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PubMed1995

Resting load regulates cytosolic calcium-force relationship of the contraction of bovine cerebrovascular smooth muscle.

1. We determined the effects of a change in preload, or resting load, on the development of force and on cytosolic calcium concentration ([Ca2+]i) during the contraction induced by high K+ depolarization and by the stable analogue of thromboxane A2, U-46619, using front-surface fluorometry and medial strips of bovine middle cerebral artery loaded with fura-2. 2. Increase in resting load of strips from 0.495 mN (low load; 0.85L(max)) to 1.98 mN (optimal load; L(max)) elevated resting levels of [Ca2+]i slightly, and, significantly, after a delay of a few seconds. The force developed by high K+ depolarization at resting load of 1.98 mN was much greater than that at a resting load of 0.495 mN (191.8% of that at 0.495 mN); however, there was no difference in [Ca2+]i elevation induced by high K+ depolarization between resting loads of 0.495 and 1.98 mN. 3. Both in the presence and absence of extracellular Ca2+, the force developed by U-46619 (0.1 microM) at resting load of 1.98 mN was also much greater than that at a resting load of 0.495 mN. Both in the presence and absence of extracellular Ca2+, there was no difference in the [Ca2+]i transients induced by U-46619 between two different resting loads. 4. The [Ca2+]i-force relationship during the contraction induced by high K+ depolarization was shifted to the left when the resting load was increased from 0.495 to 1.98 mN. At 0.495 mN resting load, this Ca(2+)-force relationship was shifted to the left by U-46619. This left-side shift of the curve by U-46619 was further enhanced by the increase in resting load from 0.495 to 1.98 mN. 5. The augmentation of force development induced by the change in resting load (from 0.495 to 1.98 mN) was not affected by a relatively specific inhibitor of protein kinase C, 1-(5-isoquinolinesulphonyl)-2-methylpiperazine dihydro-chloride (H-7; 10 microM). 6. We conclude that (1) at a given degree of [Ca2+]i elevation, the developed force induced by U-46619 was greater than that induced by high K+ depolarization, and (2) preload, or resting load (below optimal load), regulates contractile responsiveness of cerebrovascular smooth muscle to various stimulations, mainly by modulating the [Ca2+]i-force relationship, without affecting the extent of [Ca2+]i elevation. The results suggest the possibility that Ca(2+)-insensitive pathways may be involved in the stretch-dependent regulation of Ca2+ sensitivity of the contractile apparatus in smooth muscle.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed2005

Human thermoregulatory function during exercise and immersion after 35 days of horizontal bed-rest and recovery.

The present study evaluated the effect of 35 days of experimental horizontal bed-rest on exercise and immersion thermoregulatory function. Fifteen healthy male volunteers were assigned to either a Control (n = 5) or Bed-rest (n = 10) group. Thermoregulatory function was evaluated during a 30-min bout of submaximal exercise on a cycle ergometer, followed immediately by a 100-min immersion in 28 degrees C water. For the Bed-rest group, exercise and immersion thermoregulatory responses observed post-bed-rest were compared with those after a 5 week supervised active recovery period. In both trials, the absolute work load during the exercise portion of the test was identical. During the exercise and immersion, we recorded skin temperature, rectal temperature, the difference in temperature between the forearm and third digit of the right hand (DeltaT(forearm-fingertip))--an index of skin blood flow, sweating rate from the forehead, oxygen uptake and heart rate at minute intervals. Subjects provided ratings of temperature perception and thermal comfort at 5-min intervals. Exercise thermoregulatory responses after bed-rest and recovery were similar. Subjective ratings of temperature perception and thermal comfort during immersion indicated that subjects perceived similar combinations of Tsk and Tre to be warmer and thermally less uncomfortable after bed-rest. The average (SD) exercise-induced increase in Tre relative to resting values was not significantly different between the Post-bed-rest (0.4 (0.2) degrees C) and Recovery (0.5 (0.2) degrees C) trials. During the post-exercise immersion, the decrease in Tre, relative to resting values, was significantly (P < 0.05) greater in the Post-bed-rest trial (0.9 (0.5) degrees C) than after recovery (0.4 (0.3) degrees C). DeltaT(forearm-fingertip) was 5.2 (0.9) degrees C and 5.8 (1.0) degrees C at the end of the post-bed-rest and recovery immersions, respectively. The gain of the shivering response (increase in VO(2) relative to the decrease in Tre; VO(2)/Tre) was 1.19 l min(-1) degrees C(-1) in the Recovery trial, and was significantly attenuated to 0.51 l min(-1) degrees C(-1) in the Post-bed-rest trial. The greater cooling rate observed in the post-bed-rest trial is attributed to the greater heat loss and reduced heat production. The former is the result of attenuated cold-induced vasoconstriction and enhanced sweating rate, and the latter a result of a lower shivering VO(2) response.

Bed Rest↗
PubMedDate not supplied

The "virtual focus group": using the Internet to reach pregnant women on home bed rest.

OBJECTIVE: The purpose of this qualitative study was threefold: to investigate the effectiveness of a 'virtual focus group" as a mechanism for collecting qualitative data, to explore the lived experience of pregnant women confined to home bed rest following a diagnosis of preterm labor, and to assess the value of the virtual focus group as an online peer support group for women on home bed rest. DESIGN: A qualitative, exploratory, descriptive investigation, carried out through the use of a virtual focus group, defined as an Internet-based research method that utilizes electronic mail (e-mail) to unite spatially and temporally separate participants in a text-based group discussion. SETTING: Data collection was conducted via the Internet and consisted of a series of sequential questions presented by the researchers to the participants via e-mail over a 4-week period. PARTICIPANTS: A purposive sample of 7 women who were on home bed rest for the treatment of preterm labor. Four participants were recruited from a World Wide Web site dedicated to discussions of high-risk pregnancy, and 3 from the perinatal service center of a large health maintenance organization in Northern California. RESULTS: The virtual focus group process generated rich and detailed qualitative data. Three major categories and seven subcategories regarding the lived experience of home bed rest were identified: the effect of bed rest on participants' lives (transitioning onto bed rest, loss of control and activities, changes in identity and role, coping and personal growth, transitioning off bed rest), the effect of bed rest on relationships with others (relationships with the fetus and other children, relationships with husbands and extended family members), and the virtual focus group as an online peer support group. Participants were unanimous in their appreciation of the virtual focus group. All participants stated that their participation was valuable and beneficial in helping them to cope with the hardships of bed rest. CONCLUSION: The findings suggest that the virtual focus group is a useful tool for both collecting qualitative data and mediating the challenges and isolation of home bed rest. Confinement to bed rest at home dramatically alters women's daily activities, self-perceptions, and interpersonal relationships. Understanding the impact of bed rest on women's lives can help nurses to develop appropriate interventions for this unique population. The use of the virtual focus group allows nurses to embrace the technology of the Internet to study and connect women on home bed rest, as well as other isolated and understudied patient groups.

Adaptation, Psychological↗
PubMed2003

Bed rest attenuates sympathetic and pressor responses to isometric exercise in antigravity leg muscles in humans.

Although spaceflight and bed rest are known to cause muscular atrophy in the antigravity muscles of the legs, the changes in sympathetic and cardiovascular responses to exercises using the atrophied muscles remain unknown. We hypothesized that bed rest would augment sympathetic responses to isometric exercise using antigravity leg muscles in humans. Ten healthy male volunteers were subjected to 14-day 6 degrees head-down bed rest. Before and after bed rest, they performed isometric exercises using leg (plantar flexion) and forearm (handgrip) muscles, followed by 2-min postexercise muscle ischemia (PEMI) that continues to stimulate the muscle metaboreflex. These exercises were sustained to fatigue. We measured muscle sympathetic nerve activity (MSNA) in the contralateral resting leg by microneurography. In both pre- and post-bed-rest exercise tests, exercise intensities were set at 30 and 70% of the maximum voluntary force measured before bed rest. Bed rest attenuated the increase in MSNA in response to fatiguing plantar flexion by approximately 70% at both exercise intensities (both P < 0.05 vs. before bed rest) and reduced the maximal voluntary force of plantar flexion by 15%. In contrast, bed rest did not alter the increase in MSNA response to fatiguing handgrip and had no effects on the maximal voluntary force of handgrip. Although PEMI sustained MSNA activation before bed rest in all trials, bed rest entirely eliminated the PEMI-induced increase in MSNA in leg exercises but partially attenuated it in forearm exercises. These results do not support our hypothesis but indicate that bed rest causes a reduction in isometric exercise-induced sympathetic activation in (probably atrophied) antigravity leg muscles.

Adult↗
PubMed1990

[Left high R wave amplitude and blood pressure levels before and after 5 minutes' rest in a mass screening program].

In order to evaluate the implication of blood pressures measured without 5 minutes' rest in mass screening programs, blood pressures were measured before and after 5 minutes' rest on 820 subjects in a rural community, aged 35 to 65 years and not receiving hypertensive treatment. Although the systolic blood pressure showed a significant drop of an average of 3 mmHg among males and 4 mmHg among females after rest, 23.3% of 820 subjects had higher systolic blood pressure reading after rest than before. The relationship between left high R (LHR) in electrocardiograms and blood pressure (BP) before and after rest was studied. The presence of LHR was significantly related to BP both before and after rest among males, but more strongly associated to BP before rest. The relationship of the difference between BP before and after rest to the prevalence of LHR was analyzed by multiple logistic method. A significantly higher prevalence of LHR with greater difference between systolic BP before and after rest was observed among males, even with age and systolic BP level after rest taken into account. These findings suggest the potential significance of blood pressure readings before 5 minutes' rest which may be a response to mental stress of having the initial blood pressure reading taken by the observer. It would seem worthy to obtain blood pressure before rest as well as after rest in detecting blood pressure abnormalities.

Adult↗
PubMed1984

Excitation-contraction coupling in rested-state contractions of guinea-pig ventricular myocardium.

Different types of rested-state contractions were examined under the influence of various inotropic agents. In magnesium-free solution, in low sodium (40 mmol/l) solution or in the presence of dihydroouabain, an "early" rested-state contraction developed without delay after stimulation. A distinctive "late" rested-state contraction was observed under the influence of noradrenaline. It is characterized by a latent period of about 100 ms between stimulation and onset of contraction. This latency was not reduced by increasing the catecholamine concentration, despite a concentration-dependent increase in the height of the "late" rested-state contraction. The late rested-state contraction under the influence of noradrenaline was suppressed by the slow inward current inhibitor nifedipine whether or not the nifedipine-dependent shortening of the action potential duration was prevented by caesium. When the slow inward current was not inhibited, the prolongation of the action potential duration by caesium resulted in an increase of the late rested-state contraction because of a prolongation of the time to peak force. High concentrations of dihydroouabain led to the appearance of an early contraction component without appreciably influencing the noradrenaline-dependent late component. From this it was deduced that the activator calcium for the late rested-state contraction was not stored intracellularly during rest prior to stimulation and, consequently, could not have been released by inflowing calcium. Instead, it is proposed that the activator calcium for the late rested-state contraction entered the sites of the sarcoplasmic reticulum and subsequently released from its release sites as long as the cell was depolarized. The "early" rested-state contractions in Mg2+-free solution, in low sodium solution or in the presence of dihydroouabain were not influenced in their contraction velocity by high concentrations of nifedipine which fully inhibited the late rested-state contractions. Nifedipine caused only a slight reduction in peak force due to a shortening of the time to peak force as a result of a shortening in action potential duration. This indicates that the activator calcium for the "early" rested-state contractions had accumulated in the sarcoplasmic reticulum during rest prior to stimulation and that it was released immediately by depolarization without a participation of the slow inward current.

Action Potentials↗
PubMed1991

Altered pattern of post-rest contractions in hypertrophied rabbit ventricle.

The pattern of contractions elicited after rest periods of 0.25-10 min duration was investigated in right ventricular papillary muscles from control and hypertrophied rabbit hearts. Hypertrophy was induced by pressure overload following coarctation of the pulmonary artery. In control hearts, the first post-rest contraction was always of a smaller amplitude than the preceding steady-state (0.5 Hz stimulation) contractions, and the amplitude of this first post-rest contraction decreased as the rest interval increased. In contrast, the amplitude of the first post-rest contraction of muscles from hypertrophied hearts exceeded the steady-state amplitude for rest durations of up to at least 2 min. In the hypertrophied muscles, force in the first post-rest contraction (expressed as a percentage of the pre-rest steady-state) was potentiated compared to the control muscles at all rest intervals studied. There was no significant difference in the second post-rest contraction between control and hypertrophied muscles at any rest interval. Following the second post-rest contraction, force increased monotonically toward the steady-state levels in all the muscles. The recovery of force was, however, somewhat faster in the hypertrophied muscles. Upon resumption of 1-Hz stimulation following rest intervals of 2 min or greater, pulsus alternans were invariably observed in the hypertrophied muscles but never in the control muscles. These differences in the non-steady-state contractile behavior of ventricular muscle from normal and hypertrophied hearts are suggestive of some alteration in the normal pattern of Ca2+ translocation in pressure overload hypertrophy of rabbit ventricle.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2005

Short rest periods after static lumbar flexion are a risk factor for cumulative low back disorder.

The objective of this work was to study the effect of rest periods of various durations applied between six 10-min sessions of static flexion on the development of cumulative low back disorder (CLBD). Three experimental groups of a feline model were used, and the rest duration between sequential static load periods was set to 5, 10, and 20 min, with a corresponding load-to-rest ratio of 2:1, 1:1 and 1:2, respectively. The reflex electromyographic (EMG) activity from the multifidus muscles and supraspinous ligament displacement (creep) were recorded during the flexion periods and over 7 h of rest following the load-rest cycles. It was found that a minor disorder developed in all the groups whereas a severe neuromuscular disorder including a delayed hyperexcitability was observed only in the group subjected to 5 min rest. The two-way ANOVA showed a significant effect of time post loading (p<0.001) and rest duration (p<0.001) on the Normalized Integrated EMG (NIEMG) recovery data; a significant effect of time post loading on the Displacement data (p<0.001) was observed as well. The post hoc Fisher test performed on the NIEMG data during the recovery phase showed a significant difference between the group subjected to 5 min rest and the other two groups (p<0.001). These results suggest that while a short rest period of 2:1 load-to-rest ratio leads to CLBD, longer rest at 1:1 and 1:2 load-to-rest ratio are more favorable for preventing or attenuating the development of CLBD. Short rest periods between sessions of static lumbar flexion, therefore, are a risk factor for the development of CLBD.

Animals↗
PubMed2003

Fatigue resistance of cast occlusal rests using Co-Cr and Ag-Pd-Cu-Au alloys.

STATEMENT OF PROBLEM: Fatigue failure in a removable partial denture framework includes fracture of the occlusal rest at the rest-minor connector angle. PURPOSE: This in vitro study evaluated the fatigue resistance of 0.8-mm-thick occlusal rests cast with Co-Cr and Ag-Pd-Cu-Au alloys. MATERIAL AND METHODS: The specimen consisted of occlusal rest (0.8 x 2.0 x 10 mm), vertical minor connector (0.9 x 2.0 x 5.0 mm), and denture base connector (1.5 x 5.0 x 25 mm). Twenty-five specimens each were cast with Co-Cr and Ag-Pd-Cu-Au alloys. From each group, 5 specimens were subjected to a load-deflection test conducted to determine the amount of deflection to be used in fatigue test. The fatigue test was performed such that the occlusal rest component was deflected by displacing the denture base component in a tissueward direction. Predetermined denture base displacement values of 0.25 and 0.49 mm for Co-Cr and Ag-Pd-Cu-Au specimens, respectively, were repeated at a rate of 500 cycles/min by use of a displacement-controlled fatigue testing machine, until occlusal rest failure occurred or a preset limit of 2 million cycles was achieved. The survival rates of the occlusal rests were calculated assuming a chewing cycle of 2 x 10(5) per year. Scanning electron microscopy (SEM) photographs were made to examine the fracture surfaces and to identify casting defects. The relationship between fatigue cycles and number of casting defects was determined by Spearman rank correlation analysis (P<.01). RESULTS: All 20 Co-Cr specimens outran the preset limit, whereas 18 Ag-Pd-Cu-Au specimens fractured. After 3 years of simulated clinical use, only 50% of the Ag-Pd-Cu-Au occlusal rests survived. Statistical analysis showed that the fatigue cycles and number of casting defects were inversely related (P<.01). Fatigue crack initiation occurred at the inner-curvature surface of the rest-minor connector angle. The typical Ag-Pd-Cu Au fatigue fracture surface consisted of smooth propagation and dimpled and smooth final fracture areas. CONCLUSIONS: This study suggests that cast Co-Cr rests are more rigid and fatigue resistant than Ag-Pd-Cu-Au rests. The fatigue resistance of 0.8-mm-thick occlusal rests may be adequate if cast with Co-Cr alloy. An increased number of casting defects may hasten the fatigue failure of occlusal rests.

Chromium Alloys↗
PubMed1991

Nephrogenic rests in Wilms tumor patients with the Drash syndrome.

The histological specimens from 12 patients with the Drash syndrome were identified from the National Wilms Tumor Study Group and reviewed for the presence of nephrogenic rests. Of 7 patients with the complete Drash syndrome 6 were evaluable for nephrogenic rests, including 5 (83%) who demonstrated intralobar nephrogenic rests. Of 5 (80%) partial Drash syndrome cases 4 (80%) were also intralobar nephrogenic rest positive. Neither group had perilobar nephrogenic rests identified. In a control population of Wilms tumor patients without the Drash syndrome only 39 of 274 (14%) with unilateral tumor had intralobar nephrogenic rests identified, whereas 26 of 92 (28%) bilateral cases had intralobar nephrogenic rests. There was a significantly higher rate of intralobar nephrogenic rests in complete and partial Drash syndrome cases than in the general Wilms tumor population (p less than 0.001). Wilms tumor patients with intralobar nephrogenic rests and the Drash syndrome present at a younger age and have a higher rate of bilaterality than rest negative Wilms tumor patients. The strong association of intralobar nephrogenic rests in the Drash syndrome approaches that found in the aniridia complex. However, in other syndromes associated with Wilms tumor, such as the Beckwith-Wiedemann syndrome and hemihypertrophy, there is a high prevalence of perilobar nephrogenic rests. In view of the high incidence of intralobar nephrogenic rests in complete and partial Drash syndrome patients, it is probable that events leading to Wilms tumor in patients with the Drash syndrome occur at an early stage in nephrogenesis.

Disorders of Sex Development↗
PubMed2000

Significance of resting wall motion abnormalities in 2-dimensional echocardiography in patients without previous myocardial infarction referred for pharmacologic stress testing.

BACKGROUND: Resting wall motion abnormalities (WMA) in 2-dimensional echocardiography may be encountered in patients without previous myocardial infarction or known coronary artery disease (CAD) who are referred for stress testing. However, the functional significance of these abnormalities has not been evaluated by an independent technique. The goals of this study were to assess the value of resting WMA in the prediction of an ischemic response during dobutamine stress testing independent of other clinical characteristics in patients without known CAD, and to evaluate whether the presence of resting WMA is related to the presence or extent of myocardial perfusion abnormalities during dobutamine stress testing. METHODS: We studied 116 patients (mean age 57 +/- 13 years, 50 men) without known CAD or a history of myocardial infarction by dobutamine-atropine (dobutamine: </=40 microg/kg/min; atropine: </=1 mg) stress echocardiography and simultaneous stress and rest technetium sestamibi single-photon emission computed tomography imaging. Ischemia was defined as new or worsening wall motion abnormalities and reversible perfusion defects, respectively. RESULTS: Resting WMA were detected in 24 patients (21%). Patients with resting WMA had a higher prevalence of abnormal perfusion (75% vs 25%, P <.001) and a higher prevalence of ischemia by single-photon emission computed tomography (50% vs 24%, P <.05) and by echocardiography (42% vs 9%, P <.001) compared with patients without resting WMA, respectively. Stress and rest perfusion defect scores were significantly higher in patients with than in those without rest WMA (3.25 +/- 2.67 vs 0.88 +/- 1.77, P <.0001; and 1.46 +/- 1.69 vs 0.21 +/- 0.70, P <.0001; respectively). Independent predictors of the occurrence of ischemia by echocardiography were the presence of resting WMA (P <.01, chi(2) = 6.7), ST-segment depression (P <.005, chi(2) = 11.3), and angina during the test (P <. 05, chi(2) = 5.3) by using multivariate analysis of clinical and stress test variables. The presence of resting WMA was the only independent predictor of an abnormal perfusion (P <.0001, chi(2) = 20). CONCLUSION: The presence of resting WMA in patients without known CAD or a previous myocardial infarction who were referred for pharmacologic stress testing is highly predictive of abnormal myocardial perfusion. Resting WMA are powerful independent predictors of an ischemic response during dobutamine stress testing and identify a population with a higher prevalence and extent of myocardial perfusion abnormalities.

Atropine↗
PubMed2001

Biological activity of RE-1 silencing transcription factor (REST) towards distinct transcriptional activators.

The zinc finger protein RE-1 silencing transcription factor (REST) is a transcriptional repressor that represses neuronal genes in non-neuronal tissues. We have analyzed the ability of REST and the REST mutants, RESTDeltaN and RESTDeltaC lacking either the N-terminal or C-terminal repression domains of REST, to inhibit transcription mediated by distinct transcriptional activator proteins. For this purpose we have designed an activator specific assay where transcription is activated as a result of only one distinct activation domain. In addition, binding sites for REST were inserted in the 5'-untranslated region or at a distant position downstream of the polyadenylation signal. The results show that REST or the REST mutants containing only one repression domain were able to block transcriptional activation mediated by the transcriptional activation domains derived from p53, AP2, Egr-1, and GAL4. Moreover, REST, as well as the REST mutants, blocked the activity of the phosphorylation-dependent activation domain of Elk1. However, the activity of the activation domain derived from cAMP response element binding protein 2 (CREB2), was not inhibited by REST, RESTDeltaN or RESTDeltaC, suggesting that REST is able to distinguish between distinct transcriptional activation domains. Additionally, the activator specific assay, together with a positive-dominant mutant of REST that activated instead of repressed transcription, was used in titration experiments to show that REST has transcriptional repression and no transcriptional activation properties when bound to the 5'-untranslated region of a gene.

Activating Transcription Factor 4↗
PubMed1998

Biological activity and modular structure of RE-1-silencing transcription factor (REST), a repressor of neuronal genes.

The zinc finger protein RE-1-silencing transcription factor (REST)1 is a transcriptional repressor that represses neuronal genes in nonneuronal tissues. Transfection experiments of neuroblastoma cells using a REST expression vector revealed that synapsin I promoter activity is controlled by REST. The biological activity of REST was further investigated using a battery of model promoters containing strong promoters/enhancers and REST binding sites. REST functioned as a transcriptional repressor when REST binding motifs derived from the genes encoding synapsin I, SCG10, alpha1-glycine receptor, the beta2-subunit of the neuronal nicotinic acetylcholine receptor, and the m4-subunit of the muscarinic acetylcholine receptor were present in the promoter region. No differences in the biological activity of these REST binding motifs tested were detected. Moreover, we found that REST functioned very effectively as a transcriptional repressor at a distance. Thus, REST represents a general transcriptional repressor that blocks transcription regardless of the location or orientation of its binding site relative to the enhancer and promoter. This biological activity could also be attributed to isolated domains of REST. Both repressor domains identified at the N and C termini of REST were transferable to a heterologous DNA binding domain and functioned from proximal and distal positions, similar to the REST protein.

Animals↗
PubMed1988

Spontaneous sarcoplasmic reticulum calcium release in rat and rabbit cardiac muscle: relation to transient and rested-state twitch tension.

Scattered light intensity fluctuations (SLIF) (which monitor spontaneous Ca2+ release from the sarcoplasmic reticulum [SR]) and resting and twitch tension were measured during intervals after stimulation in rat and rabbit papillary muscles. For 1 to 5 seconds after stimulation of rat muscle bathed in 1.5 mM [Ca2+] (Cao), twitch and resting tension are depressed and SLIF are transiently abolished. SLIF and resting tension then recover simultaneously and monotonically but lag behind the restitution of twitch tension. In the absence of further stimulation, SLIF persist and the rested state twitch amplitude remains potentiated. When Cao is increased above 2.5 mM, the restitution of all parameters following stimulation is accelerated and becomes oscillatory; the lag of SLIF and resting tension restitution behind that of the twitch increases such that twitch amplitude increases, overshoots, and decreases to a nadir as SLIF and resting tension reach their initial maximum. In a given muscle, the maximum twitch amplitude occurs at approximately the same level of SLIF; when this level is exceeded, either transiently during monotonic or oscillatory recovery after stimulation in a given Cao or in the steady rested state by an increase in Cao, twitch tension decreases. Ryanodine (1 microM), caffeine (10 mM), or replacement of Cao with strontium abolishes SLIF and causes twitch amplitude to decay with rest. In contrast to rat, twitch amplitude in rabbit muscle bathed in physiological Cao decays with rest and SLIF are nonmeasurable at any interval following stimulation. When Cao is increased to 20 mM during rest, SLIF occur and the rest decay of the twitch is abolished. We interpret the parallel behavior of SLIF and rest potentiation to indicate that in the presence of SLIF, the average SR Ca2+ load within the tissue is high. Depolarization of a tissue exhibiting SLIF causes a large twitch but also a transient depletion of the average SR Ca2+ load. That the restitution of SLIF lags behind recovery of twitch amplitude suggests that the onset of spontaneous SR Ca2+ release requires a delay following SR Ca2+ replenishment. The simultaneous occurrence of spontaneous Ca2+ release in a sufficient number of cells places an upper limit on twitch amplitude either during recovery following stimulation or at rest.

Action Potentials↗
PubMedDate not supplied

A preliminary study on the effect of occlusal vertical dimension increase on mandibular postural rest position.

The effect of increasing the occlusal vertical dimension on the mandibular postural relation was studied for eight subjects. Interocclusal rest space measurements were made weekly for 1 month prior and subsequent to increasing the occlusal vertical dimension by 3.5 to 4.5 mm interincisally using luted acrylic resin, complete-arch, fixed partial dentures. Interocclusal rest space measurements were made at the clinical rest position, which was established by requesting the subjects to close in maximum intercuspation and immediately relax their mandible. Interocclusal rest space measurements were also made at the more open resting position when the subjects were repeatedly instructed to relax and lapse into a semi-hypnotic condition termed "relaxed resting posture." Initial speech difficulties and muscle discomfort subsided after 1 to 2 weeks. Analysis of variance using repeated measures showed no significant difference in interocclusal rest space after increasing the occlusal vertical dimension for both clinical rest position and relaxed resting posture. A significant difference was found between clinical rest position and relaxed resting posture (P = .001), and no interaction was determined between clinical rest position, relaxed resting posture, and time.

Adaptation, Physiological↗
PubMed2004

Bed rest in singleton pregnancies for preventing preterm birth.

BACKGROUND: Bed rest in hospital or at home is widely recommended for the prevention of preterm birth. This advice is based on the observation that hard work and hard physical activity during pregnancy could be associated with preterm birth and with the idea that bed rest could reduce uterine activity. However, bed rest may have some adverse effects on other outcomes. OBJECTIVES: To evaluate the effect of prescription of bed rest in hospital or at home for preventing preterm birth in pregnant women at high risk of preterm birth. SEARCH STRATEGY: We searched the Cochrane Pregnancy and Childbirth Group trials register (July 2003), the Cochrane Central Register of Controlled Trials (The Cochrane Library, Issue 2, 2003), MEDLINE (July 2003), LILACS (July 2003), EMBASE (July 2003), POPLINE (July 2003) and bibliographies of relevant papers. SELECTION CRITERIA: Randomized and quasi-randomized controlled trials with reported data that assess clinical outcomes in women at high risk of spontaneous preterm birth who were prescribed bed rest in hospital or at home for preventing preterm birth, and their babies. DATA COLLECTION AND ANALYSIS: Two reviewers independently assessed eligibility, trial quality and extracted data. MAIN RESULTS: One study met the inclusion criteria (1266 women). This trial has uncertain methodological quality due to lack of reporting. Four hundred and thirty-two women were prescribed bed rest at home and a total of 834 women received a placebo (412) or no intervention (422). Preterm birth before 37 weeks was similar in both groups (7.9% in the intervention group versus 8.5% in the control group), and the relative risk was 0.92 with a 95% confidence interval from 0.62 to 1.37. No other results were available. REVIEWER'S CONCLUSIONS: There is no evidence, either supporting or refuting the use of bed rest at home or in hospital, to prevent preterm birth. Although bed rest in hospital or at home is widely used as the first step of treatment, there is no evidence that this practice could be beneficial. Due to the potential adverse effects that bed rest could have on women and their families, and the increased costs for the healthcare system, clinicians should not routinely advise women to rest in bed to prevent preterm birth. Potential benefits and harms should be discussed with women facing an increased risk of preterm birth. Appropriate research is mandatory. Future trials should evaluate both the effectiveness of bed rest, and the effectiveness of the prescription of bed rest, to prevent preterm birth.

Bed Rest↗
PubMed1993

Changes in markers of bone formation and resorption in a bed rest model of weightlessness.

To study the mechanism of bone loss in physical unloading, we examined indices of bone formation and bone resorption in the serum and urine of eight healthy men during a 7 day -6 degrees head-down tilt bed rest. Prompt increases in markers of resorption--pyridinoline (PD), deoxypyridinoline (DPD), and hydroxyproline (Hyp)/g creatinine--during the first few days of inactivity were paralleled by tartrate-resistant acid phosphatase (TRAP) with significant increases in all these markers by day 4 of bed rest. An index of formation, skeletal alkaline phosphatase (SALP), did not change during bed rest and showed a moderate 15% increase 1 week after reambulation. In contrast to SALP, serum osteocalcin (OC) began increasing the day preceding the increase in Hyp, remained elevated for the duration of the bed rest, and returned to pre-bed rest values within 5 days of reambulation. Similarly, DPD increased significantly at the onset of bed rest, remained elevated for the duration of bed rest, and returned to pre-bed rest levels upon reambulation. On the other hand, the other three indices of resorption, Hyp, PD, and TRAP, remained elevated for 2 weeks after reambulation. The most sensitive indices of the levels of physical activity proved to be the noncollagenous protein, OC, and the collagen crosslinker, DPD. The bed rest values of both these markers were significantly elevated compared to both the pre-bed rest values and the post-bed rest values. The sequence of changes in the circulating markers of bone metabolism indicated that increases in serum OC are the earliest responses of bone to head-down tilt bed rest.

Acid Phosphatase↗
PubMed2006

Work to rest durations ratios exceeding unity are a risk factor for low back disorder; a feline model.

Low back disorders are prominent among the work force engaged in static anterior flexion during the workday. As a continuing part of a long-term research aimed to identify the biomechanical and physiological processes and corresponding risk factors leading to such cumulative trauma disorder (CTD), we ventured to assess the effect of rest and the work-to-rest duration ratios that may prevent CTD. Three groups of the feline model were subjected to three load/rest paradigms: two 30 min loading periods spaced by 10 min rest in Group I, two 30 min loading period spaced by 30 min rest in Group II and one 60 min loading period for Group III. The cumulative loading duration in the three groups was 60 min. Each of the groups were allowed 7h of rest while monitoring EMG and lumbar viscoelastic tissue creep each hour. The results demonstrate that for two 30 min load periods with a 30 min in between rest, an acute neuromuscular disorder was not present whereas for two 30 min loading with a 10 min rest it was. Similarly, for a 60 min loading with long-term rest, the disorder was present. Post hoc Fisher analysis demonstrated significant differences in the delayed hyperexcitability between the first and second group (P<0.0001) and the third and second (P<0.0001) group. Statistical difference in the displacement data of the three groups was not present. ANOVA showed a significant effect of time post-loading (P<0.0001 and different rest durations (P<0.0001) on the EMG data during the 7h recovery. The new data allow us to conclude that a work-to-rest duration ratio of 1:1 can prevent the development of CTD as long as the work periods are not too long (<60 min). Longer static flexion durations do not respond favorably to rest even if it is of equal or longer duration. It is suggested that appropriate durations of rest may be a viable tool to avert CTD in a certain range whereas long static flexion durations should be avoided at all cost.

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