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Biomedical subjects

L R Proctor

Publications and source records attributed to L R Proctor.

14 recordsLinked to original sources
PubMed1979

The stimulus controlled caloric tests: a reliability study.

Preliminary studies have shown that a new caloric testing method described by Proctor and Dix offers several advantages over conventional methods. However, it had not been established that the Proctor-Dix method would prove reliable and practical when routinely applied in a clinical setting. Therefore, we administered the test to 60 patients referred for evaluation of vestibular function and compared the test scores with results from the conventional Fitzgerald-Hallpike test applied during the same test session. The analysis was based on the average slow phase eye speed of nystagmus during the most intense 20 seconds of individual responses. A close agreement was found between "right-left difference" and "directional preponderance" scores when results of the Proctor-Dix and Fitzgerald-Hallpike tests were compared in the 54 patients who completed all steps in the experiment. Larger differences between the results of the two tests were confined to subjects who were "normal" or only slightly abnormal. Order effects and additional analysis of correlations are discussed. The present study demonstrates that reliable results, comparable to those obtained from conventional methods, can be obtained when the new Proctor-Dix test is applied in a clinical setting.

Caloric Tests↗
PubMed1978

Vestibular responses in schizophrenia.

In a study of vestibular responses to caloric stimulation that controlled opportunity for fixation and state of alertness, we evaluated previous findings of diminished nystagmus in schizophrenia. We failed to replicate earlier reports in these respects: (1) None of the psychotic patient groups, when compared with normal controls, showed lower response intensity, latency, or culmination time of the nystagmic response. (2) The schizophrenic groups did not manifest a prevalence of clinically significant asymmetry. We did, however, observe that chronic deteriorated schizophrenics and recent schizophrenics have significantly greater dysrhythmic responses. This diminished orderliness of nystagmus may explain previous reports of absent or diminished nystagmus in the schizophrenics. The results are not compatible with peripheral vestibular disease in schizophrenia, but they may reflect state-related phenomena consistent with disturbances in alertness, which are not necessarily voluntary or motivational in origin.

Acute Disease↗
PubMed1977

Visual interference on vestibular response. A case study.

Eliminating opportunity for visual fixation as well as providing for the maintenance of an optimal degree of a patient's mental alertness are necessary for a valid assessment of nystagmic response to caloric stimulation. Controlling only for alertness can result in suppressed, absent, or dysrhythmic nystagmus. Data from four normal patients dramatically illustrate the suppressing effects of fixation opportunity despite an alert state. A new clinical instrument for obtaining optimal control over visual influences is described.

Adult↗
PubMed1977

Abnormal-pursuit eye movements in schizophrenia. Evidence for a genetic indicator.

Disordered smooth-pursuit eye movements occur in a high percentage of schizophrenic patients and their first-degree relatives. A Test of the hypothesis that these disorders represent a genetic indicator of schizophrenia was undertaken by testing pursuit eye movements in a sample of monozygotic and dizygotic twins discordant for clinical schizophrenia. Deviant eye tracking is significantly concordant within monozygotic twin pairs, and less so with dizygotic twin pairs discordant for schizophrenia. A genetic interpretation is consistent with these results.

Adult↗
PubMed1977

Air caloric test: irrigation technique.

The technique of using air to perform the caloric test is discussed. Greater temperature differences and larger volumes of air are needed to achieve stimulations equal to those caused by water irrigations. Special consideration must be given to the design and operation of air irrigation equipment. The effects of irrigating a wet canal and of misdirecting the air jet are discussed. A new air irrigation apparatus is described.

Air↗
PubMed1976

Smooth pursuit eye movements, attention, and schizophrenia.

In previous studies, smooth pursuit eye movements (SPEM) have been shown to be disordered in about 70% of schizophrenics and about 45% of their first-degree relatives. In this report, the role of attention in these eye movements is addressed in three experiments (using as subjects schizophrenics, their first-degree relatives, and normals administered chloral hydrate) that recruit focused attention to the task. These studies show that voluntary attention in the form of inattention, "heedless negligence," or failure to cooperate, is not the specific attentional quality that is disordered in SPEM of schizophrenics and their relatives. Rather, the data both indicate that nonvoluntary attending is specifically disordered in these persons, and implicate a neurophysiological substrate that can be described as a failure of inhibitory, synchronizing integrating systems which may be located in the brain stem.

Adult↗
PubMed1976

Construction of a practical and inexpensive air stimulator for caloric vestibular testing.

An inexpensive and practical method for delivering air into the aural canal at a selected stable temperature is described. A water-air heat exchanger utilizing the external circulation of a constant-temperature water bath brings the temperature of the air stream to a chosen value. Measurements indicate stable air outflow temperatures are maintained when proper nozzle design and air flow rates are employed. The apparatus is easy to construct and has proven convenient and effective when used in the clinical vestibular laboratory.

Air↗
PubMed1975

Smooth-pursuit eye movements, and diazepam, CPZ, and secobarbital.

This study examined the effects on smooth-pursuit eye tracking of single doses of CPZ (0.667 and 1.334 mg/kg), diazepam (0.071, 0.142, and 0.284 mg/kg), and secobarbital (100 mg). Only the barbiturate significantly affected the ability to follow a moving target with smooth-pursuit eye movements. In repeated testing of a single subject, 130 mg of secobarbital disrupted smooth-pursuit movements at least until 24 hrs after ingestion.

Adult↗
PubMedDate not supplied

New approach to caloric stimulation of the vestibular receptor.

A new caloric testing method is described. During continuous aural irrigation, fluid is switched between hot and cold values at times computed according to a mathematical model of heat conduction in the labyrinth area. As a result, the induced temperature difference across the lateral semicircular canal describes an approximately sinusoidal time course, reaching peak values of equal magnitude but opposite sign. The magnitude of the caloric stimulus may be selected by choosing appropriate irrigation durations from a graph or table. Application of the test to clinical subjects demonstrated that the heat conduction model and analysis used in timing the sequence of thermal pulses was accurate. The new procedure causes less patient discomfort and requires less time to complete than does the conventional Fitzgerald-Hallpike test.

Animals↗
PubMedDate not supplied

Results of new air caloric testing method among normal subjects. I. Biphasic testing.

A new air caloric testing method is described in which the temperature of a continuous aural irrigation is switched hot and cold values at times calculated to control the intensity of the resulting vestibular stimulation. Applications of low or high caloric stimulus intensities to normal subjects were well tolerated and reliably produced appropriate low or high intensity nystagmic responses. Nystagmus intensity values obtained from this study were compared with predicted intensity values from a computerized simulation of the actual test conditions, and also with values obtained when using biphasic water irrigations. As a result, further improvements in our methodology have been effected.

Air↗
PubMedDate not supplied

Results of new air caloric testing method among normal subjects. II. Monophasic testing.

A new caloric irrigation method is described. In the new method, the temperature of a continuous aural irrigation is switched between hot and cold values at precisely specified times. The durations of hot and cold pulses have been calculated to produce specific caloric stimulation intensities based on known heat transmission characteristics of the labyrinth area. A brief "washout" irrigation is used to eliminate promptly all caloric stimulation effects at the conclusion of each test. The present study concentrated upon the question of how long the "washout" pulse should be in order to obtain optimum results. Repetitive application of a uniform stimulus intensity to 6 normal subjects indicated that short inter-test intervals can be used without causing vestibular habituation. Prompt removal of the caloric stimulus can be accomplished by proper timing the "washout" phase of the new technique.

Caloric Tests↗