Treatment of age-related hearing loss in dogs with the vibrant soundbridge middle ear implant: short-term results in 3 dogs.

BACKGROUND: Age-related hearing loss (ARHL), or presbycusis, is the most common form of acquired hearing loss in dogs. Middle ear implants have been used successfully in people with ARHL who cannot benefit from conventional hearing aids. HYPOTHESIS: Audibility improves in dogs with ARHL after implantation of the Vibrant Soundbridge (VSB) middle ear implant. ANIMALS: Three Beagle dogs with ARHL, mean age 11.1 years. METHODS: The dogs were assessed pre- and postoperatively by brainstem-evoked response audiometry (BERA), otoscopy, and computed tomography scans of the ears. A VSB middle ear implant was implanted unilaterally. Three months later the functionality of the implants was assessed by auditory steady-state responses (ASSRs), after which the dogs were euthanized for histopathological examination. RESULTS: The VSB was implanted successfully in all dogs. Recovery from surgery was uneventful, except for transient facial nerve paralysis in 2 dogs. ASSRs showed that hearing improved after activation of the implants with a mean of 20.7, 13, and 16.3 dB at 1, 2, and 4 kHz, respectively. The implantation procedure did not affect residual hearing (with inactive implants) as measured by BERA. CONCLUSIONS AND CLINICAL IMPORTANCE: Implantation of the VSB resulted in lower ASSR thresholds, but only at the higher gain settings of the audioprocessor. As in humans, a more powerful audioprocessor is required to treat sensorineural hearing loss exceeding 20 dB in dogs. A substantial improvement in patient-owner communication will have to be demonstrated in future studies before the procedure can be recommended in clinical practice.

Effects of aging on inner ear morphology in dogs in relation to brainstem responses to toneburst auditory stimuli.

BACKGROUND: Age-related hearing loss (ARHL) is the most common form of hearing loss in humans and is increasingly recognized in dogs. HYPOTHESIS: Cochlear lesions in dogs with ARHL are similar to those in humans and the severity of the histological changes is reflected in tone audiograms. ANIMALS: Ten geriatric dogs (mean age: 12.7 years) and three 9-month-old dogs serving as controls for histological analysis. METHODS: Observational study. Auditory thresholds were determined by recording brainstem responses (BERA) to toneburst auditory stimuli (1, 2, 4, 8, 12, 16, 24, and 32 kHz). After euthanasia and perfusion fixation, the temporal bones were harvested and processed for histological examination of the cochleas. The numbers of outer hair cells (OHCs) and inner hair cells (IHCs) were counted and the spiral ganglion cell (SGC) packing density and stria vascularis cross-sectional area (SVCA) were determined. RESULTS: A combination of cochlear lesions was found in all geriatric dogs. There were significant reductions (P .001) in OHC (42%, 95% confidence interval [CI]; 24-64%) and IHC counts (21%, 95% CI; 62-90%) and SGC packing densities (323, 95% CI; 216-290) in the basal turn, SVCA was smaller in all turns. The greatest reduction in auditory sensitivity was at 8-32 kHz. CONCLUSIONS AND CLINICAL IMPORTANCE: ARHL in this specific population of geriatric dogs was comparable histologically to the mixed type of ARHL in humans. The predominance of histological changes in the basal cochlear turn was consistent with the large threshold shifts observed in the middle- to high-frequency region.

Effects of aging on brainstem responses to toneburst auditory stimuli: a cross-sectional and longitudinal study in dogs.

BACKGROUND: It is assumed that the hearing of dogs becomes impaired with advancing age, but little is known about the prevalence and electrophysiologic characteristics of presbycusis in this species. HYPOTHESIS: As in humans, hearing in dogs becomes impaired with aging across the entire frequency range, but primarily in the high-frequency area. This change can be assessed quantitatively by brainstem-evoked response audiometry (BERA). ANIMALS: Three groups of 10 mixed-breed dogs with similar body weights but different mean ages were used. At the start of the study, the mean age was 1.9 years (range, 0.9-3.4) in group I, 5.7 years (3.5-7) in group II, and 12.7 years (11-14) in group III. METHODS: In a cross-sectional study, the BERA audiograms obtained with toneburst stimuli were compared among the 3 groups. In a longitudinal study, changes in auditory thresholds of group II dogs were followed for 7 years. RESULTS: Thresholds were significantly higher in group III than in groups I and II at all frequencies tested, and higher in group II than in group I at 4 kHz. The audiograms in group II indicated a progressive increase in thresholds associated with aging starting around 8-10 years of age and most pronounced in the middle- to high-frequency region (8-32 kHz). CONCLUSIONS AND CLINICAL IMPORTANCE: Age-related hearing loss in these dogs started around 8-10 years of age and encompassed the entire frequency range, but started and progressed most rapidly in the middle- to high-frequency area. Its progression can be followed by BERA with frequency-specific stimulation.

Middle-latency auditory-evoked potential in acepromazine-sedated dogs.

The middle-latency auditory-evoked potential (MLAEP) has been investigated as means of monitoring anesthesia in dogs. The goals of this study were to develop a technique to record MLAEPs in awake dogs and to determine the effects of sedation. The MLAEP was recorded in 12 dogs with and without sedation with acepromazine. Three needle electrodes were inserted SC. Click stimuli were delivered biaurally. Signal acquisition, averaging, and analysis were performed by software developed in-house. Signals were recorded for 128 milliseconds, and the responses to 1,024 stimuli were averaged. The waveforms from 10 recordings were averaged, and the amplitudes and latencies of peaks that could be consistently identified were measured. Data measured were compared by means of a paired 2-sided Student's t-test. Interpretable MLAEPs were recorded in 10 of the 12 dogs. Three peaks were consistently identified (Pa, Nb, and Pb). The latencies of these peaks were significantly (P = .032, .035, and .028, respectively) shorter in awake (mean +/- SD milliseconds) (Pa = 18.85 +/- 1.36, Nb = 30.50 +/- 3.55, and Pb = 47.70 +/- 5.53) than in sedated (Pa = 22.40 +/- 3.88, Nb = 35.75 +/- 6.77, and Pb = 55.30 +/- 10.55) dogs. The Pb amplitude was not significantly different (2.51 +/- 1.30 microV awake and 2.19 +/- 1.10 microV sedated). This study demonstrates that acepromazine sedation causes changes in MLAEP.

Click and low-, middle-, and high-frequency toneburst stimulation of the canine cochlea.

A method was developed to deliver tonebursts ranging in frequency from 1 to 32 kHz for frequency-specific assessment of the canine cochlea. Brainstem auditory-evoked responses (early latency responses, 0-10 ms) to a click (CS) and to 1-, 2-, 4-, 8-, 12-, 16-, 24-, and 32-kHz toneburst stimulations (TS) were compared at 80-dB sound pressure level stimulus (SPL) intensity in 10 adult dogs. All stimulations yielded a 5-7 positive wave pattern, with the exception of the 1-kHz TS, which evoked a frequency-following response (FFR). Thresholds were lowest for the CS and the 12- and 16-kHz TS. All individual peak latencies for TS were significantly (P < or = .05) longer than for CS. Peak I latencies were significantly (P < or = .05) shorter for the 12- and 16-kHz TS than for the other TS. Interpeak latencies I-V were significantly (P < or = .05) longer for the 4- to 32-kHz TS than for CS. Differences in interpeak latencies I-III were not significant. Amplitudes of waves I and V were significantly (P < or = .05) lower for TS than for CS, except for higher wave V amplitude (P < or = .05) at 2- and 32-kHz TS. Peak I-V amplitude ratios were significantly (P < or = .05) higher for the 2-, 4-, 16-, 24-, and 32-kHz TS and lower for the 8- and 12-kHz TS, compared to CS. We conclude that reproducible information on frequency specificity of the canine cochlea can be obtained by TS. This report provides a normative database for parameters needed to evaluate frequency-specific hearing loss in dogs.

The rat vertex-middle latency auditory-evoked potential as indicator of anaesthetic depth: a comparison with evoked-reflex testing.

We investigated whether components from the rat Vx-MLAEP could be used to assess depth of anaesthesia induced by propofol. Propofol decreased MLAEP amplitudes and increased latencies. We propose that the P(16)-N(22) wave in the rat MLAEP is similar to the human P1, and that recovery of this wave during propofol anaesthesia correlates with behavioural measures of the regaining of consciousness.

Effect of superior laryngeal nerve transection on pharyngeal muscle contraction timing and sequence of activity during eating and stimulation of the nucleus solitarius in dogs.

The effect of unilateral or bilateral transection of the superior laryngeal nerve on the electromyographic activity in the hyopharyngeal, thyropharyngeal, and cricopharyngeal muscles was studied in 10 dogs during eating and during unilateral electrical stimulation of the solitary nucleus. In all groups of dogs, after unilateral or bilateral transection, there were some swallowing actions in which the sequence of activity in the pharyngeal muscles was disturbed during eating and during stimulation of the solitary nucleus. In the dogs in which the transection was unilateral, this fraction was 18% in the ipsilateral muscles during eating and 7% in the contralateral muscles. After bilateral transection it was 8% in the left muscles and 16% in the right muscles. The fractions were not significantly different when swallowing was evoked by stimulation of the solitary nucleus. Swallowing actions having a normal sequence of activity in these dogs were compared with those in a group of eight dogs in which the superior laryngeal nerves were intact. Contraction timing was not significantly different during eating, but during stimulation of the solitary nucleus the timing was significantly shorter than in the dogs with intact nerves. It was concluded that superior laryngeal nerve transection modulates the central pattern generator for pharyngeal swallowing in dogs.

Functional anatomy and neural regulation of the lower urinary tract in female dogs: a review.

A review of the literature of the functional anatomy and neural regulation of the lower urinary tract is presented. The two main functions of the lower urinary tract are the storage and the periodic elimination of urine. The smooth muscle of the bladder exhibits intermittent contractions as the bladder adapts its capacity to increasing volumes and it exhibits sustained contractions associated with relaxation of the external sphincter to effect micturition. During storage, tension receptors in the bladder wall initiate external sphincter contraction (somatic), internal sphincter contraction (sympathetic), detrusor inhibition, and parasympathetic ganglion inhibition (sympathetic). The storage phase can be switched to the micturition phase either voluntarily or involuntarily. Neuroanatomical and electrophysiological studies reveal that medial and lateral cell groups in the dorsolateral pons may be regarded as micturition and storage control centres, respectively.

Evidence for recurrent laryngeal nerve contribution in motor innervation of the human cricopharyngeal muscle.

OBJECTIVE: To study the functional motor nerve supply of the upper esophageal sphincter in humans. STUDY DESIGN: Intraoperative electromyographic study. METHODS: The contribution of the recurrent laryngeal nerve and the pharyngeal plexus in the motor nerve innervation of the cricopharyngeal muscle and the inferior pharyngeal constrictor muscle was examined intraoperatively. RESULTS: Electromyography showed that there is a considerable overlap in the innervation of the cricopharyngeal muscle and the inferior pharyngeal constrictor muscle. The recurrent laryngeal nerve functionally contributes to the motor innervation of the cricopharyngeal muscle in all patients and contributes to the motor innervation of the inferior pharyngeal constrictor muscle in most patients. The pharyngeal plexus functionally contributes to the motor innervation of the inferior pharyngeal constrictor muscle but does not always contribute to the motor innervation of the cricopharyngeal muscle. CONCLUSIONS: This is the first report which provides evidence that the recurrent laryngeal nerve functionally contributes to the motor innervation of the cricopharyngeal and inferior pharyngeal constrictor muscle. Furthermore, this study shows that intraoperative electromyography in humans is a feasible method to analyze the physiology of the motor innervation of the upper esophageal sphincter.

EEG evaluation of reflex testing as assessment of depth of pentobarbital anaesthesia in the rat.

Electroencephalography (EEG) was applied to evaluate the validity of the paw pinch reflex as an indicator of anaesthetic depth in rats which are anaesthetized with a single intraperitoneal dose of pentobarbital. After induction of the anaesthesia, characterized by the rapid loss of the animals' ability to maintain upright posture, the EEG of 10 out of 11 rats was dominated by paroxysmal (burst suppression) activity, associated with unconsciousness. In seven out of 11 rats, the paw pinch reflex was lost after onset of paroxysmal electroencephalographic activity. However, the paw pinch reflex remained present in four out of 11 animals, demonstrating that the response is independent of cortical activity. In five out of seven rats, the EEG still showed paroxysmal activity when the paw pinch reflex was regained. However, in two other rats the EEG returned to a pattern similar to that shown by awake animals, 4 and 21 min respectively, before the reflex was regained. These data indicate that in the pentobarbital-anaesthetized rat, presence of the paw pinch reflex is not related to the level of depression of electrical activity in the cerebral cortex, and consequently is probably not related to the level of consciousness. Based upon these findings it is concluded that the paw pinch reflex is unreliable as a sole indicator of anaesthetic depth.

Effect of stimulating peripheral and central neural pathways on pharyngeal muscle contraction timing during swallowing in dogs.

The effect of stimulating peripheral and central neural pathways on the electromyographic activity in the hyopharyngeal, thyropharyngeal, and cricopharyngeal muscles was studied in eight dogs during 1) eating, 2) unilateral electrical stimulation of the superior laryngeal nerve, and 3) unilateral electrical stimulation of the solitary nucleus. The duration of pharyngeal swallowing was significantly shorter during eating than during stimulation of the solitary nucleus in the anesthetized dog (mean difference 127 ms, SEM 9, n = 15). The duration of pharyngeal swallowing was significantly shorter during eating than during stimulation of the superior laryngeal nerve in the awake dog (mean difference 84 ms, SEM 13, n = 9). The duration of pharyngeal swallowing during stimulation of the superior laryngeal nerve under anesthesia was significantly shorter than during stimulation of the solitary nucleus under anesthesia (mean difference 58 ms, SEM 18, n = 9). The difference in duration of pharyngeal swallowing during stimulation of the superior laryngeal nerve between the awake state and during anesthesia was not significant (mean 19 ms, SEM 14, n = 9). It was concluded that stimulation of peripheral and central neural pathways resulted in different pharyngeal muscle contraction timing during swallowing in dogs.

Comparison of air- and bone-conducted brain stem auditory evoked responses in young dogs and dogs with bilateral ear canal obstruction.

Brain stem responses to air- and bone-conducted stimuli were analyzed in 11 young dogs, using an in-the-ear transducer and a vibrator designed for human hearing tests, respectively. The mean thresholds were 0 to 10 dB for air-conducted stimuli and 50 to 60 dB for bone-conducted stimuli. The wave forms and inter-peak latencies of the waves of the auditory evoked responses elicited by air-conducted and bone-conducted stimuli were similar. This indicated that the signals had the same origin and thus both the air-conducted and the bone-conducted responses could be considered to be auditory responses. Measurement of air-conducted and bone-conducted brain stem-evoked responses in five dogs with bilateral chronic obstructive ear disease revealed thresholds of 50 to 60 dB for air-conducted stimuli and 60 to 70 dB for bone-conducted stimuli. By comparison of these results with those in the 11 young dogs, it could be concluded that there was hearing loss other than that caused by obstruction of the ear canals.

Immunoglobulin concentrations in nasal lavage fluids in dogs with non-specific rhinitis.

The pathophysiology of non-specific chronic rhinitis(NSCR) in dogs is still unknown. In this study the possible role of immunological mechanisms in NSCR is examined, by comparing immunoglobulin concentrations in nasal lavage fluids of dogs with NSCR with those of healthy dogs. The immunoglobulin IgA was detected in nasal lavage fluids of both groups of dogs and the differences in relative levels of IgA in dogs with NSCR were not significant. IgM, IgG(a,b), and IgG(d) were detected more frequently in dogs with NSCR (P<0.05), and the relative levels were higher. The presence of IgG(a,b) may indicate the chronic character of rhinitis, and the presence of IgG(d) the possibility of an allergic component in its pathophysiology. The role of IgM is not completely clear.