THE EFFECTS OF ETHYL ALCOHOL ON CONTRALATERAL AND IPSILATERAL ACOUSTIC REFLEX THRESHOLDS Edward N. Cohill A Dissertation Submitted to the Graduate College of Bowling Green State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY June 1978 XI ABSTRACT Acoustic reflex thresholds were measured at intervals in response to 500, 1000 and 2000Hz pure tones after the ingestion of a 50% solution of 100 proof vodka. These measurements were conducted to determine: 1. the effects of ethyl alcohol on the contralateral and ipsilateral acoustic reflex; 2. the relationship between acoustic reflex thresholds and blood alcohol concentration, and; 3. the relationship between acoustic reflex threshold shift following alcohol ingestion and the frequency of the elicit­ ing stimulus. Sight male and eight female normal-hearing adults served as subjects. Acoustic reflex threshold mea­ surements were obtained pre-ingestion and at blood alcohol concentrations of 0.02 to 0.10% in 0.01% increments. Blood alcohol measurements were made by the use of an electronic a 1c ohol-in-breath analyzer. Acoustic reflex measurements continued until blood alcohol concentrations were reduced to 0.02%. The greatest acoustic reflex threshold shifts occurred at 0.10% blood alcohol concentration. The shifts were approximately 11dB for contralateral stimulation and 7dB for ipsilateral acoustic reflexes for all frequencies. Thus, the effects of ethyl alcohol were more pronounced on contralateral than on ipsilateral reflexes. These effects iil were linear, and the rate of increase in acoustic reflex thresholds was only significantly different at the extremes of the measured blood alcohol concentration levels. Acoust­ ic reflex threshold shifts which resulted from the ingestion of ethyl alcohol did not show significant differences as a function of the frequency of the reflex eliciting stimuli. This was true for both ipsilateral and contralateral stimulation. This study concluded that ethyl alcohol affects the acoustic reflex arc neural system, particularly the contra­ lateral pathway to different degrees depending upon the amount of alcohol in the individual. Small acoustic reflex threshold shifts were seen for low blood alcohol concentra­ tions. Thus, interpretation of acoustic reflex threshold data on an individual who is known or suspected to have ingested ethyl alcohol should be done with caution. XV ACKNOWLEDGMENT I would like to thank Michigan Auditory Instrument Company, Detroit, Michigan and Doug Vogal of CMI, Inc., Vail, Colorado for the use of their equipment. „ Their concern in this research is appreciated. Also, I would like to thank Mr. Edward Roth, President, W. A, Taylor and Co, for his financial support of this research. To my committee, Drs, Joyce Statz, Ray Tucker, Jeff Danhauer, and George Herman, I appreciate their time and comments. Dr, Herbert J. Greenberg, my chairman and friend, a special thanks for his time and companionship. His profes­ sional critisism and help will never be forgotten. A note of thanks and love to my sister, Donna, for her H iterailstic review of the work. Also, Mother, Dad, Bart, D C ridget, and Kathy, we did it, Many cases, cords, and four years later- »If its to be, its up to me’. Mary, thanks for so much. Your love, time, patience, a very thing, this work is yours. V TABLE OF CONTENTS INTRODUCTION » . ........................................................................ .. 1 ACOUSTIC REFLEX........a,....,,,,,,,.,...,.,.......,.......5 Diagnostic importance of the acoustic reflex,......... 5 Psychoacoustic experiments and the acoustic reflex....9 Theories of acoustic reflex activity.,.,.,....,.,,,,..? Neuroanatomy and neurophysiology.,11 Contralateral and ipsilateral reflex measurements..,,17 EFFECTS CF DRUGS ON THE CENTRAL NERVOUS SYSTEM ............ 19 ACTION Of ALCOHOL ON MAN..................................21 E FFECTS CF M ANIPULATIVE AGENTS ON THE ACOUSTIC EEFLEX. 24 STATEMENT OF THE PROBLEM..,......................................... 29 VI METROE.......................... 31 Sub jects, .......... ..................... 31 Instrumentation......................................32 Test pr ocedure....... .............................. ..33 RESULTS, ... .. ................ .. ......... ...............................36 Eat a analysis........................... ............. 36 Ipsilateral versus contralateral stimuli tion., 39 Blood alcohol concentration.39 Frequency46 DISCUSSION. ................. .................................................................... .. ................ 48 Ipsilateral versus contralateral............. .. 48 Blood alcohol concentration.49 E re q uen cy,................... .........................51 Effects of drugs on the acoustic reflex51 Conclusions....... .............................. ,,..,52 REFERENCES.... .............54 APPEN EICES................................................ 68 vii LIST OF TABLES Table 1. Means and standard deviations of contralateral and ipsilateral ear acoustic reflex threshold shifts as a function of blood alcohol concen­ tration and stimulus frequency................... 37 Table 2. Summary of three-way analysis of variance.. .. .... 38 Table 3. Mean values for Scheffe Test of Multiple Com­ parisons for ipsilateral and contralateral acoustic reflex threshold shifts at 0.02 to 0.10% blood alcohol concentration................ 42 Table 4» Mean values for Scheffe Test of Multiple Com­ parisons for contralateral acoustic reflex shifts as a function of blood alcohol concen­ tra tion........................................ ..44 Table 5. Mean values for Scheffe Test of Multiple Com­ parisons for ipsilateral acoustic reflex threshold shifts as a function of blood alco­ hol concentration................................44 Table €. Main effect intervals, formulas, and values for the linear, quadratic and cubic expression of acoustic reflex threshold shift is a func­ tion of blood alcohol concentration.............. 45 Table 7. Mean values for Scheffe Test of Multiple Com­ parisons for the rate of change in acoustic reflex thresholds for ipsilateral and contra­ lateral ear stimulation as a function of blood alcohol concentration ..................... 47 LIST OF FIGURES Figure 1. Neuronal organization of the acoustic reflex. ...14 Figure 2. Mean contralateral and ipsilateral acoustic reflex threshold shifts as a function of blood alcohol concen tration........................... 41 ISTRODOCT ION The acoustic reflex in man has been stalled extensively for almost forty years. It has been define! as the contraction of the stapedius or tensor tympani muscles that will usually produce a measureable, time-locked change in acoustic impedance at the lateral surface of the tympanic membrane (Lilly, 1972). The reflex is bilateral, that is, the stimulation of one ear causes a contraction of the stapedius muscle in both ears (Simmons, 1960; Klockhoff, 1961; Jepsen, 1963; Greisen and Rasmussen, 1970) . Holler (1962) reported that in 1934, Geffcken showed that a contraction of the middle ear muscles changed the acoustic impedance of the hearing mechanism in humans.. The acoustic reflex is due to contraction of the stapedius or the tensor tympani muscle, with the former being the most important. The stapedius muscle receives its nerve supply from a branch of the facial na rve (VII CN), (Byrne, 1938; Borg, 1976). The contraction of the stapedius muscle occurs when stimulation is delivered to the afferent pathway of the acoustic nerve. Following tha synthesis of the stimulation in the brain stem, the efferent, or motor neurons react (Greisen and Rasmussen, 1970). A reflex arc system is the feeder power for the acoustic reflex. The determination of acoustic reflex thresholds can be employed as a testing procedure in the diagnosis of a hearing impairment. The utilization of the acoustic reflex in acoustic impedance audiometry relies on the relationship between the pure tone thresholds and the acoustic reflex thresholds. Sedenberg ( 1963) cited the importance of acoustic reflex thresholds in their evaluations of hearing sensitivity in young children. As Feldman (1967) has pointed out, such measurements provide information concern­ ing the middle ear mechanism independent of a patient’s subjective response. Also, Lamb and Norris (1969) indicated a similar importance in the hard-to-test individual, such as the mentally retarded. Perhaps the most important implication of acoustic reflex thresholds is the determination of the type and degree of hearing loss that a person may have. Conductive versus sensorineural involvement in a hearing loss can be differentiated by acoustic reflex thresholds (Metz, 1946; Liden, 1S69; Jerger, 197C) . In addition, the presence of either ossicular disarticulation or otospongeosis can be determined (Lilly and Shepherd, 1964; Feldman, 1967; Jerger, 1970; Liden, Peterson and Hartford, 1970; Anderson and Barr, 1971). The existence of recruitment in an individual can also be determined by utilizing the acoustic reflex (Liden, 1969, 2 1 970; Alberti and Kristenson, 1970), in that a difference of less than 70 to 90dB between the pure tone thresholds and acoustic reflex thresholds is indicative of recruitment (Thomsen, 1955; Feldman, 1963; Lindstrom and Liden, 1964). Three factors can contribute to abnormal reflex find­ ings or the absence of an acoustic reflex. First, patholog­ ical changes in the afferent pathway of the reflex arc lead to moderate or severe hearing loss. Second, changes in the afferent part are reflected in facial