Effects of combinations of sodium salicylate and noise on the auditory threshold.

Thirty-nine monaural chinchillas were used to study the interaction between sodium salicylate and various TTS-producing noise paradigms. Five animals were included in each of the following three groups: 1) sodium salicylate (400 mg/kg) plus 2-4 kHz, 95 dB SPL noise band for one hour; 2) sodium salicylate (400 mg/kg) plus 4 kHz CF octave band noise at 80 dB SPL for 96 hours; and 3) sodium salicylate (400 mg/kg) plus 50 impulses having 50 musec A-duration and 158 dB peak SPL, presented at one per minute. The remaining 24 animals served as various controls in groups exposed to sodium salicylate or the noise paradigm alone. Thresholds were estimated before, during, and after exposure using the AER technique and cochleagrams were mapped for each cochlea 30 days after exposure. When sodium salicylate was combined with the various noise conditions, the maximum TTS values obtained from the combination studies were comparable to those obtained from the single agent producing the greatest TTS at a particular frequency. No consistent alteration in either magnitude or time course of posttreatment threshold shift was found following the combination treatments as compared to the individual agents alone. Hazard to the auditory system resulting from a combination of sodium salicylate and noise was concluded to be no greater than the hazard presented by either agent alone. This result is also substantiated in the histological results.

Sci-Thurs PM: Delivery-07: Evaluation of prospects to use daily megavoltage CT studies for adaptive radiotherapy.

PURPOSE: To evaluate gross tumor volume (GTV) changes for non-small cell lung cancer (NSCLC) patients using daily megavoltage CT (MVCT) studies acquired before each treatment fraction on helical tomotherapy, and to relate the potential benefit of adaptive image-guided radiotherapy to changes in GTV. METHODS: 17 patients were prescribed 30 fractions of radiotherapy on helical tomotherapy for NSCLC at London Regional Cancer Program from December 2005 to March 2007. The GTV was contoured on the daily MVCT studies of each patient. Adapted plans were created using merged MVCT-kVCT image sets to investigate the advantages of replanning for patients with differing GTV regression characteristics. RESULTS: The average GTV change observed over 30 fractions was -38%, ranging from -12 to -87%. No significant correlation was observed between GTV change and patient's physical or tumor features. The pattern of GTV changes of the 17 patients could be broadly divided into 3 groups with distinctive potential for benefit from adaptive planning. CONCLUSIONS: GTV changes are difficult to predict quantitatively based on patient or tumor characteristics. If changes do occur, there are points in time during the treatment course when it may be appropriate to adapt the plan to improve sparing of normal tissues. If the GTV decreases by greater than 30% at any point in the first twenty fractions of treatment, adaptive planning is appropriate to further improve the therapeutic ratio.

Initial experience in treating lung cancer with helical tomotherapy.

Helical tomotherapy is a new form of image-guided radiation therapy that combines features of a linear accelerator and a helical computed tomography (CT) scanner. Megavoltage CT (MVCT) data allow the verification and correction of patient setup on the couch by comparison and image registration with the kilovoltage CT multi-slice images used for treatment planning. An 84-year-old male patient with Stage III bulky non-small cell lung cancer was treated on a Hi-ART II tomotherapy unit. Daily MVCT imaging was useful for setup corrections and signaled the need to adapt the delivery plan when the patient's anatomy changed significantly.

Asymptotic noise-induced temporary threshold shift in chinchilla measured by the auditory evoked response.

Monaural chinchillas were exposed to octave band (4 kHz center frequency) noise at 80 dB SPL for 96 h. Auditory threshold at frequencies of 1, 2, 4, and 8 kHz was estimated by the auditory evoked response (AER) technique prior to noise exposure, and on a fixed schedule, both during exposure and following removal from the noise. Results were analyzed in terms of both threshold and threshold shift. Results indicate that the AER is adequate measure of asymptotic noise-induced temporary threshold shift. Advantages of the use of AER as opposed to behavioral means of threshold determination are discussed. Threshold during this long-term noise exposure was found to be determined by the spectral and intensity components of the noise independent of pre-exposure threshold. Implications for future research in long-term noise exposure are discussed.

The effect of calibration tolerance values on obtained audiometric threshold: a hearing conservation perspective.

Auditory threshold was assessed at six commonly used audiometric test frequencies and for frequencies just within calibration tolerances for frequencies above and below these. Results indicate that differences of up to 23 dB in obtained auditory threshold values result from variation in frequency within tolerances. These findings are discussed in terms of their importance in industrial hearing conservation.

Screening measurements and procedures. Exemplified by an identification audiometry program.

To summarize, an effective procedure in audiometric screening may be using skilled testers to screen 1, 2, and 4 kHz at 20 dBHL (with oto immittance measures) on all students up to and including grade 3, 9th and 12th year high school students, and high-risk groups including those repeating a grade, having a history of recurrent middle ear disease, having speech and/or language problems, known to participate in high noise activities, for example, guns, dirt bikes, or model planes, and those failing previous screenings. Testing is done in a quiet, nondistracting environment, with each person tested individually, although instructions may be given to small groups. Any person not responding to one or more of the stimuli is rescreened. All failing the rescreening at any frequency in either ear are referred to an audiologist. Progress is monitored to ensure that the student is seen by an audiologist and that any audiological recommendations are followed. Screening procedures such as oto immittance measures and audiometric screening are effective identification procedures used in combination by skilled persons. When follow-up procedures are adequate, the program can work effectively in ensuring help for those with auditory problems. In addition, such programs can prevent many of these problems. The general principles of screening discussed earlier are applicable to identification of a wide variety of conditions including disordered speech, language, and hearing. Application of these principles will result in realization of identification objectives which are both pragmatic and quantifiable.

Acoustic reflex threshold and loudness discomfort level: relationships in children with profound hearing losses.

Acoustic reflex thresholds (ART) and loudness discomfort levels (LDL) were obtained from 51 ears of 34 deaf children using broad band noise and pure tones. Both thresholds and levels were recorded using the psychophysical method of tracking. Results indicate that the relationship between ART and LDL is at variance with similar data for normal hearing individuals. Specifically, in over 39% of these deaf children LDL was obtained at a lower intensity than ART. Implications for hearing aid fitting with deaf children are discussed.

Threshold-duration function of the acoustic reflex in man.

The threshold-duration function of the acoustic reflex was investigated in 5 male and 5 female adult, normal-hearing humans and in 3 adult male subjects with hearing loss of cochlear etiology. Reflex threshold was obtained at stimulus durations of 10, 20, 50, 100, 200, and 500 msec and at frequencies of 500, 1 000, 2 000, 3 000, and 4 000 Hz. Three commercially available acoustic bridges were employed, the Madsen ZO-70 and Grason-Stadler 1720 electroacoustic bridges, and the Grason-Stadler-Zwislocki model 3 mechanical-acoustic bridge. A probe-tone frequency of 220 Hz was used in all measures. The reflex threshold-duration function for normal-hearing subjects was found to encompass a much greater range of intensity than the psychophysically assessed auditory threshold temporal integration function. A sex difference was found which may be explained by subclinical noise-induced cochlear pathology in the male subjects with subsequent truncation of the reflex threshold-duration function. The function was also found to be truncated in the 3 subjects with hearing loss diagnosed to be of cochlear etiology. The implications of these findings for control of stimulus duration in clinical reflex measurement was discussed.

The prevention of noise-induced hearing loss in the school-aged population: a school educational hearing conservation program.

A questionnaire assessing knowledge of hearing and hearing loss, and planned hearing conservation practices, was collected from 71 high school students before and after an educational hearing conservation program (HCP) consisting of a film, a lecture and a handout. An average increase of 16.7% correct responses from pre- to postexposure to the HCP was found. Moreover, substantial percentages of respondents stated that they now plan to use hearing protection devices and procedures, when appropriate, and about 80% stated they found the HCP helpful to them.

In vitro and in vivo studies with sodium hyaluronate as a carrier for intraocular gentamicin.

We compared the in vitro growth of common intraocular pathogens Staphylococcus aureus, Staphylococcus epidermidis and Pseudomonas aeruginosa in rabbit vitreous and in sodium hyaluronate (SH) with and without gentamicin. The minimal inhibitory concentration for gentamicin/SH was 0.5, 0.062 and 2.0 mcg/ml for these pathogens, respectively. After posterior capsulotomy, P. aeruginosa was inoculated into the anterior vitreous and all 15 untreated eyes developed endophthalmitis. In a similar group, aqueous gentamicin administered in the anterior chamber reduced the incidence of endophthalmitis to 10 of 15 eyes. Under similar circumstances, the SH/gentamicin combination lowered the incidence of endophthalmitis significantly to 4 of 15 eyes. The half-life of aqueous gentamicin was 0.9 h, which was shorter than the 2.2 h for SH/gentamicin combination. These results suggest that SH may be a useful carrier for intraocular drug therapy.

Sodium hyaluronate as a carrier for intravitreal gentamicin. An experimental study.

Fifty mcg of gentamicin was combined with saline or with 0.8% sodium hyaluronate and injected into the vitreous cavity of rabbit eyes with moderate to severe Staphylococcus aureus endophthalmitis. Endophthalmitis was controlled in 9 of 10 eyes. There was no evidence of toxicity with either treatment regimen. Although the clearance study demonstrated statistical differences at all time points studied, the half-lives of both treatment regimens were similar (3.3 h for aqueous gentamicin and 3.6 h for sodium hyaluronate/gentamicin). These results suggest that the vitreous played a role in keeping the aqueous gentamicin in the eye for a longer time, as similar half-lives were shown with both types of treatment. Thus, if a vitrectomy has to be done for the treatment of endophthalmitis, as much as possible of the vitreous should be left in situ to maintain the drug for longer periods in the eye. Also, if it is necessary to remove all vitreous during vitrectomy, it may be more effective to administer the drug with sodium hyaluronate so as to prolong its action inside the eye.