Biomedical subjects
Publications and source records attributed to H C Larsen.
The regional cochlear blood flow has been studied in the rabbit cochlea by mapping the distribution of non-radioactive microspheres in serial sections of plastic embedded cochleas. By using microspheres of two different colors injected at two different times, it is now possible to measure the 'regional' cochlear blood flow twice in the same animal.
The cochlear and cerebral blood flow were simultaneously measured with the microsphere method in albino rabbits before and after administration of prazosin (0.5 mg/kg body weight) and before and during an increase in intracranial pressure (ICP) and intracochlear pressure. Increments in ICP were induced by intracranial infusion of Ringer solution prewarmed to body temperature. The increments were accompanied by an intravenous administration of prazosin to abolish the Cushing effect. The cochlear blood flow was unaffected by the intravenously administered prazosin. A decrease was found when the perfusion pressure of the cochlear, i.e. mean arterial blood pressure minus ICP fell below 5 kPa.
Cochlear blood flow in the rabbit was determined before and after injection of hyperosmotic solutions of galactose and isosorbide. After doses similar to those which can produce hearing improvements in patients with Ménière's disease, cochlear blood flow was increased by 30-60%.
As Tetrahymena thermophila cells differentiate from their vegetative life cycle to sexual reproduction, their polypeptide pattern undergoes a series of changes. These changes have been traced in extracellular, cellular, and subcellular compartments. The first alteration is induced by the nutritional shift-down and results in stimulation of at least one ciliary polypeptide and affects a series of polypeptides from other compartments. The second alteration is induced by mixing starved cells of complementary mating types and this stimulates the synthesis of nine ciliary polypeptides before pairs have formed and eight afterwards. At least five of these early and one of the late conjugation-related ciliary polypeptides are removed by low concentrations of EDTA, indicating that they are located on the external side of the plasma membrane. No differences were observed between polypeptides excreted during starvation and after mixing of complementary mating types. At Tris concentrations restrictive for conjugation, cilia lack the conjugation-related polypeptides. Some of these are instead found among the excreted polypeptides. Using O'Farrell gels and silver staining on isogenic cells of all possible mating types, we have been unable to correlate changes in polypeptide patterns to specific mating types.
A quantitative estimation of the vestibular blood flow was made in normal rabbits using the microsphere method. The total inner ear blood flow was 4 mg per minute, the cochlear blood flow was 3 mg per minute, and the vestibular blood flow was 1 mg per minute.
A new technique evaluates microcirculation in the different parts of the cochlea. It is a synthesis of two previously known methods--the microsphere method and the soft surface-specimen method. We studied the cochlear blood flow in ten albino rabbits using nonradioactive microspheres. The local distribution of microspheres in the cochlea was determined and the total cochlear blood flow calculated.
The regional blood flow to the rat cochlea has been studied using a method which combines the microsphere method with observation of serially-sectioned, plastic-embedded cochleas. Direct quantitation of the microspheres in a reference blood sample and in the different vascular areas of the cochlea allows the analysis of blood flow patterns with respect to the different capillary beds.
The regional blood flow in the cochlea has been studied by mapping the distribution of microspheres in 22 micron thick serial sections of plastic embedded rat and rabbit cochleas. Using a computer-assisted reconstruction technique, a graphic display of the microspheres in each cochlea is obtained. From this display, microspheres may be counted and their distribution may be observed both in relation to the different vascular areas and with respect to the length of the cochlea. This technique, coupled with quantitation of the microspheres in a reference blood sample, offers a method for calculating total and regional cochlear blood flow using non-radioactive microspheres. In addition, this technique allows analysis of blood flow patterns with respect to the different capillary beds along the length of the cochlea. Thus it may be possible to determine if regional blood flow displays a longitudinal gradient, as do other functional, morphologic and biochemical characteristics of the cochlea.
Glycerol and urea can induce positive threshold shifts in Menire's disease whereas mannitol and ethanol do not seem to possess this ability. As an impaired blood supply is suspected to be part of the mechanism behind Menière's disease, the difference in ability of the various hyperosmotic solutions to improve hearing might depend on different effects on the cochlear blood flow. The microsphere method was used to study the cochlear blood flow in albino rabbits before and after administration of hyperosmotic solutions of glycerol, urea and mannitol. The cochlear blood flow increased by about 30% after administration of all solutions. As no difference was found in the effect on cochlear blood flow by the different substances and as the increase in cochlear blood supply was only modest, it would appear that the increment of cochlear blood flow is not a main factor behind the hearing improvements in Menire's disease after glycerol and urea ingestion.
Cochlear and cerebral blood flows were measured in albino rabbits by the microsphere method before and 15 min after intravenous administration of glycerol. Both cochlear and cerebral blood flow were significantly increased. The increase in cochlear blood circulation is interpreted as a contributory factor in producing the improvements in hearing threshold seen in the positive glycerol test in Ménière's disease.
Hearing was studied in nineteen patients with Meniere's disease before and after administration of three different hyperosmolar solutions-glycerol, ethanol, and Mannitol. Ethanol and Mannitol were found to be much less effective than glycerol in producing hearing gain. Alternative mechanisms underlying the observed differences are discussed.
The cochlear and cerebral blood flow was studied in rabbits with the microsphere method before and 15 min after i.v. administration of ethanol. In a series of control experiments only saline was injected. No alteration was measured in the cochlear and cerebral blood flow after the administration of saline, whereas both cochlear and cerebral blood flow showed an increase after ethanol administration. The results are discussed in relation to changes in serum osmolality and hearing in patients with Menière's disease.
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The cochlear blood flow was measured with the microsphere methods, before and during CO2-inhalation, in anesthetized rabbits. Different gas mixtures and exposure times were used. The greatest increase of cochlear blood flow was measured after 5 min inhalation of 7% CO2 in air (115%) and the least increase (44%) in animals breathing 7% CO2 in oxygen. The difference is explained as due to a vasoconstriction caused by a high oxygen tension counteracting the vasodilating effect of CO2.
The cochlear blood flow was measured with the microsphere method before, during and after CO2 inhalation in anesthetized rabbits. Different gas mixtures and exposure times were used. The greatest increase of cochlear blood flow was measured after 5 min inhalation of 7% CO2 in air (115%) and the least increase (44%) in animals breathing 7% CO2 in oxygen. The difference is explained as due to a vasoconstriction caused by a high oxygen tension counteracting the vasodilating effect of CO2. The treatment with CO2 of supposed vascular diseases in the cochlea is discussed and the negative effects due to respiratory acidosis are emphasized.
Using the microsphere method combined with light microscopic observation of serially sectioned plastic-embedded cochleas, the distribution of microspheres trapped within the cochlea can be observed and the regional blood flow can be determined. In the guinea pig, the blood flow is greatest in the lateral wall, high in the modiolus, and low under the organ of Corti.
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The cochlear blood flow was investigated in rabbits with the microsphere method before and during an induced increase of intracerebral and intracochlear pressures. The increase was accomplished by infusing Ringer solution into the lateral cerebral ventricles. The cochlear blood flow was found to autoregulate in response to decreases in perfusion pressures down to 5-6 kPa. This finding is discussed in relation to known effects of intracochlear and intracranial pressure on hearing.