Influence of stimulus duration and intensity on acoustic reflex parameters

Four acoustic reflex parameters (latency, duration, amplitude, recruitment time) in response to stimuli lasting 1 000 to 50 msec with an initial intensity of 95 dB SPL p.e. were studied in four sets of experiments. In each set of experiments, each halving of the stimulus duration was accompanied by a 3, 4, 5 and 6 dB SPL p.e. increase respectively (exchange rates: 3, 4, 5 and 6 dB SPL p.e.). It was found that latency was dependent on the threshold only and unaffected by either duration and intensity. Amplitude and recruitment time were mainly determined by energy content of the stimulus, whereas duration of contraction was solely dependent on the stimulus duration. These experiments also demonstrate that, with reference to stimuli employed, an increase of 3 dB SPL p.e. each halving of the stimulus duration is unable to maintain unchanged the environmental acoustic energy reaching the inner ear.     

Optimal current intensity for supramaximal stimulation during electroneurography for facial palsy

ObjectiveTo determine the optimal current intensity for supramaximal stimulation during electroneurography (ENoG) for facial palsy.MethodsForty patients with unilateral facial palsy (32 Bell's palsy, 7 Ramsay Hunt syndrome, and 1 temporal bone fracture) were enrolled. All patients were initially treated with intravenous steroid injections and examined using ENoG. Compound muscle action potentials (CMAPs) of the orbicularis oris muscle were measured on the paralyzed and healthy sides. Stimulation current intensity was varied every 5 mA from 20 mA to 50 mA using two recording methods (the midline and standard methods). The CMAPs of both sides were monitored to see whether they would saturate under the high current intensity stimulation or not.ResultsNo obvious saturation of CMAPs was observed in either side with the midline or standard methods. Statistically, a current of 35 mA and above in the healthy side, and 30 mA and above in the paralytic side, resulted in no difference to each side when using the midline recording method. On the other hand, a current of 35 mA and above in the healthy side, and 25 mA and above in the paralytic side, resulted in no difference to each side when using the standard recording method.ConclusionsThese results indicate that a current intensity of at least 35 mA is required to achieve supramaximal stimulation on the healthy side in a patient with unilateral facial nerve palsy. Clinically, for simplicity or standardization purposes, if the same current intensity is introduced bilaterally for ENoG measurements, adopting 40 mA (35 mA plus 10-20%) stimulation would be appropriate for supramaximal stimulation, while being cognizant of the potential effects of artifacts from other muscles.     

Motor responses of the esophagus and lower esophageal sphincter (LES) to vestibular stimulation in man

Pressure recordings in the esophageal body, LES and stomach were performed in 10 healthy subjects before and after caloric stimulation of the labyrinth. While esophageal and stomach responses varied or were absent, all subjects showed variations at the LES level. Duration of LES relaxation was increased and both time and amplitude of LES augmentation were significantly reduced. The physiological mechanism of labyrinthine-digestive connections and the possibility of clinical applications are discussed.     

Reduction in excitability of the auditory nerve following electrical stimulation at high stimulus rates. IV. Effects of stimulus intensity.

High rate intracochlear electrical stimulation using stimulus intensities well above clinical limits can induce a significant reduction in the excitability of the auditory nerve as measured by a reduction in the amplitude of the electrically evoked auditory brainstem response (EABR). The purpose of the present study was to assess the effect of stimulus intensity on these stimulus induced changes by comparing the effects of acute stimulation using stimulus intensities within normal clinical levels (6 dB and 12 dB above EABR threshold) and significantly above normal clinical levels (> 20 dB above EABR threshold; 0.34 microC/phase). Stimulus rates of 200, 400, or 1000 pulses/s (pps) were delivered to bipolar scala tympani electrodes. EABRs were recorded before and periodically following 2 h of continuous stimulation. No reduction in EABR amplitude was observed following stimulation at 6 dB above EABR threshold for the three stimulus rates examined. However, EABRs were reduced when stimulated at 12 dB above EABR threshold at 400 pps, and significantly reduced when stimulated at a rate of 1000 pps. Immediate post-stimulus response amplitudes of wave III were 63% and 35% of the pre-stimulus amplitude at 400 and 1000 pps respectively. More significant reductions in EABR amplitude were observed following stimulation at levels more than 20 dB above EABR threshold for both 400 and 1000 pps stimuli. Our findings indicate that stimulus induced changes in EABR amplitude are related to both stimulus rate and stimulus intensity. Moreover, stimulation using intensities within the normal clinical range show little evidence of prolonged reductions in auditory nerve excitability at stimulus rates of up to 1000 pps.     

Effects of stimulus duration and stimulus off time on the auditory and acoustic reflex thresholds

The effects of stimulus duration and stimulus off time on the thresholds of hearing and the acoustic reflex were investigated in 10 normal-hearing subjects and 10 subjects with sensorineural hearing loss. A 1000-Hz stimulus with on-off times of 500-500 msec and 30-30 msec was used to obtain hearing sensitivity and acoustic reflex thresholds via a tracking method. Auditory threshold was poorer for the 30-30 msec tone than the 500-500 msec stimulus in both groups. Using the different stimuli, no significant difference in acoustic reflex threshold was observed in either group. These results suggest that the addition of a short off time modifies the previously observed effects of both duration and off time on the acoustic reflex and auditory threshold.     

Structural and functional organization of the upper esophageal sphincter

Using traditional anatomical and histological methods, the muscle envelope of the pharynx-esophagus junction was investigated in humans and dogs. In the upper (cranial) portion of the esophagus of man and dogs, an inferior anatomical sphincter was detected which histologically can be referred to the group of rhabdo-sphincters. The upper esophageal sphincter is a purely esophageal structure which in man is located at a distance of 25-30 cm from the maxillary incisors. In adult humans, it is 25-30 mm long and is situated obliquely to the long esophageal axis. The posterior semicircle of the sphincter is located higher than the anterior one. In the area of the upper esophageal sphincter the esophageal wall is of different thickness. Due to the muscle envelope and submucous membrane of the base, the right wall is 1.7-2.0 times thicker than the left, anterior or posterior wall. The data obtained from fiber esophagoscopy of patients and electromyography of the pharynx-esophagus junction of dogs have shown that the upper (cranial) esophageal sphincter control food passage from the pharynx to the esophagus and prevents food reflux to the laryngopharynx, protecting airways from aspiration.     

Efficacy of botulinum toxin A for treatment of upper esophageal sphincter dysfunction

OBJECTIVES: To investigate the efficacy of botulinum toxin A (BTA)-induced chemodenervation of the upper esophageal sphincter (UES) in patients with dysphagia and UES dysfunction. STUDY DESIGN: Prospective clinical trial in 10 selected patients with pure UES dysfunction. METHODS: In each patient 30 units of BTA were injected into the UES under brief general anesthesia. Videofluoroscopic swallowing study (VSS) was done and a clinical symptom score was determined before and after treatment. RESULTS: On VSS relative opening of the UES improved in all patients (mean +/- SD: 47 +/- 14% before versus 71 +/- 24% after treatment; P < .01). Hypopharyngeal retention or laryngeal penetration of barium was significantly reduced in four of seven patients. Clinical symptom scores improved in all patients. One patient was free of symptoms, mild dysphagia persisted in six patients, and moderate dysphagia persisted in three patients. CONCLUSIONS: Our results support the use of BTA in selected patients with pure UES dysfunction. Its efficacy is limited by the possibility of a persistent structural stenosis of the UES and the risk of BTA diffusion into the larynx or hypopharynx.     

Role of pharyngeal propulsion as an indicator for upper esophageal sphincter myotomy

Thirty-eight patients with swallowing disorders underwent cricopharyngeal myotomy. The causes of the disorders were muscular in 12 cases, neurologic in 12, cricopharyngeal achalasia in 7, and unknown in 7. Surgery succeeded in 21 patients, gave a partial improvement in 4, and failed in 13. The quality of residual pharyngeal propulsion on clinical, manometric, and radiologic assessment appeared to be a more important predictor of surgical outcome than upper esophageal sphincter relaxation and the major factor in establishing the indications for cricopharyngeal myotomy. Achalasias in the elderly and oculopharyngeal muscular dystrophies had the most favorable outcome.     

Optimal stimulus level conditions for measurements of distortion product otoacoustic emissions

Objective: Distortion product otoacoustic emission (DPOAE) is a tool for an objective examination of the cochlea function. While the clinical application of DPOEA test is in progress, the measurements vary depending on the stimulus conditions. We aimed to determine the most appropriate stimulus level in the clinical application of DPOAE test. Methods: Ninety-seven normal hearing ears and 80 hearing-impaired ears (total 177) were subjected to this study. Two levels of stimulations (L1 and L2) were applied as follows: L1=L2=70 dB; L1=L2=60 dB and L1=60/L2=50 dB, and DP level was measured at each stimulation, and compared with hearing level. Results: DP level was highest at L1=L2=70 dB. Normal hearing ears and hearing-impaired ears were well differentiated at L1=L2=60 dB. Conclusion: In clinical application of DPOAE test, DP levels should be measured at the stimulus level most appropriate for the purposes.     

Long-term results of laryngeal suspension and upper esophageal sphincter myotomy as treatment for life-threatening aspiration

OBJECTIVES: We evaluated the long-term results of laryngeal suspension and upper esophageal sphincter (UES) myotomy in patients with life-threatening aspiration. METHODS: In the period 1995 to 2004, 17 patients with severe aspiration caused by insufficient laryngeal elevation and absent or negligible pharyngeal constrictor muscle activity during deglutition resulting in aspiration pneumonia were surgically treated with a laryngeal suspension procedure and UES myotomy. Preoperative and postoperative videofluoroscopy was performed to assess swallowing and aspiration. RESULTS: In 9 of the 17 patients, long-term (more than 1 year) full oral intake without aspiration was achieved. Three other patients demonstrated improvement of deglutition with partial restoration of oral intake with adjusted food consistency, but remained partly dependent on gastrostomy feeding for adequate nutrition. Two patients no longer had cases of aspiration pneumonia, but were unable to achieve even modified oral intake. Three patients finally underwent total laryngectomy--2 of them after initial successful full oral intake without aspiration but with recurrent aspiration as a result of progression of neuromuscular disease. None of the patients succumbed to aspiration pneumonia. CONCLUSIONS: In most of our patients, life-threatening aspiration was successfully treated by UES myotomy and laryngeal suspension with restoration of oral intake.     

Human auditory middle latency responses: influence of stimulus type and intensity

Human auditory middle latency responses (MLR) to click and tone pip stimuli of different intensities were recorded by means of magnetoencephalography (MEG) and electroencephalography (EEG). Clicks elicited larger responses with significantly shorter latencies than the tone pips at the same intensity in dB sensation level (SL). Most MLR amplitudes increased and their latencies decreased with increasing stimulus intensity for both types of stimulation. Pa and Nb amplitudes saturated at intensities of 60 dB SL in the case of click stimulation. The shorter latencies of MLR evoked by the click were explained by its short rise time and the high frequency content of its spectrum. MEG source analysis yielded MLR sources which were clearly different from those of the slow cortical wave N1. They seem to be located in primary auditory areas along Heschl's gyrus.     

Injection of botulinum toxin A for the treatment of dysfunction of the upper esophageal sphincter

OBJECTIVE: The objective was to evaluate changes in swallow safety and dietary status after the transcutaneous injection of botulinum toxin A into the upper esophageal sphincter in a series of outpatients with dysphagia. STUDY DESIGN: This was an experimental, prospective, nonrandomized study. METHODS: Patients who were at risk for aspiration and who had an unsuccessful trial of swallowing therapy were admitted to the study. All patients showed significant pooling of fluids in the postcricoid region. All patients were treated in the office; none had previous esophageal dilatation. The upper border of the cricoid cartilage was identified using standard electromyogram procedures and 100 U of botulinum toxin (Botox A) were injected. Outcomes were assessed using the penetration-aspiration scale, patients' short-term and long-term subjective impressions of their ability to swallow, and change in dietary status. RESULTS: Thirteen patients underwent an instrumental evaluation of swallowing function at approximately 6 months after treatment to corroborate the self-reported changes in swallowing. Of the 13 patients, 12 showed an overall improvement in their ability to take an oral diet safely as evidenced by the penetration-aspiration scale. Of the 12 patients who were on a non-oral or nearly non-oral diet, 9 resumed a normal oral diet. The remaining 3 were on an oral diet supplemented by percutaneous endoscopic gastrostomy feeding. One patient remained on a non-oral diet. CONCLUSIONS: Injection of Botox A in the office with no additional treatments resulted in a long-term increase in swallow safety, a reduction of penetration and/or aspiration, and a reduced need for non-oral feeding. Injection of Botox A in the office should be considered when there is failure of the cricopharyngeus muscle to relax after the swallow, significant pooling in the cricopharyngeal region, and a risk for penetration and aspiration.     

Effects of hearing aid amplification and stimulus intensity on cortical auditory evoked potentials

Hearing aid amplification can be used as a model for studying the effects of auditory stimulation on the central auditory system (CAS). We examined the effects of stimulus presentation level on the physiological detection of sound in unaided and aided conditions. P1, N1, P2, and N2 cortical evoked potentials were recorded in sound field from 13 normal-hearing young adults in response to a 1000-Hz tone presented at seven stimulus intensity levels. As expected, peak amplitudes increased and peak latencies decreased with increasing intensity for unaided and aided conditions. However, there was no significant effect of amplification on latencies or amplitudes. Taken together, these results demonstrate that 20 dB of hearing aid gain affects neural responses differently than 20 dB of stimulus intensity change. Hearing aid signal processing is discussed as a possible contributor to these results. This study demonstrates (1) the importance of controlling for stimulus intensity when evoking responses in aided conditions, and (2) the need to better understand the interaction between the hearing aid and the CAS.     

纯音和言语刺激声强度对听觉事件相关电位的影响

目的:探讨分别以纯音和言语作刺激声时声强度对听觉事件相关电位(AERP)的影响.方法:采用不同强度的纯音和言语作为刺激声对正常年青人进行AERP测试,比较纯音和言语诱出典型P300的强度范围,分析不同强度对P300的影响是否同时存在于纯音和言语刺激声.结果:言语刺激声比纯音更容易在40～70 dBSL范围内连续记录到典型波形,差异有统计学意义(P＜0.01).言语或纯音刺激时,强度对P300潜伏期的影响差异均有统计学意义(P＜0.01),在40～70 dBSL范围内潜伏期随强度增加而减小,强度对P300幅值的影响差异均无统计学意义.结论:强度对AERP的影响在纯音和言语刺激时基本相同,但言语得到典型AERP波形的强度范围较纯音宽,其原因可能与言语刺激声包含的信息较纯音刺激声丰富,受试者对汉语言语刺激声较纯音更熟悉有关.     

Comparison of upper esophageal sphincter opening in healthy asymptomatic young and elderly volunteers.

Deglutitive upper esophageal sphincter opening (UES) in the elderly has been incompletely studied. Our aim was to determine in the elderly the temporal and dimensional characteristics of deglutitive UES opening; anterior and superior hyoid and laryngeal excursions as measures of distracting forces imparted on the UES; and hypopharyngeal intrabolus pressure (IBP). Fourteen healthy elderly and 14 healthy young volunteers were studied by concurrent videofluoroscopy and hypopharyngeal manometry during swallowing of 5- and 10-mL barium boluses. The anteroposterior UES diameter, as well as the anterior hyoid bone and laryngeal excursion, was significantly smaller in the elderly compared to the young (p < .05) for 5-mL barium boluses, but not for 10-mL boluses. The lateral diameter of UES opening was similar between groups for all boluses. The IBP for 5- and 10-mL swallows in the elderly was significantly higher than that in the young (p < .05). We conclude that anteroposterior deglutitive UES opening and hyoid bone and thyroid cartilage anterior excursion are reduced in the elderly. These changes are associated with increased IBP, suggesting a higher pharyngeal outflow resistance in the elderly compared to the young.