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Veterinary Quarterly Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tveq20
Relationship between latency of brainstem auditory‐evoked potentials and head size in dogs B. P. Meij
a b
a
, A. J. Venker‐van Haagen & W. E. van den Brom
a
a
Department of Clinical Sciences of Companion Animals , University of Utrecht , the Netherlands b
Department of Clinical Sciences of Companion Animals , University of Utrecht , Postbox 80.154, Utrecht, 3508 TD, the Netherlands Published online: 01 Nov 2011.
To cite this article: B. P. Meij , A. J. Venker‐van Haagen & W. E. van den Brom (1992) Relationship between latency of brainstem auditory‐evoked potentials and head size in dogs, Veterinary Quarterly, 14:4, 121-126, DOI: 10.1080/01652176.1992.9694347 To link to this article: http://dx.doi.org/10.1080/01652176.1992.9694347
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
ORIGINAL PAPERS
RELATIONSHIP BETWEEN LATENCY OF BRAINSTEM AUDITORY-EVOKED POTENTIALS AND HEAD SIZE IN DOGS B. P. Meij, A. J. Venker-van Haagen, and W. E. van den Brom' Veterinary Quarterly 1992; 14: 121 - 6
Downloaded by [Moody Bible Institiute] at 18:05 20 November 2014
SUMMARY Cranium and brainstem dimensions were measured in 32 postmortem dog heads. Positive correlations were found between
INTRODUCTION
Waveform, wave latencies, and wave amplitudes of brainstem auditory-evoked potentials (BAEPs) have been determined in
cranium length (CL) and brainstem length (BL) (r=0.87), between cranium width (CW) and brainstem width (BW) (r=0.83), and between cranium distance (CD = CL + CW/2)
clinically normal anaesthetized and non-anaesthetized dogs (6,21,30,34,35). To develop this technique further as a hearing
estimation of the brainstem distance (BD) from CL and CW values was BD = 10.9 + 0.16 (CL + CW/2) (BD, CL and CW
wave V and the I-V interpeak latency are of particular
and brainstem distance (BD = BL + BW/ 2) (r=0.91). Positive correlation coefficients were also found between CL and CW (r=0.90), and between BL and BW (r=0.85). It was concluded that head size accurately reflected brainstem size. A least squares
in mm).
Brainstem auditory evoked potentials (BA EPs) and cranium dimensions were measured in 43 dogs (86 ears) with different head size, body size, sex and age. Wave form, absolute and interpeak latencies and correlation coefficients, relating latencies to cranium dimensions and body weight, were analysed CL,
CW, and CD were positively correlated with body weight (r=0.93, 0.70 and 0.93, respectively), and CL, CW, and CD were correlated with age (r=0.33, 0.52 and 0.40, respectively).
consisted of five distinct positive peaks (I to
test and to assess brainstem abnormalities in dogs, it is essential to determine which factors affect BAEPs in order to minimize intersubject variability. Analysis of BAEPs involves identification of waves and measurement of component wave latencies and amplitudes. Factors affecting the absolute wave latency of
importance, since it is believed that these latencies represent central conduction time along the auditory pathway (39). Thus abnormal latencies may be indicative of auditory pathway or brainstem abnormalities. A number of factors have been shown to affect normal latency values in humans. Latencies of BAEPs have been shown to be related to sex and age (5,8,13,18,22,28). Females exhibit shorter absolute and interpeak latencies than males. Latencies of BAEPs in humans are positively correlated with head size and body size (4,7,11). A generally accepted theory is that brainstem dimen-
V).
sions, and therefore BAEP latencies, increase with cranium
Secondary positive peaks following peaks I and II were seen in
dimensions. Since the canine population is very diverse with respect to head size and body size, it is important to determine the effect of these factors on BAEP characteristics in the dog. In a study by Pook and Steiss (27), 9 male and 11 female clinically normal mature
BA EPs
60% (I') and 90% (II') of the recordings. Late waves were recorded in 90% (VI), 50% (VII), and 25% (VIII) of the recordings. Latencies increased with decreasing stimulus intensity level (from 90 dB to 10 dB hearing level, HL),especially for
peaks I, II, V, and the I-V interpeak interval Absolute and interpeak latencies were positively correlated with cranium distance and body weight. Correlation coefficients increased as wave latencies increased At 90 dB HL, the highest correlation coefficients, relating cranium distance to peak V and the I-V interpeak latency, were 0.55 and 0.53 (P < 0.00001), respectively. Regression analysis showed that each 1 cm increase in cranium distance was accompanied by an increase of 0.006 ms in the latency of wave I, 0.03 ms for wave III, 0.05 ms for wave V,
and 0.05 ms for the I-V interpeak interval Regression analysis showed that an increase of 1 kg in body weight was accompanied by an increase of 0.001 ms in the latency of wave I, 0.005 ms for wave III, 0.011 ms for wave l< and 0.01 ms for the I-V interpeak interval. It is concluded that head size, which accurately reflects brain size, is a relevant source (25%) of intersubject variance of BAEP latencies in the dog.
1
Department of Clinical Sciences of Companion Animals, University of Utrecht, the Netherlands. Address for correspondence: B.P. Meij, DVM, Department of Clinical Sciences of Companion Animals, University of Utrecht. Postbox 80.154, 3508 TD Utrecht, the Netherlands.
121
T
11:1.1
VETER
I
NAR
dogs, weighing between 2 and 36 kg, were investigated to correlate brainstem auditory-evoked potentials with cranium size and body weight. A positive correlation was observed between cranium length, cranium width, nasion-external auditory meatus interval, and body weight for wave V latency and the I-V interpeak latency. It was recommended that the effect of variation of dog size on brainstem auditory-evoked potentials
should be compensated for by making use of regression equations based on cranium length (27). The aim of the present study was two-fold: first, to investigate whether head size measurements accurately reflect brainstem size, and second, to determine the effect of head measurements on the latencies of BAEPs in the dog. MATERIALS AND METHODS
Anatomy Cranium and brainstem dimensions were measured in 32 postmortem dog heads collected from the Department of Veterinary Pathology of the University of Utrecht. The causes of death were known to have no effect on the dimensions of the cranium or
brainstem. The heads were fixed and stored in 10 per cent
1' Quiri:iiv. VoL
1
4.
No
.
4.
Di c
E
m B
i
R
.
1
992
formalin. Using a caliper, the cranium length (CL, distance of inion to nasion) and the cranium width (CW, distance between the left and right jugular processes) were measured on the intact skull. After the brain had been carefully removed from the skull, the brainstem dimensions were measured on the ventral aspect
of the brainstem. Using a vernier caliper, we measured the brainstem length (BL) as the distance between the point of attachment of the vestibulocochlear nerves (N. VIII) to the brainstem and the mamillary bodies. The brainstem width (BW) was measured where the vestibulocochlear nerves attach to the
brainstem. From these values the brainstem distance (BD), defined as BD = BL + 1/2 BW, and the cranium distance (CD), defined as CD = CL 1/2 CW, were calculated.
Downloaded by [Moody Bible Institiute] at 18:05 20 November 2014
Brainstem auditory-evoked potentials (BAEPs)
(years)
Minimum Maximum Median Mean So
Body Weight (kg)
0.4
4.1
11.0
50.0
6.1
17.3
5.7 3.4
20.7
CL
CW
CD
(mm)
(mm)
(mm)
65 150 106 108 19
34 89 58 59
10.8
11
were used to prevent body temperature from decreasing by more than 1 °C. Before each recording, cranium dimensions (CL and CW) were measured as described above. Measurements of BAEPs were made during stimulation of each ear of each dog.
The dogs were placed in ventral recumbency with the head resting between the forelegs or in lateral recumbancy with the ear to be studied facing upwards. The earphone was placed in the vertical part of the ear canal of the side to be measured. An
inactive earphone transducer was placed in the other ear to reduce the chance of air-conducted contralateral stimulation. No masking "white noise" was used in the contralateral ear. The sound pressure level (SPL) produced by the earphone transducer had been determined previously (35) by placing a miniature electret microphone in the outer ear canal near the tympanic membrane. At a setting of 0 dB hearing level (HL), correspon-
Animals Brainstem auditory-evoked potentials (BAEPs) and craniumdimensions were measured in 43 dogs of various breeds, both sexes, and varying in age, body weight and head size. The group consisted of 19 female aild 24 male dogs. The other characteristics are summarized in Table I. Age
the start and at the end of each recording session. Infrared lamps
ding to the human threshold for hearing the click, a sound pressure level (SPL) of 27 dB was reached. In the present study the stimulus intensity was decreased in steps of10 dB HL, from
90 dB hearing level (HL) (117 dB SPL) to 10 dB HL (37 dB SPL), or to a level at which a response could no longer be detected. The response to stimulation of both ears was measured. BAEPs for each ear at decreasing stimulus levels were plotted together
on a single graph. Wave peaks were identified and wave peak
82
latencies were measured from the onset of stimulus and stored in
189 136 138 23
a database together with data on cranium dimensions. RESULTS
,
Anatomy The data on cranium and brainstem dimensions for 32 dog
Table I. Minimum, maximum, median, mean, and standard deviation (So) of age, body weight, cranium length (CL), cranium width (CW), and cranium distance (CD) in 43 dogs.
heads are given in Table II.
Recording technique A timer, started by a computer signal, produced square-wave pulses of 100 As duration at a rate of 10 Hz. These electrical
Parameter
Ab.
Measurement
signals were fed into a power amplifier, which included a variable attenuator, connected to an earphone transducer
Cranium length Cranium width
CL
24
49
13
(Danavox, type W) positioned at the base of the vertical part of the external ear canal. BAEPs were recorded from three stainless-steel needle electrodes (Disa 13L) placed subcutaneously on the head of the dog, one over the occipital protuberance, one over the left jugular process and one over the right jugular process. The electrode positions over the occipital protuberance and the jugular process corresponded closely to electrode positions 7A and 5C, respectively, as described by others (12). The electrode ipsilateral to the
Inion to nasion Widest interparietal distance
112
CW
Brainstem length
BL
Level N.V111 to
210
39
mamillary bodies Width at level N. VIII = CL + CW/2
220
27 29 50
BW Brainstem width Cranium distance CD Brainstem distance BD
Mean
S
136 321
= BL + BW/2
Table 2. Cranium dimensions (CL=cranium length, CW=cranium width and CD=cranium distance) and brainstem dimensions (BL=brainstem length, 13W = brainstem width and BD= brainstem distance) in 32 dogs. Cranium dimensions (CL, CW, CD) and brainstem dimensions (BL, BW, BD) in mm.
stimulus side was used as the active recording electrode, the electrode contralateral to the stimulus side was used as the ground electrode and the electrode over the occipital protube-
Apparent brainstem dimensions were measured rather than real brainstem dimensions since shrinkage of brain tissue in 10 per cent formalin was not taken into account. Brainstem dimensions
rance was used as an inactive reference electrode. From previous
were positively correlated with the corresponding cranium
experiments it was known that the interelectrode impedances were less than 2 k C (35). Simultaneously, the stimulus started data acquisition by the
dimensions, as were lengths with widths. The linear correlation
coefficients varied between 0.83 and 0.91 (n=32, P < 10-6). The relationship between cranium distance. and brainstem distance is shown in figure 1. A least-squares fit to the data presented in figure 1 gives: BD = 10.9 + 0.16 CD (BD and CD in mm), which makes it possible to estimate the brainstem distance by measuring the dimensions of the cranium.
computer, which functioned as an averager. The BAEP response signal was preamplified, fed to a variable amplifier (gain 2.105 -
4.106, frequency range 2 Hz - 2kHz) and to an 8-bit ADC, interfaced to the computer. Usually 256 measurements were averaged by the computer and stored on diskettes for further analysis.
Brainstem auditory-evoked potentials (BAEPs)
Thirty minutes before recording, each dog received 0.3 mg chlorpromazine /kg, 1 mg methadone2/kg and 0.1 mg atro-
Anatomy Data on age, body weight, and cranium dimensions (CL, CW, CD) of 43 dogs of various breeds and sexes are given in table I.
pine3/kg, intramuscularly. Body temperature was measured at
122
Titi
VI
I
I.
R
I
N A
R
YQUA
R
I
L R
I
Y,
VOI
.
1
4,
No
.
4.
D L c i.
r
uE
R
,
1
992
Cranium dimensions (CL, CW and CD) were strongly correlated with body weight (r=0.93, 0.70 and 0.93, respectively) but weakly correlated with age (r=0.33, 0.52 and 0.40, respecti-
range of 90 and 40 dB HL. Waves I and II were followed by smaller but distinct secondary waves in 60% and 90% of the cases, respectively. These waves were labelled I' and II' and
vely). Cranium length (CL) and cranium width (CW) were
were observed mainly in the range of 90 to 40 dB HL. Waves III and IV were identified between waves II and V but were far less
intercorrelated (r=0.70). All these correlation coefficients were significant (n=43, P < 0.005). 45 y = 0.1556x + 10.8761
75% of the recordings. Wave IV could usually not be identified at 90 dB HL, but when the stimulus intensity was decreased to 80
r = 0.91
40 -
n = 32 -E.- 35
or 70 dB HL it emerged from wave III or V. As the stimulus
a ca 30
intensity decreased from 70 to 40 dB HL, waves III and IV were no longer observed while waves I, II, V, and VN persisted. Below
25
40 dB HL waves I and II disappeared while waves V and VN were still discernable. Late waves were recorded after waves V and VN, and were labelled VI, VII, and VIII; they were detected in 90%, 50% and 15% of the recordings, respectively. These late
20 50
100
75
150
125
175
200
CD (mm)
Downloaded by [Moody Bible Institiute] at 18:05 20 November 2014
consistent in form. Wave III was identified as the first wave following II and II' between stimulus intensities 90 and 70 dB HL and was present in all recordings. Wave IV was present in
Figure 1. The relationship between cranium distance (CO) and brainstem distance (BD) in 32 dogs.
Body temperature measured during each recording session ranged from 36.6 to 39.7 °C (median 38.1 °C). Analysis of BAEPs: Wave form A representative example of a series of BAEPs at decreasing stimulus levels is shown in figure 2. For stimulus levels in the range of 90 to 20 dB HL, five peaks were usually detected in the responses and were labelled waves I, II, III, IV, and V. Waves I and II were easily identified by their sharp and consistent peaks between 90 and 70 dB HL. Identification of wave V was done by screening all stimulus intensities and in particular lower stimulus intensities. Wave V was always followed by a large negative deflection (VN). Both became more prominent at the intermediate stimulus intensities, whereas VN persisted even at the lowest stimulus intensities. At lower stimulus intensities wave V and VN shifted to longer latencies which became visible for the eye. The form of waves I, II, V, and VN was consistent between the I
I
11
III
I
I
IIII VII VIII
significant changes in absolute and interpeak latencies were observed as the stimulus intensity decreased from 90 to 70 dB HL.
At 90 dB HL stimulus intensity, average latencies (mean ± SD ms) for all ears (n=86) were calculated for wave I (1.16± 0.07), II (2.01 ± 0.12), III (2.90 ± 0.17), IV (3.41 ± 0.25), V (3.89 ± 0.21), VN (4.48 ± 0.23), VI (5.01 ± 0.23), VII (6.16 ± 0.29) and VIII (7.22 ± 0.50). The I-V interpeak latency (mean ± SD ms) at 90 dB HL was 2.73 ± 0.19 ms. Mean latencies and standard deviations at 90 dB HL were 1.49
± 0.11 ms for peak I' and 2.30 ± 0.16 ms for peak II'. Mean dB HL
corresponding latencies of waves I and II in the stimulus intensity range of 90 to 40 dB HL (Student's 1-test, P
Veterinary Quarterly Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tveq20
Relationship between latency of brainstem auditory‐evoked potentials and head size in dogs B. P. Meij
a b
a
, A. J. Venker‐van Haagen & W. E. van den Brom
a
a
Department of Clinical Sciences of Companion Animals , University of Utrecht , the Netherlands b
Department of Clinical Sciences of Companion Animals , University of Utrecht , Postbox 80.154, Utrecht, 3508 TD, the Netherlands Published online: 01 Nov 2011.
To cite this article: B. P. Meij , A. J. Venker‐van Haagen & W. E. van den Brom (1992) Relationship between latency of brainstem auditory‐evoked potentials and head size in dogs, Veterinary Quarterly, 14:4, 121-126, DOI: 10.1080/01652176.1992.9694347 To link to this article: http://dx.doi.org/10.1080/01652176.1992.9694347
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
ORIGINAL PAPERS
RELATIONSHIP BETWEEN LATENCY OF BRAINSTEM AUDITORY-EVOKED POTENTIALS AND HEAD SIZE IN DOGS B. P. Meij, A. J. Venker-van Haagen, and W. E. van den Brom' Veterinary Quarterly 1992; 14: 121 - 6
Downloaded by [Moody Bible Institiute] at 18:05 20 November 2014
SUMMARY Cranium and brainstem dimensions were measured in 32 postmortem dog heads. Positive correlations were found between
INTRODUCTION
Waveform, wave latencies, and wave amplitudes of brainstem auditory-evoked potentials (BAEPs) have been determined in
cranium length (CL) and brainstem length (BL) (r=0.87), between cranium width (CW) and brainstem width (BW) (r=0.83), and between cranium distance (CD = CL + CW/2)
clinically normal anaesthetized and non-anaesthetized dogs (6,21,30,34,35). To develop this technique further as a hearing
estimation of the brainstem distance (BD) from CL and CW values was BD = 10.9 + 0.16 (CL + CW/2) (BD, CL and CW
wave V and the I-V interpeak latency are of particular
and brainstem distance (BD = BL + BW/ 2) (r=0.91). Positive correlation coefficients were also found between CL and CW (r=0.90), and between BL and BW (r=0.85). It was concluded that head size accurately reflected brainstem size. A least squares
in mm).
Brainstem auditory evoked potentials (BA EPs) and cranium dimensions were measured in 43 dogs (86 ears) with different head size, body size, sex and age. Wave form, absolute and interpeak latencies and correlation coefficients, relating latencies to cranium dimensions and body weight, were analysed CL,
CW, and CD were positively correlated with body weight (r=0.93, 0.70 and 0.93, respectively), and CL, CW, and CD were correlated with age (r=0.33, 0.52 and 0.40, respectively).
consisted of five distinct positive peaks (I to
test and to assess brainstem abnormalities in dogs, it is essential to determine which factors affect BAEPs in order to minimize intersubject variability. Analysis of BAEPs involves identification of waves and measurement of component wave latencies and amplitudes. Factors affecting the absolute wave latency of
importance, since it is believed that these latencies represent central conduction time along the auditory pathway (39). Thus abnormal latencies may be indicative of auditory pathway or brainstem abnormalities. A number of factors have been shown to affect normal latency values in humans. Latencies of BAEPs have been shown to be related to sex and age (5,8,13,18,22,28). Females exhibit shorter absolute and interpeak latencies than males. Latencies of BAEPs in humans are positively correlated with head size and body size (4,7,11). A generally accepted theory is that brainstem dimen-
V).
sions, and therefore BAEP latencies, increase with cranium
Secondary positive peaks following peaks I and II were seen in
dimensions. Since the canine population is very diverse with respect to head size and body size, it is important to determine the effect of these factors on BAEP characteristics in the dog. In a study by Pook and Steiss (27), 9 male and 11 female clinically normal mature
BA EPs
60% (I') and 90% (II') of the recordings. Late waves were recorded in 90% (VI), 50% (VII), and 25% (VIII) of the recordings. Latencies increased with decreasing stimulus intensity level (from 90 dB to 10 dB hearing level, HL),especially for
peaks I, II, V, and the I-V interpeak interval Absolute and interpeak latencies were positively correlated with cranium distance and body weight. Correlation coefficients increased as wave latencies increased At 90 dB HL, the highest correlation coefficients, relating cranium distance to peak V and the I-V interpeak latency, were 0.55 and 0.53 (P < 0.00001), respectively. Regression analysis showed that each 1 cm increase in cranium distance was accompanied by an increase of 0.006 ms in the latency of wave I, 0.03 ms for wave III, 0.05 ms for wave V,
and 0.05 ms for the I-V interpeak interval Regression analysis showed that an increase of 1 kg in body weight was accompanied by an increase of 0.001 ms in the latency of wave I, 0.005 ms for wave III, 0.011 ms for wave l< and 0.01 ms for the I-V interpeak interval. It is concluded that head size, which accurately reflects brain size, is a relevant source (25%) of intersubject variance of BAEP latencies in the dog.
1
Department of Clinical Sciences of Companion Animals, University of Utrecht, the Netherlands. Address for correspondence: B.P. Meij, DVM, Department of Clinical Sciences of Companion Animals, University of Utrecht. Postbox 80.154, 3508 TD Utrecht, the Netherlands.
121
T
11:1.1
VETER
I
NAR
dogs, weighing between 2 and 36 kg, were investigated to correlate brainstem auditory-evoked potentials with cranium size and body weight. A positive correlation was observed between cranium length, cranium width, nasion-external auditory meatus interval, and body weight for wave V latency and the I-V interpeak latency. It was recommended that the effect of variation of dog size on brainstem auditory-evoked potentials
should be compensated for by making use of regression equations based on cranium length (27). The aim of the present study was two-fold: first, to investigate whether head size measurements accurately reflect brainstem size, and second, to determine the effect of head measurements on the latencies of BAEPs in the dog. MATERIALS AND METHODS
Anatomy Cranium and brainstem dimensions were measured in 32 postmortem dog heads collected from the Department of Veterinary Pathology of the University of Utrecht. The causes of death were known to have no effect on the dimensions of the cranium or
brainstem. The heads were fixed and stored in 10 per cent
1' Quiri:iiv. VoL
1
4.
No
.
4.
Di c
E
m B
i
R
.
1
992
formalin. Using a caliper, the cranium length (CL, distance of inion to nasion) and the cranium width (CW, distance between the left and right jugular processes) were measured on the intact skull. After the brain had been carefully removed from the skull, the brainstem dimensions were measured on the ventral aspect
of the brainstem. Using a vernier caliper, we measured the brainstem length (BL) as the distance between the point of attachment of the vestibulocochlear nerves (N. VIII) to the brainstem and the mamillary bodies. The brainstem width (BW) was measured where the vestibulocochlear nerves attach to the
brainstem. From these values the brainstem distance (BD), defined as BD = BL + 1/2 BW, and the cranium distance (CD), defined as CD = CL 1/2 CW, were calculated.
Downloaded by [Moody Bible Institiute] at 18:05 20 November 2014
Brainstem auditory-evoked potentials (BAEPs)
(years)
Minimum Maximum Median Mean So
Body Weight (kg)
0.4
4.1
11.0
50.0
6.1
17.3
5.7 3.4
20.7
CL
CW
CD
(mm)
(mm)
(mm)
65 150 106 108 19
34 89 58 59
10.8
11
were used to prevent body temperature from decreasing by more than 1 °C. Before each recording, cranium dimensions (CL and CW) were measured as described above. Measurements of BAEPs were made during stimulation of each ear of each dog.
The dogs were placed in ventral recumbency with the head resting between the forelegs or in lateral recumbancy with the ear to be studied facing upwards. The earphone was placed in the vertical part of the ear canal of the side to be measured. An
inactive earphone transducer was placed in the other ear to reduce the chance of air-conducted contralateral stimulation. No masking "white noise" was used in the contralateral ear. The sound pressure level (SPL) produced by the earphone transducer had been determined previously (35) by placing a miniature electret microphone in the outer ear canal near the tympanic membrane. At a setting of 0 dB hearing level (HL), correspon-
Animals Brainstem auditory-evoked potentials (BAEPs) and craniumdimensions were measured in 43 dogs of various breeds, both sexes, and varying in age, body weight and head size. The group consisted of 19 female aild 24 male dogs. The other characteristics are summarized in Table I. Age
the start and at the end of each recording session. Infrared lamps
ding to the human threshold for hearing the click, a sound pressure level (SPL) of 27 dB was reached. In the present study the stimulus intensity was decreased in steps of10 dB HL, from
90 dB hearing level (HL) (117 dB SPL) to 10 dB HL (37 dB SPL), or to a level at which a response could no longer be detected. The response to stimulation of both ears was measured. BAEPs for each ear at decreasing stimulus levels were plotted together
on a single graph. Wave peaks were identified and wave peak
82
latencies were measured from the onset of stimulus and stored in
189 136 138 23
a database together with data on cranium dimensions. RESULTS
,
Anatomy The data on cranium and brainstem dimensions for 32 dog
Table I. Minimum, maximum, median, mean, and standard deviation (So) of age, body weight, cranium length (CL), cranium width (CW), and cranium distance (CD) in 43 dogs.
heads are given in Table II.
Recording technique A timer, started by a computer signal, produced square-wave pulses of 100 As duration at a rate of 10 Hz. These electrical
Parameter
Ab.
Measurement
signals were fed into a power amplifier, which included a variable attenuator, connected to an earphone transducer
Cranium length Cranium width
CL
24
49
13
(Danavox, type W) positioned at the base of the vertical part of the external ear canal. BAEPs were recorded from three stainless-steel needle electrodes (Disa 13L) placed subcutaneously on the head of the dog, one over the occipital protuberance, one over the left jugular process and one over the right jugular process. The electrode positions over the occipital protuberance and the jugular process corresponded closely to electrode positions 7A and 5C, respectively, as described by others (12). The electrode ipsilateral to the
Inion to nasion Widest interparietal distance
112
CW
Brainstem length
BL
Level N.V111 to
210
39
mamillary bodies Width at level N. VIII = CL + CW/2
220
27 29 50
BW Brainstem width Cranium distance CD Brainstem distance BD
Mean
S
136 321
= BL + BW/2
Table 2. Cranium dimensions (CL=cranium length, CW=cranium width and CD=cranium distance) and brainstem dimensions (BL=brainstem length, 13W = brainstem width and BD= brainstem distance) in 32 dogs. Cranium dimensions (CL, CW, CD) and brainstem dimensions (BL, BW, BD) in mm.
stimulus side was used as the active recording electrode, the electrode contralateral to the stimulus side was used as the ground electrode and the electrode over the occipital protube-
Apparent brainstem dimensions were measured rather than real brainstem dimensions since shrinkage of brain tissue in 10 per cent formalin was not taken into account. Brainstem dimensions
rance was used as an inactive reference electrode. From previous
were positively correlated with the corresponding cranium
experiments it was known that the interelectrode impedances were less than 2 k C (35). Simultaneously, the stimulus started data acquisition by the
dimensions, as were lengths with widths. The linear correlation
coefficients varied between 0.83 and 0.91 (n=32, P < 10-6). The relationship between cranium distance. and brainstem distance is shown in figure 1. A least-squares fit to the data presented in figure 1 gives: BD = 10.9 + 0.16 CD (BD and CD in mm), which makes it possible to estimate the brainstem distance by measuring the dimensions of the cranium.
computer, which functioned as an averager. The BAEP response signal was preamplified, fed to a variable amplifier (gain 2.105 -
4.106, frequency range 2 Hz - 2kHz) and to an 8-bit ADC, interfaced to the computer. Usually 256 measurements were averaged by the computer and stored on diskettes for further analysis.
Brainstem auditory-evoked potentials (BAEPs)
Thirty minutes before recording, each dog received 0.3 mg chlorpromazine /kg, 1 mg methadone2/kg and 0.1 mg atro-
Anatomy Data on age, body weight, and cranium dimensions (CL, CW, CD) of 43 dogs of various breeds and sexes are given in table I.
pine3/kg, intramuscularly. Body temperature was measured at
122
Titi
VI
I
I.
R
I
N A
R
YQUA
R
I
L R
I
Y,
VOI
.
1
4,
No
.
4.
D L c i.
r
uE
R
,
1
992
Cranium dimensions (CL, CW and CD) were strongly correlated with body weight (r=0.93, 0.70 and 0.93, respectively) but weakly correlated with age (r=0.33, 0.52 and 0.40, respecti-
range of 90 and 40 dB HL. Waves I and II were followed by smaller but distinct secondary waves in 60% and 90% of the cases, respectively. These waves were labelled I' and II' and
vely). Cranium length (CL) and cranium width (CW) were
were observed mainly in the range of 90 to 40 dB HL. Waves III and IV were identified between waves II and V but were far less
intercorrelated (r=0.70). All these correlation coefficients were significant (n=43, P < 0.005). 45 y = 0.1556x + 10.8761
75% of the recordings. Wave IV could usually not be identified at 90 dB HL, but when the stimulus intensity was decreased to 80
r = 0.91
40 -
n = 32 -E.- 35
or 70 dB HL it emerged from wave III or V. As the stimulus
a ca 30
intensity decreased from 70 to 40 dB HL, waves III and IV were no longer observed while waves I, II, V, and VN persisted. Below
25
40 dB HL waves I and II disappeared while waves V and VN were still discernable. Late waves were recorded after waves V and VN, and were labelled VI, VII, and VIII; they were detected in 90%, 50% and 15% of the recordings, respectively. These late
20 50
100
75
150
125
175
200
CD (mm)
Downloaded by [Moody Bible Institiute] at 18:05 20 November 2014
consistent in form. Wave III was identified as the first wave following II and II' between stimulus intensities 90 and 70 dB HL and was present in all recordings. Wave IV was present in
Figure 1. The relationship between cranium distance (CO) and brainstem distance (BD) in 32 dogs.
Body temperature measured during each recording session ranged from 36.6 to 39.7 °C (median 38.1 °C). Analysis of BAEPs: Wave form A representative example of a series of BAEPs at decreasing stimulus levels is shown in figure 2. For stimulus levels in the range of 90 to 20 dB HL, five peaks were usually detected in the responses and were labelled waves I, II, III, IV, and V. Waves I and II were easily identified by their sharp and consistent peaks between 90 and 70 dB HL. Identification of wave V was done by screening all stimulus intensities and in particular lower stimulus intensities. Wave V was always followed by a large negative deflection (VN). Both became more prominent at the intermediate stimulus intensities, whereas VN persisted even at the lowest stimulus intensities. At lower stimulus intensities wave V and VN shifted to longer latencies which became visible for the eye. The form of waves I, II, V, and VN was consistent between the I
I
11
III
I
I
IIII VII VIII
significant changes in absolute and interpeak latencies were observed as the stimulus intensity decreased from 90 to 70 dB HL.
At 90 dB HL stimulus intensity, average latencies (mean ± SD ms) for all ears (n=86) were calculated for wave I (1.16± 0.07), II (2.01 ± 0.12), III (2.90 ± 0.17), IV (3.41 ± 0.25), V (3.89 ± 0.21), VN (4.48 ± 0.23), VI (5.01 ± 0.23), VII (6.16 ± 0.29) and VIII (7.22 ± 0.50). The I-V interpeak latency (mean ± SD ms) at 90 dB HL was 2.73 ± 0.19 ms. Mean latencies and standard deviations at 90 dB HL were 1.49
± 0.11 ms for peak I' and 2.30 ± 0.16 ms for peak II'. Mean dB HL
corresponding latencies of waves I and II in the stimulus intensity range of 90 to 40 dB HL (Student's 1-test, P
