Effect of nicotinic acid on cochlear blood flow

Cigarette smoking, occupational exposure to noise, and self reported hearing difficulties

AIMS

To explore the interaction of smoking and occupational exposure to noise as risk factors for hearing difficulty in the general population.

METHODS

A questionnaire was mailed to 21 201 adults of working age, selected at random from the age-sex registers of 34 British general practices, and to 993 members of the armed services, randomly selected from pay records. Questions were asked about smoking habits, years spent in a noisy occupation, difficulty in hearing conversation, and wearing of a hearing aid. Associations of hearing difficulty with smoking habit were examined by logistic regression and compared across strata of noise exposure, with adjustment for potential confounders.

RESULTS

Around half of the respondents had ever smoked, and half of these still smoked. Among 10 418 who provided details on hearing, 348 were classed as having moderate and 311 as having severe hearing difficulty. Risk of hearing difficulty was 3-5-fold higher in those employed for >5 years in noisy work compared with those never employed in a noisy job. Within strata of noise exposure (including those who had never worked in a noisy job), ex- and current smokers had a higher risk of hearing difficulty than lifetime non-smokers. The additional risks were small compared with those of long term noise exposure, and the combination of effects was more consistent with an additive than a multiplicative interaction.

CONCLUSIONS

Smoking may adversely affect hearing, and workers should be encouraged to refrain from both smoking and exposure to noise. However, the extra risk to hearing incurred by smoking in high ambient noise levels is small relative to that from the noise itself, which should be the main target for preventive measures.

Disorders of cochlear blood flow

The cochlea is principally supplied from the inner ear artery (labyrinthine artery), which is usually a branch of the anterior inferior cerebellar artery. Cochlear blood flow is a function of cochlear perfusion pressure, which is calculated as the difference between mean arterial blood pressure and inner ear fluid pressure. Many otologic disorders such as noise-induced hearing loss, endolymphatic hydrops and presbycusis are suspected of being related to alterations in cochlear blood flow. However, the human cochlea is not easily accessible for investigation because this delicate sensory organ is hidden deep in the temporal bone. In patients with sensorineural hearing loss, magnetic resonance imaging, laser-Doppler flowmetry and ultrasonography have been used to investigate the status of cochlear blood flow. There have been many reports of hearing loss that were considered to be caused by blood flow disturbance in the cochlea. However, direct evidence of blood flow disturbance in the cochlea is still lacking in most of the cases.

Combined effect of smoking and occupational exposure to noise on hearing loss in steel factory workers

BACKGROUND

Evidence has accumulated concerning the adverse effects of smoking on hearing acuity, but it is not clear whether smoking modifies the association between exposure to noise and hearing loss.

AIMS

To examine the synergistic effect of these variables on hearing.

METHODS

Data used were derived from periodic health examinations for 4624 steel company workers in Japan and included audiometry testing and information on smoking habits. Occupational exposure to noise was determined based on company records. Logistic regression was used to examine the dose-response association between smoking and hearing loss. The Cochran-Mantel-Haenszel method was used to calculate the prevalence rate ratio (PRR) of hearing loss for each combination of smoking and noise exposure factors, taking non-smokers not exposed to occupational noise as a reference. The interaction between smoking and noise exposure was assessed using a synergistic index, which equals 1 when the joint effect is additive.

RESULTS

Smoking was associated with increased odds of having high frequency hearing loss in a dose-response manner. The PRR for high frequency hearing loss among smokers exposed to occupational noise was 2.56 (95% CI 2.12 to 3.07), while the PRR for smokers not exposed to noise was 1.57 (95% CI 1.31 to 1.89) and the PRR for non-smokers exposed to noise was 1.77 (95% CI 1.36 to 2.30). The synergistic index was 1.16. Smoking was not associated with low frequency hearing loss.

CONCLUSIONS

Smoking may be a risk factor for high frequency hearing loss, and its combined effect on hearing with exposure to occupational noise is additive.

The cochlear blood flow: a comparison between the laser Doppler and the microsphere surface methods

Since the introduction in the early 1980s, of the laser Doppler (LD) method for measuring cochlear blood flow (CBF) it has been debated whether the measured changes reflect the total or regional blood flow and whether the method per se influences the CBF. In order to answer those questions, the effect of one vasodilating drug, sodium nitroprusside, was investigated after topical application on the round window membrane (RWM) with respect to its influence on CBF. Two different techniques, the microspheres surface method and the LD method, were used. Untreated animals and animals which received saline or nicotine acid on the RWM were used as controls. The effects on CBF and blood pressure (BP) were continuously registered with LD. When a maximal flow had stabilized, 6 x 10(6) microspheres were injected into the left side of the heart. After the microspheres had been distributed within the body, the animals were killed. Both cochleae were microdissected and the microspheres counted turn by turn in the lateral wall. The number of spheres in the two ears was compared and the difference was recorded as the increase caused by the drug. The percentage change in CBF measured using the LD was compared with that obtained by using the microsphere surface method (MSM). No change in CBF measured by the two techniques was registered in the untreated animals, or after saline or nicotinic acid, while sodium nitroprusside induced a substantial increase in CBF. The mean percentage change of CBF measured with the LD method was compared with the calculated mean percentage change of microspheres for all turns in the cochlea, and in the first turn. Student's t-test and the linear correlation coefficient were calculated.(ABSTRACT TRUNCATED AT 250 WORDS)

Substance P increases cochlear blood flow without changing cochlear electrophysiology in rats

Carotid artery infusions of substance P yielded reductions in systemic blood pressure and elevations in cochlear blood flow (CoBF), measured via laser Doppler flowmeter, with no alterations in cochlear action potentials or cochlear microphonics in Wistar-Kyoto rats. Additionally, direct micro-infusions of substance P into the anterior inferior cerebellar artery, which contributes to the local vascular perfusion of the cochlea, yielded elevations in CoBF with no changes in systemic blood pressure. Pretreatment with a specific substance P receptor antagonist, ([D-Pro2,D-Trp7,9]SP) via the carotid artery or the anterior inferior cerebellar artery, diminished subsequent substance P-induced vascular responses. These results suggest that endogenous substance P, like other vasoactive peptides, may interact with a substance P-specific receptor population in the cochlea and may therefore participate in the ongoing regulation of CoBF. These findings also support the premise that vasodilatory hormones, along with vasoconstrictive agents, may be involved in the autoregulation of CoBF.

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.

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 intra-arterial infusion of arginine vasopressin on cochlear blood flow in the rat

Intra-arterially infused arginine vasopressin (AVP) elevated systemic blood pressure (BP) in the Sprague-Dawley rat according to a dose-response pattern while cochlear blood flow (CoBF), as measured by laser Doppler flowmetry, was elevated only at the highest dose. Skin blood flow (SBF) decreased significantly with AVP infusion. The local infusion of AVP into the anterior inferior cerebellar artery (AICA), which supplies the common cochlear artery, produced significant dose-dependent reductions in CoBF with no changes in systemic blood pressure. Pretreatment of the local cochlear supplying vessels with an AVP-specific V1 receptor antagonist attenuated subsequent AVP-induced decreases in CoBF, thereby demonstrating specificity of the response. These results suggest that CoBF is reasonably stable in response to systemic AVP infusion until blood pressure exceeds an elevation from base level of approximately +60 mm Hg. One of the mechanisms responsible for this autoregulatory response may be vasoconstriction mediated by the interaction of vasoactive peptides such as AVP and its receptors located in the vasculature of the inner ear or in the more peripheral vessels directly supplying the cochlea.

The effects of calcitonin gene-related peptide (CGRP) on cochlear and mucosal blood flow in the albino rabbit

The effects of intravenously infused calcitonin gene-related peptide (CGRP) on the regional blood flow of the cochlea, the middle ear and the upper respiratory tract were studied. Two series of experiments were performed without pretreatment on either conscious or pentobarbital anaesthetized animals; in one series the cervical sympathetic chain was severed on one side; in another series anaesthetized animals were subjected to ganglionic blockade with hexamethonium bromide in order to abolish reflexes involving the autonomic nervous system. In still another series conscious animals were pretreated with indomethacin in order to reduce the formation of prostaglandins. In all groups of animals where sympathetic influence was diminished cochlear blood flow increased during the infusion of CGRP. In the mucosa of middle ear and the upper airways, the blood flow increased in all groups. The results indicate that CGRP at these doses causes vasorelaxation in the mucosa of the middle ear and upper airways and does so also in the cochlea if the sympathetic influence is abolished.

Effect of arachidonic acid on the inner ear blood flow measured with a laser Doppler flowmeter

The present study was undertaken to clarify the effect of arachidonic acid (AA) on the inner ear blood flow of rats as measured with a laser Doppler flowmeter. With the rats under anesthesia with sodium pentobarbital, the middle ear was approached ventrally and a laser Doppler probe was positioned over the lateral wall of the cochlea. Drugs were administered via the subclavicular artery. The dose range of each drug was determined so as not to affect the systemic blood pressure. The AA (20 to 70 micrograms) increased the inner ear blood flow dose-dependently; this effect was abolished by indomethacin (5 mg orally). Both prostaglandin E2 (PGE2; 1 to 50 ng) and CS-570, a PGI2 analogue (12.8 to 25.6 ng) caused a dose-dependent increase in the inner ear blood flow. The response of PGI2 was shorter than that of PGE2. On the other hand, a stable thromboxane A2 (STA2; 30 to 80 ng) decreased the inner ear blood flow dose-dependently. Administration of PGF2 alpha (0.2 to 3 micrograms) showed no effect on the inner ear blood flow. These results indicated that the effect of AA was mediated mainly via PGI2 and PGE2.

Cochlear blood flow autoregulation in Wistar-Kyoto rats

Wistar-Kyoto rats (WKY) were intra-arterially infused with angiotensin II (AII) or phenylephrine for 10 min. Both vasoactive compounds produced an initial increase in cochlear blood flow (CoBF) as measured by laser Doppler flowmetry, followed by a slow steady return to baseline, despite sustained elevations in systemic blood pressure. These results suggest autoregulation of CoBF in the WKY rat. In a second experiment. All was infused directly into the anterior inferior cerebellar artery (AICA) which feeds the cochlear artery. Significant reductions in CoBF were noted without changes in systemic blood pressure. Pretreatment with the specific angiotensin-receptor antagonist, sarthran (Sar1, Thr8-AII), diminished subsequent AII-induced reductions in CoBF. These results indicate that AII binding to vascular receptors may induce vasoconstriction in the supplying vessels of the cochlea, and thus, the interaction of blood-borne AII and vascular angiotensin receptors may participate in the autoregulation of CoBF.

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.

The effect of nicotinamide on tinnitus: a double-blind controlled study

The vasodilatory drug nicotinic acid is still widely used in the treatment of tinnitus. Although neither the success rate of this drug nor the pharmacokinetic mechanism underlying the supposed suppressive effect on tinnitus is known, it is clear from the literature that the vasodilative effect is not responsible for its effect on tinnitus. In a double blind controlled trial performed in 48 patients, the value of the related drug nicotinamide was assessed and compared with the effect of a placebo. The results obtained with nicotinamide were not better than those observed for the placebo.

Cochlear blood flow in the rat. A methodological evaluation of the microsphere method

With the microsphere method it is possible to quantify the blood flow in various organs. The blood flow in the cochlea is only a very small part of the cardiac output and only relatively few microspheres are caught in this organ, which necessitates large groups of animals for such studies. The method has, however, not been fully evaluated for studies of small organs in small animals. In this study, 130 rats of various ages with normal or arterial hypertension were investigated. The blood flows of 97 animals were possible to evaluate. It was found that physiological parameters, such as PCO3, pH, PO2 and mean arterial blood pressure within the rather wide limits usually present in the anesthetized animal did not affect the cochlear blood flow to any great extent and that the method is feasible for studies of the blood flow through the inner ear in small animals.

Drug-induced alterations in cochlear blood flow as recorded by the laser Doppler flowmeter

A number of clinical entities may result from a decrease in inner ear blood flow. Investigators have attempted to determine a relationship between decreased blood flow and such entities. In this article, we shall relate the effects of administration of drugs in animal models on cochlear blood flow, using the laser Doppler flowmeter.

Cochlear blood flow studied with microspheres. A comparison between two different modifications of the microsphere method

In albino rabbits, spontaneously hypertensive rats, and guinea pigs, cochlear blood flow was measured with the microsphere method, using radioactively labelled microspheres technique and a gammaspectrometer. This 'conventional' microsphere method was compared with a new technique for measurements of cochlear blood flow: a modification of the 'radioactive' microsphere technique and the soft surface specimen technique. Values obtained for cochlear blood flow by the two different methods were similar. Consequently, the microsphere surface technique is a suitable alternative to the classical radioactive microsphere method for blood flow determinations in the cochlea.

The laser Doppler: a non-invasive measure of cochlear blood flow

The present investigation demonstrates the utility of the laser Doppler flowmeter to provide a measure of cochlear blood flow dynamics. Cochlear and cutaneous blood flow were compared with arterial blood pressure during and following exposure to Angiotensin II, 5% carbon monoxide, 100% oxygen, mannitol, and saline. The observations indicate that: 1) cochlear blood flow generally parallels cutaneous blood flow; however, 2) when cutaneous beds vasoconstrict (e.g., AII, alpha-agonists), cochlear blood flow parallels blood pressure; and, 3) under the influence of agents that affect peripheral and central circulation (5% CO, 100% O2), cochlear blood flow may dissociate from cutaneous blood flow and blood pressure. The implications of these findings are discussed in terms of local control mechanisms that may be involved in the inner ear vasculature.

The effect of blood pressure on inner ear blood flow

We investigated the effects of blood pressure on the blood flow in the inner ear as compared with other organs in normotensive rats (NR), spontaneously hypertensive rats (SHR) and renal hypertensive rats (RHR). The cardiac output and the regional blood flow were measured by a radioactive microsphere technique in conscious rats. The haemodynamics of the inner ear and other organs and the effects of a converting-enzyme inhibitor (SA-446) on the regional blood flow were compared among NR, SHR, and RHR, the blood pressure being 107, 152, and 185 mm Hg, respectively. With the exception of the heart, the organ blood flow was lower in SHR than in NR in all organs, including the inner ear. It was also lower in RHR than in SHR. The blood pressure dropped after i.v. injection of SA-446, while the regional blood flow increased. The effect was strongest in RHR, followed by SHR and finally NR.