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Biomedical subjects

H Dillon

Publications and source records attributed to H Dillon.

46 records · Page 3Linked to original sources
PubMed1984

Pharmacokinetics of cefoperazone in newborn infants.

We studied the disposition of two 100 mg/kg doses of cefoperazone given intravenously 12 hr apart in ten newborn infants. Peak levels were a mean 352 +/- SD 75 and 371 +/- 68 micrograms/ml immediately after the first and second dose, respectively, with corresponding troughs of 60 +/- 10 and 76 +/- 28 mcg/ml 12 hr later. Mean half-life was 6.5 +/- 0.9 hr and decreased with increasing gestational age and birthweight. Steady-state volume of distribution averaged 410 +/- 40 ml/kg and total clearance 0.78 +/- 0.13 ml/min X kg and neither varied with gestational age nor birthweight. No untoward physical or laboratory effects were noted. Additional studies including postnatal age effects on kinetics, efficacy, and cerebrospinal fluid penetrance are necessary prior to widespread use of this potentially valuable antibiotic in newborn infants.

Cefoperazone↗
PubMed1983

The effect of test difficulty on the sensitivity of speech discrimination tests.

The sensitivity of speech discrimination tests is defined as being large if a small change in experimental conditions causes a large and repeatable change in test score. The aim of this paper is to investigate ways by which test sensitivity can be maximized. The effect of test difficulty on sensitivity is examined by the use of a model based on signal detection theory and subjective similarity rating concepts. For several sets of assumptions about the parameters underlying the perceptual processes, the model indicates that test difficulty should be in the range 73% to 87% to achieve the maximum sensitivity with speech tests using between four and eight response foils. The model results also indicate that the sensitivity increases with the number of response foils. When the variation of test reliability with test difficulty is taken into account, the test difficulty which maximizes the sensitivity/reliability trade-off lies in the range 85% to 90%. It is argued that irrespective of the optimum test difficulty, a maximally sensitive test will contain items equal to one another in difficulty.

Humans↗
PubMed1983

The selection of modulation rates for frequency modulated sound field stimuli.

Frequency modulated (FM) tones are used in sound field audiometry in order to avoid problems caused by standing waves. The FM stimuli to be used must be specified in terms of bandwidth (twice the frequency deviation), modulation rate and modulation waveform. This paper deals with selection of the modulation rate. Improved field uniformity obtained with FM tones relies upon the ear averaging the sound intensity as the frequency sweeps. The modulation rate must be less than about 1/3 of the frequency deviation in order to provide sufficient spectral components to ensure reasonable averaging across the frequency band. If the rate is too low threshold will be determined by the peak intensity during the sweep. For normal listeners a modulation rate of 5 Hz is just satisfactory but in the hearing impaired a higher rate is required because of their altered temporal integration characteristics. A suitable value for the modulation rate can be inferred from the literature on temporal integration and the acoustic characteristics of typical test rooms. The optimum rate increases with the stimulus centre frequency, but a constant rate of 20 Hz appears to be acceptable.

Audiometry↗
PubMedDate not supplied

A quantitative examination of the sources of speech discrimination test score variability.

Several sources of variability inherent in any speech discrimination measurement are outlined. Limitations of the use of the binomial theorem to predict intrasubject (test-retest) variability are examined. First, the underestimation of variability that is caused by the inclusion of items of different degrees of difficulty is quantified by a reanalysis of published data. Second, it is shown that variability will be larger than expected if the subject's ability is different during test and retest sessions. Fortuitously, these two deviations from the model have opposing effects on the score variability. The estimates provided by the binomial theorem are thus better than if only one effect was present. The need for a clear distinction to be maintained between inter- and intra-subject variability and the effect of list differences on test-retest variability are also discussed.

Hearing↗
PubMedDate not supplied

Sound field audiometry: recommended stimuli and procedures.

Comprehensive recommendations are presented for conducting sound field audiometry with frequency specific stimuli. These recommendations are primarily based on a series of investigations by the authors. The rationale for each recommendation is presented, together with a brief overview of the supporting research. The preferred stimuli are frequency modulation tones, triangularly or sinusoidally modulated at a rate of about 20 Hz, or suitably generated narrow bands of noise. The optimal bandwidths of the stimuli, expressed in percentages of the center frequency, vary with frequency. Stimuli suitable for most purposes have bandwidths ranging from about 30% at 0.25 kHz to about 10% at 4 kHz. Stimuli having narrower or broader bandwidths are desirable for some special purposes. The test room should be as nonreverberant as possible and the subject should be seated on an adjustable height chair with headrest. The control microphone method of calibration is preferred but a method is also presented for carrying out the traditional precalibration procedure. The SPL of the complex stimulus should be taken as the peak deflections on a sound level meter set to "RMS-FAST." A conversion table is presented which allows thresholds obtained in the sound field to be expressed as dB HTL. With the materials and methods described here it is possible to achieve the same reliability for sound field testing as for audiometry under earphones.

Acoustic Stimulation↗