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drink.9 But this cannot be the whole story-nearly 50% ofNorth Americans are slow acetylators3 whereas

idiosyncratic reaction occurs in less than 1% of patientstaking sulphonamides. Susceptibility to these syndromesmay be due to a combination of increased production of areactive metabolite under control of the gene regulatingN-acetylation together with a relative inability of the tissuesto detoxify it; a secondary immunological response producesthe hallmarks of a multisystem hypersensitivity disorder.

Probing the cellular basis of drug toxicity may provide arationale for its prophylaxis and treatment. Such an

understanding has led to the successful management ofparacetamol poisoning with "antidotes" which "replenish"glutathione, allowing removal of the offending reactivespecies before it binds irreversibly to cellularmacromolecules.1O Unwelcome hypersensitivity reactionshave been responsible for the demise of many a promising(and established) therapeutic agent; prediction andavoidance of these iatrogenic disasters remains a majorchallenge.

ASSESSMENT OF DYSPHONIA

ASSESSMENT of dysphonia is an area of cooperationbetween ENT surgeons and speech therapists. For manyyears the assessment remained unchanged; the referringsurgeon would note the state of the vocal cords on indirect

laryngoscopy and the speech therapist would assess thevoice quality whilst taking a case-history, and would noterespiration, phonation, and resonance. There were few, ifany, standardised tests on which perceptions could be based.During the past few years there have been various changesthat have led to a more objective assessment of dysphonia.There has been more interest in voice disorders and a

corresponding development of suitable instrumentation.A more accurate view of the larynx, as a result of increased

use of fibreoptic nasendoscopes, has enabled ENT surgeonsto give speech therapists a more detailed description of thevocal cords and their movement. Work in related areas, suchas deafness and phonetics, has led to development ofinstruments such as the laryngograph and ’Visispeech’which have provided new ways of measuring, recording,and analysing voice. These instruments are extremely usefulboth in assessment and as a means of biofeedback.The laryngograph developed by Fourcin and Abbertonl,2

is a non-invasive instrument which assesses phonatoryability. Two electrodes are placed externally on each side ofthe thyroid cartilage, and an alternating current is passedacross the vocal fold area between the electrodes. Resistanceto the current is inversely proportional to vocal fold contact,and hence there is a close correspondence between thecurrent waveform obtained and the pattern of vocal-foldvibration. Variations in the shape of the waveform (Lx) havebeen shown to reflect certain pathological conditions, whilstthe frequency mode (Fx) provides information on pitch.

Visispeech, designed by the Royal National Institute forthe Deaf, is a microcomputer-based device providing visualdisplay and print-out of important phonatorycharacteristics. A microphone input is used, in contrast to

9. Grant DM, Tang BK, Kalow W.A simple test for acetylator phenotype using caffeine.Br J Clin Pharmacol 1984; 17: 459-64.

10. Meredith JJ, Prescott LF, Vale JA Why do patients still die from paracetamolpoisoning? Br Med J 1986; 293: 345-46

1. Abberton E, Fourcin AJ. First applications of a new laryngograph. Med Biol 1971;111: 172-82

2 Wechsler E A laryngographic study of voice disorders. Br J Dis Commun 1977; 12:19-22

the electrode input of the laryngograph. Originally designedfor use with the deaf,3 visispeech gives a visual display offundamental frequency, voice intensity, and voiced/voiceless contrast. Fundamental frequency informationseems especially relevant to dysphonia assessment andtherapy. There are indications that a hoarse voice ischaracterised not by a continuum of low frequencies, asmight be expected, but rather by exact fractions of the mainfrequency used. Fractions of Y2!, %3 ... 10 have been recorded,suggesting that the vocal cords intermittently miss out 1 in 2,2 in 3.... 6 in 7 vibrations, respectively 4 The most commonfraction recorded is Y2. A fundamental frequency histogramcan therefore be used to indicate hoarseness and comparisonof histograms before and after therapy provides a usefulobjective assessment of progress.

Collaboration of a phonetician and two speech therapistsresulted in the "Vocal Profile Analysis" which enablesfeatures of voice to be charted systematically. The therapistscores these features after listening to a sample of thepatient’s speech. The profile obtained uses defined

terminology and thus a degree of objectivity is achieved.Supralaryngeal and laryngeal features of voice quality areinvestigated, as are prosodic features (pitch and loudness)and temporal organisation (continuity and rate). Laryngealfeatures, for example, consist of tension, position, andphonation type. The scheme defines a neutral for eachparameter, and deviations are graded on a six-point scale(three normal and three abnormal). Comparison of thepatient’s voice before and after therapy is therefore possible.However, some important areas are not included-

specifically, breathing pattern and related postural andtension factors-and these features should always beconsidered by the therapist. Perhaps modification of theprofile will incorporate these features.

Technological advances, offering new ways of studyingvoice and laryngeal dynamics, have brought about a need formore precise information and documentation of theabnormal voice. It has become imperative to substantiatediagnosis with objective quantifiable data; the use ofinstrumentation satisfies these requirements. Moreover theinformation is obtained quickly and there is no discomfort tothe patient. In addition, an accurate permanent record isprovided to assist follow-up. There are disadvantages. Theequipment is expensive and specially trained operators arerequired to run it. Measurement criteria are not fullydefined and it is only possible to assess the effects of alesion-the cause has to be assumed. Single cord movementis not identifiable and occasionally anatomic variation

prevents use of the instruments. For these reasons thehuman ear remains indispensable in the assessment ofabnormal voice. Further, the data from electronic

equipment will only provide information about themechanical and perceptual features of voice, and will notidentify contributory factors such as stress, emotion, andanxiety. Hence, there remains a need for a detailed

case-history and skilled observation of the patient’sbehaviour. 6

3. King AA, Spanner M, Wnght R. A speech display computer for use in schools for thedeaf. Proceedings of IEEE International Conference on Acoustics, Speech andSignal Processing. New York Institute of Electronic and Electrical Engineers,1982: 755-58

4. Cook J, Hooker D, Webb J The application of visispeech to pathologies of voice. BullColl Speech Therapists 1986; 411: 1-2

5 Laver J, Wirz S, MacKenzie J, Hiller S. A perceptual protocol for the analysis of vocalprofiles. In. work in progress, University of Edinburgh Department of Linguistics1981; 14: 139-55

6. Aronson EE. Clinical voice disorders: an interdisciplinary approach. New York:Thieme Stratton, 1980.