The effect of topical application of vasodilating agents on cochlear electrophysiology

The aim of this investigation was to study whether increased blood flow has beneficial effects on the ear or whether it is damaging to the auditory function, expressed as the auditory gross neural response. Four vasodilating agents were examined after topical application with respect to their influence on cochlear blood flow (CBF), blood pressure, and auditory function in the normal guinea pig. CBF was recorded with laser-Doppler. The drugs used were sodium nitroprusside, hydralazine, nicotinic acid and histamine. Sodium nitroprusside and hydralazine increased CBF and induced concentration dependent loss of auditory function. Neither nicotinic acid nor histamine had any effect on CBF. Nicotinic acid had varying effects: in some cases a negative influence on threshold shifts was seen, and in others a positive one. In most cases histamine caused improvement of the auditory function. The data indicate that topical administration of drugs to the inner ear is effective to influence both CBF and auditory function.

Body growth in relation to tonsillar enlargement and tonsillectomy

Severe airway obstruction caused by tonsillar enlargement can result in disturbances in body growth. The effect of this interference and of tonsillectomy in the child with only moderate symptoms have been less satisfactoril evaluated. In this study, 122 children with symptoms and signs of tonsillar obstruction were investigated concerning the height and weight before and after tonsillectomy. None of the individuals demonstrated cardiopulmonary complications of tonsillar obstruction. Altogether 10% of the children exhibited abnormalities in body weight and/or length prior to surgery. Especially during the first postoperative year, the weight and height gain exceeded the expected in 75% of the patients. The accelerated weight gain increased with tonsil size, but there was no relation to the extent of difficulties in swallowing or sleeping disruptions. The results support the hypothesis that tonsillar hypertrophy frequently is associated with disturbances in body growth and that this is seldom demonstrable prior to tonsillectomy.

Cochlear blood flow in response to dilating agents

Reduced cochlear blood flow (CBF) has been implicated in various pathologies of the inner ear, including sudden deafness, noise-induced hearing loss and Meniere's disease. Thus the aim of some current therapeutic regimens to treat these conditions is to increase CBF and thereby improve oxygenation of the inner ear tissues. Most of the vasodilating agents in clinical use, however, do not have specific experimental evidence to support their effects on CBF. The hypotension which can follow systemic administration may limit their local effectiveness and general utility, just as it complicates the interpretation of the data in animal experiments. In the current study we investigated the effect of six agents, known for their systemic cardiovascular actions, on CBF: hydralazine, sodium nitroprusside, papaverine, nicotinic acid, verapamil and histamine. The effect of these drugs was studied after topical applications on the round window membrane (RWM) and systemic intravenous administrations. CBF was monitored with a laser Doppler flowmeter (LDF). Topical administration of sodium nitroprusside was the most effective in increasing CBF, followed, in order, by hydralazine and histamine. No change in CBF was observed for papaverine, verapamil or nicotinic acid. Systemic administrations of all the agents caused a marked decrease in blood pressure and variable effects on CBF. We discuss the CBF changes in relation to the different pharmacological mechanisms of action of each drug. The study demonstrates the effectiveness of topical application of vasodilating agents in increasing CBF.

The influence of tonsillar obstruction and tonsillectomy on facial growth and dental arch morphology

Children, who were tonsillectomized because of sleep apnea were examined with respect to facial growth and dental arch morphology. Dental casts and lateral roentgencephalograms were analysed before surgery and two years after tonsillectomy. The findings were compared to data from children without tonsillary obstruction. A higher proportion of malocclusion than normal, especially open bite and crossbite, was noticed before surgery. Two years after surgery, 77% of the open bites were normalised and 50-65% of the buccal and anterior crossbites. The best results were seen in children operated before the age of 6.

Down syndrome and sleep apnea--a therapeutic challenge

This case report describes 3 patients with Down syndrome and obstructive breathing problems, ages: 5 months, 15 months, and 22 years. The youngest one had normal cardiopulmonary function at birth, but soon developed a pulmonary hypertension. The next had a severe atrioventricular defect and additional pulmonary hypertension and there was little hope for her to survive heart surgery. The oldest one had had apneas since childhood with increasing severity, but was regarded as having normal heart function. All 3 were operated to relieve their breathing obstruction. The 5-month-old boy improved only slightly after an initial UPPP and had to be tracheotomized, which solved his problems. The tracheotomy could be removed when he was one year. The 15-month-old girl was cured of her breathing problems through an A + T and survived her heart surgery one month later. Tonsillectomy and UPPP was performed on the oldest patient. Following surgery, he had an episode of life-threatening bleeding and developed a DIC syndrome, and was critically ill for 18 days. After he recovered, his sleep apnea had improved. Once a myxoedema was diagnosed and treated, he made further progress. These cases stress the significance of early recognition of sleep apnea in children with Down syndrome and the importance of a careful preoperative investigation in collaboration with cardiologists.

Symptoms in heavy snorers with and without obstructive sleep apnea

Five hundred and eighty persons who were heavy snorers filled in a questionnaire regarding symptoms on a 5-grade scale. Of these, 178 had a complete polysomnography investigation while 402 patients underwent oxymetric screening during the night only. On the basis of these investigations. 217 were classified as suffering from the obstructive sleep apnea syndrome (OSAS) and 363 as snorers without OSAS. The symptom scores differed between the two groups, but the range was wide and some persons with OSAS claimed only minor daytime sleepiness, somnolence, etc., while a high proportion of persons without OSAS frequently suffered from such symptoms. Thus, it was not possible to discriminate between patients with and without OSAS on the basis of their symptoms only. Furthermore, there are many persons who are "only" heavy snorers but who have symptoms that affect their career and social life and who so far have only received scant interest from the medical profession. Excessive daytime sleepiness and somnolence thus do not seem to be secondary to hypoxemia at night but rather to poor quality of sleep, which may be the case in association with heavy snoring even without appreciable deterioration of oxygen saturation.

Clinical treatment of vascular inner ear diseases

A multitude of general disorders of the vascular system may also affect the blood circulation of the cochlea and cause symptoms such as fluctuating or permanent hearing loss. Such is the case for arteriosclerosis combined with hypertension or hypotension, collagenosis, and diabetes. Blood disorders, like leukemia, sickle cell anemia, and polycythemia, and infectious diseases involving the blood vessels, such as lues, may also present their primary symptoms in the ear. The otorhinolaryngologist must be able to establish the correct diagnosis and refer patients requiring more general treatment to other specialists. The use of specific vasoactive treatment should be continued to those patients with symptoms of acute or fluctuating hearing loss, vertigo, or tinnitus who exhibit no other signs. Modern techniques for cochlear blood flow measurements have verified that several of the treatment protocols in use, which have a sound theoretical background, do indeed increase cochlear blood flow.

Children with tonsillar obstruction: indications for and efficacy of tonsillectomy

One hundred and twenty-two children between 1 1/2 and 14 years of age with symptoms suggesting tonsillar obstruction have been investigated. Each patient's history was analysed and the symptoms scored according to their incidence and severity. In addition, the size of the tonsils was evaluated. Eighty-five patients were chosen for tonsillectomy. The children with signs and symptoms of tonsillar obstruction improved greatly immediately after tonsillectomy. Severe symptoms of obstruction were observed in children with nearly normal tonsil size, as well as in those with very large tonsils. It is therefore just as important to obtain a careful history as it is to evaluate the size of the tonsils before deciding about surgery.

Cochlear blood flow increases after systemic hemodilution: comparison of simultaneous laser Doppler flowmetry and radioactive microsphere measurements

Guinea pig cochlear blood flow was measured before and after systemic normovolemic hemodilution with high molecular weight dextran. Absolute determinations of blood flow (in the cochlea, brain, kidney and lung) were accomplished by use of radioactive-labeled (85Sr or 141Ce) microspheres. Relative measurements of the cochlear blood flow changes were made simultaneously by the use of a laser Doppler flowmeter. The flowmeter probe was placed on the first cochlear turn. Hemodilution to an average systemic hematocrit of 20% increased cochlear blood flow by 250% as measured with microspheres. The laser Doppler instrument significantly underestimated the actual flow increase giving an indication of 148%. Furthermore, the data, when analyzed on an individual trial basis, showed a very poor correlation between the two methods. The theoretical basis for these findings in relation to the use of the laser Doppler instrument is discussed.

Sleep apnea in children without hypertrophy of the tonsils

Two 12-year-old boys with severe sleep apnea syndrome but normal-sized tonsils were satisfactorily corrected by tonsillectomy and uvulopalatopharyngoplasty. One of the boys had muscular hypotony as contributing cause of the condition. The other had mandibular hypoplasia in combination with a long soft palate. Thorough preoperative anamnesis and examination in a sleep laboratory are necessary to determine which cases will benefit from surgery in spite of normal-sized tonsils and which surgical procedure will be most helpful.

The microsphere method for studies of inner ear blood flow

The microsphere method was adapted in 1974 for studies of cochlear blood flow. Since then it has been used in Uppsala, Sweden, at the Department of Otolaryngology, University Hospital, for investigations of the blood flow circulation in the inner ear. The experience with the technique, the subjects, the actual projects and the results are presented and discussed.

Cochlear blood flow in relation to age in normotensive and spontaneously hypertensive rats

Cochlear blood flow was studied with the microsphere method in young and old normotensive and spontaneously hypertensive rats. The young animals were 3-6 months old and the old ones 18-24 months. The cochlear blood flow in young rats was 1.64 microliter/min/cochlea for the normotensive and 1.51 for the spontaneously hypertensive rats. In the old rats, the cochlear blood flow rates were 1.40 and 1.29 microliter/min/cochlea, respectively. The differences were not significant between the age groups, nor between the normotensive and spontaneously hypertensive rats. However, there was a tendency towards lower cochlear blood flow with increasing age, especially among the spontaneously hypertensive rats. The difference between young normotensive and old spontaneously hypertensive rats was significant (p less than 0.05). The group of old hypertensive rats was also the only one with evident morphological changes in the organ of Corti.

Cochlear blood flow in noise-damaged ears

Cochlear blood flow was measured in rats with a known noise-induced hearing loss, using the microsphere technique. The animals were exposed to simulated industrial noise for 3 months. The rats were divided into four groups: young and old; normotensive (N) and spontaneously hypertensive (SH). The mean values of the cochlear blood flows were compared with those of rats from matched groups not exposed to noise. The mean cochlear blood flow in the noise-exposed groups was lower than in the non-exposed groups. The decrease in cochlear blood flow was significant for all groups except young SH rats and was more pronounced in the older age group. Cochleas from the groups of old N and SH rats were investigated in the scanning electron microscope. Extensive changes were far more common in SH than in N rats.

Effect of hemodilution on cochlear blood flow measured by laser-Doppler flowmetry

The effect of hemodilution on cochlear blood flow was studied in guinea pigs. Hypervolemic hemodilution was accomplished by infusion of 10 mg/kg of body weight of dextran 40 (as a 10% solution in normal saline), which resulted in an average hematocrit decrease from 43 to 32%. Normovolemic hemodilution was accomplished by repeated exchange of 3 ml of whole blood with 3 ml of dextran 75 (6% solution in normal saline) every 5 minutes until the hematocrit reached approximately 5%. The cochlear blood flow was measured by laser-Doppler flowmetry. Irrespective of the dilutional technique, the cochlear blood flow increased as hematocrit decreased to a maximum of approximately 200% of original value at a hematocrit near 20%. The blood pressure was not significantly influenced by the hemodilution until hematocrit values below 15% were reached. The enhancement of cochlear blood flow is consistent with the expected reduction of blood viscosity and increase of cardiac output. Normovolemic hemodilution with dextran 75 causes a smaller disturbance of systemic circulation physiology and has a more lasting effect than dextran 40 infusion.

The effect of cervical sympathectomy on cochlear electrophysiology

The purpose of this study was to examine the electrophysiologic responses to sound from guinea pig cochleas, 3--6 days after a unilateral cervical sympathectomy. After recovery from surgery the guinea pigs developed a Horner's syndrome on the sympathectomized side. Some days later their bullas were opened and electrodes were placed bilaterally on the round windows. Most of the sympathectomized cochleas showed signs of decreased sensitivity to sound. They had a smaller dynamic range for the click- and tone-burst evoked compound action potential (CAP) compared with the non-sympathectomized cochleas. The threshold sound levels for the CAPs and the sound levels to produce 1 muV of cochlear microphonic potentials were unaffected. In other animals with chronic implanted electrodes, the same electrical responses were measured with only light sedation before and after sympathectomy and showed the same results. In additional animals the crossed olivocochlear bundle (COCB) was electrically stimulated and a similar inhibition of the CAP was registered on both the intact and the sympathectomized side. The results suggest that the sympathetic nerves to the cochlea, coming from the ipsilateral cervical ganglion and ending near the habenula perforata, may be important for the sound perception as they influence the CAP.

Cochlear blood flow related to hyperosmotic solution

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.

Effect of nicotinic acid on cochlear blood flow

Effects of nicotinic acid on cochlear blood flow were studied in rats by the microsphere method. One measurement was performed before drug administration and the second after i.v. injection of the nicotinic acid 25 mg/kg body weight. No measurable effect on cochlear blood flow was observed in normal animals. In one group of animals the cervical sympathetic trunks were cut and the distal part on one side was electrically stimulated during the measurements. On the unstimulated side the cochlear blood flow was significantly higher than in intact animals, but uninfluenced by nicotinic acid. On the sympathetically stimulated side a significant increase of the cochlear blood flow occurred after nicotinic acid administration.

The effect of glycerol on cochlear blood flow

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.

Does loud sound influence the intracochlear oxygen tension?

The effect of loud sound on the perilymphatic oxygen tension was studied in anesthetized guinea pigs. Pure tone (4 kHz) and broad-band noise were given at 85-130 dB SPL for 3-8 min. No effects were seen either in the animals exposed to pure tone or in the animals exposed to 85 dB broad-band noise. In the animals exposed to noise at 130 dB SPL both increases and decreases of perilymphatic oxygen were measured but the changes were only of about 12% or less. The response to anoxia was normal. In animals with hypotension ( less than 8 kPa) the perilymphatic PO2 fluctuated with the blood pressure. When the sound was delivered directly into the opened bulla the measured PO2 dropped immediately but was found to be caused by the cooling effect of an air current produced by the noise. Flushing the opened bulla with nitrogen, air or oxygen caused the same temperature-induced drop of measured PO2. The results and the artifacts are discussed.

Effect of ethanol on cochlear blood flow

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.

The effect of CO2-breathing on cochlear blood flow

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.

Early effects of cervical sympathetic stimulation on cerebral, ocular and cochlear blood flow

Autoregulatory mechanisms may be expected to modify effects of vasomotor nerve stimulation in many tissues. Attempts were made to reveal a distinct early, but transient effect of cervical sympathetic stimulation on cerebral, retinal and cochlear blood flow. The labelled microsphere method was used to determine regional blood flow during electrical stimulation of the cervical sympathetic chain for 15-25 s and 5 min. At a frequency of 6 Hz there was 5% reduction in cerebral flow at 15-25 s and 7% at 5 min. In the choroid plexus the mean reduction was 22% at 15-25 s but decreased 10% after 5 min. In the cerebellum, optic nerve and retina, sympathetic stimulation had no appreciable effect on the blood flow. In the cochlea and iris, the blood flow reductions were 25 and 32%, respectively, on both occasions. In the choroid, vasoconstriction increased with time, whereas in the masseter muscle there was a decrease. Thus in the present experiments no indication was found of an autoregulatory escape phenomenon in the brain, the eye or the cochlea. Some escape was noted in the masseter muscle.