginate is used extensivly as a mold-making material in dentistry and prosthetics, and in textiles. It is also used in the food industry, for thickening soups and jellies. Calcium alginate is used in burn dressings that promote healing and can be removed painlessly.

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Acute vocal fold hemorrhage
From Ear, Nose & Throat Journal, 6/1/05 by Libby J. Smith

A 25-year-old actress and singer (soprano) presented to us immediately after she had experienced a sudden voice change during a Broadway performance. Her role required her to simulate coughing. When she did, she suddenly became hoarse and unable to sing in the high and low ends of her range. She also complained of a loss of projection and tightness when speaking. She had no history of trauma or sudden hoarseness, but she had been previously diagnosed with "pre-nodules" and a right vocal fold varicosity, for which she was treated with voice therapy and oral steroids. She reported that she had noticed an increase in mucus during the week prior to this incident. She was taking 1 omeprazole tablet daily, the reflux suppressant Gaviscon as needed, and zinc, vitamin C, the herbal weight-loss aid Diet Fuel, and a multivitamin. She denied taking aspirin, ibuprofen, or any other anticoagulant medication. She was not premenstrual at presentation.

Flexible nasolaryngoscopy and rigid strobovideolaryngoscopy detected an acute right vocal fold hemorrhage, bilateral cysts, and laryngopharyngeal reflux (figure 1). The patient was placed on absolute voice rest for 48 hours, followed by relative voice rest. She was started on esomeprazole 40 mg twice daily and ranitidine 300 mg once nightly. Subsequent sequential examinations demonstrated that the hemorrhage had resolved at the vibratory margin (figure 2). Erythema had persisted, but no bulging hematoma was noted. Based on these findings, no incision and drainage procedure was performed. Repeat rigid stroboscopic examinations performed over the subsequent weeks demonstrated continuing resolution of the hemorrhage and an absence of scar formation.

[FIGURES 1-2 OMITTED]

Fourteen weeks after the initial hemorrhage, stroboscopy showed that the hemorrhage had completely resolved, although a persistent varicosity remained adjacent to the right vocal fold mass (figure 3). In view of her history of hemorrhage and her high vocal demands, the patient elected to have the vessel removed. The masses were not excised because they were asymptomatic and the patient's voice and singing technique were excellent. She was warned of the possibility that her right vocal fold cyst might be inadvertently drained during the procedure, which would possibly change her vocal signature. Nevertheless, she underwent microdirect laryngoscopy with excision of the right varicosity under general anesthesia. The vessels and associated vascular malformation were excised with a vascular knife. The right cyst was not disturbed. Postoperatively, she experienced mild stiffness at the surgical site, but it resolved quickly with singing therapy.

[FIGURE 3 OMITTED]

Nearly 6 months after presentation and 2 months following the excision of the varicosity, the patient's laryngeal examination was notable only for the two cysts. There was no evidence of the hemorrhage or varicosity, and her mucosal wave was normal (figure 4). She resumed singing on Broadway.

[FIGURE 4 OMITTED]

From the Department of Otolaryngoloy--Head and Neck Surgery, Graduate Hospital, Philadelphia.

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