Whole blood viscosity and red cell filterability as factors in sensorineural hearing impairment in the elderly

Structural changes in thestrial blood-labyrinth barrier of aged C57BL/6 mice

Tight control over cochlear blood flow (CoBF) and the blood-labyrinth barrier (BLB) in the striavascularis is critical for maintaining the ionic, fluid and energy balance necessary for hearing function. Inefficient CoBF and disruption of BLB integrity have long been considered major etiologic factors in a variety of hearing disorders. In this study, we investigate structural changes in the BLB of the striavascularis in age-graded C57BL/6 mice (1 to 21 months) with a focus on changes in two blood barrier accessory cells, namely pericytes (PCs) and perivascular-resident macrophage-like melanocytes (PVM/Ms). Decreased capillary density was detectable at 6 months, with significant capillary degeneration seen in 9- to 21-month-old mice. Reduced capillary density was highly correlated with lower numbers of PCs and PVM/Ms. "Drop-out" of PCs and "activation" of PVM/Ms were seen at 6 months, with drastic changes being observed by 21 months. With newly established in vitro three-dimensional cell-based co-culture models, we demonstrate that PCs and PVM/Ms are essential for maintaining cochlear vascular architecture and stability.

Physiopathology of the cochlear microcirculation

Normal blood supply to the cochlea is critically important for establishing the endocochlear potential and sustaining production of endolymph. Abnormal cochlear microcirculation has long been considered an etiologic factor in noise-induced hearing loss, age-related hearing loss (presbycusis), sudden hearing loss or vestibular function, and Meniere's disease. Knowledge of the mechanisms underlying the pathophysiology of cochlear microcirculation is of fundamental clinical importance. A better understanding of cochlear blood flow (CoBF) will enable more effective management of hearing disorders resulting from aberrant blood flow. This review focuses on recent discoveries and findings related to the physiopathology of the cochlear microvasculature.

[Blood viscosity profile in rapidly progressive sensorineural hearing loss with positive Western-blot]

OBJECTIVE

To value a possible association between disorders in blood viscosity of patients with rapidly progressive sensorineural hearing loss (RPSHL) of autoimmune origin.

PATIENTS AND METHODS

We studied the viscoelastic properties of blood in 43 subjects bearing of RPSHL and a positive Western-blot for anticochlear antibodies: whole blood viscosity (WBV) at different shear rates and erythrocyte filterability (EF). These results were related to hearing loss initially detected and recovery average one year later from steroid therapy.

RESULTS

Just WBV at 230 sec(-1) shear rate was significatively higher in cases than in controls (p < 0.01). Hearing recovery degree correlated in an statistically way to increased values of EF (p < 0.01). There was no relation between initial hearing loss level and any rheology parameter.

CONCLUSIONS

Autoimmune RPSHL does not show a pathophysiology mechanism associated to blood hyperviscosity. So, rheoactive therapies as plasmapheresis warrant no clinical improvement.

[Non-interventional study on blood filterability changes in the clinical onset of sensorineural sudden deafness]

An hemorheological study on whole blood filterability (WBF) was done in eleven patients bearing of sudden deafness, in a continuous way, even before clinical onset. This evaluation is making usually in animal models, but not in humans. Independently of clinical diagnosis of each patient (two cases of diabetes mellitus, one of ulcerative colitis, systemic lupus erythematosus, systemic hypertension, after blood transfusion, sepsis with disseminated intravascular coagulation, upper respiratory ways infection, after surgery, and two healthy individuals), all of them showed a decreased WBF when hearing loss appeared (from 19.97 +/- 1.15 microliters/sec to 16.87 +/- 1.21 microliters/sec). This value normalized at six or seven days from the onset in cases with some kind of hearing recovery (18.83 +/- 1.01 microliters/sec, n = 4), but did not in those with no improvement even at thirty days (17.39 +/- 0.77 microliters/sec, n = 7). There were differences in WBF values of patients with and without hearing recovery in determinations at seven and thirty days from onset. Decrease in WBF accompanies this hearing disorder and confirms the cochlear microcirculation susceptibility to the impairment of blood viscoelastic properties.

Progressive sensorineural hearing loss in childhood

A progressive sensorineural hearing loss in childhood, with an extremely variable prevalence (from 4% to 30%), has been reported in the literature. This wide range of reported figures could depend on the different criteria used for identifying the deterioration, the groups, and the examined age ranges. The most frequent etiology of progressive sensorineural hearing loss in childhood includes hereditary causes, both syndromic and nonsyndromic, and developmental and infectious causes, whereas metabolic, toxic, autoimmune, traumatic, and vascular etiologies are less common; however, the origin of the hearing impairment often remains unknown. The population for this study consisted of 178 children with bilateral sensorineural hearing loss who were examined between 1971 and 1993 using audiologic tests. Syndromal genetic hearing loss was excluded from the study. A progressive loss of acuity was found in 11 subjects, with a prevalence of 6.2%. The etiology was hereditary deafness in five patients, congenital infection in one, and congenital inner ear anomaly in another patient; in the last four children the etiology was unknown. Onset of deterioration was after 4 years of age in 73% of the patients. The progressive evolution was binaural in almost all patients (10 of 11) and asymmetric in most, with a tendency to a greater deterioration at the frequencies initially least affected.

Effect of prostaglandin E1 on the rat inner ear microvascular thrombosis

1. The effect of prostaglandin E1 was investigated with a two-rat model of hearing disturbance and equilibrium dysfunction associated with inner ear microvascular thrombosis. 2. The inner ear microvascular thrombosis was induced by photochemical reaction between Rose Bengal and transmural green light (540 nm). Photochemical reaction causes endothelial injury followed by platelet adhesion, aggregation, and formation of a platelet- and fibrin-rich thrombus. 3. Under anesthesia, the cochlea or the vestibule was irradiated with green light to induce hearing disturbance or equilibrium dysfunction. 4. In the hearing disturbance model, a compound cochlear nerve action potential was recorded by electrocochleography every minute after the beginning of photoirradiation in the presence of Rose Bengal. 5. In the equilibrium dysfunction model, the photoirradiation was applied for 10 min after Rose Bengal administration. The behavior of rats was observed in the swimming test, and nystagmus was observed 24 hr after the end of photoirradiation. 6. Prostaglandin E1 significantly (P < 0.05) prolonged the time required to suppress the action potential. In the swimming test, 3 of the 6 animals treated with prostaglandin E1 did not rotate about their longitudinal axes (equilibrium dysfunction) and the duration of well-balanced swimming was significantly prolonged (P < .001). Prostaglandin E1 significantly (P < 0.05) suppressed the appearance of nystagmus. 7. In conclusion, prostaglandin E1 potentially prevents hearing disturbance and equilibrium dysfunction due to inner ear microvascular disorders.

Blood viscosity and plasma viscosity in patients with sudden deafness

Blood viscosity and plasma viscosity were measured in 51 patients with sudden deafness (SD) and 70 controls with normal hearing. Blood viscosity and plasma viscosity in patients with SD at their first medical examination were significantly higher than in the control group. The difference in viscosimetry results between the two groups was greater at higher shear rates. The data obtained in viscosimetry and pure-tone audiometry were analyzed after dividing the patients into a high viscosity group and a normal viscosity group. The correlation between average hearing level in pure-tone audiogram and blood viscosity or plasma viscosity was positive. The values of the O2-transport capacity of the blood demonstrated a negative correlation with average hearing level in patients with SD before treatment. During the course of treatment, blood viscosity and plasma viscosity decreased with the improvement of hearing impairment. When the distribution of average hearing level was 40 to 79 dB, a few of the patients with "recovery" or "good improvement" and most of patients with "fair improvement" or "no change" belonged to the low viscosity group. And, most of the patients with flat type hearing impairment and a few patients with high tone type hearing impairment belonged to the high viscosity group. These results suggest that many patients with SD have increased blood viscosity and plasma viscosity, and that this increase may play a significant role in the etiology of SD. There are also some differences in etiologic factors concerning type of hearing impairment and prognosis. In conclusion, the present study points to the importance of measuring blood viscosity and plasma viscosity in patients with SD, since blood and/or plasma viscosity may be involved in its etiology and prognosis.

Effect of ibudilast on microcirculation thrombosis in rat inner ear

The effect of ibudilast (0.1, 0.3 mg/kg), which has cerebral vasodilating and antiplatelet effects, was evaluated in two models of rat inner ear microcirculation thrombosis by using the photochemical reaction between green light (wave length: 540 nm) and intravenous injection of rose bengal. Furthermore, the inner ear blood flow was measured by a laser-Doppler flowmeter. In the hearing disturbance model, under anesthesia, the compound action potential of the cochlear nerve (AP) was measured by an electrocochleogram. The sound stimulus was an 8-kHz sine wave at 80 dB SPL. The AP was calculated 128 times. In the controls, the AP disappeared about 4 min after the intravenous injection of rose bengal (20 mg/kg). The time required to completely suppress the AP in the animals treated with ibudilast (0.1, 0.3 mg/kg) was significantly prolonged as compared with that in the controls. In the equilibrium dysfunction model, ibudilast (0.1, 0.3 mg/kg) reduced the time of abnormal swimming in the swimming test 24 hr after the completion of photo-illumination. Ibudilast (0.3 mg/kg) increased the inner ear blood flow during the 10-min observation period as compared with the controls, while it did not affect the mean blood pressure. In conclusion, ibudilast increased the inner ear blood flow and was effective in two models of rat inner ear microcirculation thrombosis.