MOTOR IMPAIRMENT FOLLOWING BLOCKADE OF THE INFRAORBITAL NERVE: IMPLICATIONS FOR THE USE OF ANESTHETIZATION TECHNIQUES IN SPEECH RESEARCH JAMES H. ABBS, JOHN W. FOLKINS, and MURALI SIVARAJAN
University of Washington, Seattle
Infraorbital nerve blocks were performed bilaterally in three subjects as a partial test of the hypothesis that some portion of the motor irmervation to the facial muscles is provided in the trigeminal nerve. To ascertain the influence of this anesthetic procedure, the magnitude and rate of upper lip displacement (for speech and nonspeech tasks), the magnitude and rate of upper lip depression force, and diadochokinetie rate were transduced and recorded, both pre~ andpostanesthesia. All measures, along with bilateral muscle action potentials from orbicularis oris superior obtained for all force and displacement tasks, were reduced in magnitude as a function of the anesthetic condition. These findings, along with results from previous speech anesthetic studies, were interpreted to suggest that anesthesia of the infraorbitalnerve produces measurable, ff not substantial motor weakness in the supraoral musculature. The implications for previous studies, where anesthesia techniques have been employed, are discussed. Most studies attempting to determine the role of afferent feedback in the motor control of speech have employed local anesthesia to eliminate sensation to the oral structures (Guttman, 1954; McCrosky, 1958; Weber, 1961; Ringel and Steer, 1963; Schliesser and Coleman, 1968; Gammon et al., 1971; Scott and Ringel, 1971; Leanderson and Persson, 1972; Putnam and Ringel, 1972; Horii et al., 1973; Putnam, 1973; Hutchinson and Putnam, 1974; Prosek and House, 1975). The nerve blocks employed in these studies have been directed at sensory components of the trigeminal nerve, including both the mandibular branch (buecal, inferior alveolar, lingual) and the maxillary branch (infraorbital, medial and posterior palatine). To assess the influence of apparent sensory deprivation, indexes of speech performance (including measures of the acoustic speech wave, iudgments of phonetic substitutions or distortions, air pressure and air flow patterns, muscle activity, and changes in speech movement) have been used before and after administration of local anesthesia. The conclusions concerning the role of afferent feedback that can be drawn from the above studies depend upon the exact influence of the anesthesia. Unfortunately, there are questions concerning the extent to which the anesthetization procedures employed in these studies produced motor weakness 19
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in addition to the intended sensory deprivation. For example, Locke (1968) reported a reduction in diadochokinetic rate of consonant-vowel syllables following local anesthesia of the buccal, lingual, and inferior alveolar branches of the mandibular nerve and the infraorbital branch of the maxillary nerve. Harris (1970) reported a reduction in activity of the mylohyoid muscle follo~:zing blockade of the buccal, inferior alveolar, and lingual branches of the mandibular nerve. In subsequent experiments, Borden, Harris, and Catena (1973) reported that with some subiects a reduction was observed also in the activity of the anterior belly of the digastric muscle. Similarly, Smith and Lee (1972) 1 and Bauer 2 (1974) have found reductions in electromyographic activity of orbicularis oris superior after blockade of the infraorbital branch of the trigeminal nerve. Similarly, in three pilot subiects observed in our laboratory, we have been unable to obtain a blockade of the infraorbital or mental branches of the trigeminaI nerve without marked reduction in orbicularis oris muscle activity. Instrumental measures of isometric lip closing force in these same pilot subiects revealed corresponding reductions following anesthesia. These findings of motor weakness typically have been interpreted as the result of inadvertent infiltration of anesthetic agent into motor nerves or muscles which lie in the vicinity of the sensory nerves that were intended for blockade. However, a second explanation for these results becomes apparent with examination of the literature in neuroanatomy and clinical neurology. Reports by Martin and Helsper (1957, 1960); Bowden, Mahran, and Gooding (1960); Conley, Papper, and Kaplan (1963) ; Conley (1964); and Baumel (1974) suggest that classical descriptions of the motor and sensory division in the trigeminal and facial nerves may be only partially correct. In particular, these authors suggest that the buccal and inferior alveolar branches of the mandibular nerve and the infraorbital and palatine branches of the maxillary nerve may carry motor fibers to the facial musculature. Data supporting this suggestion have been available for some time. For example, Cushing (1904) and Davies (1907) observed a degree of facial paresis in most patients following gasserian ganglion destruction (a procedure employed for the relief of trigeminal neuralgia). More recent observations on the issue of facial motor innervation by trigeminal branches have been made following destruction of the facial nerve. Martin and Helsper (1957) and Conley et al. (1963) reported cases where motor control of the facial muscles returned a few months after facial nerve destruction. Subsequent studies by these authors demonstrated that the reestablished facial motor integrity was not the result of facial nerve fiber regeneration (Martin and Helsper, 1960) and could be abolished by local anesthesia of the trigeminal nerve (Conley 1964). In attempts to corroborate these reports with more controlled observations, Sutton 3 used a cuff electrode to directly stimulate peripheral branches of the trigeminal 1T. Smith and C. Lee, unpublished manuscript (1971). 2L. Bauer, personal communication (1975). aD. Sutton, personal communication (1975). 20 Journal o[ Speech and Hearing Research
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19 19-35 1976
nerve in nonhuman primates. Using this procedure, Sutton found early (direct) motor discharges in one or more facial muscles and a later reflex discharge in the same muscles. Transection of the nerve distal to the stimulating electrodes abolished the direct motor responses, while in several cases the later reflex responses remained unchanged. The neuroanatomical basis for these observations appears to relate to tho overlap and communications between the trigeminal and facial nerves both intracranially (within the brain stem) and extracranially (Bowden et al., 1960; Baumel, 1974). On reviewing the evidence for an accessory trigeminal pathway for facial motoneurons, Baumel (1974) suggests from a teleological perspective, that a dual nerve supply of the facial muscles would have a "selective advantage" similar to the plurisegmental innervation of the limb muscles. These reports imply, in turn, that facial motor weakness may be created by local anesthesia of certain trigeminal nerve branches. Since most speech investigators have not incorporated specific evaluations of facial muscle weakness following trigeminal anesthesia, some of the reported effects of these procedures upon speech may be the result of motor impairment rather than sensory deprivation. In this context, the purpose of the present paper is to evaluate motor integrity of the facial musculature following anesthesia of one sensory branch of the trigeminal nerve-the infraorbital. METHOD
Subjects Three normal adult males, ranging in age from 26 to 33 years, served as subjects.
Administration of the Nerve Block All subiects were administered a bilateral infraorbital nerve block at a site determined by palpation of the infraorbital foramen and exploration with the hypodermic needle until a nerve "contact paresthesia" was reported. Although experiments in the speech literaturo have not reported the use of contact paresthesia as an iniection criteria for infraorbital anesthetization, some anesthesiologists believe that contact paresthesia is crucial to insure that the anesthetic agent is placed in the immediate vicinity of the nerve (Moore, 1953, page 57). To identify when the needle had contacted the nerve, subiects were instructed to report sensations (paresthesias) resulting from needle exploration that produced an "electrical" shock which traveled from an area below the eye to the corner of the mouth. This sensation was elicited at least twice for each infraorbital site prior to iniection of anesthetic agent. The anesthetic agent employed was 2~ lidocaine (Xylocaine) with 1:100,000 epinephrine and is the same as employed in most previous investigations in the speech literature (Hutchinson, 1973). For each site 1.25 cc of anesthetic agent was iniected. This quantity of anesthesia is slightly less than 1.4 cc per ABBS ET AL.: Motor
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Impairment
21
injection employed for this nerve branch by previous investigators.* This quantity of locally injected lidocaine produces anesthetic block levels which are far lower than those observed to influence general nervous system function (Bromage and Robson, 1961; De Jong~ 1970, Chapters 10 and 11). Facial sensation prior to and following the blockade was determined with von Frey hairs applied to the facial skin. Tests to Determine Motor Integrity
When one observes a reduction or modification of muscle activity following anesthesia, it is difficult to say with certainty that this reduction is due to blockade of motoneurons since afferent feedback might play a role in control of that activity. Moreover, inasmuch as the speech production system demonstrates a substantial capability for interarticulator and intermuscle compensation, observation of movement and muscle activity for speech tasks, in particular, is subiect to misinterpretation. Given these difficulties, we have devised a series of tests for the motor integrity of the supraoral muscles that were an attempt to minimize these ambiguities. These tests, described in detail, were administered before and after anesthetization. Discrete Speech Production Task. To reduce the complexity that is typically associated with physiological analysis of a continuous speech sample (or even a speech sample in a carrier phase), our first task involved observation of production of the isolated CV syllable [p~e] using a reaction time paradigm. With this task, we were interested in the magnitude and rate of upper lip depression and associated muscle activity. Subiects were asked to relax the labial musculature (in the reaction time foreperiod signaled by the onset of a tone) and then produce the CV upon cessation of that tone (Netsell and Daniel, 1974). A bite block was inserted between the upper and lower molars to provide a rest position with an intercisor distance of 18-20 mm. The bite block was employed to create a situation that required a supraminimal level of upper lip movement and labial muscle activity, and to stabilize the mandible and eliminate the possibility of mandibular compensation ff upper lip immobility occurred. During production of these syllables several channels of physiological activity were transduced and recorded: (1) speech acoustic signal; (2) upper lip movement, inferior-superior; (3) lower lip movement, inferior-superior; (4) bilateral muscle activity in orbicularis oris superior (OOS); and (5) bilateral muscle activity in depressor anguli oris (DAO). Muscle activity from DAO was recorded because while this muscle may act to depress the upper lip it should not be influenced by infraorbital anesthesia. Lip movement was transduced with a strain gauge system similar to that reported by Abbs and Gilbert (1973). Electromyographic signals were recorded from bipolar hooked wire electrodes. Each wire of the bipolar pair was inserted separately with a 30-gauge needle, providing a larger recording aqeld than is generally obtained 4j. Hutchinson, personal communication (1974). 22 lournal of Speech and Hearing Research
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19 19-35 1976
when both wires are inserted with a single needle. Electrode placement sites were determined, a priori, on the basis of information provided by cadaveric studies (Kennedy, 1974) and verified, a posteriori, with nonspeech movement tests. Electrodes were placed prior to the preanesthesia tasks and left undisturbed until the postanesthesia tasks were completed. Muscle activity was not recorded from the levator labii superior muscle, since placement sites for this muscle are in the immediate vicinity of the area that had to be probed to obtain contact paresthesia for anesthesia. That is, it was suspected that positioning and repositioning of the hypodermic needle (in attempts to elicit nerve contact paresthesia) would dislodge electrodes placed in this muscle, creating a situation where changes in the pre- and postanesthesia electromyograms would be uninterpretable. Diadochokinetic Rate. Diadochokinetic rate was included primarily to provide a basis for comparison of our results with those of earlier investigators (Ringel and Steer, 1963; Locke, 1968; Schliesser and Coleman, 1968; Gammon et al., 1971; Hutchinson, 1973). To make the task specific to the labial system, the subjects were asked to repeat the syllables [p~e], [b~e], and [m~e] as fast as possible. The bite block and the channels of physiological monitoring were the same as those for the discrete speech task. Non-speech Elevation and Depression of the Upper Lip. To determine the influence of the infraorbital anesthesia upon the range of upper lip displacement, subiects were asked to maximally elevate and depress the upper lip. For each subject, inferior-superior displacement of the upper lip was transduced for four to six depression movements and four to six elevation movements. A bite block was employed for this task to provide an interlabial separation that allowed the upper lip to be fully depressed without obstruction by the lower lip. Lip Closing Force. A strain gauge system was constructed to transduce the maximum force generated by the upper lip (exclusive of the lower lip) in the inferior direction. Measures of isometric muscle strength have been employed extensively to determine alpha motorneuron integrity following anesthetic procedures (Matthews and Rushworth, 1957; Landau, Weaver, and Hornbein, 1963; Shambes, 1968; Smith, Roberts, and Atkins, 1972; Abbs, 1973). In addition to the voltage analog of force, bilateral electromyograms from the OOS and DAO were recorded. Each subject was asked to produce approximately 10 maximum force efforts. During the task subjects monitored a voltage analog of the upper lip depression force on an oscilloscope. Visual feedback was employed to reduce the possibility that decreased sensory awareness of the upper lip would result in a reduction in upper lip force, independent of motor weakness. In pilot experiments it was noted that the rate at which force was generated, as well as the magnitude of static force, was reduced as a result of infraorbital anesthesia. Therefore in the present experiment, a force reaction time task was employed (in addition to the static test described above) to obtain some indication of the influence of anesthesia on the rate of upper lip force generation. Values of the rate of upper lip depression force were obtained A~s ~r xL.: Motor Impairment 23
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9
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1ournal o[ Speech and Hearing Research
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19
19-35
1976
by measuring the magnitude of force change and dividing that value by the time interval over which that change occurred. Subiects were asked to depress the lip against the force transducer "as quickly as possible" at the cessation of a stimulus tone. Approximately 12 repetitions of this task were obtained for each subiect, both before and after anesthesia. RESULTS Following administration of the anesthesia all subiects reported substantial loss of sensation in the upper lips and cheeks. These reports were confirmed by applying yon Frey hairs to the skin and eliciting subiect responses. It was found, with this technique, that the loss of sensation was bilaterally symmetric for all three subiects. In addition, perioral reflexes (elicited before and after anesthesia with mechanical stimuli) were abolished in all three subiects after anesthesia (Kugelberg, 1952; Netsell and Abbs, 1973). Due to a false report of contact paresthesia, an extra 1.0 cc of anesthetic agent was iniected on the fight side of Subject 3. However, this additional anesthesia did not appear to result in disproportionate reductions in the EMG measures from the fight side of this subiect. No formal iudgments of speech were made; however, the speech of all subiects after anesthesia was grossly normal with a slight tendency to make articulatory errors. All tests of motor integrity yielded results supporting the same general conclusion: blockade of the infraorbital nerve results in a measurable, if not substantial, decrement in motor performance of the upper lip. Inspection of the individual test results provides a more detailed perspective on this conclusion. Student's two tailed, t tests were applied to all pre- and postanesthesia measures except for diadochokinetic rate. Discrete Speech Production Task. Figure 1 provides examples of the speech acoustic signal and movement recorded during the discrete speech task for all three subiects. In Figure 2A and B the mean displacements and velocities of the upper lip movement (before and after anesthesia) are presented. The vertical dashed lines in Figure 1 indicate the source of the displacement measurements shown in Figure 2. It is apparent from Figure 2A and B that there is a substantial and consistent reduction in both upper lip displacement and velocity as a result of anesthesia. The reductions in displacements ranged from 55~ for Subiect 1 to 30~ for Subiect 2. The reductions in velocity are comparable. The results of Student's t test showed significant differences in both displacement and velocity (p < 0.01 ) for each subiect. Also as a result of anesthesia, average lower lip elevation movement for all subiects increased, apparently to compensate for reductions in upper lip movement. The increase in lower lip movement was manifest in two different forms: (1) an increase in the phasic movement, initiated from the same prespeech posture as for the preanesthesia condition (as seen in Figure 1 for Subiect 3), or (2) a more elevated prespeech posture for the lower lip upon which the phasic speech movement was superimposed (as seen in Figure 1 for Subiects i and 2). ABBs ET AL.: Motor Impairment 25
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SUBJECT
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ORBICULARIS ORIS SUPERIOR
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left D)
right
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left
right
DEPRESSOR pre- anesthesia
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ANGULI
9
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4"/.
§ 4
left
mght
ORIS
post -anesthesia
~
Fxotrt~ 9.. Mean values of (A) upper lip displacement, (B) upper lip velocity and corresponding muscle activity levels from (C) orbicularis oris superior and (D) depressor anguli oris muscles, pre- and postanesthesia for all subjects. Muscle activity values were obtained from muscle action potentials which had been smoothed and rectified. Brackets indicate one standard deviation above and below the mean.
26 ]eurnal of Speech and Hearing Research
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19 19-35 1976
SUBJECT
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-anesthesia
FxgtaaE 3. Mean values of diadochokinetic rate for (A) [pae], (B) [bae], and (C) [rnae] pre- and postanesthesia for all subjects.
Figure 2C and D show the mean peak values of rectified and smoothed electromyography from OOS and DAO. In four out of six measurements (p < 0.01), it can be seen that the reduction in upper lip movement was accompanied by a corresponding reduction in OOS activity. On the left side of Subject 1, there was a significant (p < 0.01) increase in electromyography from OOS. The apparent asymmetry observed here may be the result of asymmetry in administration of the anesthesia or perhaps asymmetry in the motor innervation of the supraoral muscles by the trigeminal nerve. While asymmetry can be documented most adequately by repeated applications of anesthesia in the same subjects, Sutton z has observed comparable asymmetry in trigeminal innervation in nonhuman primates. Baumel (1974) discusses the common findings of asymmetry in the facial and trigeminal nerves. As a parenthetical comment it is worth noting that sensory tests (yon Frey hairs) did not reveal a corresponding sensory asymmetry. It is also of interest that only on the fight ABBS ET AL.I Motor Impairment 27
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,6a
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Journal of Speech and Hearing Research
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v
19
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1976
SUBJECT
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SUBJECT -
-
39
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UPPER LIP ELEVATION post -anesthesia
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FIctraE 5. Mean values of upper lip (A) elevation and (B) depression as a function of anesthesia. Brackets indicate one standard deviation above and below the mean. side of Subject i did we see a compensatory increase in DAO after anesthesia
(p
University of Washington, Seattle
Infraorbital nerve blocks were performed bilaterally in three subjects as a partial test of the hypothesis that some portion of the motor irmervation to the facial muscles is provided in the trigeminal nerve. To ascertain the influence of this anesthetic procedure, the magnitude and rate of upper lip displacement (for speech and nonspeech tasks), the magnitude and rate of upper lip depression force, and diadochokinetie rate were transduced and recorded, both pre~ andpostanesthesia. All measures, along with bilateral muscle action potentials from orbicularis oris superior obtained for all force and displacement tasks, were reduced in magnitude as a function of the anesthetic condition. These findings, along with results from previous speech anesthetic studies, were interpreted to suggest that anesthesia of the infraorbitalnerve produces measurable, ff not substantial motor weakness in the supraoral musculature. The implications for previous studies, where anesthesia techniques have been employed, are discussed. Most studies attempting to determine the role of afferent feedback in the motor control of speech have employed local anesthesia to eliminate sensation to the oral structures (Guttman, 1954; McCrosky, 1958; Weber, 1961; Ringel and Steer, 1963; Schliesser and Coleman, 1968; Gammon et al., 1971; Scott and Ringel, 1971; Leanderson and Persson, 1972; Putnam and Ringel, 1972; Horii et al., 1973; Putnam, 1973; Hutchinson and Putnam, 1974; Prosek and House, 1975). The nerve blocks employed in these studies have been directed at sensory components of the trigeminal nerve, including both the mandibular branch (buecal, inferior alveolar, lingual) and the maxillary branch (infraorbital, medial and posterior palatine). To assess the influence of apparent sensory deprivation, indexes of speech performance (including measures of the acoustic speech wave, iudgments of phonetic substitutions or distortions, air pressure and air flow patterns, muscle activity, and changes in speech movement) have been used before and after administration of local anesthesia. The conclusions concerning the role of afferent feedback that can be drawn from the above studies depend upon the exact influence of the anesthesia. Unfortunately, there are questions concerning the extent to which the anesthetization procedures employed in these studies produced motor weakness 19
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in addition to the intended sensory deprivation. For example, Locke (1968) reported a reduction in diadochokinetic rate of consonant-vowel syllables following local anesthesia of the buccal, lingual, and inferior alveolar branches of the mandibular nerve and the infraorbital branch of the maxillary nerve. Harris (1970) reported a reduction in activity of the mylohyoid muscle follo~:zing blockade of the buccal, inferior alveolar, and lingual branches of the mandibular nerve. In subsequent experiments, Borden, Harris, and Catena (1973) reported that with some subiects a reduction was observed also in the activity of the anterior belly of the digastric muscle. Similarly, Smith and Lee (1972) 1 and Bauer 2 (1974) have found reductions in electromyographic activity of orbicularis oris superior after blockade of the infraorbital branch of the trigeminal nerve. Similarly, in three pilot subiects observed in our laboratory, we have been unable to obtain a blockade of the infraorbital or mental branches of the trigeminaI nerve without marked reduction in orbicularis oris muscle activity. Instrumental measures of isometric lip closing force in these same pilot subiects revealed corresponding reductions following anesthesia. These findings of motor weakness typically have been interpreted as the result of inadvertent infiltration of anesthetic agent into motor nerves or muscles which lie in the vicinity of the sensory nerves that were intended for blockade. However, a second explanation for these results becomes apparent with examination of the literature in neuroanatomy and clinical neurology. Reports by Martin and Helsper (1957, 1960); Bowden, Mahran, and Gooding (1960); Conley, Papper, and Kaplan (1963) ; Conley (1964); and Baumel (1974) suggest that classical descriptions of the motor and sensory division in the trigeminal and facial nerves may be only partially correct. In particular, these authors suggest that the buccal and inferior alveolar branches of the mandibular nerve and the infraorbital and palatine branches of the maxillary nerve may carry motor fibers to the facial musculature. Data supporting this suggestion have been available for some time. For example, Cushing (1904) and Davies (1907) observed a degree of facial paresis in most patients following gasserian ganglion destruction (a procedure employed for the relief of trigeminal neuralgia). More recent observations on the issue of facial motor innervation by trigeminal branches have been made following destruction of the facial nerve. Martin and Helsper (1957) and Conley et al. (1963) reported cases where motor control of the facial muscles returned a few months after facial nerve destruction. Subsequent studies by these authors demonstrated that the reestablished facial motor integrity was not the result of facial nerve fiber regeneration (Martin and Helsper, 1960) and could be abolished by local anesthesia of the trigeminal nerve (Conley 1964). In attempts to corroborate these reports with more controlled observations, Sutton 3 used a cuff electrode to directly stimulate peripheral branches of the trigeminal 1T. Smith and C. Lee, unpublished manuscript (1971). 2L. Bauer, personal communication (1975). aD. Sutton, personal communication (1975). 20 Journal o[ Speech and Hearing Research
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19 19-35 1976
nerve in nonhuman primates. Using this procedure, Sutton found early (direct) motor discharges in one or more facial muscles and a later reflex discharge in the same muscles. Transection of the nerve distal to the stimulating electrodes abolished the direct motor responses, while in several cases the later reflex responses remained unchanged. The neuroanatomical basis for these observations appears to relate to tho overlap and communications between the trigeminal and facial nerves both intracranially (within the brain stem) and extracranially (Bowden et al., 1960; Baumel, 1974). On reviewing the evidence for an accessory trigeminal pathway for facial motoneurons, Baumel (1974) suggests from a teleological perspective, that a dual nerve supply of the facial muscles would have a "selective advantage" similar to the plurisegmental innervation of the limb muscles. These reports imply, in turn, that facial motor weakness may be created by local anesthesia of certain trigeminal nerve branches. Since most speech investigators have not incorporated specific evaluations of facial muscle weakness following trigeminal anesthesia, some of the reported effects of these procedures upon speech may be the result of motor impairment rather than sensory deprivation. In this context, the purpose of the present paper is to evaluate motor integrity of the facial musculature following anesthesia of one sensory branch of the trigeminal nerve-the infraorbital. METHOD
Subjects Three normal adult males, ranging in age from 26 to 33 years, served as subjects.
Administration of the Nerve Block All subiects were administered a bilateral infraorbital nerve block at a site determined by palpation of the infraorbital foramen and exploration with the hypodermic needle until a nerve "contact paresthesia" was reported. Although experiments in the speech literaturo have not reported the use of contact paresthesia as an iniection criteria for infraorbital anesthetization, some anesthesiologists believe that contact paresthesia is crucial to insure that the anesthetic agent is placed in the immediate vicinity of the nerve (Moore, 1953, page 57). To identify when the needle had contacted the nerve, subiects were instructed to report sensations (paresthesias) resulting from needle exploration that produced an "electrical" shock which traveled from an area below the eye to the corner of the mouth. This sensation was elicited at least twice for each infraorbital site prior to iniection of anesthetic agent. The anesthetic agent employed was 2~ lidocaine (Xylocaine) with 1:100,000 epinephrine and is the same as employed in most previous investigations in the speech literature (Hutchinson, 1973). For each site 1.25 cc of anesthetic agent was iniected. This quantity of anesthesia is slightly less than 1.4 cc per ABBS ET AL.: Motor
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Impairment
21
injection employed for this nerve branch by previous investigators.* This quantity of locally injected lidocaine produces anesthetic block levels which are far lower than those observed to influence general nervous system function (Bromage and Robson, 1961; De Jong~ 1970, Chapters 10 and 11). Facial sensation prior to and following the blockade was determined with von Frey hairs applied to the facial skin. Tests to Determine Motor Integrity
When one observes a reduction or modification of muscle activity following anesthesia, it is difficult to say with certainty that this reduction is due to blockade of motoneurons since afferent feedback might play a role in control of that activity. Moreover, inasmuch as the speech production system demonstrates a substantial capability for interarticulator and intermuscle compensation, observation of movement and muscle activity for speech tasks, in particular, is subiect to misinterpretation. Given these difficulties, we have devised a series of tests for the motor integrity of the supraoral muscles that were an attempt to minimize these ambiguities. These tests, described in detail, were administered before and after anesthetization. Discrete Speech Production Task. To reduce the complexity that is typically associated with physiological analysis of a continuous speech sample (or even a speech sample in a carrier phase), our first task involved observation of production of the isolated CV syllable [p~e] using a reaction time paradigm. With this task, we were interested in the magnitude and rate of upper lip depression and associated muscle activity. Subiects were asked to relax the labial musculature (in the reaction time foreperiod signaled by the onset of a tone) and then produce the CV upon cessation of that tone (Netsell and Daniel, 1974). A bite block was inserted between the upper and lower molars to provide a rest position with an intercisor distance of 18-20 mm. The bite block was employed to create a situation that required a supraminimal level of upper lip movement and labial muscle activity, and to stabilize the mandible and eliminate the possibility of mandibular compensation ff upper lip immobility occurred. During production of these syllables several channels of physiological activity were transduced and recorded: (1) speech acoustic signal; (2) upper lip movement, inferior-superior; (3) lower lip movement, inferior-superior; (4) bilateral muscle activity in orbicularis oris superior (OOS); and (5) bilateral muscle activity in depressor anguli oris (DAO). Muscle activity from DAO was recorded because while this muscle may act to depress the upper lip it should not be influenced by infraorbital anesthesia. Lip movement was transduced with a strain gauge system similar to that reported by Abbs and Gilbert (1973). Electromyographic signals were recorded from bipolar hooked wire electrodes. Each wire of the bipolar pair was inserted separately with a 30-gauge needle, providing a larger recording aqeld than is generally obtained 4j. Hutchinson, personal communication (1974). 22 lournal of Speech and Hearing Research
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19 19-35 1976
when both wires are inserted with a single needle. Electrode placement sites were determined, a priori, on the basis of information provided by cadaveric studies (Kennedy, 1974) and verified, a posteriori, with nonspeech movement tests. Electrodes were placed prior to the preanesthesia tasks and left undisturbed until the postanesthesia tasks were completed. Muscle activity was not recorded from the levator labii superior muscle, since placement sites for this muscle are in the immediate vicinity of the area that had to be probed to obtain contact paresthesia for anesthesia. That is, it was suspected that positioning and repositioning of the hypodermic needle (in attempts to elicit nerve contact paresthesia) would dislodge electrodes placed in this muscle, creating a situation where changes in the pre- and postanesthesia electromyograms would be uninterpretable. Diadochokinetic Rate. Diadochokinetic rate was included primarily to provide a basis for comparison of our results with those of earlier investigators (Ringel and Steer, 1963; Locke, 1968; Schliesser and Coleman, 1968; Gammon et al., 1971; Hutchinson, 1973). To make the task specific to the labial system, the subjects were asked to repeat the syllables [p~e], [b~e], and [m~e] as fast as possible. The bite block and the channels of physiological monitoring were the same as those for the discrete speech task. Non-speech Elevation and Depression of the Upper Lip. To determine the influence of the infraorbital anesthesia upon the range of upper lip displacement, subiects were asked to maximally elevate and depress the upper lip. For each subject, inferior-superior displacement of the upper lip was transduced for four to six depression movements and four to six elevation movements. A bite block was employed for this task to provide an interlabial separation that allowed the upper lip to be fully depressed without obstruction by the lower lip. Lip Closing Force. A strain gauge system was constructed to transduce the maximum force generated by the upper lip (exclusive of the lower lip) in the inferior direction. Measures of isometric muscle strength have been employed extensively to determine alpha motorneuron integrity following anesthetic procedures (Matthews and Rushworth, 1957; Landau, Weaver, and Hornbein, 1963; Shambes, 1968; Smith, Roberts, and Atkins, 1972; Abbs, 1973). In addition to the voltage analog of force, bilateral electromyograms from the OOS and DAO were recorded. Each subject was asked to produce approximately 10 maximum force efforts. During the task subjects monitored a voltage analog of the upper lip depression force on an oscilloscope. Visual feedback was employed to reduce the possibility that decreased sensory awareness of the upper lip would result in a reduction in upper lip force, independent of motor weakness. In pilot experiments it was noted that the rate at which force was generated, as well as the magnitude of static force, was reduced as a result of infraorbital anesthesia. Therefore in the present experiment, a force reaction time task was employed (in addition to the static test described above) to obtain some indication of the influence of anesthesia on the rate of upper lip force generation. Values of the rate of upper lip depression force were obtained A~s ~r xL.: Motor Impairment 23
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9
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19
19-35
1976
by measuring the magnitude of force change and dividing that value by the time interval over which that change occurred. Subiects were asked to depress the lip against the force transducer "as quickly as possible" at the cessation of a stimulus tone. Approximately 12 repetitions of this task were obtained for each subiect, both before and after anesthesia. RESULTS Following administration of the anesthesia all subiects reported substantial loss of sensation in the upper lips and cheeks. These reports were confirmed by applying yon Frey hairs to the skin and eliciting subiect responses. It was found, with this technique, that the loss of sensation was bilaterally symmetric for all three subiects. In addition, perioral reflexes (elicited before and after anesthesia with mechanical stimuli) were abolished in all three subiects after anesthesia (Kugelberg, 1952; Netsell and Abbs, 1973). Due to a false report of contact paresthesia, an extra 1.0 cc of anesthetic agent was iniected on the fight side of Subject 3. However, this additional anesthesia did not appear to result in disproportionate reductions in the EMG measures from the fight side of this subiect. No formal iudgments of speech were made; however, the speech of all subiects after anesthesia was grossly normal with a slight tendency to make articulatory errors. All tests of motor integrity yielded results supporting the same general conclusion: blockade of the infraorbital nerve results in a measurable, if not substantial, decrement in motor performance of the upper lip. Inspection of the individual test results provides a more detailed perspective on this conclusion. Student's two tailed, t tests were applied to all pre- and postanesthesia measures except for diadochokinetic rate. Discrete Speech Production Task. Figure 1 provides examples of the speech acoustic signal and movement recorded during the discrete speech task for all three subiects. In Figure 2A and B the mean displacements and velocities of the upper lip movement (before and after anesthesia) are presented. The vertical dashed lines in Figure 1 indicate the source of the displacement measurements shown in Figure 2. It is apparent from Figure 2A and B that there is a substantial and consistent reduction in both upper lip displacement and velocity as a result of anesthesia. The reductions in displacements ranged from 55~ for Subiect 1 to 30~ for Subiect 2. The reductions in velocity are comparable. The results of Student's t test showed significant differences in both displacement and velocity (p < 0.01 ) for each subiect. Also as a result of anesthesia, average lower lip elevation movement for all subiects increased, apparently to compensate for reductions in upper lip movement. The increase in lower lip movement was manifest in two different forms: (1) an increase in the phasic movement, initiated from the same prespeech posture as for the preanesthesia condition (as seen in Figure 1 for Subiect 3), or (2) a more elevated prespeech posture for the lower lip upon which the phasic speech movement was superimposed (as seen in Figure 1 for Subiects i and 2). ABBs ET AL.: Motor Impairment 25
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SUBJECT
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DEPRESSOR pre- anesthesia
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9
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left
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ORIS
post -anesthesia
~
Fxotrt~ 9.. Mean values of (A) upper lip displacement, (B) upper lip velocity and corresponding muscle activity levels from (C) orbicularis oris superior and (D) depressor anguli oris muscles, pre- and postanesthesia for all subjects. Muscle activity values were obtained from muscle action potentials which had been smoothed and rectified. Brackets indicate one standard deviation above and below the mean.
26 ]eurnal of Speech and Hearing Research
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19 19-35 1976
SUBJECT
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Figure 2C and D show the mean peak values of rectified and smoothed electromyography from OOS and DAO. In four out of six measurements (p < 0.01), it can be seen that the reduction in upper lip movement was accompanied by a corresponding reduction in OOS activity. On the left side of Subject 1, there was a significant (p < 0.01) increase in electromyography from OOS. The apparent asymmetry observed here may be the result of asymmetry in administration of the anesthesia or perhaps asymmetry in the motor innervation of the supraoral muscles by the trigeminal nerve. While asymmetry can be documented most adequately by repeated applications of anesthesia in the same subjects, Sutton z has observed comparable asymmetry in trigeminal innervation in nonhuman primates. Baumel (1974) discusses the common findings of asymmetry in the facial and trigeminal nerves. As a parenthetical comment it is worth noting that sensory tests (yon Frey hairs) did not reveal a corresponding sensory asymmetry. It is also of interest that only on the fight ABBS ET AL.I Motor Impairment 27
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v
19
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1976
SUBJECT
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FIctraE 5. Mean values of upper lip (A) elevation and (B) depression as a function of anesthesia. Brackets indicate one standard deviation above and below the mean. side of Subject i did we see a compensatory increase in DAO after anesthesia
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