Sven-Erik Larsson

changes of trapezius muscle blood flow and electromyography in chronic neck pain due to trapezius myalgia

Chronic neck pain may increase the transmitter activity of neuropeptides in the upper cervical medulla causing impairment of the blood flow in the local muscle because of a lack of vasodilatatory substances excreted axonally. We have been using a new single-fibre technique for clinical determination of the microcirculation (LDF) in the trapezius muscles in relation to electromyography (EMG). This study pertains to the 76 patients (46 women and 30 men) who received a final diagnosis of chronic trapezius myalgia out of a total series of 300 cases with chronic neck pain which had been remitted to the National Insurance Administration Hospital in Tranås, Sweden, because their complaints interfered with their working ability. The purpose was to derive more objective medical information upon which to base rehabilitation. Sixty percent had continuous pain and 40% had pain after physical effort, or at work. Twenty healthy women volunteered to participate as a normal control group. The right and left trapezius muscles of all individuals were examined simultaneously with laser-Doppler flowmetry (LDF) and surface EMG during a fatiguing series of stepwise-increased contractions, each of 1 min duration with 1 min rest in between. The most painful side was compared with the opposite side in all patients and, in the female patients, also with the right shoulder of the healthy control women. The patients showed consistently low local blood flow in the painful side. The difference was statistically significant at low contraction intensities. Muscle tension was somewhat elevated, as evidenced by a slight increase of the rms-EMG that was statistically significant at high contraction intensities. The mean power frequency (MPF) of the EMG showed no change. The lowered local blood flow was not explained by a changed intramuscular pressure which is low in the trapezius during ordinary activities that do not normally impair the local blood flow (Larsson, S-E., Cai, H. and (Oberg, P.A., Microcirculation in the upper trapezius muscle during varying levels of static contraction, fatigue and recovery in healthy women. A study using percutaneous laser-Doppler flowmetry and surface electromyograpy, Eur. J. Appl. Physiol., 66 (1993) 483-488). We conclude that an impaired regulation of the microcirculation in the local muscle is of central importance in chronic trapezius myalgia, causing nociceptive pain which can be differentiated objectively from neuralgic neck-shoulder pain by the atraumatic technique described.

Effects of psychophysiological stress on trapezius muscles blood flow and electromyography during static load.

Mental stress was induced by the Stroop colour word task (CW task) and the effects on the micro-circulation and electromyography (EMG) in the upper portion of the trapezius muscle were studied during a series of fatiguing, standardized static contractions. A lowered blood flow of the skin recorded continuously by laser-Doppler flowmetry (LDF) was used as a stress indicator in addition to an elevated heart rate. Muscle blood flow was recorded continuously by LDF using a single optical fibre placed inside the muscle, and related to surface EMG. A group of 20 healthy women of different ages was examined. Recordings were made during a 50-min period in the following sequence: a 10-min series of alternating 1-min periods of rest and stepwise increased contraction induced by keeping the arms straight and elevated at 30, 60, 90 and 135° with a 1-kg load carried in each hand; a 10-min recovery period without load; a repeated contraction series with simultaneous performance of the CW task; a second 10-min recovery period, and a second contraction series without CW task. Signal processing was done on line by computer. The LDF and root mean square (rms)-EMG values were calculated, as well as the EMG mean power frequency (MPF) for fatigue. The CW-task added to the contraction series caused an increase in the heart rate accompanied by a decrease in the blood flow to the skin and a 30% increase in the blood flow in the exercising muscle. Both returned to normal during the subsequent recovery period and showed normal levels during the final contraction series without CW. The rms-EMG showed a 20% increase that persisted during the final contraction series performed without CW. There was no influence on MPF. This CW has previously been shown to evoke an increased secretion of adrenaline from the adrenal medullae to the blood. The increased blood flow in the exercising muscle would therefore appear to have been caused by β-adrenoceptor vasodilatation, and the fall in the blood flow in the skin by α-adrenoceptor vasoconstriction. The findings may have implications for work situations characterized by repetitive static loads to the shoulder muscles and psychological stress.

Electromyographic changes in work-related myalgia of the trapezius muscle

SummaryIn 11 patients, all women, 21–55 years of age, with unilateral work-related myalgia of the trapezius muscle, the right and left trapezius muscles were examined simultaneously for electromyogram (EMG) signs of localized muscle fatigue. All patients were tested with 0-kg hand load for 5 min, holding the arms straight at 90° of elevation in the scapular plane. Only 4 of the patients tolerated exposure to higher load levels. They were tested with 1 kg hand load for 3 min and 2 kg hand load for 2 min, with a period of rest of 30 min between the trials. The EMG mean power frequency (MPF) and root mean square (rms) were calculated. Data were normalized with the initial value as a reference and regression analyses were performed. On both sides a decrease of MPF and an increase of rms were found with increasing time and load, i.e. classical EMG signs of localized muscle fatigue. Compared with the nonaffected side smaller changes were found on the affected side, possibly due to pain inhibition, impaired microcirculation and biochemical changes along the muscle fibres. At 0-kg hand load we found no change of MPF on either side despite subjective feelings of fatigue and pain. We interpreted these findings as an indication of reduced capacity of the affected trapezius muscle to sustain static load with early development of pain-associated local fatigue.

Microcirculation in the upper trapezius muscle during varying levels of static contraction, fatigue and recovery in healthy women —a study using percutaneous laser-Doppler flowmetry and surface electromyography

SummaryMicrocirculation in the upper portion of the trapezius muscle was measured percutaneously by continuous laser-Doppler flowmetry (LDF) during two 10-min series of alternating 1-min periods of static contraction and rest determined electromyographically (EMG). Stepwise increased contraction was induced by keeping the arms straight and elevated at 30, 60, 90 and 135°, which was repeated with a 1-kg load carried in each hand. Thereafter, fatigue and recovery were recorded while the subject kept her arms straight and elevated at 45° carrying the 1-kg hand load as long as possible, followed by rest with arms hanging and no load. A group of 16 healthy women of different ages was studied. Signal processing was done on line using a 386 SX computer. The LDF- and root-mean-square (rms) EMG signals were normalized. Spectrum analyses of EMG mean power frequency (MPF) and median spectrum frequency were performed. The rms-EMG increased significantly with an increase in the calculated shoulder torque (r=0.75). Accumulated local fatigue was indicated by a decrease in MPF with increased shoulder angle and added load (r = −0.54). Blood flow increased with increased shoulder angle (r=0.82, with hand loadr=0.62) and with increased shoulder torque (r=0.72), and also showed a significant increase with increased EMG activity (r=0.74). The LDF showed a negative correlation to MPF (r= −0.67), with increased values when MPF was lowered. During the endurance test, a moderate increase of LDF occurred which reached its maximum during the 1st min of recovery. Then, a slow return to the base level was recorded. The ability to increase the flow in the microcirculation with increasing muscle load was not diminished with age.

Continuous percutaneous measurement by laser-Doppler flowmetry of skeletal muscle microcirculation at varying levels of contraction force determined electromyographically

SummaryLaser-Doppler flowmetry (LDF) and electromyography (EMG) were used simultaneously for measuring skeletal muscle blood perfusion in relation to static load and fatigue. Percutaneous single-fibre LDF and bipolar surface EMG of the trapezius muscle were performed continuously during a 10-min series of alternating periods of static contractions and rest, each of 1-min duration. The muscle was exposed to static load expressed as shoulder torque, by keeping the arms straight and elevated at 30, 60, 90 and 135°. On-line computer processing of the LDF and EMG signals made possible the interpretation of the relationship between the perfusion and the activity of the muscle. The LDF and root mean square (rms)-EMG were normalized by using the average value of the serial examinations of each individual as a reference value. Spectrum analyses of EMG showed the lowest variability for median frequency (MDF) in the frequency range 10–1000 Hz and mean power frequency (MPF) at 2–1000 Hz. The LDF power spectrum density during low (muscle rest) and high (high-force muscle contraction) perfusion indicated that disturbances were small when measurements were performed during sustained static contraction with as little movement as possible. Vasomotion, i.e. rhythmic variations in the blood flow, were present and showed a frequency of 5–6 cycles · min−1. Application of a tourniquet to the upper arm caused an arrest of the microcirculation in the distally situated brachioradial muscle which was followed by a postischaemic hyperaemia upon removal of the torniquet. In ten healthy men, regression analyses showed positive correlation between rms-EMG and shoulder torque (r=0.77), negative correlation between MPF and arm elevation angle (r= −0.89) indicating accumulated fatigue, and almost positive correlations between LDF and rms-EMG (r=0.65), and between LDF and shoulder angle (r=0.67) when the right trapezius muscle was examined.

Microcirculation in the upper trapezius muscle during sustained shoulder load in healthy women--an endurance study using percutaneous laser-Doppler flowmetry and surface electromyography.

Microcirculation in the upper portion of the trapezius muscle was measured percutaneously in a group of 16 healthy women of different ages by continuous laser-Doppler flowmetry (LDF) in relation to electromyography (EMG) during an endurance test. During the measurements the subject kept her arms straight and elevated at 45° in the scapular plane and held a 1-kg load in each hand as long as possible. This was followed by rest with the arms hanging and carrying no load. The 10-min recording period comprised 1-min initial rest followed by the endurance test and then recovery. Signal processing was done by computer on line. The LDF and root-mean-square (rms) EMG signals were normalized. Spectrum analyses of EMG mean power frequency (MPF) were performed. The amount of load produced was on average 2,267 (SD 939) N · m · s, i.e. shoulder torque × time expressed as Newton meter seconds, and the endurance time was 4.3 (SD 1.20) min. The rms-EMG as well as the LDF increased significantly during endurance, both when related to endurance time and to amount of load. The MPF showed no significant changes. The mean total increase in muscle blood flow was 175% of that recorded in the initial rest period. The average increase per each 10 s of contraction was 2.9%. Maximum was reached during the 1st min of recovery followed by a fall to the base level that was reached within 77 s on average. The amount of load produced and the blood flow increase was smaller than that found in a separate study of men, indicating a lower functional capacity. This may be of importance for the development of neck-shoulder disability in women.

A new single-fibre laser Doppler flowmeter based on digital signal processing

A new laser Doppler flowmeter, based on a personal computer with a digital signal processor for detecting the blood perfusion in skeletal muscle, was designed and evaluated. An infrared laser diode (750 nm) fed a single optical fibre, 400 microns in diameter, which was introduced into the muscle. A PC equipped with a digital processing unit was used for emulation of the laser Doppler algorithm and for presentation of the measurement results. The Doppler signal power spectral density and corresponding flow values were visualized on the computer screen continuously in real-time, and could also be saved on the hard disk for off-line analyses. The graphic-user interface supported by Labwindows software made the system easy to use. It is possible to alter in the software the signal processing and the ways in which the signals and results are presented. The new system was evaluated by using a flow model as well as a mechanical model. The model studies showed linear relationships between particle velocity and flow in the range of 0-5 mm s-1. The system was also tested in measurements of the blood flow in the brachioradial muscle, and was found to have advantages over our previously used systems.

Single-fibre laser Doppler flowmetry and electromyography for evaluating microcirculation in forearm muscle during static and continuous handgrip contractions

A technique is described for intramuscular measurement of muscle blood flow in the forearm, by using a 0.5-mm thin optical single-fibre for laser Doppler flowmetry (LDF) inserted percutaneously. Continuous recordings were performed of the brachioradial muscle during an 11-min series of alternating 1-min periods of increased static contraction and rest determined by an electronic handgrip forcemeter and surface electromyography (EMG) of the muscle. Stepwise increased handgrip contractions were performed at 10%, 20%, 30%, 40% and 50% maximal voluntary contraction (MVC). This was followed by a similar series of continuous contractions. Finally, an endurance test was performed with a handgrip force of 50% MVC maintained for as long as possible. A group of ten healthy men of different ages was studied. Signal processing was done on line by computer. Successive increases in rootmean square (rms)-EMG and a fall in the mean power frequency (MPF) of the EMG spectrum occurred during the series of static contractions, which evoked perceived local fatigue in the forearm. Muscle blood flow recorded simultaneously showed no change from resting level during contractions at 10%, 20% and 30% MVC, while at 40% and 50% MVC mean increases of 150% and 200% were recorded. Blood flows measured during the rest periods showed large variability with no significant changes. This was also found after continuous contractions of the same intensities. The endurance time was 1.2–3.5 min (mean 2.4 min). Muscle blood flow showed mean increases of 214%, 256% and 229% of resting level each minute of the maintained contraction. Nevertheless, EMG signs of local fatigue developed, such as a rise in rms-EMG and a fall in MPF, and the subject experienced local fatigue. To conclude, this technique of percutaneous, continuous LDF recorded, at high sensitivity, the microcirculation at different fluxes and EMG-defined muscle activity.

Laser Doppler flowmetry: characteristics of a modified single-fibre technique

The single-fibre percutaneous laser Doppler technique has been used in previous studies of intramuscular blood flow. This method facilitates studies of blood flow in deep tissue volumes and minimises the tissue trauma. The technique has been further developed with the aim of improving the signal quality. This has been accomplished by modifying the geometry of the fibre tip. By melting the fibre core material, lenses of different shapes are formed. Flat, spherical and ‘pears-type tips have been manufactured and are evaluated theoretically and experimentally. The paraxial theory cannot accurately predict the position of zones of highest irradiance. Therefore, a ray-tracing program has been developed in the C language, by means of which some of the optical properties of the modified fibre tips can be simulated. Isoirradiance graphs and beam profiles are calculated for the three different fibre tips. Measured and calculated irradiance curves are used for evaluation of the properties of the ray-tracing model. The three types of fibre tips are also evaluated and compared in flow models. The sphere and pear-type probes show a higher flow sensitivity than the flat-end type. These improvements in flow sensitivity are interpreted as being related to the larger, strongly irradiated tissue volumes in front of the fibres. Intramuscular measurements with the pear-type probe show high sensitivities to induced blood flow changes.

Outcome of surgery for cervical radiculopathy evaluated by determination of trapezius muscle microcirculation and electromyography.

Surgery for cervical radiculopathy was evaluated in 27 patients after anterior Cloward procedure (19 patients) or posterior decompression (eight patients). In addition, we examined 10 conservatively treated patients. Each patient was studied prospectively with regards to the effects on microcirculation in the local trapezius muscle during a fatiguing series of stepwise increased contractions. The right and left muscles were simultaneously examined pre‐operatively and postoperatively after 9 months using laser‐Doppler flowmetry and simultaneous surface electromyography (EMG). Preoperatively, a reduced microcirculation was found in the most painful side compared with the opposite side. This is in accordance with earlier reports on patients with chronic neurogenic neck pain, who also show reduced muscle tension on EMG. Postoperatively, the muscle blood flow became increased, but only in patients operated on via a posterior approach. A tendency at increased EMG‐amplitude and reduced mean power frequency of the EMG was noted. These EMG signs of muscle fatigue suggest increased ability to exhaust the trapezius muscle postoperatively. The observed postoperative changes were consistently more frequent in the less painful side. We conclude from these objective measurements showing only a tendency at increased microcirculation and muscle tension postoperatively, that the effect on the trapezius muscle is limited.