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Biomedical subjects

M McClean

Publications and source records attributed to M McClean.

10 recordsLinked to original sources
PubMed1999

Can sensitivity to auditory frequency modulation predict children's phonological and reading skills?

Understanding how letter units represent particular speech sounds is a crucial skill for developing competent reading skills. However it is not known whether such phonological ability is constrained by basic auditory capacities such as those necessary for detecting the frequency modulations characteristic of many phonemes. Here we show that nearly 40% of the variability in normal children's phonological and reading skills can be predicted from their sensitivity to 2 Hz frequency modulated (FM) tones. This relationship does not hold for sensitivity to 240 Hz FM. Because lower but not higher rates of FM provide information important for speech comprehension, dynamic auditory sensitivity is likely to play an important role in children's phonological and reading skill development.

Acoustic Stimulation↗
PubMed1998

Effects of NMDA receptor antagonists on nociceptive responses in vivo: comparison of antagonists acting at the glycine site with uncompetitive antagonists.

We have shown that members of a new series of tricyclic pyridophthalazine diones, defined as glycineB site NMDA antagonists in vitro, are selective and systemically active NMDA antagonists in vivo. In electrophysiological tests in alpha-chloralose anaesthetised rats, these compounds reduced nociceptive reflex responses. In conscious rats they displayed analgesic properties. These glycineB antagonists were compared electrophysiologically with several uncompetitive NMDA channel blockers. The degree of voltage dependence previously reported in vitro related to the effectiveness of the agents against different amplitude nociceptive responses of spinal cord neurones in vivo.

Animals↗
PubMed1998

Relationship between airway microvascular leakage, edema, and baseline airway functions.

This study was designed to examine the relationship among microvascular leakage, edema, and baseline airway function. Microvascular leakage was induced in the airways of anesthetized, tracheostomized New Zealand White rabbits (n = 22) by using nebulized N-formyl-methionyl-leucyl-phenylalanine (10 mg) and was measured in the trachea by using the Evans blue dye technique. Airway wall thickness was assessed morphometrically in the right main bronchus after Formalin fixation at a pressure of 25 cmH2O. Areas calculated included the mucosal wall area, the adventitial wall area, the total wall area, and the percentage of total wall area consisting of blood vessels. A neutrophil count was also performed by analyzing numbers of cells in both the mucosal wall area and the adventitial wall area. Airway function was assessed before and 30 min after challenge with N-formyl-methionyl-leucyl-phenylalanine by determining airway resistance, functional residual capacity, specific airway resistance, and flow-volume and pressure-volume curves (after paralysis of the animals with suxamethonium). The concentration of Evans blue dye in tracheal tissue ranged from 31.3 to 131.2 micrograms. There was a significant correlation between this concentration and both the adventitial wall area (P < 0.01) and mucosal neutrophil numbers (P < 0.005). There was no correlation between Evans blue concentration and either blood vessel area or changes in respiratory physiology parameters before and after challenge. There was no significant difference between any respiratory physiology measurements before and after challenge. We conclude that an increase in microvascular leakage correlates with airway edema in the adventitia; however, these airway changes have no significant effect on airway elastic or resistive properties.

Air Pressure↗
PubMed1994

Comparison of sulphur dioxide and metabisulphite airway reactivity in subjects with asthma.

BACKGROUND: In asthmatic subjects bronchoconstriction is induced by inhalation of the common food preservatives sulphur dioxide (SO2) and metabisulphite (MBS). SO2 and MBS challenges share many similarities, but it is not known whether they are equivalent. In this study of subjects with mild clinical asthma equivalence was assessed by comparing SO2 and MBS reactivity by estimating the total dose of SO2 inhaled during SO2 and MBS challenges, and by calculating SO2 uptake during both challenges. In addition, as the MBS solutions inhaled were acidic and hyperosmolar, the effect of these factors on MBS responsiveness was investigated. METHODS: Fifteen subjects were challenged on separate days with doubling (0.5 to 8.0 ppm) concentrations of SO2 gas inhaled during three minute periods of isocapnic hyperventilation and MBS administered in doses ranging from 0.1 to 12.8 mumol using the Wright protocol. On two other days SO2 and MBS challenges were preceded by a challenge with phosphate buffered saline (PBS) solutions of pH and osmolarity similar to MBS solutions. Response was measured as the dose or concentration causing a 20% fall in FEV1 (PD20 or PC20). RESULTS: All subjects reacted to MBS and 14 responded to SO2. Geometric mean histamine PD20 was 1.61 mumol (95% confidence interval 0.72 to 3.60). MBS and SO2 airway responsiveness were not significantly related. Estimates of the mean concentration of SO2 inhaled during SO2 and MBS challenges differed, as did estimates of the mean SO2 uptake during both challenges. MBS and SO2 reactivity were not affected by prior challenge with PBS solutions. CONCLUSIONS: SO2 and MBS challenges are not comparable. MBS reactivity was not affected by the hyperosmolar, acidic nature of its solutions.

Administration, Inhalation↗
PubMed1984

Lower-lip EMG and displacement during bilabial disfluencies in adult stutterers.

The purpose of this study was to describe the temporal patterns and spectral characteristics of antagonist lip muscle EMG and lip displacement during bilabial disfluencies in adult stutterers. Selective EMG recordings were obtained in five adult stutterers of mentalis and depressor labii inferior motor units (MENT and DLI) that were activated in a reciprocal manner during fluent speech. During disfluencies (N = 91) these same motor units were activated primarily in a reciprocal manner or DLI was not activated. These findings are not consistent with previous reports that stutterers' disfluencies involve cocontraction and overall increases in the activation levels of antagonist muscles. Spectral analysis of bilabial disfluencies revealed peaks at 5-9 Hz in the MENT EMG spectra of the five subjects and at 5-6 Hz in the displacement spectra of two subjects. A refinement in the classification of stutterers' disfluencies is suggested on the basis of individual differences in lip EMG and displacement spectra, and the mechanisms of stuttering tremor are discussed.

Adult↗
PubMed1978

Variation in perioral reflex amplitude prior to lip muscle contraction for speech.

The purpose of this study was to examine variations in the amplitude of the perioral reflex that may occur during the reaction time interval before voluntary muscle contraction for speech. Four normal adults produced the syllable /wi/ as quickly as possible in response to a low level electric shock while electromyographic recordings of the orbicularis oris inferior muscle (OOI) were made. During the reaction time interval a precise mechanical stretch was applied at the corner of the mouth to elicit the first component of the perioral reflex. Analysis of the resulting data revealed a significant increase in perioral reflex amplitude occurring between 30 and 50 msec before the onset of voluntary OOI contraction. It is concluded that the observed increases in reflex amplitude were the result of increased excitability of brainstem interneurons and/or motoneurons mediating the perioral reflex. The central mechanisms underlying such excitability increases and their significance for understanding speech motor control are discussed.

Action Potentials↗
PubMed1977

Effects of auditory masking on lip movements during speech.

This study describes the effects of unpredictably presented masking noise on selected parameters of lip movement during speech. Four normal subjects produced a simple speech utterance while vertical displacements of the upper and lower lips were transduced and recorded. During selected productions a masking noise was presented dichotically at one of two distinct phases of lip movement. Analysis of the resulting data revealed the following for all subjects: (1) significant changes in the duration, displacement, and velocity of lip movement caused by masking and (2) significant reductions in the velocity of lip movement occurring approximately 50 msec after the onset of the masker. Possible explanations of these and certain speaker-dependent effects are discussed.

Acoustic Stimulation↗