Auditory Brain Stem Response Spectral Content in Comatose Head-Injured Patients

Abstract

Auditory brain stem response (ABR) spectral content was analyzed for 25 normal subjects and 70 comatose, severely headinjured subjects. The normal ABR spectrum was characterized by energy peaks in three main regions: 0 to 200 Hz, 500 to 600 Hz and 900 to 1000 Hz. Head-injured subjects, in contrast, showed less overall ABR spectral energy. Even head-injured subjects with normal ABR interwave latency values had reduced spectral energy in comparison to the normal group. Among these subjects, there were differences in spectral content for subjects with good neurologic outcome versus those who died within 2 weeks post injury. Finally, head-injured subjects with abnormal interwave latency intervals typically showed distinctive spectral patterns. This subject group demonstrated energy peaks in frequency regions which, for the other groups, were void of energy peaks. Rationale for further study of ABR spectral content is offered.The auditory brain stem response (ABR) is a complex electrophysiologic waveform typically recorded in the time domain. Analysis of ABR data usually involves determination of the absolute latency and amplitude of major wave components, and often relative latency or amplitude measures such as the wave I-V latency interval or the wave V/I amplitude ratio [see Hall (1) for review]. By means of spectral analysis techniques, it is now also possible with commercially available instrumentation to calculate the frequency composition of an ABR waveform. That is, ABR amplitude is described in the frequency domain rather than the customary time domain. ABR spectral analysis is usually done with fast Fourier transformation which deconvolutes a complex waveform into its frequency components (2, 3).There is a modest literature on the spectral content of the ABR in persons with normal peripheral and central nervous system (CNS) status (4-1 1). Reported data on the ABR spectrum are based on normative studies with a This work was in part supported by the 1985 Braintree Award for Outstanding Research in Head Injury.cumulative total of less than 20 subjects (5-10). There is general agreement that the ABR consists of a relatively high energy, low-frequency component (1 50 Hz and below), a component in the 500 to 600 Hz region, and a relatively high-frequency component in the 900 to 1100 Hz region, and that spectral energy is minimal above 2000 Hz. Less clear is the relationship of ABR spectral characteristics to the individual wave components recorded in the time domain, e.g., waves I, 111, and V. Kevanishvili and Aphonchenko (7), for example, concluded from digital filtering and power spectral analysis techniques that the major energy contributions of the ABR waves were 400 to 1000 Hz for waves I and 11, 100 to 900 Hz for wave 111, and 100 to 500 Hz for waves IV through VI. Using similar techniques, Suzuki et a1 (10) supported these. findings. Boston (5) studied ABR spectrum with digital filtering techniques. He attributed the high-frequency spectral component (900 to 1100 Hz) to the early ABR waves (I, 11, 111), th...

Improving the prediction of outcome in severe acute closed head injury by using discriminant function analysis of normal auditory brainstem response latencies and amplitudes

“…In opposition to our study's findings are Hall 12 and Facco, et al 7 Hall showed no significant differences (p Ͻ 0.05) between normal ABR latencies and amplitudes in his severe ACHI-lived compared with ACHI-died groups, whereas Facco, et al, predicted that 95% of severe head injury survivors would have a Wave I-V interwave latency ranging between 3.82 and 4.5 msec. Reasons for these disagreements could lie in patient sample differences, and/or, as has been argued earlier in this article, the use of higher-level multivariate analysis (DFA) in this study compared with simpler univariate statistical analyses in the studies by Hall and Facco, et al…”

“…The ABR test is noninvasive, safe, mobile, brief, objective, reliable, a sensitive and comprehensive index of neurological status, anatomically specific, highly independent of level of consciousness, highly resistant to the effects of drugs, cost-effective, and it has the potential to be automated. 4,5,[12][13][14]22,27 Limitations of the ABR as a Predictor of Outcome in Patients With Severe ACHI. Possibly the greatest limitation of the ABR as a predictor of outcome in patients with severe ACHI (at least numerically) is that 30 to 35% of these patients who present with normal ABR results on their initial assessment later die or remain in a persistent vegetative state.…”

Spectral and synchrony differences in auditory brainstem responses evoked by chirps of varying durations

“…These ABRs had central FFT frequencies that were significantly higher than for 100 s clicks and A-Chirps in band A, and significantly higher than for 100 s clicks in band B. Head trauma, coma, epilepsy, multiple sclerosis, and neurinomas of the acoustic nerve are all conditions that are known to affect the location of each of the major FFT peaks, 65,66 but these conditions were absent in our healthy subjects. The position of the recording electrode is also known to shift the frequencies of the FFT peaks, as is stimulus polarity.…”

Signal processing of the auditory brainstem response: clinical effects of variations in fast Fourier transform analysis

“…This approach has proven to be valuable as a more sensitive indicator of auditory dysfunction as it has the ability to detect ABR abnormalities in the frequency domain that were not evident in the time domain. The most successful clinical applications in this role have included the early detection of head injury [6] and spinocerebellar degeneration [7].…”

“…Some authors mention the use of specific windows without jus-ng their decision [8, 9, 10, 111, whilst other authors make no mention of windowing (or absence thereof) at all [6,12,13,141. This is despite the well known mathematical fact that different windows will have different effects on FFT output.…”