Biomedical subjects
Publications and source records attributed to R J McClelland.
The nature and extent of psychological and social disability following head injury remain issues of considerable practical and theoretical interest. Practical because of the size of the problem and the resulting burden of care; theoretical because head injury should provide a powerful model for an improved understanding of the relationships between cerebral disorder and psychological impairment.
A successful feature of the 4th-year curriculum in the Medical Faculty of the Queen's University, Belfast has been the development of interdisciplinary teaching in a three-week joint course to which several clinical departments contribute...Co-ordinated teaching of topics of common interest in small groups included, until the academic year 1987/88, a three-hour session on medical ethics. In the spring of 1987 the authors approached the Department of Philosophy at Queen's; subsequently proposals for a formal multidiscipinary course in medical ethics for 4th-year clinical students in the Medical Faculty, for the academic year 1987/88, were approved by the Education Committee of the Medical Faculty.
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This study of auditory brainstem potentials in 123 normal hearing subjects examines the contributions of age and gender to intersubject variability of the response form and latency. The main features, wave I, wave III, and wave V, and the I-V interval were separately examined in premature infants, neonates, infants, children, and young adults. Perinatal changes in response latency were confirmed and significant additional shortening in the I-V interval was observed through childhood and adolescence. Significant gender differences in I-V interval were also observed in both children and adults. Whereas the age changes were consistent with the effects of myelination on conduction time, the nature and magnitude of the gender differences were in keeping with the differential growth changes in the central nervous system, reflected in the skull diameters of females and males. These two sources of intersubject variability, age and gender, should be considered when using the auditory brainstem potentials in clinical studies.
Sedation is widely used to improve the quality of auditory brain stem response (ABR) recording. This study demonstrated a small but significant increase in I-V interval following diazepam administration. There was no apparent effect on the ABR amplitudes.
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The amplitude spectra of the auditory brainstem potentials evoked by free-field stimuli revealed significant differences from the corresponding spectra of pre-stimulus records. This was most marked for low order harmonics and in response to high intensity stimuli. In general, however, the shape of the amplitude spectrum for pre-stimulus and post-stimulus epochs was similar and the magnitude of the differences between corresponding harmonics became progressively smaller as stimulus intensity was reduced. Given that the spectrum of each coherent grand average is a function of the amplitude and phase spectra of the response ensemble, these were separately examined. Ensemble mean amplitude of individual harmonics diminished with stimulus intensity while their phases became progressively less aggregated. Phase standard deviation, used as a parameter of this aggregation, was found to change more systemically with stimulus intensity than ensemble mean amplitude. Phase standard deviation values for threshold responses were generally significantly smaller than corresponding harmonics obtained from sub-threshold responses. By contrast the amplitude differences between populations of threshold and sub-threshold responses were generally non-significant. These findings suggested that fully objective methods of threshold determination might more successfully be based on ensemble phase measures rather than amplitude measures.
The advent of the microprocessor, and its incorporation in relatively low-cost microcomputer systems, offers a new range of possibilities for the recording of evoked and event-related potentials. A flexible system for recording evoked potentials, entitled DAN, has been developed using an Apple microcomputer. The main objective in developing DAN was to make it sufficiently flexible so that it could be used in both a research and a clinical environment for a wide range of responses, from the auditory brainstem to much slower cortical responses. A specific response can be selected from a standard range of evoked responses, or if a non-standard response is required, it is a simple matter to specify the response stimulus parameters, time duration and data sampling rate. This degree of versatility is achieved by designing a programmable audiometer, a special-purpose hardware interface for the Apple and software to generate the stimulus and control the data-acquisition interface. The main hardware components of the DAN system are listed (a) Apple microcomputer operating under U.C.S.D. PASCAL operating system; (b) dual 5 1/4 inch floppy disk drives and controller; (c) Video monitor; (d) DAN data-acquisition interface; (3) programmable audiometer; (f) Epson MX-80 printer/plotter. Disk drive 1 of the dual drive set is used to store the PASCAL operating system and the DAN programs. Drive 2 is used to store the data. The data-acquisition interface and audiometer interface plug into slots in the Apple. The software includes routines to generate the stimulus and store it in the audiometer prior to the data-acquisition phase.(ABSTRACT TRUNCATED AT 250 WORDS)
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The potential usefulness of the auditory-evoked brain stem potentials in audiological assessment has been the subject of increased clinical enquiry. Several requirements need to be met by any response parameter if it is to be clinically useful: parameters should show a clear, and ideally simple, relationship with stimulus intensity; they should be stable within any subject under fixed stimulation conditions and intersubject variability within any clinical group should be small. Response latency has been shown to satisfy the first two of these conditions. However, intersubject variability has been less clearly defined. In a sample of normal controls we have found that the standard deviation of latency at any specific intensity was substantial, exceeding the difference found between mean responses at neighbouring intensities of auditory stimulation. In an investigation of the origins of this variability we have found a clear gender difference, maximal for later components in which the male responses were significantly later than the female responses. The clinical significance of this finding can be seen in the latency intensity input/output function. By treating each gender group separately, intersubject variance values were reduced by approximately 40% compared with the total group variance, so enhancing the usefulness of latency as a parameter in the objective assessment of auditory function.