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Appl. Neurophysiol. 38: 161-171 (1975)
Physiological Postrotatory Nystagmus1 I. Mean Normal Values and Differences between Both Sides
V. Simón, J. B artual and M. L lopis Cátedra de Otorrinolaringología, Cádiz; Cátedra de Fisiología, and Centro de Documentación e Informática médica, Valencia
Key Words. Postrotatory nystagmus • Human vestibular apparatus • Oculomotor responses Abstract. Nystagmus elicited by means of rotatory stimuli has been studied in 55 healthy subjects. In each case, 5 different end-velocities have been employed and each postrotatory nystagmus has been quantitatively evaluated by measuring various parameters of its quick phase. The mean values that could be considered as normal were searched for by means of a statistical study, but a great variability in the res ponses was found. Likewise, the responses of both labyrinths have often been rather asymmetrical. Therefore, such a functional asymmetry of the oculomotor responses, due to a variety of central factors, seems to be a serious difficulty for the practical use of postrotatory nystagmus as a clinical test. The particular meaning of the num ber of beats is discussed.
1 This work was supported by a ‘Beca para formación de personal investigador’ of the ‘Ministerio de Educación y Ciencia’.
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Study of the physiology of the vestibular system generally concerns two areas. On one side is the electrophysiological work that deals with the behavior of the neurosensory elements. In this field stand out the studies of L edoux [6], D uensing and Schaefer [3] T rincker [9, 10] and T rincker et al. [11], On the other side are the studies on the characteris tic response of the system to diverse stimuli, i.e., nystagmus. Nystagmus is an easily observable phenomenon; it can be induced by means of caloric, electric or rotatory stimuli. The use of rotatory stimuli in order to study the functional state of the vestibular system can be traced back to the time of B arany [2], This au thor popularized the test that bears his name. It consists of two series of
Simon/B artual/L lopis
rotations, one to the right, the other to the left, each series consisting of 10 revolutions in 20 sec each, and measurement of the duration of the postrotatory nystagmus produced after the sudden stop. V an E gmond el al. [4] improved B arany’s method [2] and increased the number of stimuli in each subject. They studied postrotatory nystag mus and sensation, and by relating them with the stimulus, the graphics called cupulograms were obtained. According to their results, there would be a linear relationship between the intensity of the stimulus and the du ration of the response. A schan et al. [1] explored a large number of healthy subjects employ ing the cupulometric method and endeavored to characterize the normal values. In the explored end-velocities, from 9 to 52 degrees per second, they also found a linear relationship between the stimulus and the re sponse, although the range of normal was quite broad. The parameter studied by these authors was exclusively the duration of the postrotatory nystagmus. Subsequently, researchers deviated from the study of the postrotatory nystagmus, centering their interest on the caloric tests or on the accelera tion thresholds of the perrotatory nystagmus. On the other hand, the electronystagmographic and photoelectronystagmographic techniques have made possible the faithful record of the nystagmus and the quantitative evaluation of many of its characteristics. Among them, the one that has received most regard among researchers and clinicians is the angular velocity of the slow phase, considering the slow component of the nystagmus as the more genuinely vestibular. The course of the slow phase of the postrotatory nystagmus was studied by Kornhuber et al. [5]. These authors observed an exponential decrease of the angular velocity of the slow phase in the first postrotatory nystagmus. Furthermore, they found a linear relationship between the maximal angu lar velocity of the slow phases of the postrotatory nystagmus and the rota tory velocity before the stop. In the present work, employing a stimulation method similar to the cupulometria of Jongkees and taking advantage of the possibilities intro duced by electronystagmography, we studied postrotatory nystagmus elic ited in healthy subjects with diverse stimulus intensities, making a quanti tative evaluation of the amplitude of the quick phases. On this experi mental basis we attempt - to study several characteristic parameters of the nystagmus and to find out which are the most significant; - to define their normal values, thinking of a possible diagnostic use; - to explore the
Downloaded by: Karolinska Institutet, University Library 130.237.122.245 - 1/30/2019 5:36:00 AM
162
Physiological Postrotatory Nystagmus
163
possible relationship existing between rotatory stimulus and nystagmic re sponse, and - to study the peripheral and central influences involved in the experimental results. Material and Methods Material The experiments have been carried out with human beings, normal with refer ence to the vestibular system and without any record of clinical, otoscopic or audi ometric cochleovestibular abnormalities. A total of 59 subjects have been studied, 4 of which had to be excluded for different reasons; the 55 cases presented in this work remained. The stimulation device used was the rotatory chair of Tonnies n. D-291. This equipment permits the attainment of accelerations and velocities of well-known and controlled magnitudes. The ocular movements corresponding to the provoked post rotatory nystagmus were registered by recording the variations of the corneoretinal potential, amplifying them with an A-C amplifier and inscribing them on thermo sensitive paper with the aid of an adequate recording system. The time constant employed was 1 sec.
Evaluation Once the electronystagmographic traces were obtained, they were quantitatively evaluated by measuring the amplitude of each of the beats and determining its tem poral appearence. In this way a translation of nystagmus into numerical data was obtained.
Downloaded by: Karolinska Institutet, University Library 130.237.122.245 - 1/30/2019 5:36:00 AM
Exploration Once the subject is seated in the Tonnies chair und the periocular electrodes set, visual calibration is carried out. The visual calibration permits the inference of the degree of ocular displacement from measurement of the nystagmographic trace. With this purpose, the system is adjusted so that 10° of ocular displacement in the horizontal plane correspond to 10 mm of displacement of the recording needle on the thermosensitive paper. This visual calibration is made with the help of the Mad dox cross. After this, with eyes closed and in darkness, the experiment begins. The subject is instructed to maintain the position of the head (forward inclination of 30°), and, without being stiff, to be attentive to the progress of the test. In the pauses between two successive rotations (pauses of 3 min duration) the lights are turned on and a little conversation is held with the subject in order to maintain his attention level. In each one of the rotations, a fixed acceleration is employed to reach the constant ve locity required. This velocity is maintained during 2f/2 min and then the chair is ab ruptly stopped (in 1 sec). At this moment, the postrotatory nystagmus appears and is recorded. With each subject, 10 rotations have been performed, 5 clockwise and 5 counter clockwise, beginning with a clockwise rotation. The final velocities are 30, 60, 90, 120 and 180 °/sec.
164
Simon/B artual/L lopis
Table I. Mean values of the distinct parameters and significance Velocity 1, 30 °/sec counterclockwise clockwise
t
Velocity 2, 60 °/sec counterclockwise clockwise
t
Amplitude, degrees % s sx
127.5740 76.8626 10.459
91.3333 69.3130 9.432
4.0356**
220.7090 138.2370 18.639
210.3272 127.0616 17.133
0.6779
16.7296 7.5061 1.0214
2.7488**
24.1309 8.5849 1.157
23.6400 9.0350 1.2182
0.0041
29.6666 14.1754 1.9290
3.1893**
51.7454 16.8788 2.276
52.3454 17.7641 2.3953
0.2963
1.8203 0.5374 0.731
2.1607*
2.2090 0.6083 0.0820
2.2400 0.6302 0.0849
0.5179
2.9611 1.4529 0.1977
3.1666**
4.1800 2.0996 0.2831
4.1072 1.9371 0.2611
0.3325
5.2259 2.4502 0.3334
4.3519s*
8.7490 3.4140 0.4603
9.0490 4.4061 0.5941
0.6294
Duration, sec x s sx
19.8111 9.6239 1.309
Number o f beats x s sx
36.2037 14.4553 1.967
Mean frequency x s sx
1.9759 0.6442 0.0876
Mean amplitude H s sx
3.4259 1.4804 0.2014
Typical velocity x s sx
6.5203 2.7764 0.3778
Likewise, a graphic representation is carried out permitting the quick and clear examination of the course, amplitude and duration of nystagmus and also the com parison with the corresponding contralateral nystagmus [7, 8], Knowing the amplitude of all the nystagmic beats and the duration of nystag mus, the remaining parameters studied in this work can be easily deduced. They are (1) total amplitude (the sum of the amplitudes of all the quick phases of the nystag mus; in degrees); (2) duration (corresponds to the length of the postrotatory nystag-
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* p
Appl. Neurophysiol. 38: 161-171 (1975)
Physiological Postrotatory Nystagmus1 I. Mean Normal Values and Differences between Both Sides
V. Simón, J. B artual and M. L lopis Cátedra de Otorrinolaringología, Cádiz; Cátedra de Fisiología, and Centro de Documentación e Informática médica, Valencia
Key Words. Postrotatory nystagmus • Human vestibular apparatus • Oculomotor responses Abstract. Nystagmus elicited by means of rotatory stimuli has been studied in 55 healthy subjects. In each case, 5 different end-velocities have been employed and each postrotatory nystagmus has been quantitatively evaluated by measuring various parameters of its quick phase. The mean values that could be considered as normal were searched for by means of a statistical study, but a great variability in the res ponses was found. Likewise, the responses of both labyrinths have often been rather asymmetrical. Therefore, such a functional asymmetry of the oculomotor responses, due to a variety of central factors, seems to be a serious difficulty for the practical use of postrotatory nystagmus as a clinical test. The particular meaning of the num ber of beats is discussed.
1 This work was supported by a ‘Beca para formación de personal investigador’ of the ‘Ministerio de Educación y Ciencia’.
Downloaded by: Karolinska Institutet, University Library 130.237.122.245 - 1/30/2019 5:36:00 AM
Study of the physiology of the vestibular system generally concerns two areas. On one side is the electrophysiological work that deals with the behavior of the neurosensory elements. In this field stand out the studies of L edoux [6], D uensing and Schaefer [3] T rincker [9, 10] and T rincker et al. [11], On the other side are the studies on the characteris tic response of the system to diverse stimuli, i.e., nystagmus. Nystagmus is an easily observable phenomenon; it can be induced by means of caloric, electric or rotatory stimuli. The use of rotatory stimuli in order to study the functional state of the vestibular system can be traced back to the time of B arany [2], This au thor popularized the test that bears his name. It consists of two series of
Simon/B artual/L lopis
rotations, one to the right, the other to the left, each series consisting of 10 revolutions in 20 sec each, and measurement of the duration of the postrotatory nystagmus produced after the sudden stop. V an E gmond el al. [4] improved B arany’s method [2] and increased the number of stimuli in each subject. They studied postrotatory nystag mus and sensation, and by relating them with the stimulus, the graphics called cupulograms were obtained. According to their results, there would be a linear relationship between the intensity of the stimulus and the du ration of the response. A schan et al. [1] explored a large number of healthy subjects employ ing the cupulometric method and endeavored to characterize the normal values. In the explored end-velocities, from 9 to 52 degrees per second, they also found a linear relationship between the stimulus and the re sponse, although the range of normal was quite broad. The parameter studied by these authors was exclusively the duration of the postrotatory nystagmus. Subsequently, researchers deviated from the study of the postrotatory nystagmus, centering their interest on the caloric tests or on the accelera tion thresholds of the perrotatory nystagmus. On the other hand, the electronystagmographic and photoelectronystagmographic techniques have made possible the faithful record of the nystagmus and the quantitative evaluation of many of its characteristics. Among them, the one that has received most regard among researchers and clinicians is the angular velocity of the slow phase, considering the slow component of the nystagmus as the more genuinely vestibular. The course of the slow phase of the postrotatory nystagmus was studied by Kornhuber et al. [5]. These authors observed an exponential decrease of the angular velocity of the slow phase in the first postrotatory nystagmus. Furthermore, they found a linear relationship between the maximal angu lar velocity of the slow phases of the postrotatory nystagmus and the rota tory velocity before the stop. In the present work, employing a stimulation method similar to the cupulometria of Jongkees and taking advantage of the possibilities intro duced by electronystagmography, we studied postrotatory nystagmus elic ited in healthy subjects with diverse stimulus intensities, making a quanti tative evaluation of the amplitude of the quick phases. On this experi mental basis we attempt - to study several characteristic parameters of the nystagmus and to find out which are the most significant; - to define their normal values, thinking of a possible diagnostic use; - to explore the
Downloaded by: Karolinska Institutet, University Library 130.237.122.245 - 1/30/2019 5:36:00 AM
162
Physiological Postrotatory Nystagmus
163
possible relationship existing between rotatory stimulus and nystagmic re sponse, and - to study the peripheral and central influences involved in the experimental results. Material and Methods Material The experiments have been carried out with human beings, normal with refer ence to the vestibular system and without any record of clinical, otoscopic or audi ometric cochleovestibular abnormalities. A total of 59 subjects have been studied, 4 of which had to be excluded for different reasons; the 55 cases presented in this work remained. The stimulation device used was the rotatory chair of Tonnies n. D-291. This equipment permits the attainment of accelerations and velocities of well-known and controlled magnitudes. The ocular movements corresponding to the provoked post rotatory nystagmus were registered by recording the variations of the corneoretinal potential, amplifying them with an A-C amplifier and inscribing them on thermo sensitive paper with the aid of an adequate recording system. The time constant employed was 1 sec.
Evaluation Once the electronystagmographic traces were obtained, they were quantitatively evaluated by measuring the amplitude of each of the beats and determining its tem poral appearence. In this way a translation of nystagmus into numerical data was obtained.
Downloaded by: Karolinska Institutet, University Library 130.237.122.245 - 1/30/2019 5:36:00 AM
Exploration Once the subject is seated in the Tonnies chair und the periocular electrodes set, visual calibration is carried out. The visual calibration permits the inference of the degree of ocular displacement from measurement of the nystagmographic trace. With this purpose, the system is adjusted so that 10° of ocular displacement in the horizontal plane correspond to 10 mm of displacement of the recording needle on the thermosensitive paper. This visual calibration is made with the help of the Mad dox cross. After this, with eyes closed and in darkness, the experiment begins. The subject is instructed to maintain the position of the head (forward inclination of 30°), and, without being stiff, to be attentive to the progress of the test. In the pauses between two successive rotations (pauses of 3 min duration) the lights are turned on and a little conversation is held with the subject in order to maintain his attention level. In each one of the rotations, a fixed acceleration is employed to reach the constant ve locity required. This velocity is maintained during 2f/2 min and then the chair is ab ruptly stopped (in 1 sec). At this moment, the postrotatory nystagmus appears and is recorded. With each subject, 10 rotations have been performed, 5 clockwise and 5 counter clockwise, beginning with a clockwise rotation. The final velocities are 30, 60, 90, 120 and 180 °/sec.
164
Simon/B artual/L lopis
Table I. Mean values of the distinct parameters and significance Velocity 1, 30 °/sec counterclockwise clockwise
t
Velocity 2, 60 °/sec counterclockwise clockwise
t
Amplitude, degrees % s sx
127.5740 76.8626 10.459
91.3333 69.3130 9.432
4.0356**
220.7090 138.2370 18.639
210.3272 127.0616 17.133
0.6779
16.7296 7.5061 1.0214
2.7488**
24.1309 8.5849 1.157
23.6400 9.0350 1.2182
0.0041
29.6666 14.1754 1.9290
3.1893**
51.7454 16.8788 2.276
52.3454 17.7641 2.3953
0.2963
1.8203 0.5374 0.731
2.1607*
2.2090 0.6083 0.0820
2.2400 0.6302 0.0849
0.5179
2.9611 1.4529 0.1977
3.1666**
4.1800 2.0996 0.2831
4.1072 1.9371 0.2611
0.3325
5.2259 2.4502 0.3334
4.3519s*
8.7490 3.4140 0.4603
9.0490 4.4061 0.5941
0.6294
Duration, sec x s sx
19.8111 9.6239 1.309
Number o f beats x s sx
36.2037 14.4553 1.967
Mean frequency x s sx
1.9759 0.6442 0.0876
Mean amplitude H s sx
3.4259 1.4804 0.2014
Typical velocity x s sx
6.5203 2.7764 0.3778
Likewise, a graphic representation is carried out permitting the quick and clear examination of the course, amplitude and duration of nystagmus and also the com parison with the corresponding contralateral nystagmus [7, 8], Knowing the amplitude of all the nystagmic beats and the duration of nystag mus, the remaining parameters studied in this work can be easily deduced. They are (1) total amplitude (the sum of the amplitudes of all the quick phases of the nystag mus; in degrees); (2) duration (corresponds to the length of the postrotatory nystag-
Downloaded by: Karolinska Institutet, University Library 130.237.122.245 - 1/30/2019 5:36:00 AM
* p
