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Biomedical subjects

P Lycett

Publications and source records attributed to P Lycett.

10 recordsLinked to original sources
PubMed1983

Vestibular asymmetry. Some theoretical and practical considerations.

Pathological vestibular asymmetry can be divided into static and dynamic types. Static asymmetry results from a unilateral change of the resting neural input. Acute, chronic, and recovery stages can be recognized if one interprets the direction and intensity of the resultant spontaneous nystagmus relative to the clinical picture. Static asymmetry is additive with induced asymmetry and manifests itself as directional preponderance or as the direction-fixed or direction-changing feature of positional nystagmus. Dynamic asymmetry refers to abnormal asymmetry induced by normal head movements. For example, with unilateral hypofunction, a greater gain is observed with head movement toward the unaffected side, suggesting nonlinearity as specified by Eswald's second law. Visually induced vestibular asymmetry is a form of dynamic asymmetry generated by convergence of visual-vestibular information, and causing symptoms in certain "motion-active" visual environments.

Eye Movements↗
PubMed1982

Diazepam as an anti-motion sickness drug.

Diazepam has been used empirically for the relief of vertigo and, in addition, there are animal studies to suggest that this drug suppresses the vestibular system. One might anticipate therefore that diazepam would be an effective antimotion sickness drug. To study this, motion sickness was generated in four groups of normal subjects by having the subject make controlled head movements while rotating at constant velocity. Every subject was subjected (using a double-blind technique) to four different drug states, namely no drug, placebo, dimenhydrinate, and diazepam. Each group of subjects received the drug state at a different time interval (i.e. 30, 60, 90, and 120 min) prior to the motion sickness exposure. Motion sickness endpoints were measured subjectively using a nausea scale and objectively using a sweat sensor. The results showed significant antimotion sickness properties for both dimenhydrinate and diazepam as compared to the placebo. For the time intervals studied, the maximum effect was obtained at 120 min for both drugs.

Adolescent↗
PubMed1981

Recovery nystagmus in Ménière's disease.

Spontaneous nystagmus occurs during a Meniere's attack although the literature indicates that the direction can be variable. Previous observations made during the acute and recovery stages of a Meniere's attack suggested that the direction of the spontaneous nystagmus was consistent with the primary-secondary sequence of nystagmus that occurs with relatively prolonged stimulation of the normal vestibulo-oculomotor system. To evaluate this nystagmus pattern further, spontaneous nystagmus was monitored in eight patients using DC electronystagmography during an acute Meniere's attack. All showed an initial contralateral nystagmus during the acute phase of the attack with reversal to an ipsilateral (or recovery) nystagmus, as the acute symptoms subsided. Such a pattern of nystagmus occurring over a few hours is a helpful diagnostic aid, and when surgery is being considered, it provides objective evidence of the ear with active disease.

Adult↗
PubMed1980

Effect of round window removal on auditory thresholds in cats.

Round window fistula is a recognized and proven pathological entity that can cause sudden hearing loss. The study reported here, using cats, measured changes in the brainstem evoked response threshold to click stimuli after total removal of the round window membrane. The results showed an immediate 25 dB threshold decline followed by a further 35 dB decline over four hours. The response threshold then remained constant for 20 hours. In one animal there was no response to a stimulus of 110 dB SPL immediately post-op, and this animal, on re-examination, had a hole in the basilar membrane. In two animals, a membrane formed spontaneously over the round window area. In one, the response threshold did not change postoperatively, and in the other the threshold partially recovered following an initial decline.

Animals↗
PubMed1978

Recovery nystagmus.

Secondary nystagmus is frequently seen following cessation of prolonged unidirectional vestibular stimulation. It is explained on the basis of an adaptation during the application of the stimulus which leads to an apparent stimulus in the opposite direction when the stimulus is removed. The same phenomenon would be expected with vestibular disease when after a period of adaptation to the vestibular asymmetry, the affected ear recovers some or all of its function. The seondary nystagmus in this instance beats toward the affected ear and has been termed recovery nystagmus because it is generated by recovery of function. Two cases with recovery nystagmus following acute attacks of vertigo are presented.

Adaptation, Physiological↗
PubMed1977

Vestibular dysfunction associated with benign paroxysmal vertigo.

Benign paroxysmal vertigo (BPV) is a clinical syndrome of vestibular origin although generally no evidence of vestibular dysfunction can be demonstrated with conventional tests. In a review of 1350 consecutive dizzy patients, there were 125 with BPV and of these, 33 underwent a quantitative rotational test of vestibular function. The rotational results showed reduces vestibular system gain for these BPV patients. In addition, they could be subdivided on the basis of a normal or shorter cupular time constant (Tc). Separation of patients into diagnostic categories revealed that those categorized as cupulolithiasis and viral labyrinthitis had a normal Tc range and those categorized as trauma and idiopathic had a short Tc. The reduced gain and short Tc in the latter group suggest hair cell and/or nerve damage since these same changes occur in patients with destructive peripheral vestibular disease.

Adult↗
PubMed1976

A quantitative rotational test of vestibular function.

This paper describes a quantitative vestibular test in which the stimulus is a constant angular acceleration of 3 degrees/sec2 for 80 sec. The nystagmus output is plotted as cumulative slow phase eye displacement against time and is displayed on an oscilloscope screen along with the output from a mathematical model describing vestibulo-oculomotor function. External dials allow one to change the equation constants thereby altering the shape of the model output. Values for equation constants which match the model output to the patient can be read directly from the dials, thus providing a description of the vestibular system under test. Results indicate that vestibular asymmetry (manifest by spontaneous nystagmus is not uncommon in normals, and only when spontaneous nystagmus is coupled with vestibular gain does one get a measure of abnormality. The significance of altered vestibular parameters in certain pathological states is discussed.

Acceleration↗
PubMedDate not supplied

Effect of high perilymphatic potassium on brainstem evoked response audiometric thresholds.

The perilymphatic space of the cat cochlea was perfused with a solution containing a high potassium ion concentration. The auditory response threshold was monitored with brainstem evoked response audiometry. In the majority of animals the initial perfusion produced a reversible decline in response threshold. With repeat perfusions, there was a variable degree of non-reversible response decline leading ultimately to a total loss of the auditory response.

Animals↗