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At least 19 recordsLinked to original sources
PubMed1992

Acoustic myography of the human quadriceps muscle during intermittent fatiguing activity.

Integrated acoustic myography (IAMG) and electromyography (IEMG) were recorded over rectus femoris (RF) in six healthy subjects during a series of intermittent isometric contractions of quadriceps. Contractions were held for 10 sec with 10 sec rest between each, commencing at 75% maximum voluntary contraction (MVC) force and continuing to 40% MVC. The IAMG activity initially decreased (75%-60% MVC) in a linear relationship (r = 0.9) with fatigue (i.e. force loss) but then plateaued and increased once force fell below 52% MVC. The AMG/force relationship for the whole fatiguing protocol (i.e. 75%-40% MVC) was quadratic (r = 0.87). The IEMG also showed a quadratic relationship with force (r = 0.85) but activity initially increased before decreasing. The results of the present study quantify the relationship between AMG and force in quadriceps during fatigue from intermittent contractions commencing at 75% MVC. The findings confirm previous observations that AMG decreases with fatigue during strong contractions but the quadratic relationship found in the present study differs to that for other muscles during sustained contractions. The results also suggest that simultaneous recordings of AMG and EMG may help distinguish central and peripheral fatigue. Acoustic myography may therefore be a useful non-invasive monitor of force during early fatiguing activity using the present protocol but the need to study AMG during fatigue of different muscles and force levels is stressed.

Acoustics↗
PubMedDate not supplied

Acoustic myography: a noninvasive monitor of motor unit fatigue.

Acoustic myography is the recording of sounds produced by contracting muscle. These sounds become louder with increasing force of contraction. We have compared muscle sounds with surface EMG to monitor the dissociation of electrical from mechanical events (presumably, the loss of excitation-contraction coupling) which occur with motor unit fatigue. Acoustic signals were amplified using a standard phonocardiograph, recorded on FM magnetic tape, and digitally analyzed. Muscles were examined at rest, with intermittent contractions, and with sustained contractions. We found that with fatigue, the acoustic amplitude decayed, but the surface EMG amplitude did not. With decreased effort, however, the acoustic and the surface EMG amplitudes declined simultaneously. By simultaneously recording acoustic signals and needle EMG, individual motor units were resolved acoustically in two muscles with decreased numbers of motor units and increased motor unit size. Fasciculations also produced acoustic signals, although no acoustic signal has yet been found that correlates with fibrillations. Analysis of acoustic signals from muscle provides a noninvasive method for monitoring motor unit fatigue in vivo. It may also be useful in distinguishing muscle fatigue from decreased volition.

Acoustics↗
PubMed1992

Electro and acoustic myography for noninvasive assessment of lumbar paraspinal muscle function.

In 31 normal subjects (17 male), aged 19-48 years, and 8 patients with chronic low back pain (4 male), aged 37-55 years, the repeatability of surface recordings of acoustic myography (AMG) and electromyography (EMG) were examined in the lumbar paraspinal muscles. Five isometric test positions were examined. In 21 of the normal subjects, four positions tested were: quiet standing, half extension from prone lying, full extension from prone with and without resistance. In 10 of the normal subjects and the 8 back pain patients, a standardised, unsupported horizontal position with the upper body over the end of a couch was tested. The AMG and EMG signals were full-wave rectified and integrated (iAMG and iEMG). The variability of recordings during repeated 5-s isometric contractions was assessed by analysis of variance (ANOVA) and the coefficient of variation (CV) was calculated from the ANOVA. Both recording techniques produced the most repeatable results during the unsupported, horizontal hold position. In the normal subjects, CV were, iAMG 5.6%, iEMG 4.9%; and in the patients, iAMG 4.4%, iEMG 2.6%. The CV for the other four isometric test positions ranged from 15.3% to 29.4% for iAMG, and 8% to 15.7% for iEMG. These results demonstrated that a controlled test manoeuvre for examining AMG and EMG of the paraspinal muscles was vital for repeatable recordings. The CV for the standardised, horizontal position were lower than for previously published results.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Acoustic myography reflects force changes during dynamic concentric and eccentric contractions of the human biceps brachii muscle.

The relationship between acoustic myography (AMG), electromyography (EMG) and force during submaximal dynamic contractions was examined in the biceps brachii muscles of eight healthy males (aged 17-26 years). Different weights were lifted and lowered at a constant speed, using a wall pulley system, to perform concentric and eccentric contractions, respectively. Integrated AMG (iAMG) and integrated EMG (iEMG) activity both increased linearly with force during concentric (iAMG r = 0.94; iEMG r = 0.99) and eccentric (iAMG r = 0.90; iEMG r = 0.94) contractions. The slopes of the concentric regression lines were significantly different from the eccentric slopes (P less than 0.01) for both iAMG and iEMG with concentric contractions showing greater levels of activity. The results indicated that AMG can be used to detect changes in force during dynamic contractions which has important implications for the use of AMG in rehabilitation. The differences in iAMG activity between concentric and eccentric contractions are discussed in relationship to the origin of the AMG signal.

Adolescent↗
PubMed1993

Ultrasound myography: application in nerve conduction velocity assessment and muscle cooling.

A new application of ultrasound for studying muscle twitch induced by electrical stimulation is described and some preliminary results are presented. The method, called "ultrasound myography" (UMG), uses Doppler ultrasound to measure muscle movement velocity. The Doppler signals were measured simultaneously with the electromyography (EMG) signals from the thenar muscle of a healthy subject. Averaged EMG and full-wave rectified UMG responses to repeated electrical stimuli were measured after cooling of the hand and adaptation to room temperature. Latency times over the wrist of cold hands adapted to a surrounding temperature of 8 degrees C were 4.5 ms and 16.9 ms for the EMG and averaged rectified UMG responses, respectively. Both latency times decreased considerably after 1 h adaptation to a room temperature of 21 degrees C:20% for the EMG response and 35% for the UMG response. The conduction velocities of the median nerve in the forearm determined by both methods yield comparable results. The results of both methods are discussed. It is concluded that UMG possibly offers a new method in clinical practice for the assessment of nerve conduction velocities in the forearm, and basically is a new simple-to-use technique for noninvasive analysis of deep biomechanical processes.

Adult↗
PubMed2003

[Opacification of a coronary vein during left ventriculography with inadvertent myography in a 78-year-old woman with aortic stenosis].

A 78 year-old woman had a NYHA II dyspnoea, which was related to a calcified aortic stenosis. Functional aortic valvular surface was calculated to 0.75 cm2 by echocardiography. In addition, there were important mitral calcifications without mitral stenosis. The left ventricular contractility was normal, but there was a significant left ventricular hypertrophy. At the time of the coronary angiography, the aortic valve was crossed with difficulty. A "pigtail" probe was positioned and during left ventricular angiography, an unexpected aspect of myography was observed with an unusual opacification of the interventricular posterior coronary vein, draining in the coronary sinus. The patient remained strictly asymptomatic during all the procedure. Two echographic controls carried out in the 24 following hours appeared normal, without pericardial effusion nor new parietal anomaly of the left ventricle. Five weeks later, the patient underwent an aortic valve replacement without complication.

Aged↗
PubMed1998

Acoustic myography, electromyography and bite force in the masseter muscle.

Acoustic myography (AMG) offers some advantages over electromyography (EMG) in certain circumstances, but the use of AMG on the jaw-closing muscles has not been fully tested. The purpose of this study was to examine the relationship between AMG, EMG and force in the masseter muscles of nine healthy male subjects. The AMG was recorded using a piezoelectric crystal microphone and the EMG was recorded simultaneously with surface electrodes. Force was recorded between the anterior teeth with a strain-gauge transducer. Analysis showed that Pearson's correlation coefficient was 0.913 for force/AMG and 0.973 for force/EMG in all subjects, indicating a linear relationship between force, AMG and EMG at the four different force levels tested (25-75% of maximum). It is apparent that AMG may be used as an accurate monitor of masseter muscle force production, although some care is required in the technique.

Acoustics↗
PubMed1993

Acoustic myography in the assessment of human masseter muscle.

The feasibility of examining electro-mechanical activity of the human masseter muscles using non-invasive recording techniques was examined in six healthy dentate adults (aged 34-57 years). Electrical activity of the muscle was examined by surface electromyography (EMG) and the mechanical activity, in the form of muscle sounds, was examined by acoustic myography (AMG). Bilateral recordings of EMG and AMG were made simultaneously using composite probes which were placed on the skin over the masseter muscles. A standardized pressure was applied to the probes via adjustable rods attached to a safety helmet. Pressures were monitored by strain gauges placed between the ends of the rods and the probes. With the subject seated, recordings of AMG and EMG were obtained during maximal jaw clenching for 4 s and the raw signals were stored on a computer. Of three maximal contractions performed, the last two were used in the analysis. The raw amplified signals underwent frequency analysis by fast Fourier Transform. Total activity was also assessed after amplification, full-wave rectification and integration, and repeatability of the results was assessed. The AMG frequency range was 6-15 Hz and was similar to values for other human skeletal muscles. The integrated values for EMG and AMG were repeatable on both sides of the face (IEMG, right r = 0.99, left r = 0.99; IAMG right r = 0.70, left r = 0.71). Simultaneous recordings of AMG and EMG from the masseter muscles may be useful for assessing electro-mechanical muscle function but further validation studies are required before the technique can be used clinically.

Acoustics↗
PubMed1991

Acoustic myography for investigating human skeletal muscle fatigue.

Sounds produced during voluntary isometric contractions of the quadriceps muscle were studied by acoustic myography (AMG) in five healthy adults. With the subject seated, isometric force, surface electromyography (EMG), and AMG were recorded over rectus femoris, and the EMG and AMG signals were integrated (IEMG and IAMG). Contractions lasting 5 s each were performed at 10, 25, 50, 60, 75, and 100% of maximum voluntary contraction (MVC) force. Fatigue was then induced by repeated voluntary contractions (10 s on, 10 s off) at 75% MVC until only 40% MVC could be sustained. After 15 min of rest, the different force levels were again tested in relation to the fresh MVC. Both before and after fatiguing activity the relationships between force and IEMG [r = 0.99 +/- 0.01 (SD), n = 10] and force and IAMG (r = 0.98 +/- 0.02) were linear. After activity, however, the slopes of the regression lines for force and IEMG increased (P less than 0.01) but those for force and IAMG remained the same (P greater than 0.05). The present results clarify the relationship between AMG and isometric force in fatigued muscle without the problem of fatigue-induced tremor, which hampered previous studies of prolonged activity. This study contributes to the validation of AMG and shows that it is a potentially useful method for noninvasive assessment of force production and fatigue. Further studies to establish the origin of AMG activity are required before AMG can be accepted for use in neuromuscular physiology or rehabilitation.

Acoustics↗
PubMed1986

Acoustic myography as a control signal for an externally powered prosthesis.

Contracting skeletal muscle produces sounds that are easily recorded with a standard microphone. The recording of these sounds is known as acoustic myography, or AMG. As a control signal for an externally powered prosthesis, some advantages of AMG over surface EMG are: there is no need for direct skin contact; the AMG signal is unaffected by changes in skin impedence; AMG intensity is high enough to produce a 50 mV output from a standard microphone, requiring less amplification and electrical shielding; the AMG signal is qualitatively less sensitive to placement on the muscle than EMG. Disadvantages, such as the susceptibility of AMG to interference by extraneous environmental noise, are relatively easy to overcome. To demonstrate this, we have constructed a myoacoustically controlled prosthetic hand, whose tristate control via a single microphone (vs differential control) proves its feasibility in the more difficult case. The control circuitry for this device costs less than $50. The existing device utilizes a free-standing hand; a prosthetic shell which will allow comparison of AMG vs EMG control is currently being designed. The two patients who have tried it have learned to open and close the hand reliably after only three minutes of practice. Protocols are being established for functional assessment of AMG control.

Acoustics↗
PubMed1993

Frequency of acoustic myography during isometric contraction of fresh and fatigued muscle and during dynamic contractions.

The frequency of the acoustic myographic (AMG) signal was examined during fresh and fatigued isometric contractions of quadriceps and during dynamic contractions of biceps brachii (BB) in healthy subjects. Recordings were obtained from quadriceps over a range of forces between 10% and 100% maximal voluntary contraction prior to, and 15 minutes after, a fatiguing exercise. Recordings from BB were obtained over a range of submaximal forces (0-8.5 kg) during concentric and eccentric contractions. The mean power frequency (MPF) of the AMG signal was analyzed during each of these contractions by fast-Fourier transform (FFT). The MPF was not significantly different (P > 0.05) during fresh and fatigued contractions of quadriceps and increased quadratically with force in both states (r = 0.81, fresh; r = 0.77, fatigued). During concentric contractions of BB the MPF initially increased with force, but then decreased at the heavier loads (> 5.5 kg). The MPF of eccentric contractions did not significantly (P > 0.05) alter with force. The AMG MPF was within a similar low frequency range for both muscles, during different types of contraction, and was unaltered with fatigue.

Adolescent↗
PubMed1993

Technical aspects of acoustic myography (AMG) of human skeletal muscle: contact pressure and force/AMG relationships.

The effect of contact pressure on acoustic myographic (AMG) recordings was examined during voluntary isometric contractions of the human quadriceps muscle in 20 normal males. A piezoelectric disk for recording muscle sounds was placed over rectus femoris at approximately mid-thigh and secured with a rubber electromyography (EMG) strap. Contact pressure was monitored by a load cell placed between the AMG device and the strap. With the subject seated, force at different percentage levels of maximum voluntary contraction (MVC) were held for 5 s each. Both AMG and EMG recordings were full-wave rectified and integrated (IAMG and IEMG) and expressed as a percentage of activity at MVC. Two contraction series were performed with 2 different contact pressures. Pressure 1 (P1), of 180 Pa was applied in all subjects. A higher pressure of either 790 Pa (P2; in 5 subjects) or 1200 Pa (P3; in 15 subjects) was also applied. No significant changes in IAMG activity (P > 0.1) occurred between P1 and P2 but P3 produced increases in IAMG at all force levels (P < 0.05 at 10, 50 and 75% MVC). Both linear and non-linear relationships between force and IAMG were observed in different subjects but the relationship also varied with the 2 contact pressures within some subjects. The force/IEMG relationship was linear in all cases. These results provide quantitative evidence that contact pressure can influence the degree of IAMG activity if the pressure is high enough. The change in the force/IAMG relationship with pressure in some subjects suggests that the different relationships observed are not determined by physiological differences between subjects but rather by technical factors.

Acoustics↗
PubMed1995

Differential diagnosis of periodic paralysis aided by in vitro myography.

In vitro twitch tests were performed on excised muscle bundles from 30 periodic paralysis (PP) patients in an attempt to verify the somatic origin of PP, and to differentiate between the hypokalemic (HypoPP) and the hyperkalemic forms (HyperPP). Seventeen PP patients with a definite diagnosis of familial HypoPP, familial HyperPP (subsequently confirmed by SCN4A mutations), or thyrotoxic PP entered the study, as well as 13 patients with a history of attacks of weakness but with negative clinical provocation tests and therefore ambiguous diagnosis; 15 normal subjects served as controls. In contrast to control, bundles from patients with clear diagnosis went into sustained paralysis on exposure to Cl-free solution. Exposure to K+ channel activators induced a large increase in force. Specifically for HypoPP muscle, low extracellular [K+] decreased twitch force which was further reduced by addition of insulin or adrenaline, whereas HyperPP bundles responded with an irreversible decrease in twitch force when extracellular [K+] was elevated. Out of the 13 patients with unclear diagnosis, the in vitro studies made it possible to classify 10 as HypoPP and one as HypePP (later confirmed by a M1592V mutation). In the remaining two patients who claimed to suffer from paralytic attacks, all in vitro tests were normal, questioning the occurrence of dyskalemic PP. The results demonstrate that in vitro tests can be used to ensure the proper diagnosis to a high percentage when clinical provocative tests have failed.

Adult↗