F. Ottaviani

Auditory brain-stem (ABss) and middle latency auditory responses (MLRs) in the prognosis of severely head-injured patients

Auditory brain-stem responses (ABRs) were studied in 66 subjects with severe head trauma. Middle latency responses (MLRs) were also recorded in 22 of them. Patients were carefully selected to avoid conditions such as pre-existing or acute deafness, hypothermia or ethanol intoxication. In order to evaluate the usefulness of potentials in predicting recovery, patients were classified according to the Glasgow Coma Scale (GCS). ABR tracings were classified into 5 groups and MLR into 2 groups. The recovery was good in the presence of a type 1 ABR, poor in the presence of types 3, 4 and 5. Concerning type 2 ABR, the outcome is related to the MLR type, and to the presence of an electrophysiological improvement within the first 3 months following trauma. The reliability of ABR and MLR in predicting the outcome of severe head injury appears to be greater than other usually considered clinical and instrumental data (age, GCS, CT scan, EEG).

40-Hz Steady-State Responses in Newborns and in Children

The authors investigated the 40-Hz steady-state responses (SSR) in 32 full-term newborns and in 10 normal children (5-8 years old), using 500-Hz tone bursts. The 40-Hz SSR threshold is located at about 50 and 30 dB nHL in newborns and older children, respectively. The latencies of both P1 and N1 waves decreased significantly with age, while the amplitudes increased. No significant latency and amplitude intersex differences have been observed. Moreover, with age, the 40-Hz SSR became more stable, their test-retest replicability improved, and P1-N1 wave occurrence increased. The authors finally discuss the possible underlying mechanisms of these findings and conclude that the 40-Hz SSR are difficult to obtain and are scarcely reliable in defining the low-frequency threshold in newborns. The stability and reliability of the responses increase with age, and the electrophysiological and behavioral thresholds to low-frequency stimuli tend to overlap.

Mucociliary Clearance and Mucosal Surface Characteristics before and after Total Laryngectomy

Forty heavy smokers, all males aged between 40 and 70 and affected by laryngeal cancer underwent mucociliary clearance evaluation the day before total laryngectomy, 60 days after and, in 6 of them, 5 years later. Specimens of nasal and tracheal mucosa were obtained during laryngectomy and other subsequent operations. Before total laryngectomy, no significant changes in nasal mucociliary clearance were observed in smokers and controls, and the nasal ciliary carpet was fairly well preserved. Bronchial mucociliary clearance was impaired in all patients, owing to the coexistent chronic obstructive bronchitis. 60 days after the operation, nasal mucociliary clearance was significantly improved when compared with the preoperative data and controls, owing to the increase in the endonasal temperature and humidity, and to the reduction of the nasal blood flow and disappearance of the nasal cycle, which follow tracheostomy. Surface morphologic studies show a change in the squamous epithelium of the anterior third of the nasal fossa into a columnar ciliated one. During the first 3 months after the operation, tracheobronchial mucociliary clearance increased of 50% vis-à-vis the preoperative data. During this period a clinically evident bronchial hypersecretion was observed. The reduction in nasal and tracheobronchial mucociliary clearance function which became evident 6 years after the operation, is probably due to secondary chronic infections.

Auditory Brainstem Responses (ABR) in the Aged

86 male subjects, aged between 60 and 86 years (M = 69.5), underwent pure-tone audiometry, impedance tests and brainstem response audiometry (BRA). Subjects have been classified into four age-related groups: 1) 34 subjects, aged between 60 and 65; 2) 22, aged between 66 and 70; 3) 22 aged between 71 and 75; 4) 8, aged between 76 and 86. They have also been classified into four groups on the basis of their mean auditory threshold at 0.5, 1, 2, 4 and 8 kHz: 1) 14 subjects with mean auditory threshold less than or equal to 30 dB HL; 2) 16, between 31 and 40; 3) 24, between 41 and 50; 4) 32, with mean auditory threshold greater than or equal to 51 dB HL. 19 normally hearing adults, aged between 28 and 42, were chosen as controls. Statistically significant correlations have been found between age and mean auditory threshold (P less than or equal to 0.001), between wave latency V and age (P less than or equal to 0.001), between wave latency V and the mean pure-tone auditory threshold at 0.5, 1, 2, 4 and 8 kHz (P less than or equal to 0.001) and between the V-I interval and age (P less than or equal to 0.001). The discrepancy between the mean auditory threshold and the ABR waveform, the overall amplitudes reduction of ABR waves and the progressive lengthening of V-I interval values, seem to indicate that age-related changes involve not only the end organ but also the brainstem auditory structures.

Contribution to the Differentiation of Peripheral versus Central Tinnitus via Auditory Brain Stem Response Evaluation

Auditory brain stem response (ABR) parameters were evaluated in 54 subjects with unilateral idiopathic subjective tinnitus in order to verify the possibility of detecting its site of origin. All the subjects had normal hearing or a symmetrical bilateral sensorineural hearing loss. All the cases in whom middle or inner ear disease had been diagnosed, were excluded. Subjects, classified on the basis of their mean auditory threshold and masking curves according to Feldmann, underwent a residual inhibition (RI) test and ipsilateral narrow-band noise masking before a second ABR test was performed. Patients with positive RI made up the A+ group, while those with negative RI made up the A- group. The main characteristics observed were an increase of the mean latency values of wave I in the tinnitus ear in the A+ group while, after masking, the values of the affected and unaffected ears almost overlapped. An increase in the latency values of wave V, unaffected by the masking procedure, could be observed in A- patients. The occurrence of waves I and III was often affected in the tinnitus ears in both groups, but it increased, after masking, only in the A- patients. Based on the obtained data, the authors conclude that there may be a substantial difference concerning ABR parameters between the patients in whom residual tinnitus masking is demonstrable compared with those in whom it is not.

Middle-latency auditory components in response to clicks and low- and middle-frequency tone pips (0.5-1 kHz).

Middle-latency auditory components (MLC) in response to clicks and tone pips have been recorded in 20 normal subjects, aged between 26 and 32 years, in order to verify their reliability in response to frequency-specific stimuli (0.5 and 1kHz). The results indicate a good reliability of MLC obtained when using tone pips. The responses show the conventionally labeled Po, Na, Nb, Pb waves. The latencies of these waves tend to be greater than those of the corresponding waves elicited by clicks and their amplitudes are smaller. This is probably due to an asynchrony of the responses. The Po and Pa waves are the most resistant to decreasing stimulus intensity, as both are clearly detectable down to 20 dB nHL, but Po is the best threshold index because at 20 dB it has a more clear-cut shape than Pa. According to the latency values obtained for MLC elicited by both clicks and tone pips, the Po wave is probably generated at the inferior colliculus level. The latency shift towards the click-elicited Jewett wave V is mainly due to the different filter settings employed. The morphology of MLC elicited by tone pips is less affected by changes in stimulus frequency than that of corresponding auditory brainstem responses. Thus, MLC are a reliable indicator for defining low- and middle-frequency auditory thresholds.

Adenoid hypertrophy and nasal mucociliary clearance in children. A morphological and functional study

The authors have studied nasal mucociliary function and adenoid surface characteristics in a group of 86 children, aged between 4 and 10 years, divided in two groups according to the presence or absence of clinical, instrumental and röntgenographic signs of nasal obstruction due to hypertrophied adenoids. Each group was divided into 3 age-related subgroups (group I: 4-5 years; group II: 6-7 years; group III: 8-10 years). A population of normal adults was chosen both for functional and ultrastructural characteristics. Nasal mucociliary clearance velocity values were evaluated by means of the saccharine method and the surface characteristics of the adenoid tissue by means of scanning electron microscopy. The data obtained show that the nasal mucociliary function is generally reduced in children but, while in the group with poorly developed adenoids an early and progressive improvement can be observed, the children with severely hypertrophied adenoids show an impaired function up to 10 years, without age-related improvements. At almost 10 years, children with poorly developed adenoids reach normal adult clearance values. These functional data can be related to the surface characteristics of adenoid tissue. In fact, while poorly developed adenoids are characterized by a compact layer of ciliated cells, severely hypertrophied adenoids are characterized by a metaplasic epithelium, with almost complete loss of cilia. Such findings, which are probably due to the inflammatory events frequently complicating adenoid hypertrophy, could explain, together with the obstructive effects, the impairment of the nasal mucociliary clearance in childhood.

Audiological findings in Down's children.

The authors have investigated the auditory function in 35 Downs subjects, aged between 1 month and 16 years. Clinical examination revealed the occurrence of impaired nasal breathing in 18 subjects (51.4%), while otoscopy results were bilaterally normal in 12 cases (34.3%). Behavioural pure-tone audiometry yielded reliable results in 10 children (28.6%), impedance tests in 28 (80.0%), and brainstem audiometry in 29 (82.9%). A clinical and audiological follow-up has been performed in 11 cases (31.4%). Pure-tone audiometry, which may be employed in all cases only beyond 8 years of age, revealed a conductive hearing loss in 7 cases (20.0%). Impedance tests, whose usefulness is limited by the high occurrence of external ear canal stenosis, showed bilateral type A tympanograms only in 8 cases (28.6%). Stapedial reflex data were often missing, even in presence of a type A tympanogram, due to the weakness of tubaric muscles and to the presence of ossicles abnormalities. ABR has been performed in 29 cases (82.9%) and resulted to be as effective as in the normal population. It revealed a normal configuration concerning threshold and morphology in 16 cases (55.1%). The authors conclude that middle ear pathology in the Downs population is more frequent than expected on clinical basis and that objective tests are mandatory in order to obtain a reliable evaluation. While impedance tests are very sensible in detecting mild middle ear pathologies, but are not effective in threshold definition, brainstem audiometry is the choice tool in the uncooperative child, even if it cannot allow a differential diagnosis between normality and mild low-frequency conductive hearing losses.

Auditory brainstem responses to middle- and low-frequency tone pips

Auditory brainstem responses (ABR) evoked by clicks allow a threshold evaluation for the high-frequency range (2-4 kHz) but not for middle and low frequencies (0.5-1 kHz). In 19 normally hearing subjects aged between 24 and 40 years. ABRs have been recorded using clicks and 0.5- and 1-kHz tone pips, with durations of 6 and 3 ms, respectively, and rise-decay times of 3 and 1.5 ms. The input signal was filtered by a passband filter of 20-5 000 Hz. Parameters of tracings elicited by the different kinds of stimuli are compared. Tone-pip ABR morphology does not show the conventional seven peaks but a single large vertex-positive wave. On the ascending branch high-frequency potentials, probably corresponding to the I, II, III and IV-V click-evoked peaks, were visible in some cases, but they rapidly disappeared as the stimulus intensity was decreased. Their 2.3-3 ms greater mean latency values are presumably related to the rise times of the stimuli employed. In terms of bioelectric generators, this large vertex-positive peak probably corresponds to the Jewett V wave. It probably represents a generalized asynchronous dendritic activity. Thus it is possible to obtain ABRs to middle- and low-frequency stimuli. Mean amplitude values of the slow wave are considerably higher than those of the Jewett V wave, but standard deviations are also larger. The positive wave has been identified in response to 1-kHz tone pips in 100% of cases at 30 dB nHL and in 52% of cases at 20 dB, while for 0.5-kHz tone pips in 73.7% of cases at 30 dB and in 57% at 20 dB. On the whole the threshold is located between 15 and 30 dB nHL.

Auditory brainstem responses in the full-term newborn: changes in the first 58 hours of life.

The authors have studied auditory brainstem responses (ABR) in 33 full-term newborns at 0-9, 10-30, 31-58 h, in order to evaluate changes in the first hours after birth, particularly in relation to different repetition rates and recording procedures. The data obtained show that the characteristic newborn 3-peak tracing is observed in almost all the cases at the third recording session while, at the first, wave I is absent in two-thirds of the cases. The most reliable waves at birth are waves III, V and N II, which is often present even when other vertex-positive peaks are absent. Latency values of the considered peaks tend to decrease in a statistically significant way and this decrease is almost complete at the second recording session (30 h), while V-I interval values decrease, especially when the 9 stimuli/s repetition is employed. Stimulus repetition rate affects ABR replicability and synchronization, but it hardly influences latency values. Contralaterally recorded potentials are often absent at birth and become evident 58 h later. The authors conclude that the maturational processes probably affect both peripheral and central auditory structures in the first hours after birth. In this period, increasing repetition rates seem to have a greater effect on wave replicability than on latency values.