Journal of the Royal Society of Medicine Volume 71 February 1978
129
convenience, DHSS call-off contracts have been placed for the more commonly used models, but it should be noted that prescription is not restricted to the call-off aids. Binaural fitting is possible in two ways: by the use of two earphones on a pocket aid using a Y-cord (for series connection) or a V-cord (for parallel connection), or by the use of two aids. Experience from the Scandinavian countries indicates that patients tend to reject the use of two aids, probably because of the added inconvenience and a feeling of total dependence on artificial aids. However, such fittings may be of great value in certain cases, especially for severely deaf children and for the deaf-blind. This is necessarily a very brief review and it has not been possible to consider the details of hearing aid facilities and performance; these details are given in the new DHSS 'Guide to Services for Hearing-Impaired People' (DHSS 1976). This is essentially an information file which will be added to by regular instalments and distributed to staff concerned in NHS ear, nose and throat and audiology services. As well as providing technical and supply data on the aids, it also gives the addresses of DHSS branches from whom further information may be obtained. Originally issued in October 1976, it should form a valuable and expanding source of reference on NHS audiology services. References Department of Health and Social Security (1976) Guide to Services for Hearing-Impaired People. DHSS (SH2C), London Medical Research Council (1947) Hearing Aids and Audiometers. Special Report No. 261. HMSO, London
Individual hearing aids: selection and prescription M C Martin BSC
Scientific and Technical Department, Royal National Institute for the Deaf, 105 Gower Street, London WCIE 6AH In the current Royal National Institute for the Deaf (RNID) list of hearing aids there are some three hundred models produced by twenty-seven different manufacturers. This very large range obviously presents difficulties in deciding which aid is most suitable for any particular patient. However, the problem can be eased considerably if the aids are divided into a small number of performance categories, and a logical approach is then adopted for determining the type of aid that might be of greatest value to the patient.
Categories ojfhearing aid One way in which hearing aids can be categorized is in terms of the manner in which they are worn and whether air or bone conduction is to be used (Figure 1). Another possible categorization is based on the performance of the aid itself. Initially aids can be divided into groups with respect to their degree of amplification and maximum output. Table 1 gives a suggested grouping of gain and maximum acoustic output. It should be remembered that it is possible to have all combinations of gain and output as the two Hearing aids
Body worn
Heod worn | Spectacles Behind the ear In the ear
Air conduction Bone conduction Air conduction Bone conduction
Figure 1. Manner of using air and bone conduction hearing aids
130
Journal of the Royal Society of Medicine Volume 71 February 1978
Table 1. A possible grouping of gain and maximum acoustic output br hearing aids
Low Medium High Very high
Gain dB
Maximum acoustic output dB SPL
65
135
parameters are largely independent, i.e. high gain can be combined with low output, low gain with high output, and so on. Frequency response can be divided into a similar number of ranges based on the manner in which the aid responds to high and low frequency sounds. Again these cut-off frequencies may be independent and, depending upon the need, it is possible to have wide low frequency response, narrow high frequency, and so on (Table 2). Table 2. A possible grouping of low and high frequency cut-offfrequencies for hearing aids
Narrow Medium Wide Very wide
Aid cut off low frequency (kHz)
Aid cut off high frequency (kHz)
1.0 0.5 0.2 0.1
2 3
4-5 6
Thefitting of hearing aids Given that there is a very wide range of performance characteristics at our disposal, it is obviously very important to decide the specific characteristics for an individual patient. The majority of hearing aids supplied in the United Kingdom are fitted by a method which can be called 'the dispenser's experience'. If, however, the task of fitting a hearing aid is analysed carefully, it is possible to show that there is a logical sequence of even.ts that must be followed in order to arrive at a choice of hearing aid that is most likely to be successful. The fitting of the hearing aid may be broken up into five stages: (1) pre-fitting considerations; (2) basic audiological considerations; (3) putting the aid on the patient; (4) measurement of aided benefit; (5) trial period and after-care.
Pre-fitting considerations: Figure 2 is a flow diagram of the procedure. An assessment must be made of the patient's physical and mental capabilities. If the patient is handicapped and is unable to handle an aid, it must be ascertained whether he/she can be trained to overcome the problem. If this is possible, a training programme must be organized; if not, it is essential that someone is present to help the patient to use the aid. If neither of these conditions can be fulfilled, supplying the aid is probably of little value. The attitude of the patient is most important; it is essential that the patient should be willing to accept and use the aid. If the attitude towards using an aid is poor, this may be another reason for not supplying an aid.
Journal of the Royal Society of Medicine Volume 71 February 1978
131
Figure 2. Pre-fitting considerations
If the ear is grossly abnormal on inspection, the patient must be referred for otological advice. If it is decided that an aid should not be supplied, the patient should be made aware of the help and devices other than hearing aids that are available. Basic audiological considerations (Figure 3): Most patients will be able to undertake pure-tone air and bone conduction audiometry, but if they cannot, as in the case of small children, the possibility of using objective tests, i.e. acoustic reflex measurements, postauricular muscle responses, etc., should be considered. If equipment for these measurements is not available, general arbitrary values have to be assigned to the hearing loss. Pure-tone thresholds and loudness-discomfort levels should be measured to establish the dynamic range of each ear, followed by speech audiometry to ascertain the speech discrimination ability of each ear. Th,ese tests should indicate whether further otological advice is required, e.g. a small pure-tone loss with marked speech discrimination difficulty. The Hearing Aid Council Code of Practice specifies nine conditions which would necessitate a person being referred for fuller medical advice. It is important to assess whether the two ears are the same. If they are, then it is possible to consider a binaural hearing aid system to be fitted on whichever ear the patient prefers. If the two ears are not the same it is still possible that the combination of two ears is better than one. However, it is of the utmost importance to determine, from the data available, which ear will give maximum benefit. In doing this, consideration must be given to whether one ear can be useful without an aid; if it can, then it is generally better to try and bring the worse ear up to a useful level. If one ear is profoundly deaf and the other severely, the severely-deaf ear probably will have better speech discrimination abilities and will be the one to choose; a
132
Journal of the Royal Society of Medicine Volume 71 February 1978
Figure 3. Basic audiological considerations
Figure 4. Putting the aid on a patient
BICROS system might be considered for such a case. For the extreme case where one ear is normal or near normal and the other very deaf, a CROS system might be considered (see Martin 1976). Many clinics often adopt a rule of 'fit the good ear' or vice versa, but obviously such rules can lead to inappropriate fittings. Putting the aid on the patient (Figure 4): Having interpreted the audiometric data and decided which ear to fit, an aid is selected. The patient must have a satisfactory earmould and if one is not available then an impression must be taken and a decision made as to the type of mould to use (Grover 1974, 1976). The aid must then be placed on the patient, the controls adjusted and the patient's reactions noted. If these are unfavourable, it may be due to the patient's expectations not being fulfilled. However, it may be apparent at this point that an incorrect choice of aid has been made, and therefore a fresh instrument must be selected. Measurement of aided benefit (Figure 5): This important task of evaluation very often is not undertaken when an aid is issued. Initially it must be decided whether speech audiometry is a suitable test for the patient; for those people who are prelingually deaf, or speak only a foreign language, or who have such poor discrimination that they cannot undertake speech
Journal of the Royal Society of Medicine Volume 71 February 1978
Figure 5. Measurement of aided benefit
133
Figure 6. Trial period and after-care
audiometry, an alternative test must be used. At the RNID we have used, for a number of years, a threshold measurement aided and unaided using warble tones which allows the aided range of hearing and the subjective gain given by the aid to be assessed (Worrall & Martin, unpublished). Similar techniques have been described by Gengel et al. (1971) using bands of noise. Bands of noise or warble tones are used to minimize error due to acoustic problems, not for auditory perceptual reasons. The measurements obtained will indicate whether the aid is
appropriate. If speech audiometry is undertaken, the results through the aid should not be worse than from the speech audiometer; if they are, the aid should be checked for faults. If the aid is functioning correctly, the threshold shift test will often show where the problem lies. Often the patient finds the aid too loud, which may be due to the maximum acoustic output of the aid being too high; the output should be adjusted or, if it cannot be altered, the aid changed. The volume control on the aid should not be close to either end of its travel, but if this is the case, internal preset gain controls, where available, should be adjusted or the aid changed. If the aid is changed, loudness discomfort must be checked again. At this point the aid should be suitable for practical evaluation in the user's normal environment. It is useful to note the settings of the aid, i.e. preset controls, earphone, etc., or ideally, to obtain a measurement of the performance of the aid as used.
134
Journal of the Royal Society of Medicine Volume 71 February 1978
Trial period and after-care (Figure 6): In spite of the time spent on the tests, it is still necessary for the patient to have the aid on trial, as no system of evaluation currently exists to predict the benefit of the aid to the patient under all the conditions of everyday life. An after-care service should, where possible, ensure that the patient knows how to use the aid; deal with problems that arise; and arrange for rehabilitation in the form of lip-reading, etc. The most likely problems, if any, are that the aid has become faulty and sometimes that the hearing loss has changed. In many cases, however, the difficulty is due to the limited hearing capacity of the individual, which means re-evaluating the patient. In this paper only a basic outline of one possible method of evaluating a patient for a hearing aid has been described. With our present state of knowledge it is impossible to theorize on which aid is appropriate for any individual, and the emphasis on hearing-aid fitting must be on the measurement of the patient's ability to hear with an aid and not to predict his/her performance from unaided measurements.
Acknowledgments: I am grateful to Paul Ward and Richard Pope for their assistance in compiling the flow diagrams. References Gengel R, Pascoe D & Shore I (1971) Journal of Speech and Hearing Disorders 36, 341-353 Grover B C (1974) Hearing 29, 232-233 Grover B C (1976) British Journal ofAudiology 18, 8-12 Martin M C (1976) In: Scientific Foundations of Otolaryngology. Eds. R Hinchcliffe & D E N Harrison. Heinemann, London; p 805-823
Loop, group and radio aids
Molly Kennedy Heathlands Primary Schoolfor Deaf Children, St Albans, HertJordshire The information on loop, group and radio aids presented in this paper is based on experience of their use in schools. It is certain that all teachers have very ambivalent feelings towards any kind of hearing aid; like the proverbial little girl with the little curl 'when they are good, they are very very good, and when they are bad, they are horrid'. The usefulness of hearing aids to children who really benefit from them makes all the frustration worthwhile, but weighed against this are two factors: first, the child who does not seem to benefit from amplification; and secondly, the difficulty of keeping the aids in good working order. The basic auditory link to the hearing world for each hearing-handicapped child is his own individual hearing aid. Its use and misuse link up very much with the loop system; without the individual aid, the loop cannot be a possibility from the teacher's point of view. The efficiency of individual hearing aids can be ensured only if adequate facilities for maintenance and supply of spares is arranged. Correct harnessing of the body-worn aids is also fundamental to their efficient use; it is regrettable that the harnesses are not issued with the aids as so many breakages would thus be avoided. All those concerned with the welfare of hearing-impaired children must strive for the most productive use of their individual hearing aids if the children are to get the greatest benefit from them. However, these aids have some limitations and often fail to deliver to the child's ears the best sound patterns: (1) Individual aids are limited transmitters of very low and very high frequency sounds, and they have a restricted frequency response. Technical advances (e.g. Electret microphones) can
129
convenience, DHSS call-off contracts have been placed for the more commonly used models, but it should be noted that prescription is not restricted to the call-off aids. Binaural fitting is possible in two ways: by the use of two earphones on a pocket aid using a Y-cord (for series connection) or a V-cord (for parallel connection), or by the use of two aids. Experience from the Scandinavian countries indicates that patients tend to reject the use of two aids, probably because of the added inconvenience and a feeling of total dependence on artificial aids. However, such fittings may be of great value in certain cases, especially for severely deaf children and for the deaf-blind. This is necessarily a very brief review and it has not been possible to consider the details of hearing aid facilities and performance; these details are given in the new DHSS 'Guide to Services for Hearing-Impaired People' (DHSS 1976). This is essentially an information file which will be added to by regular instalments and distributed to staff concerned in NHS ear, nose and throat and audiology services. As well as providing technical and supply data on the aids, it also gives the addresses of DHSS branches from whom further information may be obtained. Originally issued in October 1976, it should form a valuable and expanding source of reference on NHS audiology services. References Department of Health and Social Security (1976) Guide to Services for Hearing-Impaired People. DHSS (SH2C), London Medical Research Council (1947) Hearing Aids and Audiometers. Special Report No. 261. HMSO, London
Individual hearing aids: selection and prescription M C Martin BSC
Scientific and Technical Department, Royal National Institute for the Deaf, 105 Gower Street, London WCIE 6AH In the current Royal National Institute for the Deaf (RNID) list of hearing aids there are some three hundred models produced by twenty-seven different manufacturers. This very large range obviously presents difficulties in deciding which aid is most suitable for any particular patient. However, the problem can be eased considerably if the aids are divided into a small number of performance categories, and a logical approach is then adopted for determining the type of aid that might be of greatest value to the patient.
Categories ojfhearing aid One way in which hearing aids can be categorized is in terms of the manner in which they are worn and whether air or bone conduction is to be used (Figure 1). Another possible categorization is based on the performance of the aid itself. Initially aids can be divided into groups with respect to their degree of amplification and maximum output. Table 1 gives a suggested grouping of gain and maximum acoustic output. It should be remembered that it is possible to have all combinations of gain and output as the two Hearing aids
Body worn
Heod worn | Spectacles Behind the ear In the ear
Air conduction Bone conduction Air conduction Bone conduction
Figure 1. Manner of using air and bone conduction hearing aids
130
Journal of the Royal Society of Medicine Volume 71 February 1978
Table 1. A possible grouping of gain and maximum acoustic output br hearing aids
Low Medium High Very high
Gain dB
Maximum acoustic output dB SPL
65
135
parameters are largely independent, i.e. high gain can be combined with low output, low gain with high output, and so on. Frequency response can be divided into a similar number of ranges based on the manner in which the aid responds to high and low frequency sounds. Again these cut-off frequencies may be independent and, depending upon the need, it is possible to have wide low frequency response, narrow high frequency, and so on (Table 2). Table 2. A possible grouping of low and high frequency cut-offfrequencies for hearing aids
Narrow Medium Wide Very wide
Aid cut off low frequency (kHz)
Aid cut off high frequency (kHz)
1.0 0.5 0.2 0.1
2 3
4-5 6
Thefitting of hearing aids Given that there is a very wide range of performance characteristics at our disposal, it is obviously very important to decide the specific characteristics for an individual patient. The majority of hearing aids supplied in the United Kingdom are fitted by a method which can be called 'the dispenser's experience'. If, however, the task of fitting a hearing aid is analysed carefully, it is possible to show that there is a logical sequence of even.ts that must be followed in order to arrive at a choice of hearing aid that is most likely to be successful. The fitting of the hearing aid may be broken up into five stages: (1) pre-fitting considerations; (2) basic audiological considerations; (3) putting the aid on the patient; (4) measurement of aided benefit; (5) trial period and after-care.
Pre-fitting considerations: Figure 2 is a flow diagram of the procedure. An assessment must be made of the patient's physical and mental capabilities. If the patient is handicapped and is unable to handle an aid, it must be ascertained whether he/she can be trained to overcome the problem. If this is possible, a training programme must be organized; if not, it is essential that someone is present to help the patient to use the aid. If neither of these conditions can be fulfilled, supplying the aid is probably of little value. The attitude of the patient is most important; it is essential that the patient should be willing to accept and use the aid. If the attitude towards using an aid is poor, this may be another reason for not supplying an aid.
Journal of the Royal Society of Medicine Volume 71 February 1978
131
Figure 2. Pre-fitting considerations
If the ear is grossly abnormal on inspection, the patient must be referred for otological advice. If it is decided that an aid should not be supplied, the patient should be made aware of the help and devices other than hearing aids that are available. Basic audiological considerations (Figure 3): Most patients will be able to undertake pure-tone air and bone conduction audiometry, but if they cannot, as in the case of small children, the possibility of using objective tests, i.e. acoustic reflex measurements, postauricular muscle responses, etc., should be considered. If equipment for these measurements is not available, general arbitrary values have to be assigned to the hearing loss. Pure-tone thresholds and loudness-discomfort levels should be measured to establish the dynamic range of each ear, followed by speech audiometry to ascertain the speech discrimination ability of each ear. Th,ese tests should indicate whether further otological advice is required, e.g. a small pure-tone loss with marked speech discrimination difficulty. The Hearing Aid Council Code of Practice specifies nine conditions which would necessitate a person being referred for fuller medical advice. It is important to assess whether the two ears are the same. If they are, then it is possible to consider a binaural hearing aid system to be fitted on whichever ear the patient prefers. If the two ears are not the same it is still possible that the combination of two ears is better than one. However, it is of the utmost importance to determine, from the data available, which ear will give maximum benefit. In doing this, consideration must be given to whether one ear can be useful without an aid; if it can, then it is generally better to try and bring the worse ear up to a useful level. If one ear is profoundly deaf and the other severely, the severely-deaf ear probably will have better speech discrimination abilities and will be the one to choose; a
132
Journal of the Royal Society of Medicine Volume 71 February 1978
Figure 3. Basic audiological considerations
Figure 4. Putting the aid on a patient
BICROS system might be considered for such a case. For the extreme case where one ear is normal or near normal and the other very deaf, a CROS system might be considered (see Martin 1976). Many clinics often adopt a rule of 'fit the good ear' or vice versa, but obviously such rules can lead to inappropriate fittings. Putting the aid on the patient (Figure 4): Having interpreted the audiometric data and decided which ear to fit, an aid is selected. The patient must have a satisfactory earmould and if one is not available then an impression must be taken and a decision made as to the type of mould to use (Grover 1974, 1976). The aid must then be placed on the patient, the controls adjusted and the patient's reactions noted. If these are unfavourable, it may be due to the patient's expectations not being fulfilled. However, it may be apparent at this point that an incorrect choice of aid has been made, and therefore a fresh instrument must be selected. Measurement of aided benefit (Figure 5): This important task of evaluation very often is not undertaken when an aid is issued. Initially it must be decided whether speech audiometry is a suitable test for the patient; for those people who are prelingually deaf, or speak only a foreign language, or who have such poor discrimination that they cannot undertake speech
Journal of the Royal Society of Medicine Volume 71 February 1978
Figure 5. Measurement of aided benefit
133
Figure 6. Trial period and after-care
audiometry, an alternative test must be used. At the RNID we have used, for a number of years, a threshold measurement aided and unaided using warble tones which allows the aided range of hearing and the subjective gain given by the aid to be assessed (Worrall & Martin, unpublished). Similar techniques have been described by Gengel et al. (1971) using bands of noise. Bands of noise or warble tones are used to minimize error due to acoustic problems, not for auditory perceptual reasons. The measurements obtained will indicate whether the aid is
appropriate. If speech audiometry is undertaken, the results through the aid should not be worse than from the speech audiometer; if they are, the aid should be checked for faults. If the aid is functioning correctly, the threshold shift test will often show where the problem lies. Often the patient finds the aid too loud, which may be due to the maximum acoustic output of the aid being too high; the output should be adjusted or, if it cannot be altered, the aid changed. The volume control on the aid should not be close to either end of its travel, but if this is the case, internal preset gain controls, where available, should be adjusted or the aid changed. If the aid is changed, loudness discomfort must be checked again. At this point the aid should be suitable for practical evaluation in the user's normal environment. It is useful to note the settings of the aid, i.e. preset controls, earphone, etc., or ideally, to obtain a measurement of the performance of the aid as used.
134
Journal of the Royal Society of Medicine Volume 71 February 1978
Trial period and after-care (Figure 6): In spite of the time spent on the tests, it is still necessary for the patient to have the aid on trial, as no system of evaluation currently exists to predict the benefit of the aid to the patient under all the conditions of everyday life. An after-care service should, where possible, ensure that the patient knows how to use the aid; deal with problems that arise; and arrange for rehabilitation in the form of lip-reading, etc. The most likely problems, if any, are that the aid has become faulty and sometimes that the hearing loss has changed. In many cases, however, the difficulty is due to the limited hearing capacity of the individual, which means re-evaluating the patient. In this paper only a basic outline of one possible method of evaluating a patient for a hearing aid has been described. With our present state of knowledge it is impossible to theorize on which aid is appropriate for any individual, and the emphasis on hearing-aid fitting must be on the measurement of the patient's ability to hear with an aid and not to predict his/her performance from unaided measurements.
Acknowledgments: I am grateful to Paul Ward and Richard Pope for their assistance in compiling the flow diagrams. References Gengel R, Pascoe D & Shore I (1971) Journal of Speech and Hearing Disorders 36, 341-353 Grover B C (1974) Hearing 29, 232-233 Grover B C (1976) British Journal ofAudiology 18, 8-12 Martin M C (1976) In: Scientific Foundations of Otolaryngology. Eds. R Hinchcliffe & D E N Harrison. Heinemann, London; p 805-823
Loop, group and radio aids
Molly Kennedy Heathlands Primary Schoolfor Deaf Children, St Albans, HertJordshire The information on loop, group and radio aids presented in this paper is based on experience of their use in schools. It is certain that all teachers have very ambivalent feelings towards any kind of hearing aid; like the proverbial little girl with the little curl 'when they are good, they are very very good, and when they are bad, they are horrid'. The usefulness of hearing aids to children who really benefit from them makes all the frustration worthwhile, but weighed against this are two factors: first, the child who does not seem to benefit from amplification; and secondly, the difficulty of keeping the aids in good working order. The basic auditory link to the hearing world for each hearing-handicapped child is his own individual hearing aid. Its use and misuse link up very much with the loop system; without the individual aid, the loop cannot be a possibility from the teacher's point of view. The efficiency of individual hearing aids can be ensured only if adequate facilities for maintenance and supply of spares is arranged. Correct harnessing of the body-worn aids is also fundamental to their efficient use; it is regrettable that the harnesses are not issued with the aids as so many breakages would thus be avoided. All those concerned with the welfare of hearing-impaired children must strive for the most productive use of their individual hearing aids if the children are to get the greatest benefit from them. However, these aids have some limitations and often fail to deliver to the child's ears the best sound patterns: (1) Individual aids are limited transmitters of very low and very high frequency sounds, and they have a restricted frequency response. Technical advances (e.g. Electret microphones) can
