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Biomedical subjects

K Mackenzie

Publications and source records attributed to K Mackenzie.

28 records · Page 2Linked to original sources
PubMed1990

External ear resonance in children with otitis media with effusion.

A middle ear effusion has been shown, in KEMAR, to increase the height of the resonant peak of the external auditory canal by 6 dB SPL. It has also been shown that the hearing impairment due to otitis media with effusion is related to the volume of middle ear fluid. Therefore, it was hypothesized that measurement of the height of the resonant peak of the external auditory canal could be used as a method of assessing the magnitude of any hearing impairment due to otitis media with effusion. 182 ears from 182 children aged 3-12 (mean 6.3) years were studied. Pure-tone audiometry and impedance tympanometry were performed, and the acoustics of the external auditory canal were measured using the Rastronics CC1-10 frequency response analyser. The mean height of the resonant peak (17.9 dB SPL) of children with a type A tympanogram was significantly different from the mean value (23.6 dB SPL) of those with a type B tympanogram. There was a significant correlation between the height of the resonant peak and the speech frequency average of the pure-tone thresholds. The sensitivity and specificity of using the height of the resonant peak to detect hearing impairments in different age groups were calculated and compared with the sensitivity and specificity of tympanometry. The test did not provide the same degree of sensitivity as tympanometry but was more specific. The additional advantages of the test are that it is quick, taking less than 1 min per ear, and is well tolerated by children in whom there was a 99% compliance.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Impedance Tests↗
PubMed1988

The development of phenylalanine hydroxylase in rat liver; in vivo, and in vitro studies utilizing fetal hepatocyte cultures.

Phenylalanine hydroxylase (PAH) is first detected in the liver of 21-day-gestation rats. Activity increases after birth, and in 10-day-postnatal rats it is about equal to that observed in the adult. The developmental pattern for the enzyme is reflected in the level of its mRNA determined by hybridization to 32P-cDNA, which is specific for PAH. Studies with cultured adult hepatocytes reveal that the addition of dexamethasone and dibutyryl cAMP to the medium maximizes the yield of enzyme. Hepatocytes derived from 21-day-gestation rats will produce enzyme in cultures maintained in medium supplemented with dexamethasone and dibutyryl cAMP. However, less mature cells, taken from 19-day-gestation rats do not produce measurable levels of enzyme activity. The relative amounts of PAH mRNA in the respective cultures reflect the level of PAH activity. Interestingly, after 3 days of culture, 19-day-gestation hepatocytes can be shown to express PAH mRNA. Therefore, with respect to the expression of PAH, we conclude that 19-day-gestation liver cells will differentiate during culture.

Animals↗
PubMed1981

Distal sensory latency measurement of the superficial radial nerve in normal adult subjects.

The antidromic distal sensory latency of the superficial radial nerve was studied using 2 methods: (I) Recording from a major branch of a nerve as it crosses the extensor pollicis longus tendon, using segments of 10, 12, and 14cm; (II) Recording from the thumb, using segments of 14, 16, and 18cm. The mean latency, to the peak of the negative response, using method I, was 3.1 +/- 0.4 msec (+/- 2SD) and for method 2 was 3.5 +/- 0.6 msec (+/- 2SD), both for the 14cm segment. The amplitude by method I was significantly larger than by method II, making it easier to record. The hand should be warmed if the latency value is outside the normal range and the skin temperature is less than 31C.

Adult↗