High Frequency Testing Research Articles

1112 超音波疲労試験片の発熱量と温度分布推定(OS11-3 材料の疲労挙動と損傷評価-計測-)

An ultrasonic fatigue test is an effective measure to obtain very high cycle fatigue lives, but it contains some problems due to its high test frequency. One of problems is self-heating of test pieces which hinders accurate fatigue data collection. In this study, an attempt was made to measure the amount of self-heating in the ultrasonic fatigue test specimen and to estimate the temperature distributions by FE analysis. Though the proposed method required coefficient of heat transfer which can be obtained by the combination between FE analysis and simple experiments, it showed good estimation of the specimen surface temperature in steady state. The method also made it possible to estimate the upper limit condition to perform the ultrasonic fatigue test without self-heating.

Charged defects and their effects on electrical behavior in Bi1−xLaxFeO3 thin films

Ferroelectric and dielectric characteristics of Bi1−xLaxFeO3 thin films deposited on SrRuO3 as bottom electrode have been investigated. In accordance with the Rayleigh model, it is in principle established that La doping in BiFeO3 effectively reduces the concentration of charged defects and dielectric loss, although there is a slight deviation at the high level of La doping (x=0.2). This departure is attributed to the reversible bending movement of pinned 180° domain walls, which contributes to the dielectric permittivity nonlinearly without inducing loss. In addition, the competition between domain wall pinning and depinning is determined to be the dominant fatigue mechanism, as shown by the enhanced fatigue endurance at the high La-doping level, test frequency, and electrical field.

The importance of culling in Johne's disease control

Johne's disease is caused by Mycobacterium avium subsp. paratuberculosis (MAP) infection and results in economic losses in the dairy industry. To control MAP transmission in herds, test-based culling has been recommended and immediate culling of high shedding animals is typically implemented. In this study, we quantified the effects of MAP control in US dairy herds, using the basic reproduction ratio R 0 . The effectiveness of culling strategies was evaluated for good and poor herd management (low- and high-transmission rates, respectively) by a phase diagram approach. To establish a quantitative relationship between culling rates and test properties, we defined the average detection times for low and high shedding animals. The effects of various culling strategies and test characteristics, such as test sensitivity, test turnaround time, and testing interval, were analyzed. To understand the overall effect of model parameters on R 0 , we performed global uncertainty and sensitivity analyses. We also evaluated the effectiveness of culling only high shedding animals by comparing three test methods (fecal culture, fecal polymerase chain reaction, PCR, and enzyme-linked immunosorbent assay, ELISA). Our study shows that, in the case of good herd management, culling of only high shedding animals may be effective in controlling MAP transmission. However, in the case of poor management, in addition to immediate culling of high shedding animals, culling of low shedding animals (based on the fecal culture test) will be necessary. Culling of low shedding animals may be delayed 6–12 months, however, if a shorter testing interval is applied. This study suggests that if farmers prefer culling only high shedding animals, faster MAP detection tests (such as the fecal PCR and ELISA) of higher sensitivity should be applied with high testing frequency, particularly on farms with poor management. Culling of infectious animals with a longer testing interval is generally not effective to control MAP.

Impedance Behavior of TiO2 Nanotubes Formed by Anodization in NaF Electrolytes

The impedance behavior of nanotubular self-organized porous (PTO) films with thickness of , pore diameter, and average spacing formed on titanium by anodization in solution was investigated and compared to the behavior of compact layers (CTO). At potentials close to the flatband potential , PTO had an apparent interfacial capacitance at that was greater than the capacitance of CTO. This effect, however, was not only related to the larger effective area of PTO. Differentiation between both surface conditions vanished both at potentials significantly higher than and with increasing test frequency to . These findings together with observations of appreciable frequency dispersion suggest that the pore walls are rich in deep-lying localized states, which become evident only at lower test frequencies and at potentials negative enough that depletion zones do not merge at pore walls. PTO did not show a transmission line effect at frequencies as high as . Model calculations based on pore dimensions and electrolyte conductivity predicted that those effects could only take place at much higher test frequencies, but the slow response of deeper states might impair observation anyway.

Changes in hearing thresholds over 10 years in older adults.

Changes in hearing thresholds over a 10-year period in a large population of older adults (2130) ranging in age from 48 to 92 years were documented. Pure-tone thresholds at frequencies from 0.5 to 8 kHz were evaluated at a baseline examination and 2.5, 5, and 10 years later. For younger age groups (50-69 years of age), threshold changes were generally greatest for higher frequencies; in older age groups (70-89 years of age), threshold changes were generally greatest for lower frequencies due to a ceiling effect at higher frequencies. At frequencies of 0.5, 1, 2, and 8 kHz, the pattern of 10-year changes in thresholds across audiometric frequencies was generally similar for men and women. Threshold changes at 4 and 6 kHz were relatively constant for all ages in men across the 10-year examination period; threshold changes at the same frequencies in women increased for the 48-59 and 60-69 years age groups and then tended to level off. Other than age and gender, the best baseline examination predictors of 10-year thresholds at a specific audiometric frequency were the baseline threshold at that frequency followed by the baseline threshold for the next higher test frequency.

Dynamic mechanical properties and in vitro bioactivity of PHBHV/HA nanocomposite

Biopolymer composite materials for potential medical applications are of current research interest. In this study, a nanocomposite based on bioresorbable polymer-poly(3-hydroxybutyrate- co-3-hydroxyvalerate) (PHBHV) was prepared by the incorporation of nano-sized hydroxyapatite (nano-HA) using a solution casting method. Homogeneous distribution of nanoparticles in the polymer matrix was validated by the observation of field emission scanning electron microscope (FE-SEM). The dynamic mechanical properties, thermal properties, and bioactivity of the nanocomposite were examined by using varieties of techniques including dynamic mechanical analyser (DMA), differential scanning calorimeter (DSC), thermogravimetric analyzer (TGA), scanning electron microscope coupled with energy dispersive X-ray analysis detector (SEM + EDXA), Fourier transforms infra-red spectrometer (FT-IR) and thin-film X-ray diffractometer (TF-XRD). The results indicated that the storage modulus ( E′) of PHBHV was considerably improved with the introduction of nano-HA. For an instance of examination at 1 Hz, the PHBHV/HA (100/30) nanocomposite showed an increment of 41.2% at −50 °C and 99.1% at 75 °C in E′ as compared with the polymer matrix. It was also found that higher testing frequencies used induce more elastic-like behavior. With the increase in the amount of nano-HA, both the glass transition temperature ( T g) and the activation energy (Δ E) for the glass transition increased, while the tangent of loss angle (tan δ) decreased due to the hindrance of the nanofillers to the mobility of the polymer segments. The thermal experiments revealed that, when incorporating HA nanoparticles, the decomposition of the polymer matrix was accelerated at the initial stage but postponed thereafter. The addition of nano-HA also resulted in a decrement in the melting enthalpy of PHBHV. The in vitro investigation indicated that the nanocomposite has an improved bioactivity over the conventional one.

Time‐resolved luminescence anisotropy studies of the relaxation behaviour of polymers. 2. On the intramolecular mobility of poly(butyl methacrylate) in dilute solution

AbstractTime‐resolved anisotropy measurements (TRAMS) have been used to study the relaxation behaviour of poly(butyl methacrylate) (PBMA) in dilute solution both in toluene and dichloromethane. Various fluorescent labels (residues from copolymerisation of BMA with ca 0.3 mol% of acenaphthylene (ACE), 1‐vinylnaphthalene (VN), 1‐naphthylmethyl methacrylate, 9‐phenyanthrylmethyl methacrylate, and 9‐anthrylmethyl methacrylate (AMMA)) were used. It was found that, as expected, ACE and VN provided information on the segmental motion of PBMA. The fluorescence anisotropies of the various ester labels reflected the influence of motion, independent of that of the PBMA backbone, upon the observed relaxation behaviour. The motion of AMMA, in particular, could be resolved, with confidence, into components corresponding to segmental relaxation of both the polymer and ester group motion. Clearly, in this system, motion of the labelled ester is not fully cooperative with that of the polymer backbone, even at the high test frequencies to which these fluorescence measurements correspond. Copyright © 2005 Society of Chemical Industry

Evaluating cochlear function and the effects of noise exposure in the B6.CAST + Ahl mouse with distortion product otoacoustic emissions

Cochlear function and susceptibility to noise over-exposure were examined in the congenic mouse strain B6.CAST + Ahl (B6.CAST) and compared to these same features in the CAST/Ei (CAST) and C57BL/6J (C57) parental strains. For both types of comparisons, the primary measure was the distortion-product otoacoustic emissions (DPOAE) at 2 f 1− f 2. Our assumption was that the B6.CAST mouse was corrected for the early onset age-related hearing loss (AHL) exhibited by one of its parental strains (C57) by the age-resistant properties of its other parental strain (CAST), and thus would exhibit neither AHL nor susceptibility to noise overstimulation effects. With respect to cochlear function, for 2.5-month mice, there was a tendency for DPOAEs to be slightly lower for mid-frequency primary tones for both C57 and B6.CAST mice, while the former mice showed clear AHL effects at the highest test frequency. However, by 5 months of age, the B6.CAST mice, like the CAST mice, displayed robust DPOAE levels that were significantly larger than DPOAE levels for the C57 mice, which were essentially absent for frequencies above about 30 kHz. To investigate the role of the Ahl gene in the susceptibility of the cochlea to the effects of noise over-exposure, two distinct paradigms consisting of temporary (TTS: 1-min, 105-dB SPL, 10-kHz pure tone) and permanent (PTS: 1-h, 105-dB SPL, 10-kHz octave band noise) threshold-shift protocols were used. The brief TTS exposure produced reversible reductions in DPOAEs that for both the B6.CAST and CAST mice recovered to within a few dB of their baseline levels by 3 min post-exposure. In contrast, the C57 mice recovered somewhat slower and, by 5 min post-exposure, emission levels were still 5 dB or more below their corresponding pre-exposure values. At 3 months of age, the TTS mice along with another group of naı̈ve subjects representing the same three mouse strains were exposed to the PTS paradigm. By 4 days post-exposure, for B6.CAST and CAST mice, DPOAE levels had recovered to their pre-exposure control levels. However, DPOAEs for the C57 mice at most of the measurable frequencies were at least 10–30 dB lower than their counterpart baseline levels. Together these data suggest that the Ahl allele in the C57 strain contributes to both the early onset AHL exhibited by these mice as well as their susceptibility to both TTS and PTS over-exposures.

Protection against cisplatin ototoxicity by adenosine agonists

Cisplatin is a commonly used antineoplastic agent that causes ototoxicity through the formation of reactive oxygen species (ROS). Previous studies have shown that cisplatin causes an upregulation of A 1 adenosine receptor (A 1AR) in the cochlea, and that application of the adenosine agonist, R-phenylisopropyladenosine ( R-PIA), to the round window (RW) results in significant increases in cochlear glutathione peroxidase and superoxide dismutase. These data suggest that adenosine receptors (ARs) are an important part of the cytoprotective system of the cochlea in response to oxidative stress. The purpose of the current study was to investigate the effect of various adenosine agonists on cisplatin ototoxicity using RW application. Auditory brainstem response (ABR) thresholds were recorded in anesthetized chinchillas at 1, 2, 4, 8 and 16 kHz. The auditory bullae were surgically opened, and 1 mM R-PIA, 10 μM 8-cyclopentyl-1,3-dipropylxanthine (DPCPX)/ R-PIA (1 mM) cocktail, 100 μM 2-chloro- N-cyclopentyladenosine (CCPA), 2-[4-(2- p-carboxy-ethyl)phenylamino]-5′- N-ethylcarboxamidoadenosine (CGS) or vehicle were applied to the RW. After 90 min, the remaining solution was removed and cisplatin was applied to the RW. The bullae were closed and the animals recovered for 72 h, after which, follow-up ABRs were performed. Cochleae were harvested for scanning electron microscopy (SEM) and for lipid peroxides. Pre-administration of the A 1AR agonists R-PIA or CCPA significantly reduced cisplatin-induced threshold changes at all but the highest test frequency. In addition, A 1AR agonists protected against cisplatin-induced hair cell damage and significantly reduced cisplatin-induced lipid peroxidation. Co-administration of the A 1AR antagonist, DPCPX, completely reversed the protective effects of R-PIA. In contrast, pretreatment with CGS-21680, an A 2A adenosine receptor (A 2AAR) agonist, significantly increased cisplatin-induced threshold changes. Our findings are consistent with the notion that the A 1AR contributes significantly to cytoprotection in the cochlea, and thereby protects against hearing loss.

Distortion-Product Otoacoustic Emissions in Ears with Normal Hearing Sensitivity: Test-Retest Variability

4 women and 4 men with normal hearing sensitivity were tested for variability in distortion-product otoacoustic emissions, with two measurement sessions per day for 4 days spread over a 2-wk. period. Most test-retest variations were small, on the order of 2 dB. Extreme variations of 6 dB or greater occurred most often at the highest test frequency and should not be considered clinically positive unless such differences are found at lower frequencies also.

Role of mannitol in reducing postischemic changes in distortion-product otoacoustic emissions (DPOAEs): a rabbit model.

The aim of this study was to observe the effects of mannitol, administered topically at the round window (RW), on cochlear blood flow (CBF) and distortion-product otoacoustic emission (DPOAE) after repeated episodes of cochlear ischemia. Ten young rabbits were used for this study. Reversible ischemic episodes within the cochlea were induced by directly compressing the internal auditory artery (IAA). CBF was measured using a laser-Doppler (LD) probe positioned at the RW niche. DPOAEs were measured at 4, 8, and 12 kHz geometric mean frequency (GMF) using 60 dB sound pressure level (SPL) primary tone stimuli. In five test ears, mannitol was administered topically at the RW for 30 minutes before the IAA compressions. In five control ears, the IAA compressions were undertaken without application of RW medication. Each ear underwent three 5 minute IAA compressions with a 60 minute rest period between compressions. In the control animals, it was observed that a progressive reduction in DPOAE level followed each successive IAA compression at all three test frequencies. The reduction in DPOAE amplitudes was consistently greater at the higher test frequencies. In the test rabbits, the RW administration of mannitol resulted in significantly less reduction in DPOAE level measures after repeated IAA compressions. For example, 30 minutes after reperfusion at 12 kHz GMF, DPOAE levels in the control ears were reduced by 1.5, 6.0, and 16 dB, compared with 1.5, 4.0, and 6.0 dB in the mannitol test ears. Mannitol appears to exert a protective effect on cochlear function after periods of ischemia. The RW appears to be an efficacious route for topical administration of mannitol into the inner ear.

The ototoxic interaction of styrene and noise

The interaction between noise and inhaled styrene on the structure and function of the auditory organ of the male Wistar rat was studied. The animals were exposed either to 600 ppm, 300 ppm or 100 ppm styrene (12 h/day, 5 days/week, for 4 weeks) alone or in combination with a simultaneous 100–105 dB industrial noise stimulant. Auditory sensitivity was tested by auditory brainstem audiometry at 1.0, 2.0, 4.0 and 8.0 kHz frequencies. Inner ear changes were studied by light microscopy. Exposure to 600 ppm styrene alone caused a 3 dB hearing loss only at the highest test frequency (8 kHz). Quantitative morphological analysis of cochlear hair cells (cytocochleograms) showed a severe outer hair cell (OHC) loss particularly in the third OHC row of the upper basal and lower middle coil. Exposure to noise alone caused only a mild hearing loss (2–9 dB), and only an occasional loss of OHCs (<1% missing). Exposure to the combination of noise and 600 ppm styrene caused a moderate flat hearing loss of 23–27 dB. The cytocochleograms showed a more severe damage of the OHCs than after exposure to 600 ppm styrene alone. The inner hair cells were found to be destroyed in some animals in the upper basal turn only after the combination exposure. Only in combination with noise exposure, the lower styrene concentrations (100 and 300 ppm) induced a hearing loss which was equivalent to that seen after exposure to noise alone. We conclude that: (1) There is an ototoxic interaction between styrene and noise. (2) Synergism is manifested only if styrene is applied in concentrations above the critical level (between 300 and 600 ppm in this study).

DISTORTION-PRODUCT OTOACOUSTIC EMISSIONS IN EARS WITH NORMAL HEARING SENSITIVITY: TEST-RETEST VARIABILITY

4 women and 4 men with normal hearing sensitivity were tested for variability in distortion-product otoacoustic emissions, with two measurement sessions per day for 4 days spread over a 2-wk. period. Most test-retest variations were small, on the order of 2 dB. Extreme variations of 6 dB or greater occurred most often at the highest test frequency and should not be considered clinically positive unless such differences are found at lower frequencies also.

Local improvement in auditory frequency discrimination is associated with hearing-loss slope in subjects with cochlear damage

Earlier data in the literature have shown local improvements in frequency discrimination performance near the cut‐off frequency of steeply sloping, high‐frequency hearing loss in subjects with cochlear damage. The general objective of the present study was to characterize further the relationships between this effect and various audiometric variables: namely, the slope, extent and shape of the hearing loss. In particular, we were interested in determining whether the effect was present in subjects with more moderately sloping hearing loss and/or other patterns of loss. Frequency difference limens (DLFs) were measured in 20 subjects (eight female, 12 male, median age 55.5 years) with high‐frequency hearing loss. At least 12 frequencies were tested at intervals of 1/8 octave over a range of 1.5 octaves around the cut‐off frequency for hearing loss (Fc). The Fc corresponded to the audiogram edge frequency and was defined as the highest test frequency, at the beginning of the slope, with a hearing threshold of no more than 5 dB HL above that of the best hearing frequency. The level of the test tones was randomized over a range of 6 dB around a nominal level, following an equal‐loudness contour curve measured at 1/2‐octave intervals. Results showed that DLFs were significantly smaller in a frequency band 1/4 octave wide centred on Fc than in the other bands. Furthermore, the average DLF measured in this band proved to be negatively correlated with the slope of hearing loss. No such significant relationship was found with the other audiometric indices considered, namely, the extent and maximum amount of hearing loss and the log‐transformed cut‐off frequency. The 20 subjects were divided into three groups according to the slope of their hearing loss relative to Fc (steep, >25 dB/1/2 octave; medium, between 12 and 25 dB/1/2 octave; and shallow, <12 dB/1/2 octave). A local improvement in DLF around Fc was observed in the steep‐ and medium‐slope groups and was confirmed statistically in the steep‐slope group. Similar measurements in subjects with low‐frequency or notched hearing loss allowed us to establish the presence of similar local improvements in DLFs around audiogram edges. These results, which suggest the slope of the hearing loss to be the most important factor for the occurrence of local DLF improvements, are consistent with both an interpretation in terms of peripheral mechanisms and one in terms of central mechanisms, i.e. injury‐induced neural reorganization.

Functional and morphological effects of styrene on the auditory system of the rat.

The effect of inhaled styrene on the structure and function of the auditory organ of the male Wistar rat was studied. The animals were exposed either to 600, 300 or 100 ppm styrene (12 h/day, 5 days/week, for 4 weeks). Auditory sensitivity was tested prior to and after the exposure by auditory brain stem audiometry (ABR) at frequencies of 1.0, 2.0, 4.0 and 8.0 kHz. Inner ear morphological changes were studied by light- and electron-microscopy. Exposure to 600 ppm styrene caused a 3 dB hearing loss only at the highest test frequency (8 kHz). Quantitative morphological analysis of cochlear hair cells (cytocochleograms) showed that 600 ppm styrene caused a severe outer hair cell (OHC) loss particularly in the third OHC row of the upper basal and lower middle coil. The inner hair cells were usually intact. Exposure to lower styrene concentrations (100 and 300 ppm) caused no unequivocal functional deficit or hair cell damage. We conclude that there appears to be a concentration threshold for styrene ototoxicity in rats (between 300 and 600 ppm).

Instrumentalanalyse, Automation und Robotics in der Klinischen Chemie

Clinical chemistry is probably the part of analytical chemistry which is under the greatest pressure with respect to productivity. This results in methods completely different from those used in classical analytical chemistry. Separation methods and the determination of the concentrations of the separated components are usually not possible because of the inherent slowness of the procedures. This is true except in situations where closely related substances that occur as mixtures in biological fluids are to be measured (amino acids, proteins, sugars, fatty acids, drugs and their metabolites). For these special conditions GC-MS, LC-MS and other instrumental methods can be used. For the bulk of tests, however, chemical (photometric), enzymatic, immunological and genetic methods are applied. The components to be measured are specifically determined within the complex biological matrix without prior separation. The often complicated reactions lead to products that can be assessed by photometry, turbidometry, nephelometry or fluorometry. Samples (serum, plasma, urine) are processed in automated devices with high test frequency. Characteristic data are: sample volume 5 to 10 ?l, time of analysis 8 to 10 min, test frequency 200 to 300 tests per hour. For the determination of simple ions ion-selective electrodes are used. Increasingly, robots are engaged for sample preparation, reading of sample identification, centrifugation, decapping of test tubes, aliquoting and identification of aliquot tubes. Instrumental analysis, automation and robotics would be useless without laboratory information systems. Such systems allow the doctor to order the tests from his office terminal. According to the request, barcodes are printed to identify the sample tubes. The samples with barcode but without any accompanying form are taken to the laboratory and the reading of the barcode triggers the download of the request into the laboratory system.

Real-time measurements on a four stage RSFQ-counter with Nb–Al2O3–Nb Josephson junctions

RSFQ-toggle-flipflops with a SFQ-trigger circuit a Josephson transmission line at the input and a SFQ/dc-circuit at the output of each stage are implemented in the Nb–Al 2 O 3 –Nb Josephson junction technology on a single chip having coplanar wave guides at input and output. The counter is tested successfully at 4.2 K via coplanar/coaxial transitions using a bit pattern generator and a digital oscilloscope at room temperature up to f I ≈2 GHz pulse repetition frequency at the input. The highest test frequency f I is limited by the available pattern generator.

Alteration in rate modulation of reflexes to lumbar motoneurons after midthoracic spinal cord injury in the rat. I. Contusion injury.

This study investigated the regulation of reflex excitability in normal and midthoracic contusion-injured animals. Recent observations revealed that rate depression, a rate-modulatory process that decreases reflex excitability, was significantly decreased following experimental midthoracic contusion injury. The present experiments were performed to extend those studies and to determine if posttetanic potentiation (PTP), a rate-modulatory process that increases reflex excitability, also was altered in lumbar monosynaptic reflexes (MSRs) following midthoracic contusion injury. In normal animals, a mean PTP of 160% of the pretetanus control was observed at 30 sec following tetanus of the tibial MSR. The decay of the PTP in normal animals followed a rapid initial, then a more gradual pattern, before returning to pretetanus values by 5 min posttetanus. Following midthoracic contusion injury, the maximal (unpotentiated) MSRs were significantly increased in amplitude, whereas the percent potentiation of the PTP of the tibial MSRs was significantly decreased. PTP decay in postcontusion animals was significantly more gradual than observed in normal animals and followed a single decay process. Further analysis of rate depression of tibial MSRs in normal animals revealed that the attenuation pattern produced by stimulation within the lower range of test frequencies was different from that produced by stimulation at the higher test frequencies. Following contusion, rate depression of tibial MSRs was significantly reduced at all test frequencies. These physiological changes in the stretch reflex neural pathway are discussed relative to the development of spasticity.

Eddy current sensor concepts for the Bridgman growth of semiconductors

Electromagnetic finite element methods have been used to identify eddy current sensor designs for monitoring CdTe vertical Bridgman crystal growth. A model system consisting of pairs of silicon cylinders with electrical conductivities similar to those of solid and liquid CdTe has been used to evaluate the multifrequency response of several sensors designed for locating and characterizing the curvature of liquid-solid interfaces during vertical Bridgman growth. At intermediate frequencies (100–800 kHz), the sensor's imaginary impedance monotonically increases as interfacial curvature changes from concave to convex or the interface location moves upwards through the sensor. The experimental data are in excellent agreement with theoretical predictions. At higher test frequencies (∼ 5 MHz), the test circuit's parasitics contribute to the sensor's response. Even so, the predicted trends with interface location/curvature were found to be still preserved, and the experiments confirm that the sensor's high frequency response depends more on interface location and has only a small sensitivity to curvature. Multifrequency data obtained from these types of sensors have the potential to separately discriminate the location and the shape of liquid-solid interfaces during the vertical Bridgman growth of CdTe and other semiconductor materials of higher electrical conductivity.

Cochlear Protection from Carbon Monoxide Exposure by Free Radical Blockers in the Guinea Pig

Acute carbon monoxide exposure produces a significant impairment in high-frequency auditory sensitivity that can be prevented using theN-methyl-d-aspartate receptor blocker MK-801. This finding suggests an excitotoxic component to carbon monoxide ototoxicity and establishes the potential for free radical formation. Free radical scavengers and inhibitors are protective in many organs, including the brain and cochlea, during hypoxic events such as ischemia/reperfusion and, in the cochlea, during noise exposure. This study evaluated the protection afforded by two such agents, phenyl-n-tert-butyl-nitrone (PBN), which acts as a general free radical scavenger, and allopurinol, which acts as a free radical inhibitor specific to the xanthine oxidase metabolic pathway. Guinea pigs were pretreated with PBN (100 mg/kg ip), allopurinol (100 mg/kg ip), or saline 1 hr prior to exposure to carbon monoxide (35 ml/kg ip) or to an equal volume of air. They were monitored at 15, 30, and 60 min after carbon monoxide exposure for alterations in compound action potential threshold and cochlear microphonic amplitude. The groups receiving carbon monoxide alone displayed characteristic compound action potential threshold elevations particularly at the higher test frequencies (16–40 kHz), consistent with earlier studies; no loss of cochlear microphonic amplitude was exhibited. Both free radical inhibitors, PBN and allopurinol, blocked loss of auditory threshold sensitivity produced by carbon monoxide. These data suggest that free radical generation may play a significant role in the impairment of highfrequency auditory sensitivity resulting from carbon monoxide.