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Biomedical subjects

M A Stone

Publications and source records attributed to M A Stone.

At least 19 recordsLinked to original sources
PubMed2006

Bcl-x(L) expression in vivo in rheumatoid synovium.

To examine the expression of the apoptosis regulatory protein, Bcl-x(L), in the synovium of patients with rheumatoid arthritis (RA) and osteoarthritis (OA). Immunohistochemistry for Bcl-x(L) was carried out on synovial samples from patients with RA and OA. Reverse transcriptase polymerase chain reaction (RT-PCR) and Western blot analysis were performed to qualitatively examine the expression of Bcl-x(L). Bcl-x(L) expression was detected in the lining, endothelium and inflammatory cells of both RA (n=20) and OA (n=10) samples. However, there was significantly more expression in the lining of RA synovium compared to OA (77 vs 61%, p<0.05). Many of the positive cells in the RA subsynovium were noted to be plasma cells. There was a significant correlation between Bcl-x(L) expression and the number of inflammatory cells in the subsynovium of RA and OA patients (r (s)=0.376, p<0.05, n=30). Age and disease duration did not correlate with Bcl-x(L) expression in rheumatoid patients. Bcl-x(L) may play a role in the extended survival of synoviocytes and inflammatory cells in rheumatoid synovium.

Aged↗
PubMed2006

The prevalence of co-morbid depression in adults with Type 2 diabetes: a systematic review and meta-analysis.

AIM: To conduct a systematic literature review in order to estimate the prevalence and odds ratio of clinically relevant depression in adults with Type 2 diabetes compared with those without. METHODS: MEDLINE, EMBASE and PSYCINFO databases were searched using MeSH terms and free text to identify relevant controlled studies. Published reference lists were also examined. Study selection and appraisal were conducted independently by two reviewers and a meta-analysis was performed to synthesize and analyse the data. RESULTS: Ten controlled studies including a total of 51 331 people were published between January 1980 and May 2005. The prevalence of depression was significantly higher in patients with Type 2 diabetes compared with those without [17.6 vs. 9.8%, OR = 1.6, 95%, confidence interval (CI) 1.2-2.0]. However, in most studies, patients with diabetes differed from those without on variables known to be associated with an increased risk of depression. The prevalence of depression was higher in females with diabetes (23.8%) compared with males (12.8%); however, the odds ratio for depression in patients with Type 2 diabetes compared with those without was higher in males (OR = 1.9, 95% CI 1.7-2.1) than females (OR = 1.3, 95% CI 1.2-1.4). Failure to report potential confounders prevented a more rigorous meta-analysis of risk. CONCLUSION: We identified raised rates of depression in people with Type 2 diabetes, however, there is a need for well-controlled and better-reported studies to inform the development of effective treatments for depression in these patients.

Adolescent↗
PubMed2004

Lip and gum lesions in sheep in two abattoirs in New Zealand.

AIM: To build a profile of the oral lesions that occur in sheep in New Zealand that need to be considered within the differential diagnosis of foot-and-mouth disease. METHODS: Lesions of the anterior lips and gums of sheep were surveyed in two abattoirs, photographed, and described grossly and histopathologically. RESULTS: A sequence of lesions in order of age and stage of healing are described and illustrated, and their pathogenesis discussed. Lesions of the midline of the lips and gums of traumatic or irritant aetiology were common, and the prevalence was higher in adult sheep than in lambs. CONCLUSIONS: The majority of lesions observed appeared to be primarily of traumatic aetiology. They probably arose from the fright/flight response behaviour of sheep, resulting in the mouth impacting against wire fences or yard railings while being handled. A smaller percentage of lesions may have been due to abrasive or irritant feed or soil. The presence of plant material and bacteria in lesions delayed healing and contributed to the formation of ulcers.

Journal Article↗
PubMed2004

Cytokine correlates of clinical response patterns to infliximab treatment of ankylosing spondylitis.

OBJECTIVE: To identify clinical and immunological markers of response to treatment with infliximab in ankylosing spondylitis (AS). METHODS: Baseline and sequential cytokine levels (IL1, TNFalpha, IFNgamma, TGFbeta and IL10) were examined after 52 weeks of infliximab treatment 5 mg/kg in 22 patients. RESULTS: At week 52, 18 patients were responders and four non-responders according to ASAS group criteria. Clinical measures of disease activity between the two groups at baseline were similar, apart from a trend towards longer disease duration in non-responders (p = 0.08). Baseline CRP and TNFalpha levels were higher in responders than non-responders (p<0.01 and p<0.006, respectively). The two groups had similar baseline cytokine levels, apart from TNFalpha. Baseline CRP levels did not correlate significantly with baseline cytokine levels in responders, but a strong correlation was noted between baseline CRP and IL1, IFNgamma, and IL10 in non-responders. Apart from an early rise in TGFbeta and a decrease in IL10 in responders after the first infusion, sequential cytokine analysis for the first six months of treatment was not related to clinical disease activity measures. CONCLUSION: Although sequential cytokine analysis does not appear to be informative, baseline CRP and TNFalpha levels are useful markers of clinical response patterns in patients with AS treated with infliximab.

Adult↗
PubMed2003

Comparative immune responses to candidate arthritogenic bacteria do not confirm a dominant role for Klebsiella pneumonia in the pathogenesis of familial ankylosing spondylitis.

OBJECTIVE: Using humoral immune responses, Klebsiella pneumoniae has been implicated as a candidate microbial trigger in ankylosing spondylitis (AS) by several investigators but refuted by others. The objective of this case-control study was to compare the cellular (T-cell proliferation) and humoral (IgG and IgA, by ELISA) immune responses of affected individuals in multiplex AS families with those of unaffected family members and normal healthy controls in order to find out whether affected individuals exhibit a predominant immune response to K. pneumoniae. METHODS: Twenty-five families with two or more individuals affected with AS and 34 normal healthy controls matched with the affected family members for age, sex and ethnicity were enrolled in the study. All affected (n = 57) and unaffected (n = 37) family members had a detailed clinical evaluation. Peripheral blood was drawn to determine T-lymphocyte proliferation and the IgG and IgA (by ELISA analysis) immune responses to K. pneumoniae, Salmonella typhimurium, Yersinia enterocolitica and Chlamydia trachomatis. Immune responses to each of the four candidate organisms were compared in affected and unaffected individuals. Each individual was classified by the predominant antigenic immune response that they showed when comparison was made among the same concentrations of the four candidate microbial antigens. This stratification was then used (i) to compare immune responses in affected and unaffected family members and (ii) to compare clinical characteristics of affected family members. RESULTS: There was no difference in mean stimulation indices or antibody responses between affected and unaffected family members for each of the candidate organisms. In terms of predominant cellular immune responses to these organisms, there was no difference between affected and unaffected family members with respect to K. pneumoniae, C. trachomatis or Y. enterocolitica. However, a higher percentage of affected family members (25.9%) exhibited a predominant response to S. typhimurium compared with unaffected family members (5.9%, P < 0.02). In assessing antibody titres, K. pneumoniae was the predominant amongst these four organisms, but there was no difference between affected family members, unaffected family members and normal healthy controls. There was no relationship between immune responses and clinical characteristics. CONCLUSION: Our analysis of affected and unaffected family members in familial AS demonstrated no significant differences with respect to cellular or humoral immune responses to K. pneumoniae and three control microbes. In addition, K. pneumoniae did not exhibit a predominant immune response in affected individuals. Thus we find no supportive evidence to implicate a causal role for K. pneumoniae in familial AS.

Adult↗
PubMed2001

Quantitative coupling of supercritical fluid extraction and high-performance liquid chromatography by means of a coated open-tubular interface.

Supercritical fluid extraction was coupled on-line with reversed-phase high-performance liquid chromatography (HPLC). An open-tubular column with a 95% methyl-5% phenyl stationary phase was utilized as an interface between the two systems. This phase allowed for good analyte focusing onto the packed analytical column and exhibited low reactivity. Due to the non-polar nature of this phase there was a low tendency for analytes to be prematurely rinsed off the interface by condensed modifier. Using this approach, it was possible to transfer the extracted analytes quantitatively to the HPLC column in the presence of as much as 10% (v/v) methanol. By placing a 10 m guard column at the head of the interface, the same could be accomplished with ethanol as the modifier: allowing the extraction to be conducted entirely with non-toxic fluids. The method also allowed the use of very practical extraction parameters in terms of amount extracted, extraction flow-rate, extraction vessel volume, and extraction time.

Chromatography, High Pressure Liquid↗
PubMed2001

Comparison of the electroacoustic characteristics of five hearing aids.

This paper describes a comparison of the electroacoustic characteristics of five hearing aids: (1) a linear BTE aid of the type dispensed under the UK National Health Service (NHS), the BE19; (2) an analogue programmable BTE aid incorporating two-channel wide dynamic range compression, the ReSound BT2; (3) and (4) two digital BTE aids incorporating multi-channel wide dynamic range compression, the Phonak Claro and the Danavox Danalogic; (5) a disposable ITE hearing aid with single-channel compression, the Songbird. Measurements of frequency response using a 2 cc coupler showed that the NHS aid had a distinct undesired peak around 1 kHz. The response rolled off at low and high frequencies, and no gain was applied above about 4000 Hz. The BT2 and Claro both showed somewhat irregular responses with effective upper frequency limits of 5000-6000 Hz. The Danalogic had a reasonably smooth response and provided gain up to 6000 Hz. The Songbird had a smooth response and provided gain up to about 7000 Hz. All aids showed reasonably low harmonic and intermodulation distortion (probably below audible levels for hearing-impaired listeners), the Phonak Claro being the best in this respect. Measures of the effective input noise were obtained using two new methods. The NHS aid had the highest (worst) effective input noise, whereas the Songbird had the lowest, especially at low frequencies. The BT2 and the two digital aids had similar noise levels on one measure, but the BT2 was superior on the other measure. The compression circuits were characterized by measuring attack and release times and by using a method described by Stone and Moore (1992). The aids varied markedly in the extent to which they compressed amplitude modulation at the rates typically occurring in speech (2-10 Hz), the Claro providing the least compression and the Danalogic and Songbird aids providing the most. Overall, the results indicate that the NHS aid performed more poorly in several respects than the other aids. There were no great differences in electroacoustic characteristics between the remaining analogue aids and the digital aids, although the Songbird had a somewhat wider frequency range and lower effective input noise than the other aids.

Acoustic Stimulation↗
PubMed2000

Assessing the aquatic toxicity of complex hydrocarbon mixtures using solid phase microextraction.

Assessing the ecotoxicity of hydrocarbon mixtures is complicated by the complex nature of these mixtures. Traditional analytical methods for characterizing hydrocarbon contamination are not good predictors of potential ecotoxicity because these methods fail to characterize the bioavailability of individual hydrocarbon components. Recent research indicates that hydrocarbons act by a common narcotic mode of action and that ecotoxicity occurs when the molar concentration in organism lipid exceeds a critical threshold. Since the ecotoxicity of narcotic mixtures appears to be additive, ecotoxicity thus depends upon the partitioning of individual hydrocarbons from the environment to lipids and the total molar sum of individual hydrocarbons in lipids. These insights have led previous investigators to advance the concept of 'biomimetic' extraction as a novel analytical tool for assessing narcosis-type or 'baseline'. Drawing from this earlier work, a simple method to quantify bioavailable petroleum hydrocarbons (BPHs) in hydrocarbon-contaminated aqueous and soil/sediment samples was developed. The proposed method combines the essential features of biomimetic extraction for simulating the bioconcentration process with the analytical advantages of solid phase microextraction (SPME). The procedure for determining BPH involves two steps. The sample is first equilibrated with a SPME fiber that serves as a surrogate for organism lipids. The total moles of hydrocarbons that partition to the SPME fiber is then quantified using GC/FID. The capability of this method to predict ecotoxicity was assessed by comparing BPH measurements for hydrocarbon contaminated aqueous samples to corresponding toxicity test results for rainbow trout. Results indicate that BPH analyses correlate to the observed acute toxicity. Consequently, BPH analyses offer a promising, cost-effective screening tool for predicting aquatic toxicity of complex hydrocarbon mixtures.

Animals↗
PubMed2000

Comparison of the NAL(R) and Cambridge formulae for the fitting of linear hearing aids.

This paper describes a laboratory-based comparison of the effectiveness of two formulae for fitting linear hearing aids, the NAL(R) formula and the Cambridge formula. The formulae prescribe the desired insertion gain as a function of frequency, based on the audiometric threshold. The two formulae have a similar rationale; both are based on the goal that, for speech with a moderate level, all frequency bands should be equally loud (equal loudness per critical band) over the frequency range important for speech (400-5000 Hz), and the overall loudness should be comfortable. However, the formulae differ; generally the Cambridge formula leads to slightly more high-frequency gain (above 2 kHz) and slightly less mid-frequency gain (between 500 Hz and 2000 Hz) than the NAL(R) formula. The two formulae were implemented using an experimental digital hearing aid whose frequency-gain characteristic could be controlled very precisely. A loudness model (Moore and Glasberg, 1997) was used to adjust the overall gains for each subject and each formula so that a speech-shaped noise with an overall level of 65 dB SPL would give the same loudness as for a normally hearing person (according to the model). The adjustments were, on average, smaller for the Cambridge than for the NAL(R) formula. A condition was also used with all insertion gains set to zero, simulating unaided listening. Evaluation was based on: (1) subjective ratings of the loudness, intelligibility and quality of continuous discourse presented in quiet at levels of 45, 55, 65 and 75 dB SPL and in babble at an 0-dB speech-to-babble ratio, using speech levels of 55, 65 and 75 dB SPL; (2) measures of the speech reception threshold (SRT) in background noise for two noise levels (65 and 75 dB SPL) and four types of background noise. Neither the subjective ratings nor the measures of the SRTs revealed any consistent difference between the results obtained using the two formulae, although both formulae led to lower (better) SRTs than for simulated unaided listening. It is concluded that the differences between the NAL(R) formula and the Cambridge formula are too small to have measurable effects, at least in a laboratory setting.

Aged↗
PubMed1999

Tolerable hearing aid delays. I. Estimation of limits imposed by the auditory path alone using simulated hearing losses.

OBJECTIVE: When people who wear hearing aids speak, there are three paths by which they hear their own voices: 1) through the air and leakage around the earmold; 2) via the solid structures of their head; 3) through the air to the hearing aid microphone, and then through the aid circuitry. These paths involve different time delays. Digital processing introduces delays in path 3 from a few to several tens of milliseconds, which could lead to a range of disturbing effects. We examined one purely auditory effect, namely hearing speech through all three of these paths. Subjective disturbance was measured as a function of delay in path 3 using simulations of hearing loss and a simulated hearing aid. With increasing hearing loss, the loudness of sound heard via paths 1 and 2 decreases, and the aid user relies more on path 3. The disturbance produced by the delay then might be less perceptible. To test this idea, four different hearing losses were simulated, varying from mild to moderately severe. DESIGN: Each of two talkers was fitted with a closed earmold, and simultaneous above-ear and in-ear recordings were made of each talker reading prose. The above-ear signal was amplified using a simulated hearing aid with 4-channel full dynamic range compression; compression ratios and gains were selected using an algorithm based on the absolute thresholds used in the simulations of hearing loss. The resultant output was then mixed with the in-ear signal with one of five values of delay, and the combined signal was processed using the four simulations of hearing loss. The resulting stimuli simulated for normal-hearing listeners the experience of having a hearing impairment and listening through a hearing aid while talking, except that the talker's voice was not that of the listener. Twenty normally hearing subjects gave subjective ratings of the disturbance of the echo for each delay and each simulated hearing loss. RESULTS: Disturbance ratings generally increased monotonically with increasing delay. Average results show that delays are rated as "disturbing" for values between 20 and 30 msec for mild to moderate losses. For a moderately severe loss, the rating "disturbing" was not quite achieved at 40 msec. For moderate losses, a speaker with low fundamental frequency (f0)(70 to 140 Hz) was less disturbing than a speaker with a medium f0, (100 to 180 Hz). This effect reversed for the mildest loss for low values of delay. CONCLUSIONS: The auditory effects of delays between bone-conducted sound and aid-conducted sound are likely to become disturbing for delays exceeding 20 msec. Somewhat longer delays may be tolerable for moderate to severe hearing losses. These delays are smaller than the delays at which audio-visual integration is disrupted.

Adult↗
PubMed1999

Benefits of linear amplification and multichannel compression for speech comprehension in backgrounds with spectral and temporal dips.

People with cochlear hearing loss have markedly higher speech-receptions thresholds (SRTs) than normal for speech presented in background sounds with spectral and/or temporal dips. This article examines the extent to which SRTs can be improved by linear amplification with appropriate frequency-response shaping, and by fast-acting wide-dynamic-range compression amplification with one, two, four, or eight channels. Eighteen elderly subjects with moderate to severe hearing loss were tested. SRTs for sentences were measured for four background sounds, presented at a nominal level (prior to amplification) of 65 dB SPL: (1) A single female talker, digitally filtered so that the long-term average spectrum matched that of the target speech; (2) a noise with the same average spectrum as the target speech, but with the temporal envelope of the single talker; (3) a noise with the same overall spectral shape as the target speech, but filtered so as to have 4 equivalent-rectangular-bandwidth (ERB) wide spectral notches at several frequencies; (4) a noise with both spectral and temporal dips obtained by applying the temporal envelope of a single talker to speech-shaped noise [as in (2)] and then filtering that noise [as in (3)]. Mean SRTs were 5-6 dB lower (better) in all of the conditions with amplification than for unaided listening. SRTs were significantly lower for the systems with one-, four-, and eight-channel compression than for linear amplification, although the benefit, averaged across subjects, was typically only 0.5 to 0.9 dB. The lowest mean SRT (-9.9 dB, expressed as a speech-to-background ratio) was obtained for noise (4) and the system with eight-channel compression. This is about 6 dB worse than for elderly subjects with near-normal hearing, when tested without amplification. It is concluded that amplification, and especially fast-acting compression amplification, can improve the ability to understand speech in background sounds with spectral and temporal dips, but it does not restore performance to normal.

Aged↗
PubMed1999

Comparison of different forms of compression using wearable digital hearing aids.

Four different compression algorithms were implemented in wearable digital hearing aids: (1) The slow-acting dual-front-end automatic gain control (AGC) system [B. C. J. Moore, B. R. Glasberg, and M. A. Stone, Br. J. Audiol. 25, 171-182 (1991)], combined with appropriate frequency response equalization, with a compression threshold of 63 dB sound pressure level (SPL) and with a compression ratio of 30 (DUAL-HI); (2) The dual-front-end AGC system combined with appropriate frequency response equalization, with a compression threshold of 55 dB SPL and with a compression ratio of 3 (DUAL-LO). This was intended to give some impression of the levels of sounds in the environment; (3) Fast-acting full dynamic range compression in four channels (FULL-4). The compression was designed to minimize envelope distortion due to overshoots and undershoots; (4) A combination of (2) and (3) above, where each applied less compression than when used alone (DUAL-4). Initial fitting was partly based on the concept of giving a flat specific-loudness pattern for a 65-dB SPL speech-shaped noise input, and this was followed by fine tuning using an adaptive procedure with speech stimuli. Eight subjects with moderate to severe cochlear hearing loss were tested in a counter-balanced design. Subjects had at least 2 weeks experience with each system in everyday life before evaluation using the Abbreviated Profile of Hearing Aid Benefit (APHAB) test and measures of speech intelligibility in quiet (AB word lists at 50 and 80 dB SPL) and noise (adoptive sentence lists in speech-shaped noise, or that same noise amplitude modulated with the envelope of speech from a single talker). The APHAB scores did not indicate clear differences between the four systems. Scores for the AB words in quiet were high for all four systems at both 50 and 80 dB SPL. The speech-to-noise ratios required for 50% intelligibility were low (indicating good performance) and similar for all the systems, but there was a slight trend for better performance in modulated noise with the DUAL-4 system than with the other systems. A subsequent trial where three subjects directly compared each of the four systems in their everyday lives indicated a slight preference for the DUAL-LO system. Overall, the results suggest that it is not necessary to compress fast modulations of the input signal.

Acoustic Stimulation↗
PubMed1999

Non-invasive testing for Helicobacter pylori.

Confirmed and potential benefits of eradicating Helicobacter pylori have led to the development of a range of diagnostic tests. As well as techniques using biopsy tissue obtained during endoscopy, a number of non-invasive tests are now available. These may be appropriate for pre-endoscopy screening of younger dyspeptics, for use in research, particularly epidemiological surveys, to confirm successful eradication after treatment, and possibly in the future for screening in asymptomatic populations. Serology requiring laboratory analysis is likely to be the least expensive option, particularly suitable for testing large numbers, while urea breath tests should yield the most accurate results and are appropriate for confirming successful eradication since only current infection is detected. The performance of near-patient tests can lack consistency, but these may be useful for small numbers and where other non-invasive testing is unavailable. Tests should be used with an awareness of their potential limitations in terms of accuracy.

Breath Tests↗
PubMed1999

Production and evaluation of guidelines for the management of inflammatory bowel disease: the Leicester experience.

Consensus guidelines for the management of patients with inflammatory bowel disease were produced by gastroenterologists, gastrointestinal surgeons and a cross-section of general practitioners (GPs) from Leicestershire in order to develop a seamless pattern of care with a common approach to diagnosis and treatment. It was hoped that the guidelines would encourage a movement towards care in the community for many patients with stable disease and so speed up new consultation rates. The study then assessed the impact of these guidelines on the referral letters of GPs to hospital consultants, the prediction of disease and adherence to them on re-referring patients after discharge. The guidelines were distributed to all 487 GPs in the Leicester Health Authority area and the gastroenterology teams within the hospitals. The value of the guidelines was assessed by an audit of referral letters, the length of time from referral letter to out-patient appointment, both before and after the launch of the guidelines, adherence to the guidelines on re-referral, and monitoring the outcome of the discharged patients. Whilst the guidelines may have helped GPs to manage stable patients in the community, the content of referral letters and the diagnostic abilities of GPs were not seen to improve since the launch of the guidelines. However, only 5% of stable patients who were discharged from one clinic were re-referred for inflammatory bowel disease.

Attitude↗
PubMed1999

Transmission of Helicobacter pylori.

Helicobacter pylori is found predominantly in human gastric mucosa. Transfer of the bacterium remains an open topic, but it is likely that infection is usually acquired at a young age, particularly where lower socio-economic conditions prevail. Transmission via an external source such as water supply is a possibility but, in general, infection is probably passed from person to person. Arguments for and against faecal-oral, oral-oral and gastric-oral transmission have been presented, but the dominance of one of these routes is still to be determined.

Age Distribution↗
PubMed1999

Use of a loudness model for hearing aid fitting: II. Hearing aids with multi-channel compression.

A model for predicting loudness for people with cochlear hearing loss was applied to the problem of the initial fitting of a multi-channel compression hearing aid. The fitting was based on two constraints: (1) The specific loudness pattern evoked by speech of a moderate level (65 dB SPL) should be reasonably flat (equal loudness per critical band), and the overall loudness should be similar to that evoked in a normal listener by 65-dB speech (about 23 sones for binaural listening); (2) Speech with an overall level of 45 dB SPL should just be audible in all frequency bands from 500 Hz up to about 4 kHz, provided that this does not require compression ratios exceeding about 3. These two constraints were used to determine initial values for the gain, compression ratio and compression threshold in each channel of a multi-channel compression system. This initial fitting was based entirely on audiometric thresholds; it does not require suprathreshold loudness measures. The fitting method was evaluated using an experimental fast-acting four-channel compression system. The initial fitting was followed by an adaptive procedure to 'fine tune' the fitting, and the aids were then used in everyday life. Performance was evaluated by use of questionnaires and by measures of speech intelligibility. Although the fine tuning resulted in modest changes in the fitting parameters for some subjects, on average the frequency response shapes and compression ratios were similar before and after the fine tuning. The fittings led to satisfactory loudness impressions in everyday life and to high speech intelligibility over a wide range of levels. It was concluded that the initial fitting method gives reasonable starting values for the fine tuning.

Acoustic Stimulation↗
PubMed1999

Use of a loudness model for hearing aid fitting: III. A general method for deriving initial fittings for hearing aids with multi-channel compression.

A model for predicting loudness for people with cochlear hearing loss is applied to the problem of the initial fitting of multi-channel fast-acting compression hearing aids. The fitting is based entirely on the pure tone audiogram, and does not require measures of loudness growth. One constraint is always applied: the specific loudness pattern evoked by speech of a moderate level (65 dB SPL) should be reasonably flat (equal loudness per critical band), and the overall loudness should be similar to that evoked in a normal listener by 65-dB speech. This is achieved using the 'Cambridge' formula. For hearing aids where the compression threshold in each channel can be set to a very low value, an additional constraint is used: speech with an overall level of 45 dB SPL should be audible over its entire dynamic range in all frequency channels from 500 Hz up to about 4 kHz. For hearing aids where the compression thresholds cannot be set to very low values, a different additional constraint is used: the specific loudness pattern evoked by speech of a high level (85 dB SPL, and with the spectral characteristics of shouted speech) should be reasonably flat, and the overall loudness should be similar to that evoked in a normal listener by 85-dB speech. For both cases, compression ratios are limited to values below 3. For each of these two cases, we show how to derive compression ratios and gains, and for the first case, compression thresholds, for each channel. The derivations apply to systems with any number of channels. A computer program implementing the derivations is described. The program also calculates target insertion gains at the centre frequency of each channel for input levels of 50, 65 and 80 dB SPL, and target gains at the eardrum measured relative to the level at the reference microphone of a probe microphone system.

Auditory Threshold↗