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At least 451 records · Page 25Linked to original sources

PubMed1986

Pupillary functional asymmetry in patients with muscle contraction headache.

Twenty-five patients with 'muscle contraction headache' (MCH) underwent tyramine pupillary tests, and 15 of them also underwent physiologic pupillary tests and cold pressor tests. Twenty healthy controls underwent tyramine pupillary tests, physiologic pupillary tests, and cold pressor tests. In the tyramine pupillary tests and the physiologic pupillary tests, the controls showed a symmetric mydriasis. In contrast, MCH patients showed asymmetric mydriasis after tyramine instillation and in the physiologic pupillary tests. In the cold pressor tests MCH patients reacted in the same manner as the controls. It is suggested that MCH patients have pupillary sympathetic imbalance. The role of this imbalance in the pathogenesis of MCH remains uncertain.

Adult↗

PubMed2001

Effect of pelvic floor muscle contraction on vesical and rectal function with identification of puborectalis-rectovesical inhibitory reflex and levator-rectovesical excitatory reflex.

The effects of pelvic floor muscle contraction on rectal and vesical function were studied in 19 healthy volunteers with the aim of shedding light on some of the hitherto vague aspects of the mechanisms involved in micturition and defecation and their disorders. Rectal and vesical pressures were recorded during puborectalis (PR) and levator ani (LA) muscle stimulation with the rectum or urinary bladder empty and full. Muscle stimulation was effected by needle EMG electrode. The pressure responses to stimulation of the PR and LA muscles were also recorded with these muscles and the rectum and urinary bladder individually anesthetized in 12 of the 19 subjects. The test was repeated using saline instead of xylocaine. PR and LA muscle stimulation produced no pressure response in the empty rectum or bladder. Upon rectal balloon distension with a mean of 156.6+/-34.2 ml of carbon dioxide the mean rectal pressure was 64.6+/-18.7 cm H2O, the subject felt the urge to evacuate and the balloon was expelled to the exterior. On PR muscle stimulation at rectal distension with the above volume, the subject did not feel the urge to evacuate, the rectal pressure was 8.2+/-1.6 cm H2O and the balloon was not expelled. Upon LA stimulation at the same volume, the urge persisted, the rectal pressure was higher and the balloon was expelled. Vesical filling with a mean of 378.2+/-23.6 ml of saline initiated the urge to urinate and elevated the vesical pressure. PR muscle stimulation at this volume aborted the urge and pressure elevation, while LA stimulation caused more elevation of the vesical pressure and spontaneous micturition. Bladder filling with a mean of 423.6+/-38.2 ml produced high vesical pressure and spontaneous urination, both of which were prevented by PR muscle stimulation but not by LA muscle stimulation. Stimulation of the PR and LA muscles during individual anesthetization of the rectum, bladder or PR and LA muscles resulted in no significant rectal or vesical pressure changes. Repetition of the test using saline instead of xylocaine resulted in rectal and vesical pressure responses similar to those without the use of saline. In conclusion, the decline in rectal and vesical responses upon PR muscle contraction indicates a reflex relationship which we term 'puborectalis rectovesical inhibitory reflex'. This reflex is suggested to abort the urge to defecate or urinate. In contrast, LA muscle contraction produced rectal and vesical pressure elevation which is suggested to be mediated through the 'levator rectovesical excitatory reflex'. 'This reflex is probably evoked to promote rectal and vesical evacuation.

Adolescent↗

PubMed1984

Cardiovascular responses to isometric neck muscle contractions: results after dynamic exercise with various headgear loading configurations.

Experiments were conducted to quantify the cardiovascular response (blood pressure and heart rate) elicited by sustained isometric contractions of the neck muscles. The response was secondary to dynamic exercise with various headgear loading combinations. The neck muscles were loaded by the head itself (CON), the standard U.S. Army SPH-4 helmet (HEL), and a combination of the SPH-4 helmet with Night Vision Goggles (H/NVG). During two exercise periods of 5 min and 35 min, each of the five subjects would rotate the head from side-to-side in the CON, HEL, or H/NVG configuration. Immediately thereafter, the subject would position his head in an isometric head dynamometer and exert a sustained right lateral (LAT) neck contraction or forward (FOR) neck contraction at 70% of a maximal voluntary contraction (MVC). During this isometric neck muscle contraction, the subject's endurance time to fatigue was recorded, the blood pressure was manually recorded, and the heart rate was continuously recorded. Characteristic increases in the systolic and diastolic blood pressure and heart rate occurred with sustained isometric neck muscle contractions. There was an average 40% increase in the systolic blood pressure, an average 50% increase in the diastolic blood pressure, and an average 45% increase in the heart rate from resting to the end of a fatiguing 70% MVC (p less than 0.05). These responses appear to be relatively independent of the duration of the exercise period, the loading during the exercise period, and the specific muscle mass involved. The mechanisms for the pressor response and the heart rate response are reviewed.

Adult↗

PubMed2001

Stimulatory effects of leptin and muscle contraction on fatty acid metabolism are not additive.

Leptin has been shown to acutely stimulate fatty acid oxidation and triacylglycerol hydrolysis in skeletal muscle. These effects are similar to those induced by muscle contraction alone. Several studies have demonstrated that, during aerobic exercise, plasma leptin concentrations are well maintained; however, none has examined whether the stimulatory effects of leptin and contraction on muscle lipid metabolism are additive. This is the first study to examine the direct effect of leptin on lipid and carbohydrate (CHO) metabolism in isolated oxidative muscle over a range of contraction intensities. We examined the effect of leptin (10 microg/ml) on the synthesis and degradation of muscle lipid pools [phospholipid (PL), diacylglycerol (DG), triacylglycerol (TG)] and palmitate oxidation in isolated resting and contracting (2, 8, and 20 tetani/min) soleus muscles. At rest, leptin increased fatty acid oxidation (+ 40%, P < 0.05) and TG hydrolysis (+ 47%, P < 0.05), while blunting TG esterification (-20%, P < 0.05). Glucose oxidation was unaffected at rest in the presence of leptin. During tetanic contraction, fatty acid oxidation (+20-114%, P < 0.05) and TG esterification (+ 19-33%, P < 0.05) as well as net TG utilization (+ 23%, P < 0.05) were all significantly increased. However, leptin was without further effect on any of these parameters during contraction. Net utilization of intramuscular glycogen, as well as glucose oxidation, was unaffected during contraction by leptin. The findings of the present study indicate that leptin has an important influence on lipid metabolism in resting muscle, but not during contraction.

Animals↗

PubMedDate not supplied

Hypoalgesic effect of caffeine in experimental ischemic muscle contraction pain.

It has been theorized that adenosine is a leading candidate for the metabolite responsible for ischemic muscle pain. The purpose of this study was to determine the effect of the non-selective adenosine receptor antagonist, caffeine, on ischemic skeletal muscle contraction pain. Seven healthy adult volunteers with no history of pain disorders, systemic disease, or habitual caffeine use, were chosen for the two-session, cross-over, double-blind study. Every subject received either 200 mg of caffeine (NoDoz, Bristol-Myers) or identical placebo 1 hour before each of the two trials. Ischemia of the forearm was achieved by inflation of a blood pressure cuff to 250 mm Hg. Forearm muscle activity was generated by performance of wrist curis using a 5-gram bar at a rate of 40 cycles per minute. Pain was rated at 15-second intervals for 1 minute using a visual analog scale (0 to 10) with verbal descriptors. Significance was determined by univariate and multivariate analyses of variance and covariance including repeated measures. Pain ratings at 15 seconds in the caffeine trial were significantly lower (P < 0.02) than those in the placebo trial. This effect continued at 30 seconds (P < 0.05). However, by 45 seconds, pain in the caffeine trial was not significantly lower (P = 0.4) than that in the placebo trial. These results show that high-dose caffeine exhibits considerable analgesic efficacy in experimental muscle pain, adding support for a role of adenosine in producing ischemic muscle contraction pain.

Adult↗

PubMed1983

Relationship between verbal command volume and magnitude of muscle contraction.

The purpose of this study was to investigate the hypothesized correlation between volume of a verbal command and magnitude of a resulting voluntary isometric muscular contraction, using a withdrawal-reinstatement (ABAB) research design. Nineteen volunteer male subjects between the ages of 18 and 30 years performed isometric contractions of the triceps brachii muscles in response to prerecorded verbal commands. With a volume increase of 22 decibels A scale, subjects averaged an 8 percent increase in muscle contraction strength, a difference that was significant at the .05 level. Through an awareness and use of the effects of voice volume on muscular contraction, the therapist may be able to improve the accuracy and consistency of examination methods, and increase the efficacy and efficiency of therapeutic procedures.

Acoustic Stimulation↗

PubMed2006

Relationship between abdominal and pelvic floor muscle activation and intravaginal pressure during pelvic floor muscle contractions in healthy continent women.

AIM: Activation of the abdominal muscles might contribute to the generation of a strong pelvic floor muscle contraction, and consequently may contribute to the continence mechanism in women. The purpose of this study was to determine the abdominal muscle activation levels and the patterns of muscle activity associated with voluntary pelvic floor muscle (PFM) contractions in urinary continent women. METHODS: Fifteen healthy continent women participated. They performed three maximal contractions of each of the four abdominal muscles and of their PFMs while in supine. Abdominal and PFM activity was recorded using electromyography (EMG), and intravaginal pressure was recorded using a custom modified Femiscan probe. RESULTS: During voluntary maximal PFM contractions, rectus abdominus was activated to 9.61 (+/-7.42)% maximal voluntary electrical activity (MVE), transversus abdominus was activated to 224.30(+/-47.4)% MVE, the external obliques were activated to 18.72(+/-13.33)% MVE, and the internal obliques were activated to 81.47(+/-63.57)% MVE. A clear pattern of activation emerged, whereby the transversus abdominus, internal oblique, and rectus abdominus muscles worked with the PFM in the initial generation of maximal intravaginal pressure. PFM activity predominated in the initial rise in lower vaginal pressure, with later increases in pressure (up to 70% maximum pressure) being associated with the combined activation of the PFM, rectus abdominus, internal obliques, and transverses abdominus. These abdominal muscles were the primary source of intravaginal pressure increases in the latter 30% of the task, whereas there was little increase in PFM activation from this point on. The external oblique muscles showed no clear pattern of activity, but worked at approximately 20% MVE throughout the PFM contractions, suggesting that their role may be predominantly in postural setting prior to the initiation of intravaginal pressure increases. CONCLUSIONS: Defined patterns of abdominal muscle activity were found in response to voluntary PFM contractions in healthy continent women.

Abdominal Muscles↗

PubMed1996

The step-size distance in muscle contraction: properties and estimates.

The step-size distance in muscle contraction is obtained using the step-size distance equation z = u/n, where z is the step-size distance, u is the actin filament velocity and n is the ATPase rate of splitting. In a previous study a step-size distance of about 17 A at no load was determined for intact frog muscle. Some properties of the step-size equation are described. We have now made estimates of the step-size distance z for a variety of muscles using existing physiological and biochemical data in the literature. The estimates are listed in Tables 1 and 2. We find that the step-size distances are clustered in the range 13-17 A for nearly all muscles.

Actins↗

PubMed1989

Muscarinic receptors: relationships among phosphoinositide breakdown, adenylate cyclase inhibition, in vitro detrusor muscle contractions and in vivo cystometrogram studies in guinea pig bladder.

The relationships between activation of muscarinic receptors in guinea pig bladder measured as carbachol-stimulated inositol phosphate (IP) accumulation, oxotremorine-induced adenylate cyclase (AC) inhibition and bladder detrusor smooth muscle contraction determined in vitro as well as in vivo in the slow filling cystometrogram (CMG), were analyzed from the potencies of a number of muscarinic antagonists to block these responses. Significant positive linear correlations were found among the inhibitory potencies of 10 muscarinic antagonists to inhibit phosphoinositide (PI) turnover and both detrusor muscle contraction in vitro, as well as peak intravesical bladder pressure in vivo in the CMG (r = 0.8, P less than .01). In contrast, there was no significant correlation between the potency of antagonists to block the AC inhibitory response and either in vitro or in vivo guinea pig bladder contractions (P greater than .05). Muscarinic agonists inhibited basal AC activity to a maximum of 20% in a GTP-dependent, Na+-sensitive manner and dose dependently stimulated both PI breakdown (3- to 4-fold) and isolated detrusor contractions. Again, a significant correlation (r = 0.9, P less than .01) was calculated among the potencies of seven muscarinic agonists to elicit PI turnover and in vitro muscle contraction, whereas no significant correlation was observed between their potencies to inhibit AC activity and contractile responses in vitro. Collectively, the data suggest that IP accumulation and presumably IP-induced Ca++ release may function as the transducing mechanism for cholinergic contraction of the urinary bladder.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenylyl Cyclase Inhibitors↗

PubMed1986

Relative effects of static muscle contraction on digital artery and nailfold capillary blood flow velocities.

Previous studies have shown that a decrease in blood flow to the finger is not necessarily accompanied by a corresponding change of blood flow in nailfold capillaries. The purpose of this study was to determine if nailfold capillary blood flow remains relatively stable during a decrease in finger blood flow induced by muscle contractions. Four male subjects 20 to 30 years of age exerted 2-min periods of static calf muscle contraction at levels of 7.5, 15, 30, and 45% of their maximum voluntary contractile force (MVC) while systemic blood pressure (BP), and flow velocities in the digital artery (VEL-A) and nailfold capillaries (VEL-C) were measured by, respectively, Doppler ultrasound and video densitometry. Each subject repeated the series five times. There was a significant linear decrease in VEL-A with increasing force of contraction for each subject individually (P less than or equal to 0.009) and for the group as a whole (P less than or equal to 0.0001); whereas VEL-C did not significantly change during muscle contraction. These results indicate that the initial cutaneous constrictor response in the finger during the onset of leg muscle exercise is not reflected to the nailfold capillaries.

Adult↗

PubMed1986

The role of tracheal smooth muscle contraction on neonatal tracheal mechanics.

The ability of tracheal smooth muscle tone to modulate the mechanical properties of neonatal airways was evaluated in six newborn lambs. Tracheal pressure-volume relationships, isovolumic compliance, hysteresis, and the relaxation time constant of the smooth muscle were evaluated as a function of incremental cholinergic stimulation. Tracheal active tensions were also determined at the graded levels of cholinergic stimulation. Data show that a maximal cholinergic stimulation resulted in a mean developed active tension value of 14.3 +/- 2.13 SEM X 10(3) dynes/cm. The resultant 55% decrease in tracheal compliance was linearly correlated to the increase in active tension (r = 0.90, p less than 0.01). Cholinergic stimulation also resulted in a 18.4% decrease (p less than 0.02) in the relaxation time constant of the smooth muscle, and in a 82% increase (p less than 0.01) in tracheal hysteresis. This study demonstrates that both elastic and viscoelastic properties of the neonatal lamb trachea are effected by tracheal smooth muscle contraction. Since neonatal airways are more compliant than adult airways, cholinergic stimulation could conceivably enhance airway rigidity and may provide a protective mechanism against pressure-induced deformation.

Animals↗

PubMed1994

Inhibitory effects of halothane on high(K+)-induced canine tracheal smooth muscle contraction and intracellular Ca2+ increment.

Halothane is a potent bronchodilator. The effects of halothane on isolated canine tracheal smooth muscle contraction and intracellular Ca(2+) increment induced by a high concentration of K+ were investigated to clarify how this anaesthetic decreases intracellular Ca2+ concentration ([Ca2+]i), an important second messenger. The tension of the muscle strips was measured using an isometric transducer, and [Ca2+]i was measured using a surface fluorescence spectroscopy. Exposure to a 72.7 mM K+ solution increased muscle tension and [Ca2+]i. Halothane (1,2,3 and 4% at the vaporiser) was introduced by bubbling in the presence of the 72.7 mM K+, and significantly decreased both this elevated muscle tension and the [Ca2+]i in a concentration-dependent manner. Similarly, slowly decreasing concentrations of K+ (48.5, 36.4, 24.2 and 18.2 mM) significantly decreased both of these variables. There was no significant difference between the slopes of the two regression lines of changes in muscle tension and changes in [Ca2+]i. From the evidence that tonic increase in [Ca2+]i by high concentrations of K+ is due to the influx of Ca2+ via L-type voltage channels, halothane may modify the L-type channels to decrease Ca2+ influx. In conclusion, halothane inhibits the high K(+)-induced canine airway smooth muscle contraction by decreasing [Ca2+]i. The decrease in [Ca2+]i by halothane might be due to inhibition of voltage-operated channels, especially the L-type channels.

Animals↗

PubMed1991

Enkephalinase inhibitor potentiates substance P- and capsaicin-induced bronchial smooth muscle contractions in humans.

To determine the roles of endogenously released tachykinins (substance P, neurokinins A and B) in human bronchial tissues, and to determine the roles of enkephalinase (neutral endopeptidase, E.C. 3.4.24.11) in regulating the effects of the tachykinins, we studied the effects of substance P and capsaicin, which releases tachykinins, on human bronchial smooth muscle contraction in the presence or absence of enkephalinase inhibitor phosphoramidon in vitro. Substance P alone caused human bronchial smooth muscle contraction at 10(-6) M or more. Phosphoramidon (10(-7) to 10(-5) M) potentiated the substance P-induced contraction in a dose-dependent fashion, and phosphoramidon shifted the dose-response curve to lower concentrations. Capsaicin (10(-5) or 10(-4) M) alone caused bronchial smooth muscle contraction in four tissues from nine patients. After the contraction by capsaicin reached a plateau, phosphoramidon (10(-5) M) increased and prolonged the contraction significantly. Furthermore, pretreatment of bronchial tissues with phosphoramidon (10(-5) M) potentiated capsaicin-induced contraction in all tissues from five patients. Phosphoramidon (10(-5) M) shifted the dose-response curve to capsaicin to lower concentrations more than 1 log unit. Captopril did not alter the contractile response to substance P, suggesting that angiotensin-converting enzyme does not regulate the contractile response to substance P in human bronchial smooth muscle in vitro. These results suggest that enkephalinase regulates the contractile effects of exogenous substance P and endogenous substances, probably tachykinins, released by capsaicin in the human bronchus.

Adult↗

PubMed1989

The Autonomic Nervous System Response Inventory (ANSRI): discrimination among migraine headache sufferers, muscle contraction headache sufferers, and normal controls.

Twenty-three migraine headache sufferers, sixteen muscle contraction headache sufferers, and thirteen no headache control subjects were selected to test the discriminant validity of the ANSRI. Significant Chi-Squares indicated reliable differences among the groups in ANSRI F scale scores under the Anger condition and in P scale scores based on the means of items across four emotions (All E). Discriminant analyses yielded 69% correct classifications for All E P scales and 58% correct classifications for Anger F scales. All E P scale analyses revealed that the Muscle Tension scale separated the headache groups from the control group. A second function separated the three groups from each other, with the Cardiac, Respiration, and Gastrointestinal scales most responsible. Anger F scale analysis showed the Peripheral Vasoconstriction, Cardiac, and Pattern 2 scales separating the headache groups from each other and from the control group. Results demonstrated discriminant validity for the ANSRI, and were consistent with muscle tension and vasoconstriction as variables in muscle contraction and migraine headache, respectively.

Adolescent↗

PubMed2001

Pelvic floor muscle contraction during a cough and decreased vesical neck mobility.

OBJECTIVE: To test the hypothesis that a voluntary pelvic muscle contraction initiated in preparation for a cough, a maneuver we call the Knack, significantly reduces vesical neck displacement. METHODS: A convenience sample of 22 women consisted of 11 young, continent nulliparas (mean age [+/- standard deviation] 24.8 +/- 7.0 years) and 11 older, incontinent paras (mean age [+/-SD] 66.9 +/- 3.9 years). With the use of perineal ultrasound, we quantified vesical neck displacement at rest and during coughs using caliper tracing and a coordinate system. The subjects coughed with and without voluntary pelvic floor muscle contraction. RESULTS: Vesical neck mobility during coughs was significantly decreased when voluntary contraction was used: from a median (range) of 5.4 (20.0) mm without volitional contraction to 2.9 (18.3) mm with volitional contraction (P <.001). The younger women demonstrated a median (range) decrease in excursion from 4.6 (19.5) to 0.0 (17.0) mm (P =.007), and the older incontinent women demonstrated a median (range) decrease from 6.2 (10.0) to 3.5 (15.4) mm (P =.003). At rest, the median vesical neck position in the group of older incontinent women was significantly further dorsocaudal (P =.001) than in the younger women. CONCLUSION: A pelvic floor muscle contraction in preparation for, and throughout, a cough can augment proximal urethra support during stress, thereby reducing the amount of dorsocaudal displacement.

Adult↗

PubMed1989

[Movement of the ear ossicles by middle ear muscle contraction].

Up to now, the function of the middle ear muscles has mainly been investigated from an acoustical point of view. However, the primary function of the middle-ear muscles, namely the induction of ossicular movements, has never been investigated systematically. For this purpose, the displacements of the ossicles, as induced by simulated muscle contractions, were measured microscopically in 13 fresh temporal bone preparations. Both muscles move all ossicles. The tensor tympani muscle pulls the umbo inwards about 100 microns. Due to the gliding motion in the malleus-incus joint, the stapes is thus pushed inwards by at the most 10 microns and, additionally, displaced anteriorly, antagonistic to the pull of the stapedius muscle. This muscle pulls the stapes backwards, lifting the anterior crus outwards and pushing the posterior crus inwards. This reduces the pressure on the cochlear fluids significantly as compared to our former concepts of the movement of the footplate, tilting outwards as a whole around an axis at the posterior pole. Furthermore, this outward displacement of the stapes is not prerequisite for the outward movement of the malleus-drumhead complex, which typically appears at the contraction of the stapedius muscle. The basic motion of the stapes is the movement backwards, which is 5 times greater and which matches the anatomic direction of the pull of the stapedius muscle. This explains the otherwise unlogical position of the stapedius muscle parallel to the footplate. Due to the gliding movement in the malleus-incus joint, this motion changes at the umbo into outward rotation, counteracting the tensor tympani muscle.(ABSTRACT TRUNCATED AT 250 WORDS)

Ear Ossicles↗

PubMed1989

Regulation of vertebrate striated muscle contraction.

Most current textbooks of cell biology and histology use the steric blocking model to describe the protein mechanism by which vertebrate striated muscle contraction is regulated. Evidence accumulated in the past decade, however, reveals the regulation of muscle contraction to be far more complex than this model predicts.

Actins↗

PubMed1975

Feedback of isotonic muscle contraction on neuromuscular impulse transmission in the frog.

The effect of isotonic contraction on neuromuscular impulse transmission was studied in the in vivo M. gastrocnemius preparation of the frog. The N. ischiadicus was stimulated regularly with single pulses at different frequencies in the range of 1/8 to 8 Hz. When steady state conditions were reached, each half-minute a second stimulus was added to one of these pulses. The interval between the pulses of the pair was varied within the contraction cycle of the first stimulus. Compound extracellular or single intracellular action potentials were recorded from the muscle. At frequencies of 1/2-2 Hz a depression of the amplitude of the second compound muscle action potential of up to 50% of the first response was found when the muscle contracted isotonically. However, the second response was facilitated during an isometric contraction. The time course of the depression was equal to that of muscle shortening during the twitch, while the time course of facilitation corresponded roughly to that of facilitation of transmitter release. At lower frequencies the "isotonic depression" or "isometric facilitation" was not or only slightly present. However, at 1/8 Hz the depression could be evoked or increased by curarization. At frequencies higher than 2 Hz facilitation dominated over depression under isotonic conditions. With flexible intracellular micro-electrodes it was shown that the depression of the amplitude of the compound muscle action potential observed during the isotonic twitch was due to a reduction in neuromuscular impulse transmission. It is concluded that the isotonic depression is a negative feedback effect of the change of length of the contracting muscle on synaptic impulse transmission, probably due to an effect of length on transmitter release.

Action Potentials↗