A longitudinal study of hearing loss was conducted among a group of lumberjacks in the years 1972 and 1974-8. The number of subjects increased from 72 in 1972 to 203 in 1978. They were classified according to (1) a history of vibration-induced white finger (VWF), (2) age, (3) duration of exposure, and (4) duration of ear muff usage. The hearing level at 4000 Hz was used to indicate the noise-induced permanent threshold shift (NIPTS). The lumberjacks were exposed, at their present pace of work, to noise, Leq values 96-103 dB(A), and to the vibration of a chain saw (linear acceleration 30-70 ms-2). The chain saws of the early 1960s were more hazardous, with the average noise level of 111 dB(A) and a variation acceleration of 60-180 ms2. When classified on the basis of age, the lumberjacks with VWF had about a 10 dB greater NIPTS than subjects without VWF. NIPTS increased with the duration of exposure to chain saw noise, but with equal noise exposure the NIPTS was about 10 dB greater in lumberjacks with VWF than without VWF. With the same duration of ear protection the lumberjacks with VWF consistently had about a 10 dB greater NIPTS than those without VWF. The differences in NIPTS were statistically significant. The possible reason for more advanced NIPTS in subjects with VWF is that vibration might operate in both of these disorders through a common mechanism-that is, producing a vasoconstriction in both cochlear and digital blood vessels as a result of sympathetic nervous system activity.Subjects exposed to occupational vibration are also often exposed to excessive noise levels. In laboratory experiments noise has been shown to assist the vasosconstriction produced by vibration,' probably by activating the sympathetic nervous system. Simultaneous exposure to vibration also seems to act synergistically with noise to cause a noiseinduced permanent threshold shift (NIPTS).2 3The frequency range,4 intensity,5 duration,6 and impulse characteristics of the noise7 are physical properties related to the vulnerability to noise. It has been suggested that the variability in the effect of noise on different subjects depends on differing hair cell metabolism or differing blood flow characteristics8 or middle ear mechanisms and anatomical factors9 or both.An overactive sympathetic vasoconstrictor reflex
There is a lack of knowledge about the effect of electroconvulsive therapy (ECT) on auditory event-related potentials (ERPs) in severe psychotic depression. The aim of this study was to investigate both the effect of ECT on attention-dependent ERP (P300) and the correlation of P300 values with depression level. We recorded the auditory ERPs of 23 patients expressing psychotic symptoms and fulfilling the DSM-III-R criteria for treatment-resistant severe major depressive episode before and a week after successful bitemporal ECT. The clinical status was assessed with Hamilton (Ham-D) and Montgomery and Asberg (MADRS) depression scales. ECT was clinically very effective with these scales. On the level of auditory processing, ECT increased P300 amplitude with no significant effect on latency. Small amplitudes over the left hemisphere before treatment were associated with bigger Ham-D-score decrement. ECT produces a significant increase in brain activity at the level of attention-dependent auditory processing in severe depression. The change in electrical responses seems to represent a largely independent variable from the clinical assessment scales, even if the recovery rate was remarkable, because the change in overall symptom scores did not correlate with the P300 changes.
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