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Biomedical subjects

R Probst

Publications and source records attributed to R Probst.

At least 37 records · Page 2Linked to original sources
PubMed1998

The influence of disappearing and reappearing spontaneous otoacoustic emissions on one subject's threshold microstructure.

The effects of a consistently disappearing and reappearing spontaneous otoacoustic emission (SOAE) at around 2280 Hz on microstructure for pure tones of varying durations in a 33 year-old woman with normal hearing was studied. The SOAE began to appear after 10-15 min in a quiet test room and increased in level by up to 22 dB over a 30-40-min period. The SOAE was measured every 12 to 15 min. Between measurements, the subject performed a signal detection task for pure tones with total durations varying from 20 to 320 ms. The signal frequencies were within a +/- 30-Hz range relative to the SOAE frequency. For signal durations of 40-320 ms, there was a local dip at the target SOAE frequency when it was either not detectable or its level was lower than -14 dB SPL. Subjective threshold levels were as much as 12 dB better than those obtained when the SOAE was -6 dB SPL or greater. The results suggest that a region of the cochlea with high sensitivity and instability can be put into self-oscillation producing an SOAE, possibly by a change of efferent activity. Hearing threshold is affected possibly due to adaptation or masking.

Acoustic Stimulation↗
PubMed1998

Direct evidence of cubic difference tone propagation by intracochlear acoustic pressure measurements in the guinea-pig.

The fine tuning mechanisms involved in the normal processing of sound in the cochlea are non-linear, hence combination tones are generated inside the cochlea when a pair of low-level pure tones with neighbouring frequencies f1 and f2 is used as a stimulus. Their detection as sounds in the ear canal proves that they undergo backward propagation in the cochlea and through the middle ear, and the non-invasive measurement of the combination tone at 2f1-f2, called the cubic difference tone (CDT), has become a routine method of monitoring cochlear function. In order to gain information on the hypothetical places where CDTs are generated, on their intracochlear levels and propagation velocities, direct measurements of CDT pressure waves were carried out in scala vestibuli and tympani of the first and second turn of the guinea-pig cochlea. Cubic difference tones at 2f1-f2 varied from 0.75 to 9 kHz and were measured with a miniature piezoresistive transducer. Its high sensitivity allowed the detection of CDTs whenever their levels exceeded 5 dB SPL in the ear canal, i.e. 40 dB SPL (re: 20 microPa) inside the cochlea. The levels of CDTs were similar in scala vestibuli of the first and second turn. Phase comparisons between measurements at 2f1-f2 in the first and second turn allowed determination of the place where the CDT phase was minimum. It provided an estimation of the generation site of the CDT, which appeared to be close to the place tuned to f2 for stimulus levels lower than 70 dB SPL. Forward and backward travel times from one turn to the other were assessed at several frequencies, and both values were shorter than 0.2 ms. In contrast, the overall 'round-trip' delay of CDTs, measured in the ear canal, was about five times larger, suggesting that local filtering processes rather than propagation delays account for the overall CDT delay.

Acoustic Stimulation↗
PubMed1997

Quantification of the neuromuscular blocking agent rocuronium and its putative metabolite 17-desacetylrocuronium in heparinized plasma by capillary gas chromatography using a nitrogen sensitive detector.

We have developed a sensitive and specific capillary GC (cGC) assay for the quantification of the quarternary aminosteroidal compound rocuronium (roc), a neuromuscular blocking agent, and its putative metabolite 17-desacetylrocuronium (17OH-roc), using 3-desacetylvecuronium (3OH-vec) as an internal standard (I.S.). This novel method has been applied to a pharmacokinetic study with roc, monitoring sixty patients who were classified according to four different body mass index (BMI) groups. The isolation of these drugs from plasma was carried out using a dichloromethane liquid-liquid extraction after ion-pairing of the positively charged ammonium compounds with iodide. To achieve thermal stability, tert.-butyldimethylsilyl-ethers were formed at the 3OH- and 17OH-steroidal positions by reaction with N-methyl-N-(tert.-butyldimethylsilyl)-trifluoroacetamide at 70 degrees C overnight. An automated cGC system fitted with a nitrogen sensitive detector with a specially prepared glass phase bead and a computer controlled data handling system was used to analyze and quantify the compounds, which were separated on a DB1 capillary column with helium as the carrier gas and a temperature program ranging from 120 to 300 degrees C. The method is linear for 50-6400 ng/ml for roc and 80-6400 ng/ml for 17OH-roc. The detection limits were 10 ng/ml for roc and 50 ng/ml for 17OH-roc. The lower limit of quantification was 50 ng/ml for roc and 80 ng/ml for 17OH-roc. Intra-assay coefficients of variation (C.V.s) were 10% and 15% and the inter-assay C.V.s 8-18% and 16-21% for roc and 17OH-roc, respectively.

Androstanols↗
PubMed1997

Concurrent platinum-based chemotherapy and hyperfractionated radiotherapy with late intensification in advanced head and neck cancer.

PURPOSE: To determine whether a course of hyperfractionated radiation therapy concomitant with escalated radiosensitizing platinum compounds can be administered with acceptable morbidity and achieve a high rate of loco-regional control for Stage III and IV head and neck cancer and whether the patients can be tumor free at the primary site after initial therapy and cured by the additional chemoradiation without radical resection of the primary tumor. METHODS AND MATERIALS: Patients with Stage III/IV head and neck cancer were treated in this multicenter Phase II Study with 1.8 Gy fraction radiotherapy for 2 weeks, with escalation to 1.2 Gy b.i.d. hyperfractionation to 46.8 Gy. Concomitant continuous infusion cisplantinum (CDDP) 20 mg per meter square on day 1 to 4 and 22 to 25 was given. Reassessment by biopsy of primary and nodes was done. Patients with a complete response continued with hyperfractionated radiotherapy to 75.6 Gy with simultaneous carboplatinum (Carbo), 25 mg per meter square b.i.d. for 12 consecutive treatment days. Patients with residual disease at 46.8 Gy required curative surgery. Seventy-four patients were treated at the three institutions; 20 were Stage III and 54 were Stage IV. All patients had daily mouth care, nutritional, and psychosocial support. RESULTS: This regime was well tolerated. Eighty-five percent of toxicities were Grade 1 or 2 and there was only one Grade 4 hematologic toxicity. Late toxicities included xerostomia in 25 patients, dysphasia in 18, and mild speech impediment in 11. Biopsies of primary site were done after the first course of treatment in 59 patients. Neck dissections were performed in 35 patients. Forty-four of 59 (75%) primary sites and 16 of 35 (46%) lymph nodes had pathologically complete response (CR). Of the 74 patients, only 12 required surgical resection of the primary site. Thirty-five of the 50 node positive patients had neck dissections, 16 of these were CRs at surgery. At 4 years (median follow-up of 26 months), disease-specific survival is 63%. The actuarial survival for all patients is 51%. Patients with pathological CR after initial treatment have disease specific survival of 73% at 4 years vs. 48% of patients with partial response (PR) only. CONCLUSION: This study, developed on the basis of radiobiological and cell kinetic precepts, produced results that compare favorably with other reports of management of patients with advanced head and neck cancer. In comparison with our previous study, these results are comparable, not impressively better. The associated morbidity was somewhat worse.

Adult↗
PubMed1997

[Follow-up of caloric test response after acute peripheral vestibular dysfunction].

This study examined retrospectively the spontaneous recovery of patients with an acute peripheral vestibular deficit in order to determine whether the caloric test response and with it vestibular function improves over time. The caloric bithermal was tested three times on 79 patients who were hospitalised with an acute deficit. The first test was recorded on emergency admission by observing nystagmus beats under the Frenzel glasses. Two to five days later a complete electronystagmus (ENG) examination was performed. A second ENG was performed, on average, 4 months later. 46% of the patients recovered a normal caloric canal paresis value (less than 32%). By comparing the canal paresis values in the first and second ENG an improvement exceeding 30% was demonstrated in 50% of the patients and there was no correlation between the extent of the canal paresis deficit and the amount of recovery. A simultaneous cochlear deficit had no influence on the recovery of vestibular function.

Adult↗
PubMed1997

[Antibiotic prophylaxis in laterobasal fractures].

A retrospective study over 5 years evaluated the medical records of 78 patients who had suffered lateral skull base fractures. The purpose of the present study was to answer the question of whether antibiotic prophylaxis reduced the risk of meningitis. Fifty-five of 78 patients (71%) were given no antibiotics, among whom four developed meningitis. In 29% of patients treated with antibiotics, two developed meningitis. This difference was not significant. Even when cases with uncomplicated ("simple") lateral skull base fractures were separated from those with severe additional lesions related to their injuries, no significant correlation was found in the occurrence of meningitis despite the use of an antibiotic. Eight of 14 patients with initial otoliquorrheas were treated with antibiotics, with two of these 8 patients developing meningitis. None of the patients who did not receive antibiotics developed meningitis. Our findings shows that it is not advisable to treat patients who have suffered from lateral skull base fractures with prophylactic antibiotics. Instead, these patients should be examined frequently and appropriate antibiotic therapy prescribed at the first clinical symptoms of meningitis.

Anti-Bacterial Agents↗
PubMed1997

Reverse middle-ear transfer function in the guinea pig measured with cubic difference tones.

Otoacoustic emissions are increasingly useful for determining cochlear function noninvasively. It is widely agreed that these acoustic signals reflect micromechanical processes in the cochlea. However, their quantitative interpretation requires knowledge of the ways in which vibrations travelling back to the ear canal from the cochlea are shaped by the middle ear. An intracochlear source is needed to derive the reverse middle-ear transfer function (rMETF) by comparing pressure in the external ear canal to the corresponding pressure in scala vestibuli. In the present study, the rMETF was obtained in vivo in the guinea pig using as intracochlear sound source the cubic difference tones (CDTs) generated by a pair of external pure tones. With a closed ear canal and open bulla, the rMETF was found to be flat (-35 dB) over a broad frequency range (1.5-8 kHz). The differences between forward and reverse METF could be explained by different loads acting on the middle ear network, which depends on the direction of signal transmission. With knowledge of the rMETF, it becomes possible to quantify CDTs within the cochlea by measuring them noninvasively in the ear canal.

Acoustic Stimulation↗
PubMed1997

[Speech audiometry with logatomes].

BACKGROUND: Logatomes are nonsense syllables used for analyzing the confusion of phonemes by hearing impaired listeners. They can provide a precise differentiation of phonemic confusions which may be useful in the exact adjustment of programmable hearing aids. METHODS: In this study, two lists of logatomes with 108 three-sound combinations with a structure of consonant-vowel-consonant (c-v-c) and vowel-consonant-vowel (v-c-v) were recorded on a compact disk. Twenty normally hearing adults and 28 patients with a sensorineural hearing loss were tested at a comfortable listening level of about 25 +/- 5 dB above the mean audiometric thresholds at 0,5. 1,0 and 2,0 kHz. An index of reduction of speech perception was calculated. RESULTS: A significant relationship between reduction of logatome perception and pure-tone audiometric thresholds at 1,2,3, and 4 kHz was demonstrated. Moreover, it was possible to distinguish between different groups of hearing impairment. CONCLUSIONS: The logatome test helps to analyze specific effects that hearing loss can have on the recognition of acoustic speech signals. The logatome test may become a valuable addition to speech audiometric tests with further standardization.

Adult↗
PubMed1997

The role of transient-evoked otoacoustic emission testing in the evaluation of elderly persons.

OBJECTIVE: The purposes of this study were: To determine the quantitative and qualitative changes that occur in transient-evoked otoacoustic emissions (TEOAEs) in older individuals without addressing the effect of aging alone and without correction for hearing loss of the subject selection. To investigate the clinical value of measuring TEOAEs in the routine audiological evaluation of older people reasoning that a finding of hearing loss in the presence of TEOAEs could indicate a form of presbycusis with a primary central component. DESIGN: Click-evoked otoacoustic emissions (CEOAEs) were measured in 201 subjects without middle ear problems aged 60 yr and older (range 60 to 97 yr) who volunteered for the study because of complaints concerning their hearing. Audiological procedures included a pure-tone audiogram, modified Speech Perception in Noise test (German version: Basler Satztest), and the Hearing Handicap Inventory for the Elderly (German version). Results from ears with a pure-tone average (PTA) at 0.5, 1, and 2 kHz of < or = 30 dB HL were further analyzed with respect to the presence or absence of CEOAEs. In addition, tone burst evoked otoacoustic emissions (TbOAEs) were tested in ears with responses to click stimuli. The test consisted of a paradigm used previously in our laboratory to assess superposition and suppression of frequency within the cochlea (see Xu, Probst, Harris, & Roede, 1994). RESULTS: CEOAEs were not detectable in ears with a PTA > 30 dB HL. The prevalence of CEOAEs in ears with a PTA < or = 30 dB HL was 60%. Response levels decreased as hearing thresholds became poorer, but there was no apparent influence on TEOAE level due to age alone. The audiological measures from ears with and without CEOAEs and with PTAs < or = 30 dB HL were similar with the exception of small between group differences at lower frequencies. The TbOAE results showed no differences in linear superposition and suppression when results were compared with those of younger subjects tested previously. CONCLUSIONS: The lower overall amplitudes of TEOAEs and the lower prevalence of 60% in comparison to results from younger subjects with normal hearing imply that cochlear changes do occur with aging. However, the preservation or loss of TEOAEs does not separate subjects with presbycusis into distinct audiological categories or handicaps. Tone burst results suggest that frequency processing within the cochlea is not affected by age alone. We conclude that TEOAEs add no relevant information in the routine clinical evaluation of elderly persons with hearing problems.

Acoustic Impedance Tests↗
PubMed1997

Noninvasive tracking of patient's head movements during computer-assisted intranasal microscopic surgery.

A noninvasive system designed for patient tracking during image-guided intranasal sinus surgery is described. It is based on optical digitizing with a custom-made registration and reference system, locatable surgical instruments, and a self-localizing operating microscope. Experimental and clinical results reveal a high degree of accuracy for the system. A mean spatial error of 0.82 +/- 0.31 mm was determined for repositioning of the reference system in a plastic model of the skull. For the positioning of the microscope, a mean error of 2.3 +/- 0.83 mm was calculated. Measurements of repositioning accuracy in 24 patients who received surgery for various sinus diseases had a mean spatial error of 1.56 +/- 0.76 mm. The 95% error interval for locating intranasal structures using the surgical instrument was 2.05 mm, and it was 4.92 mm using the microscope. These results suggest that the use of our noninvasive registration and reference system may be effective, accurate, and useful for noninvasive tracking of patient movements in computer-assisted intranasal surgery.

Head Movements↗
PubMed1997

A non-invasive patient registration and reference system for interactive intraoperative localization in intranasal sinus surgery.

A basic problem common to all systems for computer assisted surgery (CAS) is patient referencing, or the transfer of preoperative image data to the intraoperative pathology. The authors describe a highly precise CAS system with non-invasive referencing that can be used in ear, nose and throat (ENT) surgery of the paranasal sinuses. It is based on optical digitizing with several custom-made self-localizing surgical instruments. The accuracy of the system was tested in an experimental model using a plastic head. Measurements of repositioning the reference bow had a mean error of 0.81 mm +/- 0.31 mm. The system was evaluated clinically with 11 patients who received surgery for different pathologies of the paranasal sinuses. These trials met with a high rate of success and specific results are reported.

Biopsy↗
PubMed1997

Evaluation of electrically elicited stapedius reflex threshold measured through three different cochlear implant systems.

OBJECTIVE: To evaluate intraoperative electrically elicited stapedius reflex thresholds (ESRTs) measured through three different cochlear implant systems: the Nucleus Mini 22, the Clarion Enhanced Bipolar, and the Med-El Combi-40. SUBJECTS AND METHODS: Relations between intraoperative ESRT and postoperative maximum comfort level (MCL) were examined in seven children (4 Nucleus, 2 Clarion, and 1 Med-El) and one adult (Clarion). RESULTS: Preliminary results indicated most ESRTs were either higher or both higher and lower (across the electrode array within a subject) than MCLs. All systems provided satisfactory means for measuring ERSTs. CONCLUSION: It is recommended that hand-held systems have a direct readout to the programming station and that audio and visual feedback be improved for all units.

Adolescent↗
PubMed1996

Different aspects of hearing preservation in surgery of vestibular schwannoma in women and men.

Pre-operative and postoperative auditory function was reviewed retrospectively in 98 patients with vestibular schwannomas. According to their hormonal status, women were categorized as "premenopausal" and "postmenopausal". Before surgery, 48% of the women (65% premenopausal) and 16% of the men presented with sudden hearing loss. The degree of auditory function before operation was similar for women and men. Preservation of pre-operative hearing was possible for 41% of the women (21% premenopausal) and 59% of the men. Further details of the surgery and the results of histopathological examination were also compared for women and men. Our results support substantial evidence that hearing preservation after surgery of vestibular schwannoma is easier to accomplish for men than for women. The finding of significantly more sudden hearing loss in premenopausal women may suggest a hormonal influence on tumour growth, which may also be partially responsible for the difference in hearing prognosis between women and men.

Adolescent↗
PubMed1996

[Computer-assisted surgery of the paranasal sinuses with an opto-electronic stereotaxic system].

BACKGROUND: A basic problem common to all systems for computer-assisted surgery (CAS) is the exact registration and referencing, that is, the transfer of preoperative image data to the intraoperative pathology. A system for computer-assisted ENT surgery should provide high precision as well as noninvasive registration and referencing. We present a system designed for such use in paranasal sinus surgery that is based on optical digitizing with several custom-made self-localizing surgical instruments. METHODS AND RESULTS: The system tracks the correct alignment of the head during CT data acquisition and continuously throughout surgery. A transformation matrix and a plane equation of the CT scan are used to match points of the object space to the image space detecting fiducial markers on the CT scans by an automatic algorithm. For position measurements a special reference frame and surgical instruments were developed and equipped with infrared light-emitting diodes that could be detected in real time. Measurements for repositioning of the reference system in a model and during real operations demonstrated a mean error ranging from 0.69 to 1.01 mm and from 0.76 to 1.67 mm respectively. Clinical experience with the application of the system for 15 patients who underwent surgery for different paranasal sinus pathologies is reported. CONCLUSIONS: Results suggest that the non-invasive reference system and the locatable surgical tools may be effective, accurate and useful for computer-assisted identification of intranasal structures. Such systems may contribute to further improvement of minimal invasive intranasal sinus surgery.

Equipment Design↗