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Biomedical subjects

J B Snow

Publications and source records attributed to J B Snow.

At least 55 records · Page 3Linked to original sources
PubMed1983

Mechanism of the production of the negative endocochlear DC potential in the guinea pig.

Changes in endocochlear DC potential (EP) and potassium ion concentrations in endolymph were measured simultaneously during anoxia or during perfusion of the perilymphatic space with furosemide, 10(-2)M, in normal and kanamycin-deafened guinea pigs. The potassium ion conductance (Gk) through the cochlear partitions was calculated. Thirty minutes after the onset of anoxia, the Gk is 22.1 microM/min/mV in normal guinea pigs and 4.8 microM/min/mV in kanamycin-deafened guinea pigs. At that time the EP is -29.5 mV in normal guinea pigs and 1.4 mV in kanamycin-deafened guinea pigs. In the early stage of anoxia the rate of potassium ion concentration decrease in the endolymph per unit time is greater in normal guinea pigs than in kanamycin-deafened guinea pigs. These results suggest a rapid increase in the permeability of potassium ions in the organ of Corti in the early stage of anoxia might produce a large negative potassium ion diffusion potential or negative EP in normal guinea pigs and the failure to develop the negative EP in kanamycin-deafened guinea pigs might be due to the lack of such a rapid increase in the permeability because of the loss of the hair cells.

Animals↗
PubMed1982

Does preoperative irradiation increase the rate of surgical complications in carcinoma of the head and neck? A Radiation Therapy Oncology Group Report.

This is a comparison of the rate of surgical complications in a group of patients with advanced but operable carcinoma of the head and neck who underwent surgery after preoperative radiotherapy (5000 rad in five weeks, 200 rad fractions, directed to the primary tumor area and neck) versus another group operated without prior irradiation. Both groups of patients formed part of a randomized prospective multiinstitutional trial of the Radiation Therapy Oncology Group (73-03). Of 229 patients who had planned operations, 88 (38%) developed some degree of surgical complications, and in 28 (12%) the complications were rated as severe. The most frequently reported complications were delayed healing and fistula formation each occurring in approximately one-fourth of each of the two treatment groups. Carotid blow-out occurred in 5% or less of the cases. No significant statistical difference between treatment groups was noted for the overall complication rate or specific type of surgical complications. A trend was noted towards more complications in the preoperative group for patients with lesions in the oropharynx and supraglottic larynx. However, an opposite trend towards more complications in the no prior irradiation group was observed among patients with lesions in the oral cavity and hypopharynx. Surgical mortality and postoperative hospital stay were not significantly different between treatment groups. We conclude that preoperative irradiation for carcinoma of the head and neck, with the stated dose, followed by surgery in 4-6 weeks, does not substantially increase the rate of overall or specific type of surgical complications, surgical mortality or hospital stay versus those patients operated without prior irradiation.

Aged↗
PubMed1982

Nature of the endocochlear dc potential in kanamycin-poisoned guinea pigs.

The endocochlear dc potential (EP) was measured in normal guinea pigs and in a group poisoned with kanamycin sulfate for 60 minutes after the administration of furosemide intravenously (IV) or by perfusion into the scala tympani. The EP decreased rapidly and developed a large negative potential after IV administration of furosemide, but the EP decreased more slowly and did not develop a negative potential in kanamycin-poisoned animals. With perfusion of the scala media, the EP declined slowly and did not develop a large negative potential in either group. With perfusion of the scala tympani, the EP declined slowly in the kanamycin-poisoned animals and did not develop a large negative potential, while in the normal animals the EP declined rapidly and developed a large negative potential.

Animals↗
PubMed1982

Dynamics of the flow of perilymph in the cochlea of the guinea pig.

The dynamics of perilymph flow in the cochlea was studied in guinea pigs. After placement of sodium chloride crystals on the round window membrane, the potassium ion concentration in the scala vestibuli in the basal turn does not change. The potassium ion concentrations in the scala tympani in the basal turn increases rapidly, while the potassium ion concentration in the scala tympani in the third turn increases slowly and to a lesser extent. The cochlear microphonic potential decreases in the basal turn and to a lesser extent in the third turn. After placement of sodium chloride on the fenestra in the scala tympani of the third turn, the chochlear microphonic potential in the basal turn does not change. These data lend support to the theory of longitudinal flow of perilymph in the scala tympani.

Animals↗
PubMed1981

Comparative ototoxicity of chloramphenicol and kanamycin with ethacrynic acid.

Chloramphenicol is not ototoxic if administered for systemic effect, but topical applications of it to the middle ear produce severe cochlear toxic effects. Ethacrynic acid potentiates the ototoxicity of aminoglycosides. Guinea pigs were administered chloramphenicol or kanamycin sulfate with ethacrynic acid to compare the ototoxicity of chloramphenicol and ethacrynic acid with the ototoxicity of kanamycin and ethacrynic acid. Preyer's reflex audiometry and measurement of the endocochlear dc potential, the cochlear microphonics, and the negative potential of the organ of Corti indicate that ethacrynic acid does not potentiate the ototoxicity of chloramphenicol. There is not even indirect evidence that the blood-cochlear barrier for chloramphenicol is altered by ethacrynic acid. Assuming that the ototoxicity of chloramphenicol and ethacrynic acid are similar for man and guinea pig, the combination of the administration of chloramphenicol and ethacrynic acid of systemic effect in dosages commonly used clinically should not produce greater ototoxicity than either agent administered alone.

Animals↗
PubMed1981

Potentiating effects of cisplatin and ethacrynic acid in ototoxicity.

Seven milligrams per kilogram of body weight of cisplatin and 50 mg/kg of body weight of ethacrynic acid were given intravenously to guinea pigs. The threshold for Preyer's reflex, the cochlear microphonics (CM), and the endocochlear dc potential (EP) were measured during a four-day period after the injection. The changes in Preyer's reflex audiometry and the CM were more severe than that of the EP. These changes are greater than those that occur with the administration of each agent independently. The ototoxic interaction seemingly has a greater effect on the hair cells than on the stria vascularis. Baseline and periodic audiometry should be performed when both of these drugs are administered clinically.

Animals↗
PubMed1980

Randomized preoperative and postoperative radiation therapy for patients with carcinoma of the head and neck: preliminary report.

Two hundred and ninety-eight patients with squamous cell carcinoma of the oral cavity, oropharynx, supraglottic larynx, hypopharynx or maxillary sinus have been randomized for preoperative radiation therapy and surgery vs. surgery and postoperative radiation therapy plus, in the case of patients with lesions of the oral cavity and oropharynx, radical radiation therapy. Data have been analyzed on 243 patients in this interim report. The differences between the three groups with respect to local control and survival are not statistically significant at this time. Additional accrual and continued follow-up are necessary to make definite treatment comparisons.

Carcinoma, Squamous Cell↗
PubMed1980

Adenocarcinoma of the ethmoid following radiotherapy for bilateral retinoblastoma.

Adenocarcinoma of the ethmoid sinus is rare, representing only 4-8% of malignancies of the paranasal sinuses. An extraordinary case of papillary adenocarcinoma of the ethmoid sinus arising 30 years following high-dose radiotherapy for bilateral retinoblastoma is presented. Retinoblastoma, though occurring only once in every 23,000 to 34,000 births, is the most common malignant intraocular tumor of childhood. Second fatal mesenchymal and epithelial primaries have been described in 8.5% of patients with bilateral retinoblastomas previously treated with radiotherapy; however, papillary adenocarcinoma arising within the paranasal sinuses has not been reported. Histologically, the findings of a papillary pattern of poorly differentiated, mucicarmine-staining cells enclosing gland-like spaces, and the absence of pseudorosettes, melanin, mesenchymal and peripheral neural elements supports an epithelial origin of this tumor. Agressive treatment including partial maxillectomy, radical pansinusectomy, radical neck dissection followed by regional radiotherapy and systemic chemotherapy failed to prevent the development of fatal hepatic metastases. The high incidence of second fatal primary neoplasms in patients with bilateral retinoblastomas receiving radiation suggests an innate susceptibility that may add to the risk of radiotherapy. Careful long-term head and neck surveillance is mandatory if early aggressive management of these extremely lethal tumors is to be successful.

Adenocarcinoma, Papillary↗
PubMed1979

Effect of kanamycin sulfate on the endocochlear dc potential of guinea pigs.

The magnitudes of the endocochlear dc potential (EP) during adequate ventilation and during five minutes of anoxia were recorded in control guinea pigs and guinea pigs administered various dosages of kanamycin sulfate. The magnitudes of the EP after five minutes of anoxia were -44.6 +/- 5.9 mV in the controls and +26.6 +/- 9.9 mV in the guinea pigs that received kanamycin for seven or ten days. This change occurred after five or six days of administration of kanamycin. However, there was no significant change in the magnitude ot the EP with adequate ventilation with kanamycin intoxication. There is a significant correlation between the magnitude of the negative EP and the maximum output of the cochlear microphonics (r = -.770, P less than .001). These results suggest that the EP may not be the mathematical summation of the positive electrogenic potential and the negative diffusion potential. The mechanism for generating the negative EP during anoxia may have some relationship to hair cell integrity.

Animals↗
PubMed1979

Assessement of surgical procedures for Ménière's disease.

There are numerous surgical procedures for the treatment of Meniere's disease, and the current status of their efficacy is controversial. A review of the literature is presented as a basis for the evaluation of the relative merit of these procedures. Emphasis is placed on endolymphatic sac procedures, sacculotomy, vestibular neurectomy and labyrinthectomy. Vestibular neurectomy and surgical labyrinthectomy provide high rates of improvement in vertigo. The hearing is frequently made worse by vestibular neurectomy. Endolymphatic sac procedures result in improvement in vertigo less frequently. They are most likely to improve hearing. Although sacculotomies are associated with improvement in vertigo in approximately 80% of patients, they are associated with high rates of hearing loss.

Ear, Inner↗
PubMed1978

Electrical resistance of the cochlear partition.

The relationship between the calculated value of the effective electrical resistance of the cochlear partition and the distance between the electrode for measuring the EP and the stimulating electrodes has been studied. The calculated value of the effective electrical resistance of the cochlear partition declines linearly with increasing distance between these electrodes. The correlation coefficient (r) is -0.806. In calculations of the effective electrical resistance of the cochlear partition, attention must be paid to the distance between the microelectrodes.

Animals↗
PubMed1978

Etiologic factors in hypocalcemia secondary to operations for carcinoma of the pharynx and larynx.

Hypocalcemia, although a relatively uncommon sequela of operations for carcinoma of the larynx and pharynx, often presents as an acute medical emergency. In its chronic form, hypocalcemia may be a difficult disorder to control. Understanding the etiologic basis of hypocalcemia secondary to operations for carcinoma of the head and neck requires knowledge of the pathophysiology of the preoperative and postoperative factors affecting calcium homeostasis. These factors include thyroidectomy, hypoparathyroidism, hypomagnesemia, anticonvulsant therapy, estrogen replacement therapy, oral contraceptives, blood transfusions, hyperventilation alkalosis, hypoalbuminemia, corticosteroid therapy, depression, emotional stress and diet. Often the onset of symptoms and signs of hypocalcemia occurs within 24 to 48 hours after the operation. The symptoms may include mental depression, headache, tingling of the hands and perioral region and abdominal pain. Unrecognized chronic hypocalcemia may lead to the development of cataracts, convulsions and psychosis.

Alkalosis↗