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Query: UMLS:C0015672 (fatigue)
 51,768 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Susceptibility to auditory fatigue was studied in young hamsters by using an evoked-potential criterion of sound-induced threshold shift. Animals aged 15, 28, 40, 54 and 85 days were anesthetized and stimulated with a continuous tone (3 kHz, 110 dB SPL) for 10 min. Threshold shifts 1 min post-exposure were highest in animals aged 40 days, and lowest in animals aged 15 or 85 days. Threshold shifts recovered within 100 min in 15- and 85-day-old animals, but required considerably longer to recover in the other age-groups. The data suggest that young hamsters pass through a critical period of susceptibility to auditory fatigue. Comparison of this critical period with various indices of the development of hearing in the hamster suggests that the developmental events underlying the critical period do not occur in the middle ear.
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PMID:Developmental changes of susceptibility to auditory fatigue in young hamsters. 66 55

The purpose of these experiments was to determine the incidence of the middle ear reflex in response to several nonacoustic (tactile and air jet) stimuli among subjects with normal hearing who had an acoustic reflex and selected patients with severe hearing loss. The results demonstrate that the incidence of response to tactile stimulation increases as the facial area stimulated approaches the auricle. The response to an air jet stimulus directed toward the eye is high; however, the clinical utility of the air jet may be limited because it often results in a startle reaction and head movement, and the response appears to fatigue easily. In normal listeners the response to auricular air jet stimulation probably results from both acoustic and tactile stimulation. The presence of a reflex to tactile stimulation, together with normal tympanometry constitutes strong evidence of a normal middle ear; but the absence of a reflex to acoustic or tactile stimuli still leads to an ambiguous determination of potential stapedial muscle function.
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PMID:Nonacoustic stimulation of the middle ear muscle reflex. 111 36

By means of extratympanic phonometry, the middle ear muscular reflex activity in the startle reaction was measured in a control series, in patients with otosclerosis and in patients with operation cavaties without a functioning tensor tympani muscle. In comparison with the stapedius reflex, the startle reflex was found to be much more variable regarding latency, amplitude, and configuration. It was characterized by pronounced fatigue and a high alertness dependence. The period of latency was about 60 msec. It was possible to elicit a distinct startle reflex in operation cavities without a functioning tensor tympani muscle, probably because of contraction of the Eustachian tube muscles.
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PMID:Middle ear reflex activity in the startle reaction. 113 Nov

Alloplastic materials have been used in middle ear reconstruction since 1952. Biologically, biomaterials and specifically ceramics can be defined as being bioinert, bioactive or biodegradable; these terms being descriptive of the biochemical response provoked by the material in the host tissue. Various ceramics, carbons and polymers and their reactions have been studied by the author and his colleagues over the past 5 years utilising animal implantation and fibroblast culture studies aligned with experience from clinical usage. The qualities of the ideal alloplastic implant namely: biocompatibility, stabilisation and incorporation, the consistency of the implant and bioactive bonding and the biofunctionality or mechanics, are applied to the materials currently available. No single alloplastic material fulfills all criteria, the problems encountered in relation to the biomaterials are reported. A better understanding of the microstresses, fatigue and microfractures is necessary, before the ideal alloplastic biomaterial becomes available.
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PMID:Problems in alloplastic middle ear reconstruction. 160

The muscle fiber types and sizes in the M. stapedius (middle ear muscle) of the domestic chicken, Gallus gallus were determined histochemically on the basis of their reactions to myofibrillar adenosine triphosphatase (mATPase), succinic dehydrogenase and NADH diaphorase. Only type II fibers were identified at pH 9.4 and 4.2. At pH 4.6 three levels of activity were seen: high, intermediate and low. With the staining techniques three subtypes of fibers for oxidative enzymes, Types II1 (highly glycolytic), II12 (intermediately glycolytic and lipolytic) and II123 (highly lipolytic) were identified. Fiber diameter was also measured for the different fiber types. The average fiber diameter was around 20 micron for each fiber type. Although similar in size, the fiber types were markedly different in their histochemical properties. These findings plus those of earlier physiological studies suggest that the M. stapedius of G. gallus is a fast twitch, muscle with fibers of similar diameter showing mainly fatigue resistance characteristics.
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PMID:A histochemical characterization of muscle fiber types in the avian M. stapedius. 288 51

When divers are exposed to extreme atmospheric pressures they may exhibit symptoms of the high pressure nervous syndrome (HPNS). Although clinical HPNS symptoms are well described, little is known about the underlying pathophysiologic mechanisms. Special HPNS signs like vertigo and tremor suggested sensory-motor hyperexcitability resulting from brainstem dysfunction. We therefore studied brainstem auditory evoked potential (BAEP) repeatedly in four divers during an experimental deep helium-oxygen saturation dive to 450 meters of seawater (msw). Wave I (auditory nerve response) latency decreased whereas interpeak latencies (IPLs) I-III and I-V, which indicate respective cochleo-pontine and cochleo-mesencephalic transmission time, prolonged during the dive. IPLs III-V also prolonged the dive, but with greater variability among divers. Two divers showed a marked reversal of the normal attenuation effect of increased stimulus presentation rates on IV and V amplitudes during compression, an effect that subsided during the stay at bottom depth. This finding might indicate a relative enhancement of synaptic excitability and is presumed to be a feature of HPNS. Wave I latency reduction might at least partly be caused by accelerated sound conduction in dense helium. Additionally, an upward shift of middle ear resonance frequencies in helium can induce a basal shift of the main cochlear portion responding to the wide band clicks. This effect may reduce wave I latency due to greater relative input from the basal high frequency-short latency-cochlear neurons. Pressure-induced decrease of nerve conduction velocity, delay of synaptic transmission, and inhibitory modulation of midbrain auditory afferents possibly contributed to observed interpeak latency prolongations. Clinical HPNS signs, such as tiredness, dizziness, postural and intentional hand tremor, ataxia, and opsoclonus, were noted in three divers after reaching 300 msw and continued throughout the 37-h stay at bottom depth.
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PMID:Brainstem auditory evoked potentials during a helium-oxygen saturation dive to 450 meters of seawater. 758 Jul 64

The influence of contralateral white noise with levels of 50 and 60 dBnHL on the amplitude of distortion-product otoacoustic emissions (DPOAE) was measured. Thirty ears of normally hearing adults (17 women, 13 men, mean age 26.5 +/- 5.3 years) were examined. Two representative DPOAE frequencies 2f1-f2 = 1342 Hz and 6341 Hz were compared. The lower DPOAE frequency was placed in the frequency region where middle-ear pressure has a strong influence on DPOAE amplitudes, the higher DPOAE frequency respectively in the region where lesser influence is exerted by middle-ear pressure. During the application of contralateral white noise a statistically significant total of 85% of DPOAE amplitudes was reduced, although there was some variation in the individual behaviour of DPOAE amplitudes. In general the higher DPOAE frequency (6341 Hz) was reduced distinctly less than the lower DPOAE frequency (1342 Hz). The reaction of DPOAE amplitude depended closely on the time course of the contralateral stimulus and amplitude reductions were present over 10 minutes without adaptation or fatigue. It is not possible to differentiate between middle-ear or inner-ear mediate effects but the middle ear is at least involved. Based on the presence of those DPOAE amplitude reductions over ten minutes without adaptation or fatigue and the fact that lower frequencies are influenced much more than higher frequencies a synergistic effect--middle-ear and efferent mediated--is suggested.
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PMID:[Effect of contralateral noise exposure on otoacoustic distortion product emissions in man]. 775 53

Two cases of cerebral arterial gas embolism (CAGE) occurred after a decompression incident involving five maintenance crew during a cabin leakage system test of a Hercules C-130 aircraft. During the incident, the cabin pressure increased to 8 in Hg (203.2 mm Hg, 27 kPa) above atmospheric pressure causing intense pain in the ears of all the crew inside. The system was rapidly depressurized to ground level. After the incident, one of the crew reported chest discomfort and fatigue. The next morning, he developed a sensation of numbness in the left hand, with persistence of the earlier symptoms. A second crewmember, who only experienced earache and heaviness in the head after the incident, developed retrosternal chest discomfort, restlessness, fatigue and numbness in his left hand the next morning. Both were subsequently referred to a recompression facility 4 d after the incident. Examination by the Diving Medical Officer on duty recorded left-sided hemianesthesia and Grade II middle ear barotrauma as the only abnormalities in both cases. Chest X-rays did not reveal any extra-alveolar gas. Diagnoses of Static Neurological Decompression Illness were made and both patients recompressed on a RN 62 table. The first case recovered fully after two treatments, and the second case after one treatment. Magnetic resonance imaging (MRI) of the brain and bubble contrast echocardiography performed on the first case 6 mo after the incident were reported to be normal. The second case was lost to follow-up. Decompression illness (DCI) generally occurs in occupational groups such as compressed air workers, divers, aviators, and astronauts. This is believed to be the first report of DCI occurring among aircraft's ground maintenance crew.
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PMID:Cerebral arterial gas embolism in air force ground maintenance crew--a report of two cases. 1041 7

Loss of weight, dehydration, pregnancy, fatigue, and otitis media are among the factors proposed as causes of a patulous eustachian tube, but true details remain obscure. We studied patients who developed a patulous eustachian tube following otitis media and discuss the relationship between these 2 conditions. Subjects were 12 patients diagnosed with otitis media at our department who later developed a patulous eustachian tube. The initial middle ear disease progressed from acute otitis media to otitis media with effusion in 2, acute otitis media in or acute mastoiditis in 1 each, and otitis media with effusion in the remaining 8 patients. Seven patients evidenced a low body mass index (BMI), weight loss, and underlying disease, but 5 with a patulous eustachian tube following otitis media did not. We retrospectively analyzed 119 patients diagnosed with a patulous eustachian tube in our department for whether they had been diagnosed by an ENT physician as having otitis media, i.e., acute otitis media or otitis media with effusion. Some 42 (35.3%) had a history of otitis media. At acute otitis media or otitis media with effusion, the tympanic cavity becomes inflamed, accompanied by inflammation of the eustachian tube mucosa and a stenotic tendency. Healing from otitis media is accompanied by decreased eustachian tube mucosa inflammation. We surmise that, depending on how inflammation disappears, fibrosis of the eustachian tube mucosa occurs, leading to a pathologically patulous eustachian tube. Many aspects of the causation of this condition remain unclear, but we surmised that in patients with earlier otitis media, a pathological patulous eustachian tube develops during resolution of inflammation. Our findings indicate the involvement of otitis media as a causative factors in a patulous eustacian tube.
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PMID:[Patulous eustachian tube following otitis media]. 1463 69

Bones serve several mechanical functions, including acoustic amplification in the middle ear, shielding vital organs from trauma, and serving as levers for muscles to contract against. Bone is a multiphase material made up of a tough collagenous matrix intermingled with rigid mineral crystals. The mineral gives bone its stiffness. Without sufficient mineralization, bones will plastically deform under load. Collagen provides toughness to bone making it less brittle so that it better resists fracture. Bone adapts to mechanical stresses largely by changing its size and shape, which are major determinants of its resistance to fracture. Tissue is added in regions of high mechanical stress providing an efficient means for improving bone strength. Experiments have shown that small additions of bone mineral density (BMD) (5-8%) caused by mechanical loading can improve bone strength by over 60% and extend bone fatigue life by 100-fold. Consequently, it is clear that bone tissue possesses a mechanosensing apparatus that directs osteogenesis to where it is most needed for improving bone strength. The biological processes involved in bone mechanotransduction are poorly understood and further investigation of the molecular mechanisms involved might uncover drug targets for osteoporosis. Several pathways are emerging from current research, including membrane ion channels, ATP signaling, second messengers, such as prostaglandins and nitric oxide, insulin-like growth factors, and Wnt signaling.
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PMID:Bone strength: current concepts. 1683 41


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