Biomedical subjects

I M Taylor

Publications and source records attributed to I M Taylor.

At least 19 recordsLinked to original sources

PubMed1997

The contour test of loudness perception.

OBJECTIVE: This article presents the underlying rationale, normative data, and reliability data for a test of loudness perception (the Contour Test) that was devised for use in clinical hearing aid fitting. The Contour Test yields data describing the sound level required for each of seven categories of loudness ranging from very soft to uncomfortably loud. DESIGN: Two experiments are described. Experiment 1 yielded norms for the test. The subjects were 23 male and 22 female normal-hearing listeners. Test stimuli included warble tones at six frequencies and broad band speech. Experiment 2 assessed the reliability of the test results. Ten hearing-impaired listeners responded to the test at two frequencies on two occasions separated by several days. Both experiments also evaluated the effect of using different stimulus increment sizes on the measured levels of loudness categories. RESULTS: Based on the data from experiment 1, norms for each category of each stimulus are reported in terms of mean level and typical between-subject variation in responses. Data are provided in HA-12 cm3 coupler levels as well as in hearing levels (dB HL). The shape of the loudness growth function for warble tones was somewhat different from that for speech. When data were expressed in HL, there were no differences in mean loudness category levels across warble tone test frequencies. Thus, test frequencies were combined and equations were generated to describe the upper and lower limits of typical normal performance for warble tone stimuli. These equations can be used to construct a template for clinical comparison of normative values to patient loudness growth curves. Experiment 2 provided information about the test-retest variability of data yielded by the Contour Test. Reliability appears to be similar to that of the few other category scaling tests described in the literature. Most test-retest differences were 6 dB or less. Although a moderate variation in test increment size did not significantly affect the loudness category levels for young normal-hearing listeners, levels corresponding to loudness categories were significantly higher when larger increments were used with elderly hearing-impaired listeners. CONCLUSIONS: Evidence from this and other research indicates that standardized measurement of loudness perception is an achievable goal for clinical practice. The Contour Test appears to offer a viable approach to clinical measurement of loudness perception: It has good patient acceptance and combines fairly rapid administration with acceptable reliability. Details of test procedures and scoring sheets for manual administration can be downloaded from the Internet at www.ausp.memphis.edu/harl. However, it is important to keep in mind that the application of loudness perception data for narrowband stimuli (such as warble tones) to hearing aid prescription is complicated by the need to account for the effects of loudness summation across bandwidth. There is a need for additional research to establish an empirical link between clinically measured loudness perception and optimal amplification characteristics.

Adolescent↗

PubMed1996

Benefit acclimatization in elderly hearing aid users.

A previous study from this laboratory indicated that the benefit obtained from a hearing aid in a noisy environment might increase over the first few months of hearing aid use. It was hypothesized that this acclimatization of benefit was due to a process in which the individual optimized his/her use of modified or newly available high-frequency acoustic speech cues. This investigation further explored the effect in 22 elderly individuals with mild to moderate sensorineural hearing losses, fitted unilaterally with hearing aids. None of the subjects was a current or recent hearing aid wearer. Speech intelligibility testing over a 12-week post-fitting period indicated that a significant improvement in benefit was seen for the group as a whole, probably beginning after about 6 weeks of regular hearing aid use. However, the magnitude of improvement was very small for most subjects. Only three individuals experienced a dramatic improvement in their benefit for speech in noise over this period. No evidence was found for a specific role of high-frequency cues. Seven subjects participated in a long-term follow-up in which benefit was measured after several months of use of their newly acquired personal hearing aids. Further increase in benefit was noted but was due exclusively to a decline in performance for unaided listening.

Aged↗

PubMed1994

Relationship between in-situ distortion and hearing aid benefit.

In-situ hearing aid distortion is defined as distortion measured in the ear canal with stimulus inputs and hearing aid settings that are similar to those the hearing aid wearer will experience in daily life. This preliminary study examined possible relationships between in-situ distortion and benefit for appropriately fitted contemporary hearing aids. Simulated in-situ distortion was determined for 97 hearing aid fittings, divided among three typical listening environments: living room, classroom lecture, and social event. Measures included intermodulation, harmonic, and transient distortion. Overall results of between- and within-subject analyses of data suggested that there was a significant relationship between distortion and benefit in both reverberant and noisy environments similar to a classroom lecture and a social event, respectively. This outcome was seen despite the fact that distortion was quite low in absolute terms. Analyses also suggested that in-situ harmonic distortion was most closely related to benefit and that the other types of distortion measured did not make additional contributions to benefit prediction. We propose that measurements of in-situ harmonic distortion might be a valuable addition to hearing aid evaluations.

Aged↗

PubMed1992

Surface exclusion specificity of the TraT lipoprotein is determined by single alterations in a five-amino-acid region of the protein.

The TraT protein is a highly cell-surface-exposed lipoprotein specified by F-like plasmids that confers serum resistance and blocks the conjugative transfer of plasmids to cells bearing identical or closely related plasmids, a process known as surface exclusion. The TraT protein specified by the antibiotic-resistance plasmid R6-5 was purified to apparent homogeneity. When added to mating mixtures, TraT blocked the transfer of plasmids belonging to Surface Exclusion Group IV (Sfx IV) but had no significant effect on the transfer of plasmids belonging to other groups. Additionally, the purified protein has a protective effect on bacterial cells incubated in serum, indicating that it does not have to be located on the cell surface to mediate serum resistance. To localize regions of the protein that were responsible for surface exclusion specificity, the amino acid sequence of the TraT protein specified by CoIB2-K98 (Sfx II) was determined by cloning and sequencing of the corresponding gene. Comparison of the derived sequence with those of the F and R100-1 proteins indicated that surface exclusion specificity of TraT is determined by single alterations in a five-amino-acid region (residues 116-120). This was confirmed by segment swapping experiments in which the specificity of the R6-5 TraT protein (Sfx IV) was switched to that of the CoIB2-K98 protein (Sfx II). Our results suggest that the region defined by residues 116-120 is located on the external face of the outer membrane and interacts specifically with the donor cell in surface exclusion.

Amino Acid Sequence↗

PubMed1990

The TraT lipoprotein as a vehicle for the transport of foreign antigenic determinants to the cell surface of Escherichia coli K12: structure-function relationships in the TraT protein.

The TraT protein is a surface-exposed lipoprotein, specified by plasmids of the IncF group, that mediates serum resistance and surface exclusion. The structure and function of the TraT protein determined by plasmid R6-5 was probed by genetic insertion of a foreign antigenic determinant, the C3 epitope of polio virus, at residues 61, 125, 180, 200 or 216 of the protein. The chimaeric proteins were transported to the outer membrane and, in three cases, immunoassays with an anti-C3 monoclonal antibody indicated that the C3 epitope was exposed on the cell surface. Three of the hybrids, with insertions at residues 125, 180 and 200, assembled into the trypsin-resistant oligomeric form characteristic of the wild-type protein, which suggested that these regions are not involved in TraT subunit:subunit interactions. Additionally, the hybrid protein carrying the C3 epitope at position 180 functioned in a genetic suppression assay and retained partial surface-exclusion activity. Thus, its localization, folding and organization does not appear to be grossly altered from that of the wild-type protein. Applications of the protein for the transport of foreign antigenic determinants to the cell surface are discussed.

Amino Acid Sequence↗

PubMed1984

Ultrastructural changes of ischemic injury due to coronary artery occlusion in the porcine heart.

Using the ultrastructural criteria established by Schaper et al. 1979 [27] for distinguishing between different degrees of ischemic change in dog myocardium, slight ischemic changes are observed in the pig suboendocardium as early as 1 min after occlusion of the LAD artery. Moderate change throughout the thickness of the myocardium is seen after 6 to 12 min of ischemia and continues to be found up until 20 min after commencement of the ischemic period. 20 to 30 min ischemia produces severe ischemic damage and more than 30 min leads to irreversible damage. The changes are uniform at all stages of ischemia and there is no evidence of a transmural gradient of ultrastructural damage. Of particular interest in the early part of the ischemic period is the observation of ultrastructural changes in the subendocardial specialized conducting tissue. In these specialized cells, although morphological features consistent with slight and moderate ischemia are found as early as 1 to 2 min after occlusion, spontaneous recovery occurs and is complete by 15 min. This biphasic time course parallels the electro-physiological changes known to occur in ischemic Purkinje fibres.

Animals↗

PubMed1983

Effects of retinoic acid on the development of the facial skeleton in hamsters: early changes involving cranial neural crest cells.

Treatment of gravid hamsters with 60/mg of retinoic acid on the 8th day of pregnancy resulted in facial skeleton defects in 100% of the survivors examined by alizarin staining at term. An investigation of the early stages in the development of these malformations indicated that the teratogen induced delayed and disorganized patterns of cranial neural crest cell migration as well as extensive death and damage of crest cells. The results demonstrate that retinoic acid provides a useful tool for studies in the pathogenesis of facial skeletal abnormalities in vivo. Moreover, the extensive defects seen in the teratogen-treated litters at term, together with the results of the microscopical analyses, support the hypothesis that cranial neural crest cells make an important contribution to the development of the mammalian facial skeleton.

Animals↗

PubMed1980

Retinoic acid-induced heart malformations in the hamster.

In order to determine the effect of retinoic acid on the developing mammalian heart, pregnant golden Syrian hamsters were given single doses of 80 mg/kg of the teratogen by gavage, at various times in gestation. Examination of the surface features of hearts from near-term fetuses was followed by microdissection to reveal internal cardiac structures. This has proven to give more reliable results than other methods of determining congenital heart malformation. The results of the study demonstrate that retinoic acid is a potent cardiac teratogen capable of inducing high frequencies of heart abnormalities in a reproducible fashion. The highest rates of malformation resulted from maternal treatment on day 7 (69%), 8 (74%), and 9 (30%) of gestation. Ventriculo-bulbar malformations including double outlet right ventricle, complete transposition, and an overriding aorta complex were the most commonly seen abnormalities. The findings support the hypothesis that these abnormalities are not entirely discrete entities but are instead part of a single spectrum of malformation.

Animals↗

PubMed1980

Observations on the sinuatrial nodal artery of the rat.

The structure of the sinuatrial nodal artery has been investigated in young and old rats. The nodal artery is derived from the internal thoracic artery, runs centrally though the node and supplies it by several branches. An extensive cuff of nodal cells is seen within the adventitia of the artery and its branches adjacent to the smooth muscle cells of the media. The cuff cells vary in both shape and myofibrillar content and contain acetylcholinesterase. The cuff is extensively innervated by both adrenergic and cholinergic axons. The significance of these findings with regard to earlier morphological and physiological reports is discussed.

Aging↗

PubMed1978

The effects of some methyl prostaglandin derivatives on the ductus arteriosus of swine in vivo.

Three methylated analogues of prostaglandin E1 and E2 were examined for their ability to open the ductus arterious of neonatal piglets in vivo. Fifteen (S) 15 methyl prostaglandin E1 (15-Me PGE1), 15 (S) 1K methyl prostaglandin E2 (15-Me PGE2), and 16' 16' dimethyl prostaglandin E1 (16-diMe PGE1) all opened the ductus when given intravenously, intramuscularly or orally. The effects on ductal patency lasted four hours or more in many instances. Side-effects included apnea with intravenous and intramuscular dosages, and with high oral dosages of 15-Me PGE1. A transient drop in heart rate and blood pressure occurred with each dose. In one animal the ductus was kept open for 19 days with six-hourly intramuscular injections of 3 microgram/kg 15-Me PGE1. Transient sedation occurred with each dose. Death occurred on the 19th day and histological studies showed that the morphology of the ductus wall was similar to that seen in a two day old animal. These studies suggest that maintenance od ductal patency in the infant may be possible with oral administration of methyl prostaglandin derivatives.

Administration, Oral↗

PubMed1977

The development of innervation in the rat atrioventricular node.

The problem of development of the innervation of the rat atrioventricular node has been investigated by electron microscopy. Nerve bundles appear in relation to the node as early as the second postnatal day and vesiculated axons are seen throughout the entire node by the fourth day. Intimate contacts between nodal cells, axons and terminal varicosities are frequently observed. Use of the 5-hydroxydopamine tracer technique has enabled the identification of both cholinergic and adrenergic axons. It is concluded that the node has a dual innervation although cholinergic endings far outnumber those classified as adrenergic on the sixth postnatal day. These results are quite different to earlier findings made at the light microscope level and the discrepancies are discussed with respect to the histochemical techniques used. The suggestion that nodal differentiation is induced by nerves is considered in relation to the differences in cholinesterase activity exhibited by nodal cells during normal development and following neonatal sympathectomy.

Adrenergic Fibers↗

PubMed1977

The relationship between innervation and the cholinesterases of the rat atrioventricular node.

During the first 4 postnatal days, the atrioventricular specialized tissue of the rat contains butyrylcholinesterase alone. The next 7 days are associated with a mixture of both acetyl and butyryl activity, but after the 12th day, acetylcholinesterase is found to predominate largely. It is suggested that this change in activity is related to the growth of adrenergic nerves into the heart on the 4th day. Administration of antinerve growth factor prevents the development of these nerves and is found to delay the onset of the change in cholinesterase activity from butyryl to acetyl from the 5th day until the 21st. Only after the 31st day is acetylcholinesterase the most prominent enzyme in treated animals.

Acetylcholinesterase↗

PubMed1976

The cytochemical localization of cholinesterase activity in the developing chick heart.

The electronhistochemical localization of the cholinesterases of developing chick heart muscle cells has been studied with the aid of a substrate which incorporates an enzyme-susceptible thiolester group and a diazonium group into the same molecule. The embryonic chick heart exhibits cholinesterase activity from Hamilton-Hambruger stage 3 through to four days post hatching. Although enzyme activity is not demonstrated in every location at all stages studied, it has been observed on the nuclear envelope, golgi complex, rough and smooth endoplasmic reticulum, mitochondria and myofilaments. A change in the type of activity has been demonstrated, acetylcholinesterase is found during the first fourteen days of development but thereafter, non-specific cholinesterase is seen instead. As nerves have not been found in relation to the working myocardium, further support is given to the concept that an acetylcholine-cholinesterase system of myogenic origin is involved in spontaneous contraction. Consideration of the distribution of enzyme within the myocardial cell, raises the possibility that cholinesterase may be concerned in a regulatory mechanism of protein synthesis, a suggestion made previously in connection with liver cells.

Animals↗

PubMed1973