Biomedical subjects

M J Stokes

Publications and source records attributed to M J Stokes.

At least 37 records · Page 2Linked to original sources

PubMed1995

Ultrasonography of masseter muscle size in normal young adults.

The present study was planned to determine the relationship between linear dimensions of human masseter muscle cross-section and cross-sectional area (CSA), and to assess symmetry between the two sides in normal young adults. Cross-sectional images of the masseter muscle were measured bilaterally by real-time ultrasound imaging in 39 healthy dentate subjects, 19 males and 20 females, aged 21-47. From stored images, CSA and two linear measurements of muscle cross-section were obtained (the shortest and the longest distance through the muscle group). Correlation and regression analyses were performed to examine the relationship between CSA and the linear dimensions (both individually and with the linear dimensions multiplied). Symmetry of CSA between the two sides of the face was examined using the paired t-test. The significance of correlation coefficients (r) and the difference between the slopes of the regression lines were also examined. Masseter CSA was larger in males than in females. All correlation values between CSA and linear measurements were significant but muscle CSA was most accurately predicted when the linear measurements were multiplied (r = 0.97; P < 0.001). Although the correlation in this regard was high, the linear dimensions consistently overestimated the actual CSA by approximately 25%. Males showed more symmetry of CSA than females. The range of values for symmetry of masseter CSA was too large to assess abnormal asymmetry in patients with unilateral symptoms.

Adult↗

PubMed1994

Evidence of lumbar multifidus muscle wasting ipsilateral to symptoms in patients with acute/subacute low back pain.

The effect of low back pain on the size of the lumbar multifidus muscle was examined using real-time ultrasound imaging. Bilateral scans were performed in 26 patients with acute unilateral low back pain (LBP) symptoms (aged 17-46 years) and 51 normal subjects (aged 19-32 years). In all patients, multifidus cross-sectional area (CSA) was measured from the 2nd to the 5th lumbar vertebrae (L2-5) and in six patients, that of S1 was also measured. In all normal subjects, CSA was measured at L4 and in 10 subjects measurements were made from L2-5. Marked asymmetry of multifidus CSA was seen in patients with the smaller muscle being on the side ipsilateral to symptoms (between-side difference 31 +/- 8%), but this was confined to one vertebral level. Above and below this level of wasting, mean CSA differences were < 6%. In normal subjects, the mean differences were < 5% at all vertebral levels. The site of wasting in patients corresponded to the clinically determined level of symptoms in 24 of the 26 patients, but there was no correlation between the degree of asymmetry and severity of symptoms. Patients had rounder muscles than normal subjects (measured by a shape ratio index), perhaps indicating muscle spasm. Linear measurements of multifidus cross-section were highly correlated with CSA in normal muscles but less so in wasted muscles, so CSA measurements are more accurate than linear dimensions. The fact that reduced CSA, i.e., wasting, was unilateral and isolated to one level suggests that the mechanism of wasting was not generalized disuse atrophy or spinal reflex inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗

PubMed1994

A preliminary study on the radon concentrations in water in Hong Kong and the associated health effects.

Tap water, flushing water and drinking water including natural mineral water, artificial mineral water and distilled water have been investigated for their radon concentrations. It has been found that the radon concentration in natural mineral water samples is the highest and that in tap water is the second highest, while other categories have values very near to the detection limit. From these the corresponding annual effective doses for the stomach and the lung are determined. It is found that annual effective dose due to direct consumption of water (mineral and tap water) is far greater than that due to inhalation of radon emanated from tap water and flushing water. Moreover, it is also shown that the annual effective doses due to inhalation of radon emanated from tap water and flushing water is negligible when compared to the total annual effective dose for indoor radon in Hong Kong.

Hong Kong↗

PubMed1993

Pattern of asymmetry of paraspinal muscle size in adolescent idiopathic scoliosis examined by real-time ultrasound imaging. A preliminary study.

The symmetry of lumbar multifidus size was examined in 20 patients with adolescent idiopathic scoliosis, aged 12-19 years. With the subject prone, bilateral real-time ultrasound images were obtained at the level of the 4th lumbar vertebra. Cross-sectional area and linear (horizontal and vertical) measurements were made using on-screen calipers. A pattern of asymmetry of lumbar multifidus cross-sectional area was shown to exist for the different curve types. The cross-sectional area was smaller (P < 0.0001) on the opposite side to the convexity of a primary thoracic curve, and on the convex side of a lumbar or thoracolumbar curve. The combined linear measurements (multiplied) correlated with cross-sectional area (r = 0.95) and could therefore be used for rapid clinical assessment of multifidus size. These preliminary findings provide a basis for further investigation of the role of the musculature in the pathogenesis of adolescent idiopathic scoliosis.

Adolescent↗

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↗

PubMed1993

Normal paraspinal muscle electromyographic fatigue characteristics in patients with primary fibromyalgia.

Paraspinal muscle fatigue mechanisms were compared in 14 primary fibromyalgia patients and 14 age and sex matched normal subjects using a standardized 60-s isometric endurance test of the paraspinal muscles, during which surface integrated electromyographic (IEMG) activity was recorded. Fatigue-induced IEMG increases were similar for both groups during the initial 40 s (up to 112 +/- 20% and 111 +/- 6% of initial values in patients and normal subjects respectively). Thereafter, IEMG fell significantly in patients (P < 0.05) but only slightly in controls, so that at 58 s IEMG was 102 +/- 13% in patients and 109 +/- 12% in controls. If patients were divided according to body mass index (BMI, range 19-25 in controls) those with a BMI < 26 (n = 5) showed IEMG changes similar to those of control subjects throughout the test, while obese patients with BMI > 26 (n = 9) showed greater IEMG declines after 40 s than either normal subjects or in the fibromyalgia group as a whole. Paraspinal muscle fatigue mechanisms appear normal in primary fibromyalgia patients. Isometric force maintenance in overweight patients, despite IEMG declines, illustrates the action of intrinsic fatigue resistance mechanisms which were presumably utilized to a greater extent in these patients to cope with the extra load.

Adult↗

PubMed1993

Increased central drive during fatiguing contractions of the paraspinal muscles in patients with chronic low back pain.

In low back pain patients the paraspinal muscles demonstrate excess fatigability. Whether the cause is "central" as could result from impaired motor unit recruitment due to poor motivation or fear of pain, or "peripheral", and caused by defects in the contractile apparatus, is unknown. Using surface electromyography in conjunction with a standardized isometric fatigue test, this study investigates the mechanisms causing paraspinal muscle dysfunction in patients with both nonsurgical and postsurgical chronic low back pain. During the fatigue test normal subjects and both patient groups exhibited electromyographic increases. These were significantly greater in both patient groups, indicating increased central drive to their muscles. These findings may suggest that patients' excess fatigue is peripheral in origin, with increased central drive arising secondary to muscle wasting or denervation, although a central activation defect has not been excluded. Impaired physical performance in low back pain patients does not seem to be caused by lack of central drive.

Adult↗

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↗

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↗

PubMed1992

Stimulation frequency and force potentiation in the human adductor pollicis muscle.

The effect of stimulation frequency on twitch force potentiation was examined in the adductor pollicis muscle of ten normal subjects. The ulnar nerve was supramaximally stimulated at the wrist and isometric twitch force was measured from a 3-Hz train lasting 1 s. Test stimulation frequencies of 5, 10, 20, 25, 30, 40, 50 and 100 Hz were applied for 5 s each in random order (5 min apart) and the twitches (3 Hz) were applied immediately before and after (1 s) the test frequency and at intervals up to 5 min afterwards (10 s, and 1, 2 and 5 min). Poststimulation twitches were expressed as a percentage of the prestimulation twitch. Low frequency fatigue was not induced by the protocol since the 20:50 Hz ratio did not alter within each session. The degree of twitch potentiation was frequency dependent, with potentiation increasing up to 50 Hz [mean 173 (SD 16)%] but the effect was markedly less at 100 Hz [mean 133 (SD 25)%, P less than 0.01] for all subjects. The reduced potentiation at 100 Hz may have occurred due to high frequency fatigue produced by the 100-Hz test stimulation train. The optimal frequency of those examined in the experimental group was 50 Hz but this only produced maximal potentiation in six of the ten subjects and 100 Hz always produced less potentiation. These findings have implications for electrical stimulation of muscle in the clinical setting.

Adult↗

PubMed1992

Detection and severity of low frequency fatigue in the human adductor pollicis muscle.

The sensitivity of electrical stimulation tests for detecting low frequency fatigue (LFF) and its duration were examined in the adductor pollicis muscle of ten normal subjects. Supramaximal stimulation was applied to the ulnar nerve at the wrist and values for test stimulation force ratios of 10:100 Hz, 15:100 Hz and 20:50 Hz (2 sec at each frequency with 5 min rest between each ratio) were obtained for fresh muscle. Fatigue was then induced by voluntary isometric contractions at 50% maximal voluntary force (MVC) repeated until only 30% MVC could be achieved. Contractions lasted 10 sec with 5 sec rest between each. The three test ratios were then repeated to monitor recovery at intervals up to 72 h after activity. High frequency forces returned to fresh values by 24 h but low frequency forces were all still significantly reduced. Forces at 10 and 15 Hz were still significantly reduced at 48 and 72 h (10 Hz greater than fatigue than 15 Hz). The low/high frequency ratios, calculated once 50 and 100 Hz forces had recovered, also demonstrated differences in recovery rates. Repeatability tests indicated that 10 Hz force was more variable than other frequencies and forces at all stimulation frequencies were repeatable on different days with a coefficient of variation of less than 15%. Values for the 15:100 Hz ratio from fresh muscle in 22 normal subjects were 0.48 +/- 8. The 15:100 Hz ratio is suggested as the most appropriate test ratio for detecting LFF since 15 Hz force is more sensitive than 20 Hz and more stable than 10 Hz.

Adult↗

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↗

PubMed1992

Relationship between inspiratory mouth pressure and respiratory muscle activity in normal subjects.

The relationship between inspiratory mouth pressure and respiratory muscle activation was investigated in 20 normal non-smoking subjects (13 males). Surface electromyography (EMG) was recorded from the seventh intercostal space bilaterally during different levels of inspiratory effort monitored by a respiratory mouth pressure gauge. The mouth pressure and EMG relationship was non-linear between 20 and 100% of inspiratory effort. Quadratic regression analysis was performed between percent inspiration and percent EMG on each side of the chest. The regression equation and coefficient of determination (r2) for the right side were y = 9.73 (e0.024x-1), r2 = 0.91, and for left side were y = 10.79 (e0.023x-1), r2 = 0.88. An independent t-test did not reveal significant difference (P > 0.05) between the slopes of the regression lines from the two sides of the chest. Therefore, results of the two sides were pooled and the predictive regression equation for the combined results was y = 10.05 (e0.0236x-1). Reasons for such a non-linear relationship may include the loading mechanism of respiratory muscles, inefficiency of intercostal muscles at high levels of inspiration, their recruitment pattern and the histochemical characteristics of respiratory muscles. Since absolute EMG values cannot be used to assess changes in activation on different days, further work is required to establish the between-day repeatability of the technique described which is potentially useful for assessing respiratory muscle function pre- and post-operatively in chest surgery patients.

Adult↗

PubMed1992

Muscle sounds during voluntary and stimulated contractions of the human adductor pollicis muscle.

The relationships between force, electromyography (EMG), and muscle sounds recorded by acoustic myography (AMG) were investigated for both voluntary and stimulated isometric contractions in the adductor pollicis muscle. Voluntary activity was performed at 10, 25, 50, 75, 85, and 100% of maximal voluntary contraction (MVC) force. Stimulated contractions were produced by supramaximal electrical stimulation of the ulnar nerve at the wrist at frequencies of 10, 20, 30, 50, 70, and 100 Hz. Contractions lasted for 4 s each, and were performed in random order with a 3-min rest between each. The voluntary and stimulation studies were performed in random order between subjects. Simultaneous recordings were obtained for force, force oscillation (from the differentiated force signal), and raw and integrated AMG (IAMG) and EMG (IEMG). During voluntary contractions, IAMG increased with force up to MVC (r2 = 0.99, P less than 0.001) in a curvilinear fashion and a similar relationship was seen between force and IEMG (r2 = 0.99, P less than 0.001). Conversely, during stimulated contractions as stimulation frequency increased, IAMG decreased in a fashion mirroring the frequency-force curve. The frequency of the AMG signal matched stimulation frequency and declines in total IAMG were due to reductions in amplitude of the AMG signal. The stimulation frequency-oscillation of force relationship was identical to that seen for stimulation frequency and IAMG. Integrated EMG increased linearly with stimulation frequency (r = 0.99). The stimulation results suggest that muscle sounds reflect oscillation of muscle fibers and that AMG signal characteristics are determined by motor control mechanisms rather than intrinsic contractile processes.

Acoustics↗

PubMed1992

Symmetry of electro- and acoustic myographic activity of the lumbar paraspinal muscles in normal adults.

The symmetry of paraspinal muscle activity was examined in 15 healthy adults (aged 31-60 years). Acoustic myography (AMG), which provides a measure of force, was recorded with electromyography (EMG) to assess electromechanical relationships during contraction. Bilateral recordings of EMG and AMG were made over the paraspinal muscles at the level of the 4th lumbar vertebra during a fatiguing test manoeuvre. Subjects were strapped to a hinged couch in the prone position. When the upper part of the couch was lowered, subjects maintained the upper body (above the anterior, superior iliac spines) unsupported, in the horizontal position for 60 sec. The EMG and AMG signals were full-wave rectified, integrated (IEMG, IAMG) and recorded on an ink-jet oscillograph during the fatigue test. By 60 sec of activity, IEMG had increased (right 122% +/- 8.7; left 125% +/- 11.8; mean +/- 1 SD as a percentage of initial values) while IAMG (reflecting force) remained unaltered (right 99% +/- 8.2; left 100% +/- 5.3). The IAMG:IEMG ratio (reflecting efficiency of activation) thus declined (right 0.81 +/- 0.08; left 0.80 +/- 0.08). The similarly of changes on both sides of the spine have quantified normal symmetry of paraspinal muscle activity and could be used to assess asymmetry in patients with spinal pathology.

Acoustics↗

PubMed1991

Measurement of anterior tibial muscle size using real-time ultrasound imaging.

Cross-sectional images of the anterior tibial muscle group were obtained using real-time ultrasound scanning in 17 normal women. From photographs taken of the images, the cross-sectional area (CSA) and two linear measurements of muscle cross-section were determined. A measurement of the shortest distance of the muscle depth was termed DS, and a measurement of the longest distance through the muscle group was termed DL. Both linear dimensions showed a positive correlation with CSA and the best correlations were obtained when the dimensions were squared or combined (DS x DL). The correlation values were: CSA vs DS2, r = 0.9; CSA vs DL2, r = 0.75 and CSA vs DS x DL, r = 0.88. An approximate value for CSA could be calculated from DS2 by the equation 2 x DS2 + 1. A shape ratio, obtained by dividing DL by DS, was consistent within the group [mean 2.1 (SD 0.2)] and characterised the muscle geometrically. The CSA of repeated scans was assessed for repeatability between-days and between-scans by analysis of variance and the coefficient of variation (CV) calculated. Areas were repeatable between-days (CV 6.5%) and between-scans (CV 3.6%). Linear dimensions of the anterior tibial muscle group reflected CSA and their potential for assessing changes in muscle size with atrophy and hypertrophy have yet to be established.

Adolescent↗

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↗