Mitochondrial metabolism reveals a functional architecture in intact islets of Langerhans from normal and diabetic Psammomys obesus.

The cells within the intact islet of Langerhans function as a metabolic syncytium, secreting insulin in a coordinated and oscillatory manner in response to external fuel. With increased glucose, the oscillatory amplitude is enhanced, leading to the hypothesis that cells within the islet are secreting with greater synchronization. Consequently, non-insulin-dependent diabetes mellitus (NIDDM; type 2 diabetes)-induced irregularities in insulin secretion oscillations may be attributed to decreased intercellular coordination. The purpose of the present study was to determine whether the degree of metabolic coordination within the intact islet was enhanced by increased glucose and compromised by NIDDM. Experiments were performed with isolated islets from normal and diabetic Psammomys obesus. Using confocal microscopy and the mitochondrial potentiometric dye rhodamine 123, we measured mitochondrial membrane potential oscillations in individual cells within intact islets. When mitochondrial membrane potential was averaged from all the cells in a single islet, the resultant waveform demonstrated clear sinusoidal oscillations. Cells within islets were heterogeneous in terms of cellular synchronicity (similarity in phase and period), sinusoidal regularity, and frequency of oscillation. Cells within normal islets oscillated with greater synchronicity compared with cells within diabetic islets. The range of oscillatory frequencies was unchanged by glucose or diabetes. Cells within diabetic (but not normal) islets increased oscillatory regularity in response to glucose. These data support the hypothesis that glucose enhances metabolic coupling in normal islets and that the dampening of oscillatory insulin secretion in NIDDM may result from disrupted metabolic coupling.

Assessing culture via the Internet: methods and techniques for psychological research.

This study examines the acculturation experiences of Arabic immigrants and assesses the utility of the Internet as a data collection tool. Based on in-depth pilot interview data from 10 male Arabic immigrants and items selected from pre-existing measures, the Male Arabic Ethnic Identity Measure (MAEIM) was developed. Male Arab immigrants (115 males) were solicited through traditional methods in addition to the Internet. Satisfactory reliability and validity were reported for the MAEIM. No significant differences emerged between the Internet and Midwestern samples. The Internet proved to be an effective method for soliciting a relatively large, geographically dispersed sample of Arabic immigrants. The use of the Internet as a research tool is examined in the context of anonymity, networking, low-cost, perceived interactive control, methodological rigor, and external validity. The Internet was an effective vehicle for addressing concerns raised by prospective participants. It is suggested that the Internet may be an important method to assess culture-relevant variables in further research on Arab and other immigrant populations.

Eating concerns in East Asian immigrants: relationships between acculturation, self-construal, ethnic identity, gender, psychological functioning and eating concerns.

OBJECTIVE: Eating concerns in East Asian immigrants were assessed and their association with acculturation status, self-construal, ethnic identity, gender and psychological functioning was examined. METHOD: One-hundred and fifty non-clinical East Asian immigrants (75 males, 75 females) were administered a battery of psychometrically established measures with satisfactory reliability and validity. RESULTS: Females were more prone to eating concerns and these were positively related to symptoms of psychological distress. Acculturation, self-construal, ethnic identity and psychological functioning were not related to desire to be thinner, feeling guilt after eating, fear of being overweight nor preoccupation with the thought of having fat on one's body. Collective self-esteem and symptoms of psychological distress were positively related to feeling discomfort after eating sweets, while interdependent self-construal and assimilation were negatively related. DISCUSSION: Culturally relevant variables, namely acculturation, self-construal and ethnic identity, were related to only certain facets of eating concerns. The findings suggest the importance of assessing discrete, psychologically-relevant facets of culture rather than more global constructs such as westernization when examining eating concerns in immigrant populations.

Development of a new scale for measuring acculturation: the East Asian Acculturation Measure (EAAM).

Given the paucity of appropriate measures to assess the acculturation patterns of East Asian immigrants in the United States, a new acculturation instrument was developed and evaluated. One-hundred and fifty nonclinical East Asian immigrants (75 males and 75 females) were administered the East Asian Acculturation Measure (EAAM) and provided demographic information concerning length of stay in the United States and gender. Satisfactory reliability is reported for the four acculturation scales: assimilation, separation, integration, and marginalization. Length of stay was not associated with separation but was significantly positively associated with assimilation and integration and significantly negatively associated with marginalization. Gender was not associated with any of the acculturation scales. The findings suggest that the EAAM may be a useful tool for researchers and clinicians to investigate the acculturation patterns of East Asian immigrants.

Recurrent laryngeal nerve transposition in guinea pigs.

Improved control of prosthetic voice aids for laryngectomees might be possible to obtain with residual laryngeal motor nerve signals. We were able to recover motor signals from the recurrent laryngeal nerve (RLN) by transposing it into the ipsilateral denervated sternohyoid muscle (SH) in 8 guinea pigs. Reinnervation was monitored by electromyographic recordings from surface and intramuscular needle electrodes in awake animals. Within 4 to 14 weeks after surgery, all animals demonstrated laryngeal-like motor activity in the reinnervated SH, including activity during respiration, sniffing, swallowing, and/or vocalizing. After 3 to 6 months, the animals were reanesthetized, and nerve stimulation and section experiments confirmed the RLN as the source of reinnervation in all cases. In several animals, activity of the RLN-innervated SH was demonstrated to be correlated with that of contralateral laryngeal muscles. Histochemical analysis of the SH indicated a unilateral transformation from mostly fatigable to mostly fatigue-resistant fiber types ipsilateral to the RLN transposition, a phenotype more typical of laryngeal muscles. Thus, RLN transposition at the time of laryngectomy may be a method for salvaging laryngeal control signals that could be used to control prosthetic voice devices.

Quantification of first heart sound frequency dynamics across the human chest wall.

Power spectral analysis has attracted attention because of its potential for non-invasive cardiac diagnosis. However, time-frequency analysis of first heart sound frequency dynamics from canine epicardium has demonstrated that cardiac vibrations are fundamentally multi-component and non-stationary, questioning the validity of power spectral techniques. In this study, we employed time-frequency transforms to characterise first heart sound frequency dynamics from 27 sites across the human thorax. In contrast to the dynamics observed epicardially, the first heart sound frequency law was dominated by quasi-stationary and impulse-like components implying that the instantaneous power and the power spectrum contain most of the diagnostic information in the first heart sound.

Muscle sound frequencies of the frog are modulated by skeletal muscle tension.

The purpose of this study was to determine the relationships among muscle sound frequencies, muscle tension, and stiffness. Time-frequency transformations of nonstationary acoustic signals provided measures of resonant frequency during isometric contractions of frog (Rana pipiens) semitendinosus and gastrocnemius muscles. A mathematical expression for muscle transverse resonant frequency, elastic modulus and tension, based on elastic beam theory, was formulated by the Rayleigh method adapted for muscles. For thin muscles, the elastic modulus was found to have negligible influence on transverse muscle resonant frequency. Changes in muscle tension were the major determinants of changes in transverse resonant frequency. Consequently, for thin muscles, the time course of muscle tension, but not elastic modulus, can be monitored acoustically during the early phase of contraction when muscles give rise to sounds. Muscles were found to be anisotropic with a modulus of elasticity, EL, measured via length perturbations near 0.1% muscle length peak-to-peak, that was much larger than the modulus of elasticity, Eb, that resists the lateral bending that causes sound production. The elastic and resonant behavior of a thin muscle is similar to a tensioned fibrous cable with distributed mass.

Regional effects of myocardial ischemia on epicardially recorded canine first heart sounds.

To determine whether focal changes in myocardial material properties are important in determining the response of first heart sound acceleration amplitude and frequency to myocardial ischemia, cardiac vibrations were simultaneously recorded from ischemic and nonischemic regions of canine epicardium by use of ultralight acceleration transducers. Cardiac acceleration and hemodynamics were recorded before and 5 min, 15 min, 1 h, and 2 h after left circumflex coronary artery occlusion. Peak-to-peak amplitude declined transiently in the nonischemic zone during early occlusion (P < 0.05) but was not decreased at any time in the ischemic myocardium. The median frequency of first heart sound vibrations in the ischemic region increased 31% within 5 min after occlusion (P < 0.01) and remained elevated for 2 h (P < 0.05). Nonischemic zone frequency was not statistically different from baseline at any time point. The disparate regional response of first heart sound vibrational frequency to myocardial ischemia suggests that propagating mechanical transients and myocardial contractile acceleration, rather than resonant vibrations, produce the first heart sound.

Time-frequency transforms: a new approach to first heart sound frequency dynamics.

This study employed a new analytical tool, the Binomial joint time-frequency transform, to test the hypothesis that first heart sound frequency rises during the isovolumic contraction period. Cardiac vibrations were recorded from eight open chest dogs using an ultralight accelerometer cemented directly to the epicardium of the anterior left ventricle. The frequency response of the recording system was flat +/- 3 dB from 0.1 to 400 Hz. Three characteristic time-frequency spectral patterns were evident in the animals investigated: 1) A frequency component that rose from approximately 40-140 Hz in a 30-50 ms interval immediately following the ECG R-wave. 2) A slowly varying or static frequency of 60-100 Hz beginning midway through the isovolumic contraction period. 3) Broad-band peaks occurring at the time of the Ia and Ib high frequency components. The presence of rapid frequency dynamics limits the usefulness of stationary analysis techniques for the first heart sound. The Binomial transform provided much better resolution than the spectrograph or spectrogram, the two most common non-stationary signal analysis techniques. By revealing the onset and dynamics of first heart sound frequencies, time-frequency transforms may allow mechanical assessment of individual cardiac structures.

Muscle fatigue measured with evoked muscle vibrations.

Skeletal muscle vibrates laterally during voluntary and evoked muscle contractions. We hypothesized that the vibration amplitude from evoked muscle twitches is directly related to evoked twitch force from fatiguing muscle. To test the hypothesis, vibrations produced by evoked muscle twitches were recorded during short (5-second) rest periods as the muscle was intermittently exercised with voluntary contractions. Trials were performed at 30%, 50%, and 70% of maximal voluntary contraction. Evoked muscle twitches eliminated the problems of motivation and tremor that complicate sound and vibration measurements during voluntary contractions. Results from the first dorsal interosseus hand muscle in 11 normal adult volunteers revealed that the vibration amplitude is highly correlated (r2 = 0.93, at 70% MVC, r2 = 0.97, at 50% MVC; r2 = 0.85, at 30% MVC) with force. Both potentiation and reduction of force with exercise were accompanied by parallel changes in vibration amplitude, as measured with an accelerometer. Compound muscle action potentials did not increase with exercise-induced twitch potentiation, and did not correlate as highly with force during fatigue.

Vibrations and sounds from evoked muscle twitches.

Muscle sounds are related to force production, fatigue, and pathology of muscle. However, sound data are frequently contaminated by tremor and motivational artifacts. Also, sound data are frequently reported in transducer-dependent units such as millivolts. To eliminate tremor and motivational artifacts and to obtain data in fundamental, nontransducer-dependent units, an accelerometer was used to record vibrations from human hand muscle twitches evoked by percutaneous stimulation. Reliable and reproducible waveforms were obtained from normal adult volunteers by recording from abductor pollicis brevis (APB) or abductor digiti quinti hand (ADQH) muscle after median or ulnar nerve stimulation, respectively. Latencies from the stimulus to the onset of the acceleration waveform were 5.7 +/- 0.6 and 5.1 +/- 0.6 ms, peak-to-peak amplitudes were 6.5 +/- 2.4 and 7.2 +/- 2.0 m/s2 for the APB and ADQH muscles, respectively.

AAEM minimonograph #36: basic concepts of electricity and electronics in clinical electromyography.

Fundamental principles of electricity provide a basis for understanding the design and operation of electromyography equipment. An intuitive and quantitative explanation of charge, voltage, current, and impedance provides an introduction to the concepts of resistance, capacitance, and input impedance. These concepts form the basis for discussion of filters, amplifiers, electrodes, digital electronics, stimulators, and patient safety. The monograph assumes no specialized training in engineering or mathematics. The topics are discussed at an introductory level to provide understanding for readers with no electronics background and intuitive insight for more experienced readers.

Muscle sounds from evoked twitches in the hand.

Skeletal muscle emits acoustic signals during voluntary contraction and during twitches produced by electric stimulation of peripheral nerves. Supramaximal, percutaneous electric stimulation was applied to the median or ulnar nerve, while electric and sound signals were recorded from the abductor pollicis brevis or abductor digiti minimi muscles, respectively, in 27 volunteers without known disease. Reproducible waveforms were obtained with the following means and standard deviations: (1) latency from stimulus to onset of sound, median = 6.9 +/- 0.8msec, ulnar = 6.6 +/- 1.0msec; (2) latency from stimulus to peak of sound, median = 15.1 +/- 1.5msec, ulnar = 13.1 +/- 1.5msec; (3) latency from onset of surface electric to onset of sound, median = 3.6 +/- 1.0msec, ulnar = 3.9 +/- 1.1msec; (4) baseline-to-peak amplitude of sound, median = 860 +/- 270mV, ulnar = 640 +/- 230mV; and (5) baseline-to-peak amplitude of surface electric, median = 11.4 +/- 3.0mV, ulnar = 10.1 +/- 2.4mV. Stimulated muscle sounds are useful when artifacts, such as tremor, interfere with voluntary muscle sound recordings, or when quantitative information is needed to relate electric to contractile muscle activity.

Magnetic resonance imaging of avascular necrosis of the lunate.

Avascular necrosis (AVN) of carpal bones, particularly the lunate, is often an elusive cause of wrist pain. Physical examination can be indistinguishable from that of a simple wrist sprain, and standard radiographic evaluations are frequently normal. Early diagnosis is critical, since late treatment is often simple observation of the natural history of the disease, which includes progressive collapse of the lunate and derangement of the carpal architecture. Magnetic resonance imaging (MRI) produces images of high contrast, demarcating necrotic from normal bone. We present a case of lunate AVN ("Kienböck's disease") to illustrate the ability of MRI to identify necrotic bone in the wrist. We suggest that MRI is useful in diagnosing AVN in the wrist and that it may allow an earlier diagnosis of lunate AVN than is possible with standard radiographs.

Muscle sounds are emitted at the resonant frequencies of skeletal muscle.

The changes in mechanical resonant frequency of whole muscles during twitch and tetanic contractions were compared to changes in frequency components of the pressure wave produced by muscles during contraction. Resonant frequencies were determined by imposing sinusoidal length changes on a muscle and observing transverse standing waves when the frequency of length change matched the muscle's resonant frequency or a harmonic of the resonant frequency. Acoustic signal instantaneous frequency spectrums were calculated using time-frequency transformations including the Wigner transform and the exponential distribution. During a tetanic muscle contraction, the peak instantaneous frequency initially increased and then became constant as the force plateau was reached. The resonant frequencies determined during the force plateau and during relaxation spanned the same range as the peak instantaneous frequency of the acoustic signal. These results suggest that the acoustic signal may be useful as a non-invasive monitor of muscle resonant frequency during contraction.

Acoustic and surface EMG diagnosis of pediatric muscle disease.

The ratio of acoustic myography (AMG) amplitude to surface electromyography (EMG) amplitude is proposed as a measure of mechanical output compared with electrical activity of the contractile system. AMG to EMG ratios were measured from 16 children with muscle disease diagnosed by clinical criteria, EMG, and/or muscle biopsy. These were compared with the ratios from 11 normal volunteers spanning the same age range (7-16 years). AMG to EMG ratios were significantly (P less than 0.01) different for the two populations. Using a linear discriminant function to define the normal range for AMG to EMG ratios yielded a sensitivity of 82% (13 of 16 abnormals diagnosed) and a specificity of 91% (10 of 11 normals). These findings suggest that surface recordings may provide significant diagnostic information in muscle disease. The accuracy may be improved further by using additional muscles (e.g., paraspinals) and evoked twitches.

Acute somatic pain can refer to sites of chronic abdominal pain.

We report a case of a latissimus dorsi muscle strain that presented as a recurrence of chronic abdominal pain. One explanation of the referral of acute pain to a site of chronic pain is the convergence-projection theory, which hypothesizes that pain signals of visceral and somatic origin converge at some point in the sensory pathway. Upon reaching the cortex, these signals are interpreted as coming from the afferents which have previously excited this pathway. In this case an extensive gastrointestinal diagnostic evaluation was pursued unsuccessfully before the latissimus dorsi muscle strain was diagnosed. Outpatient therapy of spray and stretch combined with a home stretching program produced a prompt and persistent resolution of the symptoms.

Fluid mechanics of muscle vibrations.

The pressure field produced by an isometrically contracting frog gastrocnemius muscle is described by the fluid mechanics equations for a vibrating sphere. The equations predict a pressure amplitude that is proportional to the lateral acceleration of the muscle, inversely proportional to the square of the distance from the muscle, and cosinusoidally related to the major axis of lateral movement. The predictions are confirmed by experiments that measure the pressure amplitude distribution and by photographs of muscle movement during contraction. The lateral movement of muscle has the appearance of an oscillating system response to a step function input--the oscillation may be at the resonant frequency of the muscle and therefore may provide a means to measure muscle stiffness without actually touching the muscle.