PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Isotonic Contraction”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,441 records · Page 80Linked to original sources
PubMed1976

Pancreatic, gallbladder, and gastric responses to intraduodenal calcium perfusion in man.

To determine the effect of intraduodenal calcium on pancreatic, gallbladder, and gastric functions in healthy man, a validated perfusion method was employed to quantify total pancreatic, biliary, and gastric outputs during duodenal perfusion of either 6 mM, 12 mM,or 25 mM of elemental calcium (as isotonic calcium chloride solutions). Intraluminal calcium stimulated pancreatic enzyme secretion and gallbladder contraction in a dose-related fashion, achieving comparable responses to those produced by intravenous cholecystokinin-pancreozymin (CCK-z). Responses to calcium were reproducible when repeated in the same individual. Gastric acid outputs and serum gastrin levels increased significantly only with higher calcium perfusions (25 mM). Although duodenal calcium perfusion (25 mM) slightly increased serum calcium concentrations, induced hypercalcemia (by intravenous calcium infusion) of similar magnitude had no effect on pancreatic or gallbladder function. It is suggested that intraduodenal calcium may induce release of CCK-PZ (and/or other neurohormonal factors) from the gut, causing stimulation of these digestive organs.

Adult↗
PubMed2004

Myocardial function in early hours after coronary artery bypass grafting in patients with left ventricular dysfunction: comparison of blood and crystalloid cardioplegia.

AIM: This study was done to evaluate a myocardial function in the early hours after coronary artery bypass grafting (CABG) in patients with left ventricular dysfunction and to compare blood and crystalloid cardioplegia. METHODS: One hundred consecutive patients with left ventricular ejection fraction <35% scheduled for CABG were randomly divided into 2 groups. In the 1st group we used cold blood cardioplegia, in the 2nd group cold crystalloid cardioplegia. We measured hemodynamic data in the early hours after operation, enzyme release and we collected relevant clinical data. RESULTS: The mortality rate in the crystalloid and blood cardioplegia group was 2% and 0%, respectively. We didn't find any significant difference in the incidence of perioperative myocardial infarction, arrhythmia and use of intraaortic balloon pumping between groups. Differences between groups were found in the enzymatic response. Average creatine kinase and MB isoenzyme of creatine kinase (CK-MB), was lower in the blood cardioplegia group lower during the whole examined period. We also found some significant differences in hemodynamic data in the postoperative period. In the crystalloid cardioplegia group there was a decrease in left ventricular stroke work index immediately after operation. The preoperative value was reached in about 2 hours after operation. On the other hand, we didn't find this decrease in the blood cardioplegia group. This difference between groups was statistically significant. Other hemodynamic data didn't show any significant difference. CONCLUSION: Blood cardioplegia shows earlier improvement of myocardial function after the operation. It could be beneficial in patients with severe left ventricular dysfunction.

Aged↗
PubMed1986

beta-Endorphin in canine hemorrhagic shock.

Endogenous opiate peptides have been implicated in the cardiovascular depression of hemorrhagic shock. Beta-endorphin immunoreactivity was measured during hemorrhagic shock and the effects of beta-endorphin suppression during shock on cardiac hemodynamics and myocardial blood flow were studied. Fourteen dogs (group 1) were pretreated with 30 milligrams per kilogram of methylprednisolone (MP) prior to shock. Ten dogs (group 2) received saline solution and were the control group. All dogs were bled to a mean arterial blood pressure of 35 millimeters of mercury for two hours, then resuscitated with blood and lactated Ringer's solution. Beta-endorphin concentrations increased 600 per cent during shock in the control group. Dogs pretreated with MP had lower beta-endorphin concentrations (p less than 0.05) during shock than did dogs in the control group. The rate of left ventricular pressure rise (dp/dt) was significantly improved during shock (p less than 0.04) and after resuscitation (p less than 0.006) in dogs with suppressed beta-endorphin immunoreactivity. Blood flow from the coronary artery was higher during shock and after resuscitation (p less than 0.001) in the dogs in group 1. Our data indicate significant correlation between improved ventricular performance and decreased beta-endorphin levels in shock and after resuscitation.

Adrenocorticotropic Hormone↗
PubMed1986

[Effect of a hypertonic mannitol solution on the peri-infarct area of an isolated frog heart].

The influence of the hypertonic (3%) solution of mannitol on the process of the excitability recovery (in the near necrotic zone) appeared as a result of the necroses tissue effect on the ventricle has been investigated in the experiments on the isolated frog's heart. The analogous perfusion was conducted by Ringer solution in the control experiments. The process of isopotential phase S-T recovery was practically the same at heart perfusion with Ringer solution or with mannitol. Simultaneous registration of ventricular mechanogram showed the pronounced negative inotropic effect of mannitol. It is suggested that the positive effect of mannitol which has been noted under clinic conditions during the treatment of ischemic disease, doesn't connect with the effect of hypertonic solution on the cells excitability of periinfarcted (near necrotic) zone.

Action Potentials↗
PubMed1981

Effects of various osmotic solutions on membrane properties of smooth muscle cells of the guinea pig ureter.

Effects of various osmotic solutions on membrane properties of smooth muscle cells of the guinea pig ureter were investigated using the microelectrode and double sucrose gap methods. In Krebs solution, the mean membrane potential was -53 mV, chronaxie was 104 msec, length constant of the tissue was 1.03 mm, time constant of the membrane was 65.8 msec, and conduction velocity of excitation was 19.2 mm per sec. Hyperosmotic solution (1.5, 2.0, or 2.5 times the normal osmolarity) depolarized the membrane, generated the spike activity, reduced the length constant of the tissue, increased the time constant of the membrane, prolonged the chronaxie, and reduced the conduction velocity. Hyposmotic solutions (0.85 and 0.67 times the normal osmolarity) produced opposite changes on the passive and active characteristics of the membrane compared to findings in hyperosmotic solution except that the time constant of the membrane was increased in both hyper- and hyposmolar solutions. Increase in the time constant of the membrane and reduced length constant of the tissue in hyperosmotic solution can be explained by an increase in the internal resistance, including the cell to cell junctional resistance and shrinkage of the cell diameter (from 6.2 to 3.0 micrometer).

Animals↗
PubMed1991

[The static exercise-induced arterial hypertension test].

The exercise tests used in the detection and follow-up of hypertensive patients fall into two categories: isotonic (dynamic) and isometric (static). The isometric exercise-induced arterial hypertension test consists of an isometric contraction--usually a grip by the dominant hand--sustained for 3 minutes, with a strength that is 30 percent of maximum voluntary strength. This results in a continuous and parallel increase of systolic and diastolic blood pressures during the hand grip. The heart rate also continuously rises, though not to the level obtained by the isotonic exercise test. The increase in cardiac output observed, despite a fall in stroke volume, and the absence of decrease in peripheral vascular resistance contribute to a sometimes considerable rise in blood pressure, particularly diastolic pressure. These cardiovascular responses do not depend on the muscular mass involved but on the relative strength developed during isometric contraction. Owing to the lack of strict standardization and longitudinal studies, the isometric exercise test is of little value in the early detection of arterial hypertension. However, it is useful in the follow-up of hypertensive patients, as it provides precise information on the point of impact and mode of action of several antihypertensive drugs.

Blood Pressure↗
PubMed1996

Protein kinase C plays no role in KCl-induced vascular contraction in Ca(2+)-free medium.

AIM: To examine the role of protein kinase C (PKC) on the sustained contractile responses of rat aorta to high KCl in isotonic Ca(2+)- and Mg(2+)-free solutions. METHODS: The effects of phorbol 12-myristate 13-acetate (PMA, a PKC activator) and Calphostin C (a selective PKC inhibitor) were observed on the sustained contraction of rat aorta induced by K+ 136 mmol.L-1. EGTA (100 mumol.L-1) was added to prepare the Ca(2+)-free medium and EDTA (100 mumol.L-1) was added to reduce or remove the Mg2+. RESULTS: Aortic contraction to KCl was prominent in low Mg2+ medium and was enhanced by EDTA (K-EDTA contraction). Such contraction was concentration-dependently inhibited by Mg2+, but was not affected by Calphostin C 1 mumol.L-1. Pretreatment of the aortic preparations with PMA (0.8 mumol.L-1) potentiated the contraction to KCl in Ca(2+)-free, low Mg2+ medium and higher concentration of Mg2+ was required to cause relaxation. Such a reduced sensitivity to Mg2+ in the presence of PMA was partially reversed by Calphostin C and was accompanied by an increased sensitivity to Ca2+, which concentration-dependently caused contraction following Mg(2+)-induced relaxation. However, in the presence of EDTA 100 mumol.L-1 (eg, Mg(2+)-free medium), the maximal contraction to KCl in Ca(2+)-free medium was not affected by PMA or Calphostin C. CONCLUSION: KCl-induced contraction in Ca(2+)-free and Mg(2+)-free + EDTA 100 mmol.L-1 medium was not affected by PMA or Calphostoin C, indicating that PKC plays no role in such contractile responses.

Animals↗
PubMed1987

The mechanical response of rat myometrium to adenosine triphosphate in Ca-free solution.

The contractile response of the myometrial longitudinal muscle of pregnant and estrogen-treated rats to adenosine triphosphate (ATP) was investigated. ATP (10(-5)-4 X 10(-3) M) added to Krebs solution caused a generation of spontaneous activity consisting of phasic contractions and an elevation of muscle tone in a dose-dependent manner. Effects of the "test solution" consisting of isotonic K, 4(mM) ATP, 4 Mg, 1-20 EGTA, 20 tris(hydroxymethyl)aminomethan (Tris) maleate (pH 6.8) on the contractile response was then investigated. An initial phasic and a following tonic contraction was evoked by the application of the test solution, when applied after the equilibration of the muscle with Krebs solution. ATP was proved to be an agonist to evoke the Ca-free contraction. The phasic contraction was depressed when the muscle was incubated with Ca-free Krebs solution. The amplitude of the tonic contraction became progressively larger when application of the test solution was repeated. The amplitude was 15-70% as large as the tonic component of the K-contracture induced by 40 mM K. Theophylline (10 mM), 0.1 mM papaverine and 1 microM isoprenaline nearly abolished, and 1 mM cAMP partly depressed the tonic contraction of K-contracture, whereas the tonic contraction induced by the test solution was unaffected. A calmodulin antagonist, W-7 (100 microM) strongly suppressed both the K-contracture and the contraction induced by the test solution, whereas trifluoperazine (10-200 microM) preferentially depressed the K-contracture. The tonic contraction induced by the test solution was strongly depressed when Mg was removed and 20 mM EDTA was applied. From these results, it is discussed that some Ca-independent process is involved in the generation of tonic component of Ca-free contraction developed by the application of the test solution.

Adenosine Triphosphate↗
PubMed1996

Haemodynamic consequences and uterine contractions following 0.5 or 1.0 litre crystalloid infusion before obstetric epidural analgesia.

PURPOSE: The efficacy of infusion of 0.5 L and 1.0 L Ringer's lactate (LR) to prevent hypotension during induction of obstetric analgesia was studied. The effect of the different fluid boluses on fetal heart rate (FHR) and frequency of uterine contractions were also determined. METHODS: Ninety-two ASA 1-2 parturients were randomized to receive 0.5 L (Group 1) and 1.0 L (Group 2) LR immediately before incremental epidural injections with lidocaine to achieve T10 sensory block. Systolic blood pressure (SBP) was measured with an automated BP cuff every two minutes for 30 min after infusion of fluid bolus. Fetal heart rate monitoring and tocometry were used continuously. The number of uterine contractions were recorded 30 min before and 60 min after i.v. bolus. RESULTS: The SBP decreased in both groups, but there was no difference between groups in mean SBP or maternal heart rate. The incidence of hypotension (SBP < 90 mmHg or decrease of 20%) was 4% in both groups. The FHR record of a patient in Group 1 showed a single late deceleration, and a decrease in beat-to-beat variability occurred in one patient in Group 2. A decrease in the frequency of uterine contractions of two or more contractions per 30 min was noted more frequently in Group 2 (P < 0.05). The duration of iv bolus was longer in Group 2 than Group 1 (18.8 +/- 4.3 min vs 12.3 +/- 4.5 min, P < 0.01). CONCLUSION: Administration of 1.0 L LR i.v. does not provide added protection against maternal hypotension, and is associated with delay in providing pain relief and a risk of decreasing uterine contraction frequency.

Adult↗
PubMed2005

Experimental muscle pain increases mechanomyographic signal activity during sub-maximal isometric contractions.

This study was designed to investigate the local effect of experimental muscle pain on the MMG and the surface EMG during a range of sub-maximal isometric contractions. Muscle pain was induced by injections of hypertonic saline into the biceps brachii muscle in 12 subjects. Injections of isotonic saline served as a control. Pain intensity and location, MMG and surface EMG from the biceps brachii were assessed during static isometric (0%, 10%, 30%, 50% and, 70% of the maximal voluntary contraction) and ramp isometric (0-50% of the maximal voluntary contraction) elbow flexions. MMG and surface EMG signals were analyzed in the time and frequency domain. Experimentally induced muscle pain induced an increase in root mean square values of the MMG signal while no changes were observed in the surface EMG. Most likely this increase reflects changes in the mechanical contractile properties of the muscle and indicates compensatory mechanisms, i.e. decreased firing rate and increased twitch force to maintain a constant force output in presence of experimental muscle pain. Under well-controlled conditions, MMG recordings may be more sensitive than surface EMG recordings and clinically useful for detecting non-invasively increased muscle mechanical contributions during muscle pain conditions.

Adaptation, Physiological↗
PubMed1978

Isometric relaxation of rat myocardium at end-systolic fiber length.

In a "physiologically sequenced" contraction (PSC), which loads the isolated muscle preparation in a manner which approximates that of the intact heart, isometric relaxation precedes isotonic relaxation and occurs at minimum ("end-systolic") length. We studied the effects of inital muscle length, load, temperature, calcium, and isoproterenol on the isometric relaxation phase of physiologically sequenced contractions to define the determinants of the rate of isometric relaxation of rat left ventricular myocardium. At the baseline temperature (28 degrees C), relaxation was found to be nonexponential, and the maximum rate of decline of force (-dF/dtmax) was used to evaluate changes in relaxation. Three factors, shortening, end-systolic length, and total load, were examined as possible mechanical determinants of -dF/dtmax. We found that -dF/dtmax is linearly related to end-systolic muscle length for lengths below 94% of Lmax; -dF/dtmax is also strongly related to total load for lightly loaded contractions, but peaks at loads of approximately 80% of peak developed force and declines thereafter. Shortening is poorly correlated with -dF/dtmax. The slope of the linear portion of the relation between -dF/dtmax and end-systolic length appears to be independent of muscle-loading conditions and sensitive to factors known to alter relaxation.

Animals↗
PubMed1967

An electrophysiological study of some reticulo-ruminal and abomasal reflexes in sheep.

1. In halothane-anaesthetized sheep in which reticulo-ruminal (gastric) contractions were present, nervous discharges have been recorded electrophysiologically in sixty-four single efferent gastric units (grouped in seven types) dissected from the mid-cervical region of the left vagus. An examination was made of the reflex effects on the efferent discharges of the procedures given in paragraphs 2-5.2. Under isotonic recording conditions the total discharge was reduced but the peak frequency of most types of unit was enhanced compared with the discharge recorded under control isometric conditions.3. Abolition of reticular contractions by the use of preganglionic and post-ganglionic blocking agents resulted in an efferent discharge pattern similar to that recorded under isotonic conditions.4. Sudden deflation or inflation of the reticulum at the start of a reticular contraction had an effect that depended on the initial volume of the reticulum. It could be either excitatory and/or inhibitory.5. Acidification of the abomasal contents reflexly enhanced the discharge in three of ten efferent gastric vagal units. An abomasal pH less than 1.0 appears to be less important in providing an excitatory drive to the ;gastric centres' in halothane-anaesthetized sheep than in decerebrate sheep.6. It is estimated that the total reflex time is > 1.3 sec for reticulo-reticular reflexes and > 2.1 sec for reticulo-ruminal reflexes. The central reflex time is > 370 msec.7. It is concluded that a tonic afferent input from ;in series' reticular tension receptors during the quiescent period of the primary (reticulo-ruminal) cycle provides a reflex drive to the ;gastric centres' and largely determines the rate and amplitude of the reticular and ruminal contractions.8. The enhanced afferent input, during a reticular contraction under isometric recording conditions, modifies the size, form and duration of the later phases in the contraction sequence of the reticulum and rumen. The reflex effects are predominantly excitatory at low and moderate levels of reticular tension and inhibitory at high levels.

Journal Article↗
PubMedDate not supplied

Surface electromyographic amplitude-to-work ratios during isokinetic and isotonic muscle actions.

CONTEXT: Isokinetic and isotonic resistance training exercises are commonly used to increase strength during musculoskeletal rehabilitation programs. Our study was designed to examine the efficacy of isokinetic and isotonic muscle actions using surface electromyographic (EMG) amplitude-to-work ratios (EMG/WK) and to extend previous findings to include a range of isokinetic velocities and isotonic loads. OBJECTIVE: To examine work (WK), surface EMG amplitude, and EMG/WK during concentric-only maximal isokinetic muscle actions at 60, 120, 180, 240, and 300 degrees /s and isotonic muscle actions at 10%, 20%, 30%, 40%, and 50% of the maximal voluntary isometric contraction (MVIC) torque during leg extension exercises. DESIGN: A randomized, counterbalanced, cross-sectional, repeated-measures design. SETTING: A university-based human muscle physiology research laboratory. PATIENTS OR OTHER PARTICIPANTS: Ten women (mean age = 22.0 +/- 2.6 years) and 10 men (mean age = 20.8 +/- 1.7 years) who were apparently healthy and recreationally active. INTERVENTION(S): Using the dominant leg, each participant performed 5 maximal voluntary concentric isokinetic leg extension exercises at randomly ordered angular velocities of 60, 120, 180, 240, and 300 degrees /s and 5 concentric isotonic leg extension exercises at randomly ordered loads of 10%, 20%, 30%, 40%, and 50% of the isometric MVIC. MAIN OUTCOME MEASURE(S): Work was recorded by a Biodex System 3 dynamometer, and surface EMG was recorded from the superficial quadriceps femoris muscles (vastus lateralis, rectus femoris, and vastus medialis) during the testing and was normalized to the MVIC. The EMG/WK ratios were calculated as the quotient of EMG amplitude (muVrms) and WK (J) during the concentric phase of each exercise. RESULTS: Isotonic EMG/WK remained unchanged ( P > .05) from 10% to 50% MVIC, but isokinetic EMG/WK increased ( P < .05) from 60 to 300 degrees /s. Isotonic EMG/WK was greater ( P < .05) than isokinetic EMG/WK for 50% MVIC versus 60 degrees /s, 40% MVIC versus 120 degrees /s, and 30% MVIC versus 180 degrees /s; however, no differences were noted ( P > .05) between 20% MVIC versus 240 degrees /s or 10% MVIC versus 300 degrees /s. An 18% decrease in active range of motion was seen for the isotonic muscle actions, from 10% to 50% MVIC, and a 3% increase in range of motion for the isokinetic muscle actions from 60 to 300 degrees /s was also observed. Furthermore, the peak angular velocities for the isotonic muscle actions ranged from 272.9 to 483.0 degrees /s for 50% and 10% MVIC, respectively. CONCLUSIONS: When considering EMG/WK, peak angular velocity, and range of motion together, our data indicate that maximal isokinetic muscle actions at 240 degrees /s or controlled-velocity isotonic muscle actions at 10%, 20%, or 30% MVIC may maximize the amount of muscle activation per unit of WK done during the early stages of musculoskeletal rehabilitation. These results may be useful to allied health professionals who incorporate open-chain resistance training exercises during the early phases of rehabilitation and researchers who use isotonic or isokinetic modes of resistance exercise to examine muscle function.

Journal Article↗
PubMed1991

Thapsigargin inhibits repletion of phenylephrine-sensitive intracellular Ca++ pool in vascular smooth muscles.

Thapsigargin (TSG), a putative selective Ca(++)-ATPase inhibitor, has been used to study Ca++ mobilization in many non-excitable cell types. This study aims to determine whether TSG is effective as a selective microsomal Ca++ uptake inhibitor by studying its ability to affect repletion of the phenylephrine (PE)-sensitive Ca++ pool in rat aorta and dog mesenteric artery evaluated by contractility studies. TSG caused a concentration-dependent contraction that was dependent on the concentration of extracellular Ca++. Ca++ influx promoted by TSG was found to occur mostly through L-type Ca++ channels in the dog mesenteric artery but not in the rat aorta. When arterial rings, depleted of their PE-sensitive internal store, were allowed to replete their stores in normal Krebs' solution or in the presence of elevated K+ levels, it was found that repletion was significantly enhanced in the presence of elevated K+. In TSG-treated rings, however, repletion was significantly inhibited under both conditions as indicated by the subsequent PE-induced contraction in Ca(++)-free medium. While the rate of contraction induced by elevated K+ levels was slow immediately after pool depletion in controls, it was rapid in TSG-treated arterial rings. The slow onset of K+ contraction may reflect Ca++ uptake into the pool which was absent in TSG-treated arteries. Differences in the behavior of the two arteries were noted and these may reflect differences in the size of their Ca++ store and their coupling to the extracellular space. Single cells isolated from the dog mesenteric artery were also found to shorten in response to TSG to an amount comparable with that obtained from whole tissue experiments.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Differential depression of myocardial contractility by halothane and isoflurane in vitro.

Depressant effects of halothane and isoflurane on isolated right ventricular guinea pig papillary muscle bathed in Tyrode's solution at 37 degrees C were examined. Contractions were elicited by stimulation through external field electrodes while tension was recorded continuously and the intracellular cardiac action potential (AP) was monitored simultaneously by microelectrodes. The time differential of tension (dT/dt) and of membrane potential (V) was determined electronically and recorded also. Contractions after rest and at stimulation rates of 0.1, 0.25, 0.5, 1, 2, and 3 Hz were studied. With normal APs, isoflurane (1.3 and 2.5%) depressed peak tension significantly less at high frequencies than did equivalent doses of halothane (0.75 or 1.5%). Isoflurane depressed dT/dt max less than halothane at all frequencies. At 0.3 Hz stimulation, isoflurane (1-4%) significantly increased the normal AP duration by 7-11%. Slow calcium-dependent APs and accompanying contractions were studied in partially depolarized muscles (-40 to -45 mV resting potential in 26 mM K+ Tyrode's solution) stimulated with 0.1 microM isoproterenol. Following rest and at 0.1, 0.25, 0.5, 1, 2, and 3 Hz, both isoflurane (1.3% or 2.5%) and enflurane (1.7% or 3.5%) markedly depressed the late-peaking slow AP contraction observed with low-frequency stimulation. Halothane (0.75% or 1.5%) caused a similar contractile depression (40-60%) at all frequencies. In contrast, isoflurane depressed early peaking tension and the dT/dt max at frequencies greater than 1 Hz significantly less than did halothane or enflurane. At 0.3 Hz, 2% and 4% isoflurane caused 9% and 17% depression of slow AP maximum rate of depolarization (Vmax), but significantly prolonged the AP duration. Isoflurane altered the pattern of tension development in a different manner than halothane, suggesting differing mechanisms of myocardial depression by these anesthetics.

Action Potentials↗
PubMed1977

The effects of diphenylhydantoin on mechanical and electrical properties of isolated cat myocardium.

The effects of diphenylhydantoin (DPH) (4 X 10(-5) to 2 X 10(-4) M) on contractile activity and electrical properties were studied in isotonically shortening cat papillary muscles exposed to DPH. 1. DPH reduces amplitudes of contraction especially at low stimulation rates (6 to 12/min). At higher, more physiological rates the negative inotropic effect is comparatively small. 2. DPH accentuates the mechanical transients usually following step changes of frequency. 3. DPH reduces the maximum rate of depolarisation (MRD) of the normal action potential (AP) and slows conduction especially at high stimulation rates. AP duration is shortened especially at low stimulation rates. 4. In Ca-mediated "slow responses" DPH reduces MRD, overshoot and AP duration and abolishes the frequency-dependent alterations of these parameters. 5. The results suggest that the antiarrhythmic potency of DPH is due to a cooperative action on both the fast and the slow membrane channels. 6. It is speculated that DPH leads to an accumulation of Ca2+ within a "limited subsarcolemmal space" thereby decreasing the driving force for the slow inward current.

Action Potentials↗