Preferred Compression Threshold and Release Time in Quiet and Noisy Conditions for Elderly Korean Hearing Aid Users

BACKGROUND AND OBJECTIVES: Listeners with sensorineural hearing loss want to compensate for their narrow dynamic range from appropriate compression functions of hearing aids. The present study aimed to determine which compression threshold and release time of nonlinear hearing aids might affect speech recognition and speech quality judgments. SUBJECTS AND METHODS: Ten elderly listeners with symmetrical moderate-to-severe sensorineural hearing loss participated in the study. To compare two compression threshold (31 dB SPL vs. 61 dB SPL) and two release time (50 ms vs. 500 ms) conditions, subjects’ speech recognition was measured using the Korean version of the Hearing in Noise Test in both quiet and noisy situations. All subjects were also asked to rate the degree of speech quality in terms of loudness, sharpness, clarity, and background noise immediately after completing the speech recognition test. RESULTS: Although no significant difference emerged in speech recognition thresholds between the two compression thresholds in the quiet situation, the compression threshold of 31 dB SPL showed a lower (or better) signal-to-noise ratio of speech recognition compared to that of 61 dB SPL. The release times of 50 and 500 ms did not statistically differ in both quiet and noisy situations. Subjective categories were found to be louder and clearer in the 50 ms release time for quiet and noisy, respectively. CONCLUSIONS: We expect that these patterns of current results will apply for better-fitting protocol of elderly Korean hearing aid users.

Preferred Compression Threshold and Release Time in Quiet and Noisy Conditions for Elderly Korean Hearing Aid Users

BACKGROUND AND OBJECTIVES: Listeners with sensorineural hearing loss want to compensate for their narrow dynamic range from appropriate compression functions of hearing aids. The present study aimed to determine which compression threshold and release time of nonlinear hearing aids might affect speech recognition and speech quality judgments. SUBJECTS AND METHODS: Ten elderly listeners with symmetrical moderate-to-severe sensorineural hearing loss participated in the study. To compare two compression threshold (31 dB SPL vs. 61 dB SPL) and two release time (50 ms vs. 500 ms) conditions, subjects’ speech recognition was measured using the Korean version of the Hearing in Noise Test in both quiet and noisy situations. All subjects were also asked to rate the degree of speech quality in terms of loudness, sharpness, clarity, and background noise immediately after completing the speech recognition test. RESULTS: Although no significant difference emerged in speech recognition thresholds between the two compression thresholds in the quiet situation, the compression threshold of 31 dB SPL showed a lower (or better) signal-to-noise ratio of speech recognition compared to that of 61 dB SPL. The release times of 50 and 500 ms did not statistically differ in both quiet and noisy situations. Subjective categories were found to be louder and clearer in the 50 ms release time for quiet and noisy, respectively. CONCLUSIONS: We expect that these patterns of current results will apply for better-fitting protocol of elderly Korean hearing aid users.

The Effect of Low-Level Laser Irradiation on Activities of Dorsal Horn Neurons in Rats with Experimental Muscle Pain

OBJECTIVE: This study was performed to investigate the effects of low-level laser irradiation on the dorsal horn cell activities in the rats with experimental muscle pain. METHOD: Experimental muscle pain was induced by repeated injections of acidic saline into the gastrocnemius muscle in thirty Sprague-Dawley rats. Activities of ipsilateral dorsal horn cells were recorded with a glass microelectrode at L2-L4 spinal cord level before and after low-level laser irradiation on the injected leg. Cells were categorized as wide dynamic range (WDR) and high threshold (HT) cells by the response to the cotton, vonFrey filament, and forceps stimulation at the receptive area. RESULTS: The spontaneous and mechanically evoked activities of WDR and HT cells were significantly increased in the muscle pain models. Low-level laser irradiation reduced mechanically evoked activities of WDR and HT cells. This effect was maximal at 20 minutes after irradiation and then returned to pre-treatment level in 40~50 minutes. CONCLUSION: The low-level laser irradiation was effective for the management of muscle pain by reducing activities of dorsal horn cells. Low-level laser might be clinically used for the treatment of local and referred pain of muscle origin.

PERIPHERALLY SUPPRESSIVE EFFECTS OF KETAMINE ON SUBCUTANEOUS BEE VENOM-INDUCED PROLONGED,PERSISTENT FIRING OF SPINAL WIDE-DYNAMICRANGE NEURONS IN THE CAT / 神经解剖学杂志

By using extracellular single unit recording technique, locally suppressive effects of a single dose of ketamine on sub-cutaneous (s. c. ) bee venom-induced increase in firing of wide dynamic-range (WDR) neurons in spinal dorsal horn were investi-gated on urcthane-chloralose anesthetized cats. Injection of bee venom s.c. into the cutaneous receptive field (RF) resulted in asingle phase of prolonged, persistently increased firing of WDR neurons over background activity for more than 1 h. Local pre-treatment with ketamine (100 mM, 0. 1 m l) into the center of RF where bee venom was injected produced a dramatic suppressionof the increased neuronal firing by 60% (3.10± 0.42 spikes/s, n= 5) when compared with saline pre-treated group (7.61 ± 0.17spikes/ s. n = 5 ). Moreover, local post-treatment with the same dose of ketamine also produced a profound suppression of the in-creased neuronal activity by 81% (1.51±0.06 spikes/s, n=5) when compared with the saline post-treated group (7.76±0.15spikes s, n=5). However, s.c. administration with the same dose of ketamine into a symmetrical region on the bee venom un-treated contralateral hindpaw produced no affection on the increased firing of the WDR neurons, suggesting that the suppressiveaction of local ketamine was not the result of systemic effects. The present result suggests that ketamine may exert its localantinociceptive effects mainly through the peripheral NMDA receptors in addition to its partially potential blocking effects onsodium and voltage-sensitive calcium channels.

The role of somatostatin in nociceptive processing of the spinal cord in anesthetized cats

Somatostatin (SOM) is one of the major neuropeptides in dorsal root ganglion cells, but its role in spinal nociceptive process has not been well known. In present study we aimed to investigate the effect of SOM on the response of dorsal horn neurons to the various types of peripheral nociceptive stimuli in anesthetized cats. Using carbon-filament microelectrode, the single cell activities of wide dynamic range neurons were recorded from the lumbosacral enlargement after noxious mechanical (squeeze), thermal (radiant heat lamp) and cold (dry ice) stimulation to the receptive field. Sciatic nerve was stimulated electrically to evoke A delta- and C-nociceptive responses SOM analogue, octreotide (10 mug/kg), was applied intravenously and the results were compared with those of morphine (2 mg/kg, MOR) Systemic SOM decreased the cellular responses to the noxious heat and the mechanical stimulation, but increased those to the cold stimulation. In the responses to the electric stimuli of sciatic nerve, A delta-nociceptive response was increased by SOM, while C-nociceptive response was decreased. On the other hand, MOR inhibited the dorsal horn cell responses to all the noxious stimuli. From the above results, it is concluded that SOM suppresses the transmission of nociceptive heat and mechanical stimuli, especially via C-fiber, while it facilitates those of nociceptive cold stimuli via A delta-fiber.

Effects of electrical stimulation of brainstem nuclei on dorsal horn neuron responses to mechanical stimuli in a rat model of neuropathic pain

The aim of the present study is to examine the brainstem sites where the electrical stimulation produces a suppression of dorsal horn neuron responses of neuropathic rats. An experimental neuropathy was induced by a unilateral ligation of L5-L6 spinal nerves of rats. Ten to 15 days after surgery, the spinal cord was exposed and single-unit recording was made on wide dynamic range (WDR) neurons in the dorsal horn. Neuronal responses to mechanical stimuli applied to somatic receptive fields were examined to see if they were modulated by electrical stimulation of various brainstem sites. Electrical stimulation of periaqueductal gray (PAG), n. raphe magnus (RMg) or n. reticularis gigantocellularis (Gi) significantly suppressed responses of WDR neurons to both noxious and non-noxious stimuli. Electrical stimulation of other brainstem areas, such as locus coeruleus. (LC) and n. reticularis paragigantocellularis lateralis (LPGi), produced little or no suppression. Microinjection of morphine into PAG, RMg, or Gi also produced a suppression as similar pattern to the case of electrical stimulation, whereas morphine injection into LC or LPGi exerted no effects. The results suggest that PAG, NRM and Gi are the principle brainstem nuclei involved in the descending inhibitory systems responsible for the control of neuropathic pain. These systems are likely activated by endogenous opioids and exert their inhibitory effect by acting on WDR neurons in the spinal cord.