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Biomedical subjects

D McPherson

Publications and source records attributed to D McPherson.

26 records · Page 2Linked to original sources
PubMed1985

Acute negative intracranial pressure effects on the auditory evoked response in rabbits.

Recent clinical experience has shown that significant neurological symptoms and deficits occur in patients who have been shunted for hydrocephalus when "overshunting" produces unusual negative intracranial pressure (ICP). Therefore, the effect of acute negative ICP .on the early auditory evoked response (AER) was studied in the normal New Zealand rabbit. ICP was reduced to -50, -100, and -150 mm H2O below base line pressure. The AER after rarefaction auditory stimulation was obtained from ongoing electroencephalographic activity at the base line ICP and at each of the three negative ICP levels. Off-line statistical evaluation of the AER showed minimal changes in the absolute and interpeak latencies of N-0 to P-5 at some negative pressures. However, no statistically significant changes were observed for any of the measures for grouped data. At the negative ICP levels studied, the cerebrospinal fluid (CSF) pulse pressure was considerably augmented over base line measures. Such augmentation of the CSF pulse pressure may be the cause of the minimal effects observed on the AER, which may be due to a neuropraxic effect rather than ischemia from cerebral perfusion pressure changes.

Animals↗
PubMed1984

Intracranial pressure effects on auditory evoked responses in the rabbit: preliminary report.

Acute elevated intracranial pressure (ICP) effects on the auditory evoked response (AER) were studied in the rabbit. Simultaneous CSF infusions to increase ICP and contralateral ICP pressure recordings were done through bilateral ventriculostomies. During rarefaction auditory stimulation, a minicomputer obtained a time-locked AER from ongoing electroencephalographic activity at base line ICP mean pressure and at three levels of increased ICP (250, 500, and 700 mm CSF) above base line. The results showed a statistically significant increased latency of the N3-P3 portion of the AER as well as of the P1-P3 central conduction time. The amplitude of AERs appeared unchanged. The effect is reversible and presumably is a neuropraxic type pressure effect on brain stem auditory pathways. Its clinical relevance is discussed.

Acoustic Stimulation↗
PubMed1975

Experimental aural barotrauma. Electrophysiological and morphological findings.

The electrophysiological findings show a time and pressure related decrease in function of the CM and the N1 potentials. Sudden changes were correlated with tympanic membrane perforations. Some of the decreased function is accounted for by middle ear effusion and hemorrhages, reducing mechanically the transmission of sound energy through the middle ear. This was evidenced by an improvement of function when the fluids were removed. Remaining decreases in function were interpreted as a result of influences on the inner ear function or of undisclosed middle ear changes. No differences were noted in cochlear function between animals subjected to sustained or intermittent middle ear pressures. Neither were any morphological differences noted between these two groups in the middle or inner ear. The morphological middle ear findings correlated well with previous clinically and experimentally induced changes with increased/decreased middle ear pressure. The cochlear findings include the interesting observation of an intact round window membrane, a clear endolymph, and a normal Organ of Corti in all cases. Positive findings were a high frequency of hemorrhage, most commonly demonstrated in the scala tympani of the basal turn close to the round window. The origin of the hemorrhages could not be demonstrated with the present investigation. The hemorrhages often appeared to be related to the cochlear aqueduct. The occurrence of hemorrhage was clearly related to increased negative pressure, and the non-existence of hemorrhage was always related to either tympanic membrane perforations or low applied pressure. Further frequent findings were distention, collapse, and rupture of the inner ear membranes which must be interpreted with great circumspection due to the method used. Likewise, some of the pathological cochlear findings may be due to pathological conditions which are not necessarily related to induced middle ear pressure.

Acoustic Stimulation↗