Jonathon S. Sillman

Recent Advances in Cochlear Blood Flow Measurements

Changes in blood flow to the inner ear have been thought to influence or underlie a number of cochlear diseases, including some forms of noise-induced hearing loss, sudden hearing loss, and Menieres disease. Recently, important advances have been made in two technologies for the study of cochlear blood flow. The first is in the area of vital microscopic studies of cochlear microcirculation, and the second is based on the introduction of laser technology in the form of laser Doppler flowmetry. In this report, measurements are given of changes in cochlear circulation caused by carbon dioxide breathing, intravenous phenylephrine injection, systemic hemodilution, positive end expiratory pressure, and direct electrical stimulation of the cochlea. From these changes, we observe that cochlear blood circulation responds to systemic blood pressure alterations and is subject to local flow control mechanisms. Linearity and speed of response of the laser Doppler instrumentation also are shown. These advances show promise for contributing to our knowledge of control mechanisms of inner ear blood flow and for revealing the influence of various pharmacologic agents of potential clinical value.

Prognostic Value of Evoked and Standard Electromyography in Acute Facial Paralysis

Ninety-one patients with idiopathic (n = 62) and traumatic (n = 29) facial paralyses were available for evaluation at least 1 year after the onset of paralysis. In nine cases of idiopathic paralysis and in 12 cases of traumatic paralysis, total intratemporal nerve decompression was performed. The remaining patients were treated with steroids alone. All patients underwent evoked electromyography (EEMG) testing within 2 weeks of the onset of paralysis. Facial nerve recovery was graded using the House-Brackmann facial nerve recovery scale. Subjects were grouped according to maximal decline of compound muscle action potential (CAP), as determined by EEMG, and by level of recovery 1 year after onset of paralysis. Among patients who did not undergo surgical decompression of the facial nerve, incomplete clinical recovery (grade III or higher) was significantly associated with CAP decline of >90% (p < 0.05) for idiopathic paralysis. In contrast, there was no significant association between CAP decline of >90% and clinical outcome in traumatic paralysis. These findings support previous reports of the prognostic value of EEMG in idiopathic facial paralysis, but suggest that this test may have less predictive value in the evaluation of facial paralysis as a result of trauma.

A comparison of laser Doppler and intravital microscopic measures of cochlear blood flow

Many inner ear disorders may be caused by alterations in cochlear blood flow (CBF). However, each measurement technique used to monitor CBF has limitations in examining the relationship between otopathologic states and blood flow. This study Investigates laser Doppler flowmetry (LDF) and its fundamental drawback: The unknown relationship of LDF output to actual CBF. LDF readings are directly compared with concurrent intravital microscopy (IVM) measures of erythrocyte velocity in the lateral wall of the guinea pig cochlea. Positive end expiratory pressure, spontaneous respiration of 5% and 10% carbon dioxide, phenylephrine, and direct electrical stimulation of the cochlea were used to manipulate CBF. High, positive correlations were found between simultaneous LDF and IVM measurements of CBF. In addition, the study demonstrated that current microdissection techniques used to perform IVM do not cause changes in CBF. IVM measurements of CBF are a more sensitive indicator of CBF changes than are LDF measures. Despite the high correlation between measurement techniques within a single manipulation, simultaneous LDF and IVM measurements differed between manipulations. This may reflect regional changes in CBF affected by these manipulations and differences in the sampled vascular beds contributing to these two measures. It is unlikely that a single calibration factor can be defined that would allow the conversion of LDF output to actual units of blood flow across different manipulations used to alter CBF.

Electrically stimulated increases in cochlear blood flow: I. Frequency and intensity effects.

Charge-balanced, sinusoidal current was passed differentially between the apex and round window of the guinea pig cochlea. Cochlear blood flow was measured using a laser Doppler flow monitor. Systemic blood pressure was monitored from a cannula within the common carotid artery. Electrical stimulation increased cochlear blood flow, while systemic blood pressure was unaffected. A cochlear blood flow response parameter, normalized for transient changes in systemic blood pressure, was defined. The magnitude of the response parameter was found to be frequency selective and was also found to be an increasing function of current intensity, with maximum responses obtained with 500 Hz sinusoids. This cochlear blood flow response was not observed in dead animals; was present in preparations paralyzed with gallamine hydrochloride; and was correlated with an increase in cochlear red blood cell velocity, as directly observed by intravital microscopy. These observations imply that electrical stimulation induces a local vasodilation within the temporal bone. The fact that decreased cochlear blood flow was never observed with current injection implies that ischemia is not a likely mechanism of electrically induced tissue damage within the inner ear. The mechanism of this cochlear blood flow response is addressed in a companion report.

Electrically stimulated increases in cochlear blood flow: II. Evidence of neural mediation.

In a companion paper, we reported that electrical stimulation increased cochlear blood flow (CBF). This response was found to be an increasing function of current intensity and was frequency-selective, with the best response at approximately 500 Hz continuous sinusoidal current. The present investigation seeks to discover the mechanism of this effect. Direct measurement of cochlear temperature during electrical stimulation revealed no evidence of local heating. Autonomic neuronal activation is not likely, as neither atropine, hexamethonium, nor propranolol abolished the evoked CBF response. Strial activity could be suppressed by the use of furosemide, but the evoked CBF response persisted. Inactivation of auditory afferent neurons with kainic acid also did not change the evoked CBF response. Dimethyl sulfoxide, a potent oxygen-free radical scavenger, did suppress the evoked CBF response to a small but significant degree. This suggests that oxygen-free radicals may be produced within the cochlea during electrical stimulation. Finally, the evoked CBF response was completely suppressed by procaine and tetrodotoxin, with recovery of evoked CBF response accompanying recovery of cochlear action potentials. These data indicate that stimulation of neural fibers, distinct from autonomic and auditory afferent neurons, may modulate CBF.

Signal averaging and waveform analysis of laser Doppler flowmetry monitoring of porcine myocutaneous flaps: I. Acute assessment of flap viability

Postoperative monitoring of microvascular free-tissue transfer is essential to the early identification and correction of vascular compromise. Laser Doppler flowmetry is a noninvasive monitor of capillary bed perfusion. Its current clinical use requires continuous monitoring and trend analysis to detect changes in capillary perfusion. This study investigated the hypothesis that signal averaging of laser Doppler flowmetry output triggered by a fixed point in the cardiac cycle would provide accurate information about the microvascular flow patterns not dependent on trend analysis. These results indicate that averaged waveform analysis allowed for a rapid, objective, and statistically significant distinction between a viable myocutaneous flap and one with vascular compromise in a porcine model. Moreover, this technique allows for distinction between venous and arterial insufficiency.

First Place — Resident Clinical Science Award 1995: Signal Averaging and Waveform Analysis of Laser Doppler Flowmetry Monitoring of Porcine Myocutaneous Flaps: I. Acute Assessment of Flap Viability

Postoperative monitoring of microvascular free-tissue transfer is essential to the early identification and correction of vascular compromise. Laser Doppler flowmetry is a noninvasive monitor of capillary bed perfusion. Its current clinical use requires continuous monitoring and trend analysis to detect changes in capillary perfusion. This study investigated the hypothesis that signal averaging of laser Doppler flowmetry output triggered by a fixed point in the cardiac cycle would provide accurate information about the microvascular flow patterns not dependent on trend analysis. These results indicate that averaged waveform analysis allowed for a rapid, objective, and statistically significant distinction between a viable myocutaneous flap and one with vascular compromise in a porcine model. Moreover, this technique allows for distinction between venous and arterial insufficiency.

Intratympanic Gentamicin for Meniere's Disease

Educational objectives: To comprehensively evaluate patients with Menieres disease and determine their candidacy for gentamicin therapy and to administer intratympanic gentamicin for the treatment of vertico in Menieres disease.

The thyroplasty retractor.

Fig. 1.Thethyroplas1y retractor ends in a serrated. everted toe designed to engage the outer thyroid cartilage without penetra1ing the inner perichondrium. is under local anesthesia.P This approach has a significant advantage over both endoscopic vocal cord augmentation by injection and open thyroplasty with the patient under general anesthesia in its capacity to adjust vocal cord position reversibly on the basis of intraoperative assessment of phonation . This new method of thyroplasty is performed by positioning the vocal cord, underlying thyroarytenoideus muscle, and segment of thyroid cartilage medially after mobilizing this complex by creating a window in the thyroid cartilage. We have developed a retractor specifically designed to improve exposure of the thyroid cartilage at the level of the true vocal cords through a small horizontal neck incision.