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At least 451 records · Page 25Linked to original sources
PubMed1999

Relationship between mechanomyogram and force during voluntary contractions reinvestigated using spectral decomposition.

A mechanomyogram (MMG) is considered to represent the pressure waves resulting from the lateral expansion of contracting muscle fibers. However, the actual MMG recording appears not only to reflect lateral changes of active fibers, but also to include the effect of their longitudinal shortening, because the fiber orientation, particularly in pennate muscles, is not parallel with the MMG transducer attached at the skin surface. In the present investigation, a spectral decomposition method was developed to eliminate the interference due to fiber longitudinal movement from the MMG recording. The MMG was recorded over the belly of the rectus femoris muscle, which is a pennate muscle. Vibration over the tibial tuberosity (VTT) was used as a measure of the integrated longitudinal movement of the muscle fibers. The lateral and longitudinal components included in the MMG were separated by a spectral decomposition method that is based on the coherence function of the MMG and VTT. The MMG/force relationship was compared between the original and decomposed MMG. One-third of the 12 subjects demonstrated a curvilinear relationship between the original MMG and force throughout the range of force. In the other two-thirds, the MMG saturated or reduced beyond 70% of the maximum voluntary contraction (MVC). After decomposition, the MMG increased progressively with force up to 70% MVC, beyond which it decreased in all subjects. The spectral decomposition method described here is considered to be a useful tool with which to examine in more detail the MMG/force relationship of different pennate muscles.

Adult↗
PubMed1999

Surface mechanomyogram reflects the changes in the mechanical properties of muscle at fatigue.

The contractile properties of muscle are usually investigated by analysing the force signal recorded during electrically elicited contractions. The electrically stimulated muscle shows surface oscillations that can be detected by an accelerometer; the acceleration signal is termed the surface mechanomyogram (MMG). In the study described here we compared, in the human tibialis anterior muscle, changes in the MMG and force signal characteristics before, and immediately after fatigue, as well as during 6 min of recovery, when changes in the contractile properties of muscle occur. Fatigue was induced by sustained electrical stimulation. The final aim was to evaluate the reliability of the MMG as a tool to follow the changes in the mechanical properties of muscle caused by fatigue. Because of fatigue, the parameters of the force peak, the peak rate of force production and the peak of the acceleration of force production (d2F/dt2) decreased, while the contraction time and the half-relaxation time (1/2-RT) increased. The MMG peak-to-peak (p-p) also decreased. The attenuation rate of the force oscillation amplitude and MMG p-p at increasing stimulation frequency was greater after fatigue. With the exception of 1/2-RT, all of the force and MMG parameters were restored within 2 min of recovery. A high correlation was found between MMG and d2F/dt2 in un-fatigued muscle and during recovery. In conclusion, the MMG reflects specific aspects of muscle mechanics and can be used to follow the changes in the contractile properties of muscle caused by localised muscle fatigue.

Adult↗
PubMed1999

Cholinergic modulation of non-adrenergic, non-cholinergic relaxation in isolated, small coronary arteries from lambs.

The presence of cholinergic innervation of small coronary arteries in the lamb was investigated by measuring choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) activities and by performing in vitro experiments in a microvascular myograph to establish whether or not there is a cholinergic component in the response to electrical field stimulation (EFS). ChAT-specific activity was present in proximal coronary segments, but was significantly higher in small coronary arteries. AChE-positive ganglia and fibres were distributed within the adventitia and outer third of the media in proximal coronary segments, and dense perivascular nerve plexuses were observed in small coronary arteries. Acetylcholine induced contractions in all preparations examined and relaxations in 20% of the segments contracted with the thromboxane analogue U46619. EFS did not induce neurogenic contractions in lamb small coronary arteries. In the presence of the alpha-adrenoceptor antagonist, phentolamine, EFS caused frequency-dependent reproducible relaxations that were enhanced by the blocker of cholinergic transmission, botulinum neurotoxin. An inhibitor of AChE, physostigmine, had no significant effect on the relaxations caused by EFS, while both the muscarinic receptor antagonist, atropine, and the muscarinic M2-receptor antagonist, AFDX 116, enhanced these responses. Blockade of sympathetic neurotransmission with guanethidine or incubation with the P2-receptor antagonist, suramin, abolished the relaxations induced by EFS, whereas propranolol was without effect. Low-frequency EFS caused less relaxation in preparations activated by acetylcholine than in those contracted with U46619, while sensitivity and maximal relaxation induced by adenosine 5'-triphosphate (ATP) were not different in U46619- and acetylcholine-contracted arteries. The presence of the enzymes necessary for both biosynthesis and degradation of acetylcholine and the finding that blockers of cholinergic neurotransmission enhance EFS-induced relaxations suggest that small coronary arteries are cholinergically innervated.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed2006

Acidosis augments myogenic constriction in rat coronary arteries.

The myogenic response is a process by which blood vessels autoregulate vascular smooth muscle tone in response to changes in transmural pressure. It is characterized by vessel contraction or dilation with increased or decreased pressure, respectively. We sought to identify whether acidosis impacts the myogenic response in rat coronary resistance arteries. Ventricular septal arteries were isolated from male Sprague-Dawley rats and mounted on a pressure myograph. The myogenic response was assessed by measuring the arterial diameter at pressures of 10-120 mm Hg. The fluorescence indicators 2',7'-bis-(carboxyethyl)-5(and-6)-carboxyfluorescein and Fura-2 were utilized to measure intracellular pH (pH(i)) and intracellular free calcium concentration ([Ca(2+)](i)), respectively. A decrease in the extracellular pH (pH(o)) from 7.4 to 6.9 produced a fall in pH(i) and an increase in the myogenic response. Under nominally HCO (3) (-) /CO(2)-free conditions at a constant pH(o), blockade of the sodium-hydrogen exchanger with HOE694 also resulted in a fall in pH(i) and a similar enhancement of myogenic activity. Concentration response curves were constructed to measure the potencies of the HOE694 effects: the EC(50) was 34 microM for the pH(i) change and 19 microM for vessel constriction. Apparent [Ca(2+)](i) remained unchanged during HOE694-induced intracellular acidification. Furthermore, in the presence of HCO (3) (-) , HOE694 did not markedly affect pH(i) and vascular tone remained unaltered. Our data demonstrate that acidosis augments myogenic constriction of rat coronary arteries. These effects are due to a fall in pH(i) consequent upon the reduction in pH(o) and may reflect an increased myofilament [Ca(2+)](i) sensitivity within vascular smooth muscle cells.

Acidosis↗
PubMed2004

Clinical measurement of pelvic floor movement: evaluation of a new device.

PURPOSE: A new device that measures pelvic floor movement clinically was evaluated. METHODS: The device consists of a rectal balloon with a magnet at its exterior end. The magnet moves in an electromagnetic field synchronous with the pelvic floor movements. This movement is measured and displayed on a computer screen in front of the seated patient. Twenty-eight healthy volunteers (15 females) were examined. On a separate day, 17 of them were tested a second time by the same investigator and a third time by a different investigator. RESULTS: One volunteer developed a vasovagal reaction. The median (range) pelvic floor lift and descent was 2 (range, 0.6-4.5) cm and 1.8 (range, 0.5-5.6) cm respectively. Day-to-day and interobserver reproducibility was good. Coughing and blowing a party balloon caused pelvic floor descent in the majority of participants. Twenty of 28 volunteers were able to expel the rectal balloon. CONCLUSIONS: The device measures cranial and caudal movements of the pelvic floor with minimal discomfort and good reproducibility. The device may have a large potential as biofeedback device in pelvic floor training.

Adult↗
PubMed2006

Effect and mechanism of betaxolol and timolol on vascular relaxation in isolated rabbit ciliary artery.

PURPOSE: In order to clarify the vasodilatory mechanism of betaxolol and timolol, we studied the effects of these drugs in isolated rabbit ciliary arteries. METHODS: Rabbit ciliary artery specimens were mounted in a double myograph system, and betaxolol, timolol, or another agent was introduced into the organ chamber. The mechanical response of the arteries was studied using an isometric tension recording method. The intracellular free calcium concentration [Ca2+]i was also measured using fluorescence photometry. RESULTS: Betaxolol and timolol induced dose-dependent relaxation in the rabbit ciliary arteries precontracted by high-K+ Krebs solution. The minimum concentrations required to cause relaxation were 10 microM of betaxolol, and 30 microM of timolol. At the maximum concentration of 1 mM, betaxolol induced almost complete relaxation of the ciliary arteries, whereas timolol induced approximately 70% relaxation. These actions were not inhibited by pretreatment with 100 microM NG-nitro-l-arginine methylester (L-NAME), a nitric oxide synthase inhibitor, or by denudation of the vascular endothelium. However, 300 microM of betaxolol or timolol decreased the [Ca2+]i of the vascular smooth muscle, an action similar to that of diltiazem, a typical L-type voltage calcium-channel blocker. CONCLUSIONS: Betaxolol, a selective beta1-adrenoceptor antagonist, and timolol, a nonselective beta-adrenoceptor antagonist, both frequently used in the medical management of glaucoma, decrease [Ca2+]i by acting as Ca2+ channel blockers, thus causing relaxation of isolated rabbit ciliary artery.

Adrenergic beta-Antagonists↗
PubMed2007

Vasoactivity of blood vessels using a novel isovolumic myograph.

The vasoactivity of blood vessel is impaired by cardiovascular disease. The ex-vivo measurements of vasoactivity (wire and pressure myographs) have some inherent difficulties in the characterization of pharmacodynamics and biomechanics. Here, we introduce a novel isovolumic myograph which allows simultaneous measurement of both dynamic pressure and dimensional changes during vasoconstriction or vasodilation. The principle of the isovolumic myograph is based on the utility of a hydraulically closed system with low compliance such that contraction against an incompressible fluid increases the pressure with the closed system while dilation decreases it. We demonstrate the sensitivity and utility of the new technique by the response of elastic (carotid), muscular (femoral) arteries, and femoral veins. The results show characteristic dynamic pressure response for each vessel type. Furthermore, our results show a Hill-type equation for the tension-velocity relation for smooth muscles as well as characteristic curves for each contraction. These novel findings for blood vessels will advance our knowledge of endothelium and vascular smooth muscle mechanics and pharmacodynamics.

Animals↗
PubMed2006

Spectral moments of mechanomyographic signals recorded with accelerometer and microphone during sustained fatiguing contractions.

The aim of this study was to analyse the trends of the first three power spectral moments of the mechanomyogram (MMG) signal recorded by a microphone (MMG(MIC)) and an accelerometer (MMG(ACC)) during sustained contractions. MMG signals were recorded from the biceps brachii muscle in 14 healthy male subjects during a 3 min isometric elbow flexion at 30% of the maximal voluntary contraction. MMG absolute and normalised root mean square (RMS), mean power frequency (MNF), power spectral variance (Mc2), and skewness (mu3) were computed. For both MMG(MIC) and MMG(ACC), absolute and normalised RMS and Mc2 increased while MNF and mu3 decreased with contraction time (P<0.001). The rates of change of RMS over time were significantly correlated (P<0.001) for MMG(MIC) and MMG(ACC) but not correlated for spectral moments. The coefficient of variation of RMS was higher for MMG(MIC) than for MMG(ACC), while the opposite was observed for mu3 (P<0.05). It was concluded that higher order spectral moments of the MMG signal change during sustained contraction, indicating a complex modification of the shape of the power spectrum and not just scaling of the bandwidth. This is most likely due to the additional motor unit recruitment with fatigue and to the non-linear summation of motor unit contributions to the signal. Moreover, the characteristics of MMG signals recorded with microphones and accelerometers have important differences, which should be taken into account when comparing results from different studies.

Adult↗
PubMed2006

Adaptive potential of human biceps femoris muscle demonstrated by histochemical, immunohistochemical and mechanomyographical methods.

The goal of this study was to estimate the ability of biceps femoris (BF) muscle, a hamstring muscle crucial for biarticulate movement, to adapt to changed functional demands. For this purpose and due to ethical reasons, in a group of healthy sedentary men and of 15 sprinters, a non-invasive mechanomyography (MMG) method was used to measure the muscle twitch contraction times (Tc). These correlate with the proportions of slow and fast fibres in the muscle. To further elucidate the data obtained by MMG method and to obtain reference data for the muscle, the fiber type proportions in autoptic samples of BF in sedentary young men were determined according to histochemical reaction for myofibrillar adenosine triphosphatase (mATPase). In one BF sample also myosin heavy chain (MyHC) isoform expression was demonstrated immunohistochemically. With MMG we indirectly demonstrated that biceps femoris muscle has a strong potential to transform into faster contracting muscle after sprint training, since the average Tc in sprinters was much lower (19.5 +/- 2.3 ms) than in the sedentary group (30.25 +/- 3.5 ms). The results of the histochemical and immunohistochemical analysis of BF muscle also imply a high adapting potential of this muscle. Beside type 1, 2a and 2x (2b) fibres a relatively high proportion of intermediate type 2c fibres (5.7% +/- 0.7), which co-expressed MyHC-1 and -2a, was found. Therefore, type 2c might represent a potential pool of fibres, capable of transformation either to slow type 1 or to fast type 2a in order to tune the functional response of BF muscle according to the actual functional demands of the organism.

Adaptation, Physiological↗
PubMed1983

Cardiokymography during exercise testing: a new device for the detection of coronary artery disease and left ventricular wall motion abnormalities.

The cardiokymograph (CKG) is a device that has been shown to reflect left ventricular (LV) wall motion abnormalities. Its accuracy in detecting coronary artery disease (CAD) during treadmill exercise testing was assessed in 204 consecutive patients undergoing coronary arteriography. Of the 188 patients with a technically adequate CKG, 146 (78%) had significant CAD. The sensitivity and specificity were similar for both the exercise electrocardiogram (ECG) (66% and 86%, respectively) and the exercise CKG (73% and 95%, respectively). An abnormal exercise CKG was significantly more common in patients with 3-vessel CAD than in those with 1-vessel disease (97% versus 52%, respectively; p less than 0.001) and in patients with left anterior descending disease than in those without (85% versus 26%, respectively; p less than 0.001). Seventy patients showed both an abnormal exercise ECG and CKG; all had CAD and 86% had multivessel CAD. Forty-eight patients demonstrated a normal exercise ECG and CKG; 29% had CAD but only 6% had multivessel CAD. Among 55 patients who had simultaneous exercise radionuclide ventriculography, new septal or apical wall motion abnormalities were found in 79% (23 of 29) of patients with an abnormal CKG compared with 19% (5 of 26) of patients with a normal CKG (p less than 0.001). Thus, the CKG during exercise testing accurately reflects LV wall motion abnormalities and can be used to improve the diagnostic accuracy of exercise testing as an additional marker of myocardial ischemia.

Adult↗