Scottish GPs to be sent discussion packs on MMR vaccine.
Explore the source record for details and available documents.
Humans↗
Biomedical subjects
H Barratt
Publications and source records attributed to H Barratt.
MMR vaccine row raises questions of clinical freedom.
Explore the source record for details and available documents.
Humans↗
Intraoperative monitoring of the electrocochleogram and the preservation of hearing during acoustic neuroma excision.
We have monitored the electrocochleogram (ECochG) of 24 patients, using a transtympanic electrode, during acoustic neuroma excision. All patients had unilateral tumours with good preoperative hearing and complete excision was achieved in each case. Of the 24 patients, seven retained some hearing, however, a further two patients had normal ECochG waveforms at the end of operation but were nevertheless deaf. Thus, there is not an invariable correlation between immediate preservation of the ECochG and hearing. As expected, tumour size was important in hearing preservation. Five of seven patients with tumours less than 1.5 cm in diameter retained some hearing after operation, whereas 15 of 17 patients with tumours greater than 1.5 cm in diameter were deaf.
Audiometry, Evoked Response↗
Eye movement responses to combined linear and angular head movement.
Lateral eye movements evoked by linear head motion were evaluated in human subjects by subtracting the eye movement responses to head-centred angular oscillation in the dark, about a vertical axis, from the responses evoked by similar oscillation with the head displaced 30 cm eccentrically from the axis. The centred oscillation gave a purely angular stimulus whereas the eccentric oscillation gave an additional tangential linear acceleration acting laterally to the head. The stimuli used were relatively unpredictable, enveloped sinewaves at 0.02 to 1.2 Hz, 60 degrees/s peak angular velocity, 0.004 to 0.24 g peak tangential acceleration, and subjects were either given no instructions or were told to imagine fixating on targets at 60 cm or 5 m distance. Eye movements of significantly higher velocity were evoked in the eccentric position, particularly at the higher frequencies and when subjects imagined near targets. The increase in velocity of eye movement was attributed to the linear stimulus and probably derives from stimulation of the otolith organs. The frequency response of the gain (degree/s/g) of these movements gave an approximate slope of -1, indicating that the eye velocity bears a constant proportionality to linear head velocity. The findings are in accord with the theoretical prediction that eye movements compensating for linear head motion should only be required for viewing near targets. These otolithic influences on eye movements could either the mediated by a direct "otolith-ocular reflex" which is subservient to viewing conditions, or, alternatively, the otolith signals may modify the activity of other oculomotor mechanisms.
Acceleration↗
Testing the vestibular-ocular reflexes: abnormalities of the otolith contribution in patients with neuro-otological disease.
Conventional vestibular rotation testing with the head centered on the axis stimulates the semicircular canals evoking compensatory eye movements. If the head is placed forwards of the axis in an eccentric position the otoliths are also stimulated by a tangential linear acceleration acting laterally to the skull. In normal subjects the additional otolithic stimulus evokes compensatory eye movements with a higher gain than with head centred, particularly for high frequency (greater than 0.1 Hz) stimuli. The responses with head centred and eccentric in various patients with known/suspected neuro-otological abnormalities have been compared. Patients with vestibular neurinectomies who have asymmetrical head centred responses showed greater asymmetry with head eccentric at higher stimulus frequencies. Some patients with cerebellar lesions showed abnormally enhanced or depressed and asymmetrical responses with head eccentric in comparison with head centred responses, which could be normal. The enhancing effects could be specific to low frequency stimuli. All patients who showed abnormal responses with head eccentric also had positional nystagmus provoked by the gravity acceleration vector when the head was tilted laterally. The direction of the positional nystagmus with respect to the gravity vector was not necessarily the same as the direction of the effect on eye movements of lateral acceleration during eccentric oscillation. Patients with benign paroxysmal vertigo or chronic linear vertigo in whom otolithic abnormalities are suspected were not found to have abnormal responses with head eccentric. We conclude that this method of testing may be useful in elucidating pathophysiology but is not a decisive clinical test for the presence of disordered otolith function.
Acceleration↗
Analysis of downbeat nystagmus. Otolithic vs semicircular canal influences.
The relative strengths of vertical canal and otolithic factors influencing downbeat nystagmus (DBN) were investigated in a patient whose nystagmus was of maximum intensity with the head in the upright position and abolished with the head in the supine position. The vestibuloocular reflex (VOR) was assessed by oscillating the patient about both the supine and upright positions. During oscillation about the supine position both the upward and downward VORs had equal gains in the dark (0.6) and unity gain in the light. In contrast, during oscillation about the upright, the upward VOR became hyperactive with a gain of 1.8 in the dark and 1.2 in the light, whereas the downward VOR became hypoactive with a maximum gain of 0.86 in the light. This degree of asymmetry of the VOR is greater than would be expected from a summation of spontaneous nystagmus with normal canal reflexes. We concluded that the DBN arose from an asymmetry of vertical canal function, which became manifest when the otoliths were tilted with respect to gravity. Contrasting findings are presented in a patient whose DBN was insensitive to tilt. It would seem that other cases of DBN lie on a continuum between these extreme examples.
Adult↗
Magnetic resonance imaging in clinically isolated lesions of the brain stem.
Twenty-seven patients with an isolated brain stem syndrome, thought to be due to demyelination, were examined by magnetic resonance imaging (MRI). A brain stem lesion was identified in 25, and clinically silent lesions outside the brain stem were demonstrated in 20. MRI was more sensitive than evoked potentials in detecting brain stem and other lesions. The scan findings were compared with those in 23 patients with multiple sclerosis, who had chronic brain stem dysfunction, with particular reference to the distribution of abnormalities and the MRI characteristics of the lesions. The relaxation times, T1 and T2, of the lesions were measured by MRI. These values were seen to fall in serial studies of acute lesions, but remained unchanged in the chronic lesions. MRI may therefore allow the age of lesions to be assessed.
Adolescent↗
The differential diagnosis of congenital nystagmus.
The decision whether a nystagmus is congenital or acquired may be difficult and is of importance in patients presenting with neurological complaints. In this article, established diagnostic criteria are critically reviewed with particular emphasis on types of nystagmus waveform and their relationship to pursuit and optokinetic responses. Attention is drawn to certain acquired nystagmus which may have similar features which have hitherto been accepted as pathognomonic of congenital nystagmus. Symptoms due to congenital nystagmus are discussed and related to the oculomotor abnormalities. The importance of the characteristics of congenital nystagmus are evaluated for use in differential diagnosis.
Diagnosis, Differential↗
Tonal adaptation.
The loudness of a continuous pure tone does not appear to change with time unless an interrupted tone is introduced at intervals during the course of the test; in consequence it is held that it is the interrupted tone which induces the loudness loss. This, however, cannot be called on to account for the marked change in quality or 'timbre' of a sustained pure tone which occurs over a period of time and which has the attributes of 'tonal adaptation', matching the time course of loudness adaptation revealed by dichotic loudness balance and other procedures. It is argued that the latter have to do with the measurement of sensation while judgement of the loudness of a continuous tone in isolation involves higher-order perceptual processes.
Acoustic Stimulation↗
Normal variation in the masking effectiveness of the narrow band noises of one audiometer.
The minimum effective masking levels (MEMLs) of the narrow band masking noises (audiometric frequencies 0.25-4 kHz) of one audiometer were determined for a sample of 40 normal individuals. The variation in MEML was rather wide but it decreased with increasing frequency. After consideration of the plateau procedure for masking, it is recommended that the starting level of masking should be: Threshold of masking+mean MEML+10 dB. This should be sufficient to prevent finding false plateaux and hence obviate the possibility of obtaining a threshold for the test ear which in fact relates to the non-test ear.
Adult↗
Investigation of the mastoid electrode contribution to the brain stem auditory evoked response.
The auditory nerve and bran stem responses recorded at the vertex and mastoids were closely examined in normal subjects using a larynx electrode as a neutral reference point. With monaural stimulation, significant activity was found at the vertex and both mastoids, and the wave-forms at the ipsi- and contralateral mastoids were consistently different. With binaural stimulation the small amplitude mastoid response were largely in phase with the vertex response. The implications of the findings are discussed.
Acoustic Stimulation↗
Neurological evidence for dissociation of pursuit and optokinetic systems.
Patients with neurological disease were examined for dissociations between the performance capabilities of pursuit, immediate onset passive and active optokinetic responses to determine whether these functions are subserved by separate mechanisms. We found a patient in whom pursuit was intact in the presence of severely impaired optokinetic responses and another in whom optokinetic responses were intact in the presence of severely deranged pursuit. These dissociations suggest that pursuit and immediate onset optokinetic responses are mediated, to some extent, by separate mechanisms as the results are not explicable in terms of a continuum of performance ability related to target size. Another patient, who had virtually no pursuit or passive optokinetic responses, produced high slow phase velocities of active optokinetic response, which demonstrates that the active form of optokinetic response can be more than a linear addition of pursuit and passive optokinetic responses.
Adult↗