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

Vascular Supply of the Human Spiral Ganglion: Novel Three-Dimensional Analysis Using Synchrotron Phase-Contrast Imaging and Histology

Human spiral ganglion (HSG) cell bodies located in the bony cochlea depend on a rich vascular supply to maintain excitability. These neurons are targeted by cochlear implantation (CI) to treat deafness, and their viability is critical to ensure successful clinical outcomes. The blood supply of the HSG is difficult to study due to its helical structure and encasement in hard bone. The objective of this study was to present the first three-dimensional (3D) reconstruction and analysis of the HSG blood supply using synchrotron radiation phase-contrast imaging (SR-PCI) in combination with histological analyses of archival human cochlear sections. Twenty-six human temporal bones underwent SR-PCI. Data were processed using volume-rendering software, and a representative three-dimensional (3D) model was created to allow visualization of the vascular anatomy. Histologic analysis was used to verify the segmentations. Results revealed that the HSG is supplied by radial vascular twigs which are separate from the rest of the inner ear and encased in bone. Unlike with most organs, the arteries and veins in the human cochlea do not follow the same conduits. There is a dual venous outflow and a modiolar arterial supply. This organization may explain why the HSG may endure even in cases of advanced cochlear pathology.

Niflumic acid hyperpolarizes smooth muscle cells via calcium-activated potassium channel in spiral modiolar artery of guinea pigs

AIM

The influence of niflumic acid (NFA), a Cl(-)channel antagonist, on the membrane potentials in smooth muscle cells (SMC) of the cochlear spiral modiolar artery (SMA) in guinea pigs was examined.

METHODS

The intracellular recording and whole-cell recording technique were used to record the NFA-induced response on the acutely-isolated SMA preparation.

RESULTS

The SMC had 2 stable but mutually convertible levels of resting potentials (RP), that is, one was near -45 mV and the other was approximately -75 mV, termed as low and high RP, respectively. The bath application of NFA could cause a hyperpolarization in all the low RP cells, but had little effect on high RP cells. The induced responses were concentration-dependent. Large concentrations of NFA (>or=100 micromol/L) often induced a shift of a low RP to high RP in cells with an initial RP at low level, and NFA (up to 100 micromol/L) had little effect on the membrane potentials of the high RP cells. However, when the high RP cells were depolarized to a level beyond -45 mV by barium and ouabain, NFA hyperpolarized these cells with the similar effect on those cells initially being the low RP. The NFA-induced response was almost completely blocked by charybdotoxin, iberiotoxin, tetraethylammonium, 1,2-bis(2- aminophenoxy) ethane-N,N,N',N'-tetraacetic acid tetrakis acetoxymethyl ester, but not by 4-aminopyridine, barium, glipizide, apamin, ouabain, and CdCl2.

CONCLUSION

NFA induces a concentration-dependent reversible hyperpolarization in SMC in the cochlear SMA via activation of the Ca2+-activated potassium channels.

In vivo imaging of mammalian cochlear blood flow using fluorescence microendoscopy

AIMS

We sought to develop techniques for visualizing cochlear blood flow in live mammalian subjects using fluorescence microendoscopy.

BACKGROUND

Inner ear microcirculation appears to be intimately involved in cochlear function. Blood velocity measurements suggest that intense sounds can alter cochlear blood flow. Disruption of cochlear blood flow may be a significant cause of hearing impairment, including sudden sensorineural hearing loss. However, inability to image cochlear blood flow in a nondestructive manner has limited investigation of the role of inner ear microcirculation in hearing function. Present techniques for imaging cochlear microcirculation using intravital light microscopy involve extensive perturbations to cochlear structure, precluding application in human patients. The few previous endoscopy studies of the cochlea have suffered from optical resolution insufficient for visualizing cochlear microvasculature. Fluorescence microendoscopy is an emerging minimally invasive imaging modality that provides micron-scale resolution in tissues inaccessible to light microscopy. In this article, we describe the use of fluorescence microendoscopy in live guinea pigs to image capillary blood flow and movements of individual red blood cells within the basal turn of the cochlea.

METHODS

We anesthetized eight adult guinea pigs and accessed the inner ear through the mastoid bulla. After intravenous injection of fluorescein dye, we made a limited cochleostomy and introduced a compound doublet gradient refractive index endoscope probe 1 mm in diameter into the inner ear. We then imaged cochlear blood flow within individual vessels in an epifluorescence configuration using one-photon fluorescence microendoscopy.

RESULTS

We observed single red blood cells passing through individual capillaries in several cochlear structures, including the round window membrane, spiral ligament, osseous spiral lamina, and basilar membrane. Blood flow velocities within inner ear capillaries varied widely, with observed speeds reaching up to approximately 500 microm/s.

CONCLUSION

Fluorescence microendoscopy permits visualization of cochlear microcirculation with micron-scale optical resolution and determination of blood flow velocities through analysis of video sequences.

Microcirculatory effects of a homeopathic preparation in patients with mild vertigo: an intravital microscopic study

The effects of the homeopathic preparation Vertigoheel on variables related to microcirculation were investigated using vital microscopy techniques in patients with vestibular vertigo. In a non-randomized, open study, 16 patients given Vertigoheel were compared with 16 untreated patients. Measurements were carried out in two areas (defined by selecting 60 blood-cell perfused nodal points of arterioles, venules, and capillaries with a mean diameter > or = 40 microm): the cuticulum/subcuticulum of the inside left lower arm and an area 5 mm behind the left earlobe. After 12 weeks of treatment, patients receiving the homeopathic preparation exhibited an increased number of nodal points, increased flow rates of erythrocytes in both arterioles and venules, increased vasomotion, and a slight reduction in hematocrit vs. baseline. None of these changes were observed in the control group and the differences between treatment groups were statistically significant. Partial oxygen pressure increased significantly in the Vertigoheel group compared with the control group. In addition, in Vertigoheel patients, significantly increased numbers of cell-wall adhering leucocytes were observed, accompanied by increased local concentrations of the adhesion molecules ICAM-1. The microcirculatory changes were associated with a reduction in the severity of vertigo in the actively treated patients, both as assessed by the treating physician and by the patients themselves. The data support a pharmacological effect on microcirculation from the treatment.

Usefulness of High Doses of Glucocorticoids and Hyperbaric Oxygen Therapy in Sudden Sensorineural Hearing Loss Treatment

OBJECTIVE

We investigated the effect of pharmacologic (steroids, vasodilators, vitamins, and Betaserc) and hyperbaric oxygen therapy on patients with sudden sensorineural hearing loss.

METHODS

The pharmacologic arm of the study consisted of 52 patients with defined sudden sensorineural hearing loss treated simultaneously in the ENT Department and National Center for Hyperbaric Medicine of the Medical University of Gdansk, Poland, from 1997 to 2000 (Group A). The hyperbaric oxygen therapy consisted of exposure to 100% oxygen at a pressure of 250 kPa for a total of 60 minutes in a multiplace hyperbaric chamber. The control group included 81 patients with defined sudden sensorineural hearing loss treated in the ENT Department, Medical University of Gdansk, from 1980 to 1996 (Group B). Both groups were comparable regarding the age of the patients, season of hearing loss occurrence, tinnitus and vestibular symptom frequency, delay before therapy, and average threshold loss before the start of treatment. The treatment results (hearing gain) were estimated using pure-tone audiometry. We retrospectively analyzed the audiograms of all patients.

RESULTS

Patients from Group A (blood flow-promoting drugs, glucocorticoids in high doses, betahistine, and hyperbaric oxygen therapy) showed significantly better recovery of hearing levels compared with those from Group B (blood flow-promoting drugs and glucocorticoids in low doses) at seven frequencies (500, 1,000, 2,000, 3,000, 4,000, 6,000, and 8,000 Hz) (p < 0.05) and four groups of frequencies (pure-tone average, high-tone average, pure middle-tone average, and overall average) (p < 0.05). Percentage hearing gain in all investigated frequencies was also better in Group A versus Group B, and the differences were statistically significant (p < 0.05).

CONCLUSION

We conclude that hyperbaric oxygen therapy with high doses of glucocorticoids improves the results of conventional sudden sensorineural hearing loss treatment and should be recommended. In addition, the best results are achieved if the treatment is started as early as possible.

Effects of anterior inferior cerebellar artery occlusion on cochlear blood flow--a comparison between laser-Doppler and microsphere methods

The effects of anterior inferior cerebellar artery (AICA) occlusion on blood flow were investigated in rats using the laser-Doppler and microsphere methods. A specially designed microclamp was held in a micromanipulator and positioned to occlude the left AICA. After the middle ear mucosa had been removed, a 1.0-mm laser-Doppler probe was placed on the basal turn of the left cochlea. Non-radioactive microspheres were injected intracardially during the AICA occlusion and the numbers of microspheres in various parts of the cochlea were counted, including in the bone surrounding the cochlea. Upon AICA clamping, the blood flow measured by laser-Doppler flowmetry decreased to 46.9+/-11.9% of the baseline value, and the number of microspheres trapped in the cochlea was 17.2+/-13.3% compared with the contralateral side in 15 animals. The number of microspheres in the bone surrounding the cochlea in the AICA-clamped side was 81+/-15% of that of the contralateral side. In animals in which there were few if any microspheres in the cochlea, laser-Doppler output was 30-40% of the baseline value. From these findings, we infer that during complete interruption of cochlear blood flow in rats, residual laser-Doppler output was essentially attributable to blood flow in the bone surrounding the cochlea.

Quantitative analysis of rat inner ear blood flow using the iodo[(14)C]antipyrine technique

A number of different qualitative and quantitative techniques have been used to measure inner ear blood flow and all have required that the animal be anesthetized. It is well known that anesthesia can cause a variety of circulatory as well as other systemic changes. In this study, we have employed a technique commonly used for quantifying brain blood flow, the iodo[(14)C]antipyrine technique ([(14)C]IAP). Unlike other techniques, [(14)C]IAP can be used in unanesthetized animals under conditions that are nearly normal, it is non-invasive, it can be used reliably in regions of low local blood flow, and data can be acquired from both the periphery and central nervous system. Results show that blood flow to the lateral wall of the basal turn of the cochlea (387 +/- 19 microl/g/min) is significantly higher (P<0.001) than that of the utricular macula (189 +/- 23 microl/g/min), horizontal (186 +/- 22 microl/g/min), superior (185 +/- 22 microl/g/min), or posterior canal crista (185 +/- 25 microl/g/min). Surprisingly, blood flow to all of the vestibular end-organs is remarkably similar. The use of this technique should allow pharmacological experimentation on inner ear blood flow without the unknown complications of anesthesia or invasive procedures.

Continuous monitoring of regional cerebral blood flow: experimental and clinical validation of a novel thermal diffusion microprobe

OBJECT

Current clinical neuromonitoring techniques lack adequate surveillance of cerebral perfusion. In this article, a novel thermal diffusion (TD) microprobe is evaluated for the continuous and quantitative assessment of intraparenchymal regional cerebral blood flow (rCBF).

METHODS

To characterize the temporal resolution of this new technique, rCBF measured using the TD microprobe (TD-rCBF) was compared with rCBF levels measured by laser Doppler (LD) flowmetry during standardized variations of CBF in a sheep model. For validation of absolute values, the microprobe was implanted subcortically (20 mm below the level of dura) into 16 brain-injured patients, and TD-rCBF was compared with simultaneous rCBF measurements obtained using stable xenon-enhanced computerized tomography scanning (sXe-rCBF). The two techniques were compared using linear regression analysis as well as the Bland and Altman method. Stable TD-rCBF measurements could be obtained throughout all 3- to 5-hour sheep experiments. During hypercapnia, TD-rCBF increased from 49.3+/-15.8 ml/100 g/min (mean +/- standard deviation) to 119.6+/-47.3 ml/100 g/ min, whereas hypocapnia produced a decline in TD-rCBF from 51.2+/-12.8 ml/100 g/min to 39.3+/-5.6 m/100 g/min. Variations in mean arterial blood pressure revealed an intact autoregulation with pressure limits of approximately 65 mm Hg and approximately 170 mm Hg. After cardiac arrest TD-rCBF declined rapidly to 0 ml/100 g/min. The dynamics of changes in TD-rCBF corresponded well to the dynamics of the LD readings. A comparison of TD-rCBF and sXe-rCBF revealed a good correlation (r = 0.89; p < 0.0001) and a mean difference of 1.1+/-5.2 ml/100 g/min between the two techniques.

CONCLUSIONS

The novel TD microprobe provides a sensitive, continuous, and real-time assessment of intraparenchymal rCBF in absolute flow values that are in good agreement with sXe-rCBF measurements. This study provides the basis for the integration of TD-rCBF into multimodal monitoring of patients who are at risk for secondary brain injury.

The effect of blood flow promoting drugs on cochlear blood flow, perilymphatic pO(2) and auditory function in the normal and noise-damaged hypoxic and ischemic guinea pig inner ear

The effect of blood flow promoting drugs, such as hydroxyethyl starch (HES) either of low or high molecular weight (HES 70, HES 200), pentoxifylline, ginkgo biloba, naftidrofuryl and betahistine, and various combinations of the drugs was studied in unexposed and noise-exposed (broad-band noise, bandwidth 1-12 kHz, 106 dB SPL, 30 min) guinea pigs. The results were compared without therapy and placebo (isotonic saline, NaCl). The cochlear blood flow (CoBF) and the partial pressure of oxygen in the perilymph (PL-pO(2)) were continuously and simultaneously recorded over a period of 210 min. In addition, cochlear microphonics (CMs), compound action potentials of the auditory nerve (CAPs) and auditory brain stem responses (ABRs) were registered. Noise-induced hearing loss (NIHL) paralleled a decrease of PL-pO(2). Both were found to occur before evidence of reduced CoBF. PL-pO(2) and CoBF declined progressively post-exposure, while CMs, CAPs and ABRs showed no further deterioration or signs of recovery up to 180 min after cessation of noise. Treatment started 60 min post-exposure, respectively after 90 min, without manipulation in unexposed animals, and was then studied for a further 120 min. In unexposed animals, CoBF increased significantly during infusion of HES 70, HES 200, pentoxifylline and betahistine. NaCl, ginkgo biloba and naftidrofuryl did not alter CoBF. PL-pO(2) decreased significantly during infusion of all administered drugs and combinations, except for NaCl. CMs, CAPs and ABRs remained constant, with the exception of increased ABRs after infusion of HES 70 and HES 200. In noise-exposed animals, a sustained therapeutic effect on cochlear ischemia was achieved only by HES 200 and pentoxifylline. HES 70, betahistine and ginkgo biloba compensated cochlear ischemia only during infusion; however, 30-60 min after termination of therapy, no significant difference of values for CoBF was observed compared to the untreated noise-exposed groups. NaCl and naftidrofuryl showed no effect on CoBF. None of the applied drugs had a sustained compensatory effect on cochlear hypoxia. CMs, CAPs and ABRs improved significantly after HES 70, HES 200 and betahistine, resulting in partial recovery of CMs, and partial (betahistine) or even full (HES 70 and HES 200) recovery of CAPs and ABRs. In contrast, NaCl, pentoxifylline, ginkgo biloba and naftidrofuryl had no therapeutic effect on NIHL.

Comparison of cerebral blood flow measured by laser-Doppler flowmetry and hydrogen clearance in cats after cerebral insult and hypervolemic hemodilution

Laser-Doppler flowmetry provides a continuous measurement of blood flow without violating the natural state of circulation. The linearity of the laser-Doppler and hydrogen clearance methods of blood flow measurement were compared using a protocol that produced changes in cerebral blood flow that might be experienced in a neurosurgical setting. Cerebral blood flow was measured in both hemispheres of 12 adult cats during the snaring of one common carotid artery, the intracisternal injection of 5 mg of 5-hydroxytryptamine creatinine sulfate, and hypervolemic hemodilution, which produced a 25% reduction in blood hematocrit. The percentage of baseline laser-Doppler flowmetry and hydrogen clearance flows showed an acceptable degree of correlation (R2 = 0.762) over the range of cerebral blood flows measured. More rigorous analysis using Bland and Altman's difference against mean test showed that 10 minutes after hemodilution, the two methods displayed a level of variation outside the limits of agreement (-21.85 to 22.03%). Laser-Doppler flowmetry provided a noninvasive and continuous measure of blood flow, increasing the ability to observe instantaneous changes in cerebral microcirculation. However, laser-Doppler flowmetry did not record absolute blood flow, was affected by cerebral tissue shrinkage, and did not accurately measure flow under conditions of changed blood hematocrit.

Influence of hypotension on cochlear blood flow in polycythemic condition

We examined the influence of hypotension by infusion of acebutolol hydrochloride (AH), a cardioselective beta-receptor antagonist, on cochlear blood flow in guinea pigs with various hematocrit values. AH infusion lowered the mean blood pressure to almost the same degree in all animals, regardless of the hematocrit level. The degree of the concomitant decrease of CBF varied with the hematocrit, being greater in animals with a higher hematocrit. In those with the highest hematocrit CBF did not return to the initial level. From these values we calculated the O2 transport capacity after AH infusion and found it to be lower than in animals without AH infusion. The difference was greater at higher hematocrits. These findings suggest that the microcirculation of the inner ear is responsive to transient decreases of perfusion pressure at high hematocrits.

Possible involvement of capsaicin-sensitive sensory nerves in the regulation of cochlear blood flow in the guinea pig

Capsaicin-induced microcirculatory changes in the cochlea of anaesthetized guinea pigs were examined by laser-Doppler flowmetry. Close intraarterial capsaicin infusion into the anterior inferior cerebral artery at doses of 10-50 pmol/min was followed by dose-dependent vasodilatation. Capsaicin infused in a dose of 150-200 pmol/min or above resulted in vasoconstriction in the region examined. Topical capsaicin administration into the cochlea (50-150 pmol) resulted in very moderate vasodilation with a latency of 1-2 min. Perivascular capsaicin application onto the anterior inferior cerebellar artery elicited an elevated blood flow in the cochlea, too. It is concluded that the release of vasoactive substances from capsaicin-sensitive nerve fibres in the inner ear of the guinea pig may play a role in the control of the local microcirculation. These nerves may also be involved in the neurogenic inflammatory processes in the region.

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)

Effects of posture, hypotension and locally applied vasoconstriction on the middle ear microcirculation in anaesthetized humans

Studies by laser-Doppler flowmetry of middle ear microcirculation changes induced by physical and chemical stimuli in the animal have only recently been made. This prospective study, performed in humans, was designed to compare the effects of a postural manoeuvre (headup tilt 30 degrees), hypotension and locally applied vasoconstriction on middle ear blood flow during anaesthesia. Circulatory changes provoked by a headup tilt of 30 degrees, and successive intravenous boluses of potent vasodilators, were compared with circulatory changes provoked by locally applied adrenaline, in ten healthy patients in good physical states undergoing middle ear surgical repair. Heart rate and direct arterial pressure were continuously recorded via a radial artery cannula. Middle ear blood flow was continuously recorded via a laser-Doppler probe placed on the promontorium cavi tympani. Metabolic parameters (partial pressure of O2 and CO2 in arterial blood, pH, arterial lactate concentrations) and arterial concentrations of propofol were measured just before and just after the experiment. Headup tilt did not modify heart rate, mean arterial pressure or middle ear blood flow. Vasodilators (nicardipine, nitroprusside, nitroglycerin) provoked a fall in arterial pressure (P < 0.0001, P < 0.0001, P < 0.019, respectively), but did not induce any significant variations in heart rate; variations occurred in middle ear blood flow (P > 0.05, not significant) which were different according to patients and agents. Locally applied adrenaline provoked a fall in the middle ear blood flow (P < 0.0012), with no effect on heart rate and arterial pressure. There were no significant changes in metabolic values, or propofol serum concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

The vascular component of sodium salicylate ototoxicity in the guinea pig

Drugs of the salicylate family (aspirin-like drugs) are reversibly ototoxic. Electrophysiologic and ultrastructural evidence suggests an impairment of the sensory hair cells of the cochlea following salicylate treatment. In addition, since these drugs can cause vasoconstriction, the ototoxicity of salicylates may also involve an impairment of the blood circulation in inner ear. However, a vascular hypothesis of salicylate toxicity has not received much attention. In the current study, we simultaneously measured cochlear blood flow (by laser Doppler flowmetry) and the sound-evoked potentials from the round window. Sodium salicylate caused a decrease in cochlear blood flow that appeared within 30 min following an intramuscular injection of a low dose of sodium salicylate (100 mg/kg). This sodium salicylate dose did not cause a change in auditory sensitivity. For higher doses (200 mg/kg and 300 mg/kg), both cochlear blood flow and auditory sensitivity were affected. The 300 mg/kg dose decreased blood flow by about 25% and elevated compound action potential thresholds by 10 to 25 dB for high frequencies (> or = 8 kHz). Further experiments showed that salicylate-induced threshold shifts were significantly reduced for the mid-frequencies when cochlear blood flow is increased by the vasodilating drug hydralazine (negating the flow reduction caused by salicylate). These data indicate that in addition to the direct effect of systemically administered salicylate on neurosecretory function a decreased blood flow contributes to the ototoxicity of salicylates.

Effects of electrical stimulation of the superior cervical ganglion on cochlear blood flow in guinea pig

It has been proposed that cochlear blood flow (CBF) is controlled in part by the sympathetic nervous system. In the present study the effect of electrical stimulation of the superior cervical ganglion (SCG) on CBF in guinea pigs was investigated using laser Doppler flowmetry (LDF). Animals were anesthetized with diazepam and fentanyl and the SCG was exposed. A custom-designed bipolar cuff electrode was fixed around the ganglion and 1 ms biphasic current pulses were injected at 0.15 mA to 1.5 mA, 6 Hz. Bilateral CBF was monitored, while the ganglion was stimulated for 3 or 5 min before and after the ascending sympathetic trunk and nerve branches from SCG were sectioned. Electrical stimulation of 0.5 mA caused the ipsilateral CBF (CBFi) to decrease 11.7% +/- 1.3 from the baseline (BL), while the contralateral CBF (CBFc) increased slightly due to the change in systemic blood pressure (BP). A linear relation was observed between the level of current stimulation and evoked reduction in CBF. Cervical sympathetic trunk section (between the SCG and the middle cervical ganglion) did not influence the pattern or the amplitude of CBF change in response to electrical stimulation of SCG. Sectioning the efferent fibers of the medial inferior and medial superior branch of the SCG only minimally reduced the amplitude of the CBF decrease evoked by electrical stimulation. However, sectioning the superior lateral branch abolished this decrease.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of batroxobin on cochlear blood flow

Cochlear blood flow is considered to be closely related to cochlear function. Among several etiologic factors implicated in inner ear diseases, disturbance of local blood flow is held to be one of the most important. With this in view, various pharmaceuticals are currently being used to increase local blood flow in patients with inner ear diseases. In the control of blood flow there are three major factors; systemic blood pressure (perfusion pressure), vascular tone, and blood viscosity. Batroxobin (BX) was developed to increase local blood flow by lowering blood viscosity through defibrinogenation; it is used in the treatment of thrombosis and occasionally for the treatment of sudden deafness. In the present study, we observed the effect of BX on cochlear blood flow in guinea pigs, using a laser Doppler flowmeter, and measured the blood fibrinogen concentration after BX infusion. There was an obvious increase in cochlear blood flow during the observation period of 3 h after 10 BU/kg were infused, and a slight increase when 2 BU/kg were infused. Blood fibrinogen levels decreased dramatically by 30 min after BX infusion (10 BU/kg), and the extremely low level attained was maintained throughout the 3-h observation period. Hemorrhage from the surgically opened ear was noted in 2 animals during the experiment and rectal bleeding in one.

Influence of experimentally elevated blood viscosity on the auditory nerve-brainstem evoked response and threshold

Blood viscosity, due to its effect on blood flow, is one of the determinants of oxygen delivery. Therefore the influence of elevated blood viscosity on hearing was studied in rats using the auditory brainstem response (ABR) threshold, wave 1 latency, brainstem transmission time (BTT) and wave 1/4 amplitude ratio. Whole blood viscosity (WBV) was elevated by 15-21% in two different ways: elevating the hematocrit (Polycythemia) by acclimation in a hypobaric chamber, or elevating the plasma viscosity by infusing a solution of Polyvinylpyrrolidone-360 (PVP). ABR was recorded before and 24 h after the blood viscosity was elevated, so that each rat served as its own control. Paired t-tests showed that there was no statistically significant difference in the ABR parameters in each of the groups as a consequence of blood viscosity elevation. In conclusion, the elevation of WBV to this degree for this duration, using two different techniques had no effect either on the function of the auditory nerve and the more peripheral sites, or on the central auditory pathway as studied by ABR.

Feasibility of pulse oxymetry to measure arterial O2 saturation in studies on cochlear blood circulation

To understand the characteristics of oxygen transport to the inner ear, the relationship between arterial O2 saturation and cochlear microcirculation was investigated under different respiratory condition in guinea pigs. To monitor arterial O2 saturation a pulse oxymeter instead of an arterial blood gas analyzer was used. When the arterial O2 saturation was measured in the foot pad by a pulse oxymeter under different respiratory conditions, the data showed a close correlation with the results of blood gas analysis. For the measurement of cochlear microcirculation, a pulse oxymeter was found to be a feasible respiratory monitor for animal experiments. With this apparatus our study demonstrated a slower reaction in the decrease of perilymphatic oxygen tension than of cochlear blood flow during stepwise induction of hypoventilation monitored by a pulse oxymeter. Under certain conditions of hyperventilation in which arterial O2 saturation and perilymphatic oxygen tension increased gradually, cochlear blood flow was found to decrease. This decrease of cochlear blood flow could be attributed to chemical controls which are regulated, as in the cerebral blood circulation, by the content of CO2 and H+ in the vascular bed in the cochlea.

Effects of a depressor on cochlear blood flow and perilymphatic oxygen tension

To clarify the characteristics of the blood circulation in the cochlea, we investigated the relationship between cochlear blood flow and perilymphatic oxygen tension in guinea pigs with trimetaphan camsilate induced hypotension. Cochlear blood flow was measured by laser Doppler flowmetry, and perilymphatic oxygen tension by a polarographic method. Cochlear blood flow generally paralleled systemic blood pressure, while perilymphatic oxygen tension showed a slower response to the decrease of systemic blood pressure. Although there were individual differences in the changes of systemic blood pressure, cochlear blood flow and perilymphatic oxygen tension, they were found to be dose dependent. Since hypotension induced by trimetaphan camsilate is fairly reproducible in the dose range of this experiment, this drug can be used as a ganglion blocking agent in experiments on cochlear blood flow and perilymphatic oxygen tension during systemic hypotension. The change of perilymphatic oxygen tension with a slower response could be considered to be a factor in the homeostasis in the inner ear fluid.

Relationship between cochlear blood flow and perilymphatic oxygen tension

To clarify the characteristics of the blood circulation in the cochlea, we correlated cochlear blood flow and perilymphatic oxygen tension at various blood pressures. Cochlear blood flow was measured in guinea pigs by laser Doppler flowmetry, and perilymphatic oxygen tension by polarography. Blood pressure changes were induced by angiotensin II injection, trimetaphan camsylate injection and blood withdrawal. Cochlear blood flow generally paralleled systemic blood pressure, indicating a close correlation. In contrast, perilymphatic oxygen tension was slower to increase and decrease. However, when systemic blood pressure was lowered more gradually, perilymphatic oxygen tension did not show the same lag. These findings indicate that perilymphatic oxygen tension parallels systemic blood pressure when changes induced are slower and in a physiological range.

Laser light transmission and laser Doppler blood flow measurements on the human, rat and guinea pig cochlea

In order to test the applicability of laser-Doppler flowmetry in monitoring cochlear blood flow clinically, the thickness and the helium-neon laser light transmission of specimens of human, rat and guinea pig promontory bone and human skin were determined. Furthermore, comparative laser-Doppler measurements were taken from the promontory in patients, rats and guinea pigs. Due to the different thicknesses of the promontory bone in different species, the light transmission was found to be considerably higher for the animal cochlea (rat, 15%; guinea pig, 6.6%) than the human cochlea (1.7%). However, a clearly higher laser-Doppler signal was recorded from both the human and the rat cochleas as compared with the guinea pig. The relative laser light attenuation by the human skin specimens corresponded to that of the human promontory bone. The findings are discussed with regard to the suitability of the laser-Doppler method for blood flow measurements in the human cochlea.

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.