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Biomedical subjects

B Bishop

Publications and source records attributed to B Bishop.

At least 19 recordsLinked to original sources
PubMed1995

Depression of an inhibitory reflex, the masseteric silent period, in recovering alcoholics.

Because inhibitory deficits may contribute to motor incoordination of alcoholics, we proposed that the duration of the masseteric silent period (SP), an inhibitory reflex, might be shorter in alcoholics (ALs) than in nonalcoholics (NAs). To test this hypothesis, we measured the SP in a racially mixed group of 12 ALs and 12 NAs matched for age (31-49 years) and sex. All subjects were normotensive, had full dentition, and reported no major medical problems. Sensory and motor conduction velocities of the anterior tibialis, ulnar, and medial nerves were measured for each subject, and were not different in ALs and NAs. Jaw jerk and SP were evoked by tapping the chin manually with a rubber hammer containing a circuit to trigger the oscilloscope display of the masseter EMGs. Averaged mean latencies and durations of the SPs were not significantly different between the right and left masseters. SP latencies were significantly (0.7 msec) shorter in ALs than NAs (p < 0.01). The mean SP duration for ALs (13.9 +/- 1.6 msec) was also significantly shorter than that of the NAs (24.4 +/- 2.4 msec; p < 0.001). Results support the hypothesis that chronic alcoholism may interfere with inhibitory mechanisms in the CNS.

Adult↗
PubMed1992

Respiratory and abdominal muscle responses to expiratory threshold loading in cystic fibrosis.

We hypothesized that the hyperinflation and pulmonary dysfunction of cystic fibrosis (CF) would distort feedback and therefore alter the abdominal muscle response to graded expiratory threshold loads (ETLs). We compared the respiratory and abdominal muscle responses with graded ETLs of seven CF patients with severe lung dysfunction with those of matched healthy control subjects in the supine and 60 degrees head-up positions. Breathing frequency, tidal volume, and ventilatory timing were determined from inspiratory flow recordings. Abdominal electromyograms (EMGs) were detected with surface electrodes placed unilaterally over the external and internal oblique and the rectus abdominis muscles. Thresholds, times of onset, and durations of phasic abdominal activity were determined from raw EMGs; peak amplitudes were determined from integrated EMGs. Graded ETLs were imposed by submerging a tube from the expiratory port of the breathing valve into a column of water at depths of 0-25 cmH2O. We found that breathing frequency, tidal volume, and expired minute ventilation were higher in CF patients than in control subjects during low ETLs; a change in body position did not alter these ventilatory responses in the CF patients but did in the control subjects. All CF patients, but none of the control subjects, had tonic abdominal activity while supine. CF patients recruited abdominal muscles at lower loads, earlier in the respiratory cycle, and to a higher recruitment level in both positions than the control subjects, but burst duration of phasic activity was not different between groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Abdominal Muscles↗
PubMed1990

Effects of chewing frequency and bolus hardness on human incisor trajectory and masseter muscle activity.

Nine adults with no orofacial dysfunctions were instructed to chew a standardized piece of soft or hard gum on the right side in time with a metronome set at 46, 100 or 160 beats/min. Jaw movements were recorded with a Myotronics kinesiograph and masseter electromyograms were detected with surface electrodes. The chewing patterns on either gum were not significantly different in any of their spatial or temporal aspects, in mean or peak opening or closing velocities, or in the timing or level of activity in either masseter at any of the three chewing frequencies. These findings suggest that during metronome-paced chewing the change in sensory feedback resulting from a change in gum hardness exerts little or no effect on either the spatial or temporal aspects of masticatory motor output.

Electromyography↗
PubMed1990

Analysis of jaw movements and masticatory muscle activity.

This paper describes software developed to analyze the temporal and spatial aspects of jaw movements, the speed, direction and magnitude of these movements in three dimensions, and the associated electromyograms (EMGs) of the masticatory muscles. Data from a subject chewing gum illustrates the software application. Manipulations of the stored digitized data are described. Temporal aspects of each chewing cycle are defined by specified delimiters for the beginning and ending of jaw opening and closing; spatial aspects are quantified by measurements derived from movement trajectories; and peak and mean velocities are derived from the velocity profiles. EMGs are digitized, rectified, averaged and referenced to jaw movement. Onset latencies, burst durations, rise times to peak activity, time of occurrence of peak activity, and amplitudes of peak and mean activities are measured from the EMGs. This detailed kinematic/EMG analysis provides previously inaccessible information about jaw muscles and the movements they control.

Electromyography↗
PubMed1989

Vibratory stimulation of expiratory muscles inhibits respiration.

Induced vibration of the respiratory muscles alters the breathing pattern but controversy persists concerning the most effective site to vibrate, the relative merits of sustained versus phase-locked vibration, and the neural mechanisms involved. In this study we applied a sustained vibratory stimulus to the expiratory intercostal or the external oblique abdominal muscle and compared its effects on tidal volume, inspiratory duration and mean inspiratory flow. Our objective was to deduce from the changes in these respiratory variables whether the sensory input evoked by the vibratory stimulation modulated the central inspiratory drive, the termination of inspiration, or both. Subjects rebreathed from a spirometer which initially contained pure oxygen without a CO2 absorber. Either unilateral or bilateral sustained vibration (100 Hz, 2 mm amplitude) was applied to the 7th or 8th intercostal space anterior to the midaxillary line where the intercostal muscle is a single layer and functions in expiration. Bilateral chest wall vibration suppressed the tidal volume in 7 of 9 subjects. In 4 of 9 subjects, the inspiratory duration was shortened, reflecting premature termination of inspiration. In 5 of 9 subjects, the mean inspiratory flow was reduced, reflecting depression of the central inspiratory drive. Sustained abdominal vibration suppressed tidal volume and reduced inspiratory duration in 4 of 5 subjects. Thus, sustained vibration of either of the expiratory muscles resulted in a reduction in tidal volume. We concluded that sensory input initiated by sustained vibration of abdominal muscles acts centrally to suppress the level of activity in inspiratory neurons.

Adult↗
PubMed1988

Comparison of automatic and voluntary chewing patterns and performance.

Chewing, like respiration, is ordinarily performed as an automatic motor act, yet both can be voluntarily controlled. No in-depth analyses of voluntary chewing exist. Therefore, we have analyzed on a cycle-by-cycle basis voluntarily controlled chewing, and compared it with automatic chewing. We assessed the performance during voluntarily controlled chewing by obtaining constant error and variable error scores. Nine healthy adults with full dentition were subjects (Ss). Their three-dimensional jaw movements and movement times were derived from Kinesiograph recordings obtained while chewing a standard piece of gum on the right side of the mouth. Burst durations and onset latencies of masseter activity were obtained from surface-recorded EMGs. Frequency during automatic chewing was obtained from data recorded while the subject viewed a film. Next, the subject chewed in time with a metronome set at this "automatic" rate. Intrasubject variability among 30 consecutive chewing cycles during voluntary was less than during automatic chewing. In every S gape and ipsilateral jaw excursions and the variability of burst durations of masseter activity were less during voluntary than during automatic chewing, showing that both the spatial and temporal aspects of the two types of chewing differ significantly. Ss varied in ability to follow the metronome. A S's constant error might be small, yet his variable error might be large, as if feed-back-based corrections influenced cycle-to-cycle variability. Fast chewers had smaller constant and variable error scores than did slow chewers, suggesting a speed-accuracy relationship. In summary, both temporal and spatial aspects of voluntary chewing were modified compared with those of automatic chewing. During voluntarily controlled chewing, cycle-to-cycle variability was less compared with automatic chewing due to reductions in variability of occlusal phase and the masseter's burst durations, and total jaw excursions were less because gapes and ipsilateral deviations during closing were reduced.

Adult↗
PubMed1988

Organic food in cancer therapy.

This paper describes the principles of dietary therapy for malignant disease, as developed by a few medical pioneers since the 1920s, in particular by the late Dr Max Gerson, M.D. (1881-1959), who insisted on the exclusive use of organic produce in the treatment of cancer patients. Dr Gerson's claims for the therapeutic value of organic fruits and vegetables are reviewed in the light of current research.

Environmental Pollutants↗
PubMed1987

Electrically evoked responses of the human external oblique abdominal muscle.

An electric shock delivered to a mixed intercostal nerve of a standing human subject evokes two responses in the external oblique abdominal EMG, namely an M-wave and an electrically elicited reflex. The reflex latency is very close to that of the mechanically elicited phasic stretch reflex of the external oblique, suggesting that it is a monosynaptic spinal reflex. However, several of its characteristics make it very different from the mechanically evoked reflex and the H-responses of calf or jaw muscles. Unlike the mechanically evoked reflex, the electrically elicited reflex is neither modulated by respiration nor attenuated when the subject assumes a supine posture. Unlike the H-response of calf or jaw muscles, the electrically elicited reflex is extremely reproducible from trial to trial, displays no antidromic occlusion in response to an increase in shock strength, and is neither suppressed nor potentiated by abdominal muscle vibration. A silent period, i.e., an indicator of alpha-motoneuron suppression, follows an electrically elicited reflex only when the subject rotates his trunk away from the recording site. Presumably, inputs from external oblique muscle receptors inhibit their homonymous motoneurons effectively when the muscle is functioning as the chief power generator, but not when it is functioning as an agonist. Using single motor unit analysis, the electrically elicited reflex was shown to be comprised of monosynaptic, oligosynaptic, and multisegmental components with the major component being monosynaptic. These unique characteristics of the EER are presumably a reflection of the external oblique's multisegmental innervation, multilayered anatomy, short neuronal pathways, and diverse functions.

Abdominal Muscles↗
PubMed1987

Mandibular movements and jaw muscles' activity while voluntarily chewing at different rates.

As a way of learning about the motor control of chewing, we studied how well a subject could voluntarily chew in time with a metronome and defined the changes in the spatial and temporal aspects of the chewing pattern with changes in chewing rate. Timing and extent of mandibular movements were assessed in nine adults from Kinesiograph recordings; timing and level of activity in digastric and both masseter muscles were determined from surface EMGs. Each subject chewed gum in time with a metronome set randomly at 46, 100, 160 beats per minute or at a frequency close to his automatic chewing rate. Cycle-by-cycle analysis showed that subjects varied in their ability to keep pace with the metronome. When chewing at high frequencies, six subjects reduced gape, three did not. Contralateral deflection in opening, when present, was significantly reduced when chewing at high frequencies and this decrease was independent of vertical gape. Durations of opening, closing, and occlusal phases decreased in proportion to the decrease in total cycle duration. Burst duration of diagastric activity decreased about 29% compared with a 77% decrease in cycle duration over all chewing rates. At low frequencies onset of digastric activity occurred after onset of opening. At high frequencies digastric onset preceded opening. Burst durations of both masseter muscles decreased in concert with the decrease in cycle duration. Termination of activity in both masseters was synchronous and always occurred 100 +/- 20 ms prior to the next opening. Therefore, we conclude that (i) individuals vary in ability and strategy for controlling chewing rate voluntarily and (ii) with increases in chewing rates the shortening of burst duration for the digastrics is significantly less than for the masseters.

Adult↗
PubMed1986

Phasic stretch reflex of the abdominal muscles.

This analysis of the abdominal stretch reflex (ASR) evoked by a tap to the abdomen was designed to explore how abdominal motoneurons process signals from respiratory and nonrespiratory sources. We recorded surface EMGs from the external and internal oblique muscles in standing subjects. Amplitudes of the abdominal stretch reflex varied despite constant tap forces, but strong taps evoked a larger reflex than weak taps. Trunk rotation toward the recording side, or voluntary contraction of the external and internal oblique muscles increased the reflex amplitudes, whereas contralateral rotation reduced their occurrence. An abdominal stretch reflex during a voluntary contraction was followed by a silent period of 40 to 80 ms. Often a late wave followed a reflex by 20 to 40 ms. Amplitudes during breathholds at residual lung volume were larger than those evoked during a breathhold at functional residual capacity, suggesting that abdominal stretch reflex amplitudes are inversely proportional to static lung volume. During quiet breathing the reflex amplitude reached a maximum slightly before end-expiration and decreased progressively to a minimum close to end-inspiration. During rebreathing, background abdominal activity was augmented with highest activity in late expiration. Abdominal stretch reflex amplitudes continued to wax and wane in phase with respiration, and the maximal reflex occurred progressively earlier in expiration. In summary, the abdominal stretch reflex reflects strong control from abdominal muscle spindles, lung proprioceptors, and chemoreceptors. The relative contributions of these inputs need to be determined.

Abdominal Muscles↗
PubMed1986

Effect of gum hardness on chewing pattern.

Chewing rhythms are set by a putative central pattern generator whose output is influenced by sensory feedback. In this study we assessed how an altered feedback imposed by changing the hardness of a gum bolus modifies the timing of chewing, the maximal gape, and the activity in the masseter muscle on the chewing side. Ten adult subjects with no orofacial dysfunction chewed a standard piece of soft or hard gum for at least 3 min in random order. Vertical jaw movements were recorded with a kinesiograph and activity of the masseter muscle was recorded and integrated from surface EMG electrodes. The subjects sat in a dental chair and viewed a video lecture to distract their attention from chewing; they were instructed to chew on the right molars. Cycle-by-cycle analysis showed that 9 of the 10 subjects chewed the hard gum more slowly than the soft with no significant change in gape. The increases in cycle duration were due to changes in the duration of the opening and occlusal phases. The duration of closing was not significantly changed even though the duration and level of masseter activity were both significantly increased. We conclude that gum hardness by altering proprioceptive feedback modifies the output of the masticatory central pattern generator in such a way that the temporal aspects of chewing and the output of the masseteric motor pool are affected.

Adult↗
PubMed1985

Effects of whole-body rotation on masseteric motoneuron excitability.

Vestibular stimulation is a popular clinical treatment for enhancing the excitability of spinal motoneurons innervating trunk and limb muscles, but whether vestibular stimulation can also influence trigeminal motoneurons is not known. We determined whether or not vestibular stimulation evoked by rotation of a seated subject would modify the excitability of masseteric motoneurons. The amplitude and frequency of occurrence of masseteric compound action potentials evoked by standard chin taps provided measures for assessing masseteric motoneuron excitability. Eleven healthy adults with no orofacial or otologic disorders served as subjects. Each sat in a motorized dental chair with his head stabilized by a halo head-piece so that chair rotation caused labyrinthine excitation. The frequency (3/s) of chin taps and their impact force were maintained constant by microcomputer control. After each tap, a 16-ms sample of EMG recorded from surface electrodes over the right masseter was digitized and stored for subsequent visual inspection. Only compound action potentials meeting rigorous criteria in terms of latency, amplitude, duration, and waveform were accepted as responses. The mean frequencies of occurrence and the mean amplitudes of the responses showed wide variability. Histogram displays of every response for each subject, however, revealed enhanced output from the masseteric motoneuron pool during the decleration and postrotation phases. In subjects not immediately retested this enhancement was persistent but decayed during the next 5 min. In five subjects the experiment was repeated after 1 min. The changes in response variables during phases 3 and 4 were significantly less than on the first trial, suggesting habituation. These results provide quantitative evidence that the dynamic input from vestibular ampullary receptors in response to rotation enhances masseteric motoneuron output.

Adult↗
PubMed1984

Identification and assessment of factors contributing to variability of the jaw jerk.

Unlike limb monosynaptic reflexes, the jaw jerk reflex ( JJR ) is extremely variable. We studied 35 healthy adults to determine the relative contributions of extrinsic and intrinsic factors underlying this variability. Each subject sat in a dental chair with his head and chin securely stabilized. Chin taps, delivered by a solenoid-driven plunger, were quantified with a piezo -transducer. The reflex response was recorded from surface electrodes over the right masseter muscle. A nasal thermistor signalled phases of respiration. Five of the 35 subjects had no reflex when relaxed, but during 15 degrees neck extension or voluntary contraction of the platysma muscle, a JJR appeared. The amplitude of the reflex varied considerably from trial to trial in all but one subject. A small component of this variability was due to minute changes in tap force despite head and chin stabilization and stimulus uniformity. Mean amplitudes of the reflex tended to increase with increases in tap force, but variability was large indicating intrinsic fluctuations in motoneuron excitability. Voluntary contraction of the platysma muscle and 15 degrees neck extension reliably enhanced the reflex. The JJR showed negligible respiratory modulation during quiet breathing. The reflex's variability in and among subjects precludes the use of the JJR as an index of masseteric motoneuron excitability. Our findings suggest that branchial motoneurons innervating the masticatory muscles receive far more diverse and fluctuating inputs than do somatic motoneurons innervating limb muscles.

Adolescent↗
PubMed1984

Breathing pattern in humans: elevated CO2 or low O2 on positive airway pressure.

The purpose of this study was to determine effects on breathing pattern of pressure breathing alone and in combination with chemical stimulation. We analyzed ventilatory responses to elevated airway pressures (positive-pressure breathing, PPB) in subjects breathing air, 12% O2, or elevated CO2. Each subject sat in a body box and breathed via mouth-piece from a bag-in-box. Responses to PPB on air were increased minute ventilation (VI), tidal volume (VT), frequency (f), mean inspiratory (VT/TI) and expiratory (VT/TE) flows, decreased expiratory duration (TE) and end-tidal CO2. If end-tidal CO2 were held constant, VI, VT, and VT/TI increased less. Responses greater than predicted from summing responses to either stimulus alone were observed for VT, f, VT/TI, and VT/TE during 3 and 5% CO2 and for VT, f, and VT/TE during isocapnic hypoxia. Responses to other combined stimuli were sums of responses to the individual stimuli. Thus ventilatory responses to combined PPB and chemical stimuli cannot be predicted simply from summating responses to each independently imposed stimulus, suggesting that sensory information arises from and is integrated at multiple sites.

Adult↗
PubMed1983

Responses of cat's internal intercostal motor units to hypercapnia and lung inflation.

Single motor unit potentials from the eighth internal intercostal (IIC) muscle were recorded along with tracheal pressure and end-tidal CO2 (PETCO2) in spontaneously breathing, Dial-urethane anesthetized cats during hypercapnia (3, 5, or 7% CO2) and during lung inflation (LI, 100 ml above functional residual capacity) before and after vagotomy. Hypercapnia depressed IIC activity in 5 of 7 cats; the higher the PETCO2, the lower was the firing rate and the fewer the number of spikes per breath. LI evoked an initial silent phase (ISP) in 6 of 10 cats followed by a prolonged IIC burst. Hypercapnia combined with LI abolished or diminished the ISP and shortened the prolonged burst with an increase in firing rate and a recruitment of new units. Vagotomy silenced IIC activity in 7 of 10 cats, but LI after vagotomy activated IIC activity in 10 of 10 cats, though neither an ISP nor prolonged activity occurred. Our data suggest that major factors in controlling IIC activity are reciprocal inhibition from bulbospinal inspiratory neurons, excitatory and inhibitory inputs mediated by vagal afferents, and a modulation of IIC activity via gamma-loop. Hypercapnia affects the former two factors.

Action Potentials↗