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PubMed2005

Baroreflex impairment during rapid posture changes at rest and exercise after 120 days of bed rest.

Orthostatic intolerance is common after space flight and head-down tilt (HDT) bed rest. We hypothesized that HDT-induced impairments of arterial blood pressure (AP) control would be more marked during exercise and that recovery of baroreflex function after very long-term HDT would be delayed. Six subjects were studied before (BDC) during (day 60, D60; D113) and after (recovery day 0, R0; R3; R15) 120 days of HDT. Supine resting subjects were exposed to repeated 1 min passive tilts to upright at 3-min interval. During 50 W steady-state exercise corresponding tilt had a 2-min duration at 4-min interval. The amplitudes of the tilt-induced transient beat-by-beat deviations in AP and rate (HR) were determined during the gravity transients. At rest these deviations did not change over time, but during exercise the total peak-to-nadir range of deviations in systolic AP (SAP) at up-tilt and down-tilt increased to 168+/-16% (mean+/-SEM) of BDC at D113 with no clear recovery upto and including R15. Counter-regulatory HR responses were not increased proportionally and especially not tachycardic responses to up-tilt, resulting in a reduction of baroreflex sensitivity (deltaRR-interval/deltaSAP) by 55+/-9% of BDC at D113 with no recovery upto and including R15. We conclude that prolonged bed rest cause long-lasting impairments in AP control and baroreflex function in exercising humans.

Adaptation, Physiological↗
PubMedDate not supplied

Effects of ouabain and low-Na+ perfusion on rest-decay and post-rest recovery of cellular Ca content in ventricular muscle of guinea-pig heart.

Ca2+ shifts in isolated, perfused ventricular muscle of guinea-pig hearts were investigated with the aid of 45Ca under the conditions of complete equilibration of preparations with isotope-containing containing solutions. The content of 45Ca in stimulated preparations (rate 60/min) was 1.30 +/- 0.12 mmol/kg of wet weight (w.w.). 6 min rest resulted in the drop of this content to 0.37 +/- 0.05 mmol/kg w.w. despite continued perfusion with 45Ca containing solution. The difference of 0.93 mmol/kg w.w. is equivalent to fraction Ca2 (15) and is labelled accordingly. Ouabain (1 microM) increased the 45Ca content to 1.53 +/- 0.15 mmol/kg w.w. in the stimulated and to 1.12 +/- 0.23 mmol/kg w.w. in the rested muscle. The respective values after low (50 mM) sodium perfusion were 1.70 +/- 0.11 and 1.07 +/- 0.13 mmol/kg w.w. The differences between the stimulated and rested preparations (Ca2 fraction) were 0.41 and 0.63 mmol/kg, respectively. In the control experiments the force of the first post-rest beat dropped to 20 +/- 5% of the force of steady-state beats. During ouabain and low-sodium perfusion, the force of the first contraction increased markedly and its peak was larger than that of the few subsequent beats. It is concluded that Na-Ca exchange is the important factor in the rate-dependent control of Ca2 fraction content and of contractile force.

Animals↗
PubMedDate not supplied

Left ventricular dysfunction in coronary artery disease: comparison between rest-redistribution thallium 201 and resting technetium 99m methoxyisobutyl isonitrile cardiac imaging.

BACKGROUND: We compared rest-redistribution thallium 201 and resting technetium 99m methoxyisobutyl isonitrile (MIBI) cardiac imaging in 29 men with angiographically proven coronary artery disease and regional ventricular dysfunction. Left ventricular ejection fraction at radionuclide angiography was 35% +/- 9%. METHODS AND RESULTS: Regional left ventricular wall motion was assessed on gated 99mTc MIBI images according to a 3-point scale (0 = normal, 1 = hypokinetic, 2 = akinetic or dyskinetic). 201Tl and 99mTc MIBI uptake values were analyzed quantitatively. A total of 435 myocardial segments were classified on the basis of wall motion analysis into three groups: group 1 (normal wall motion; n = 201), group 2 (hypokinetic; n = 132), and group 3 (akinetic or dyskinetic; n = 102). 201Tl and 99mTc MIBI uptake values were significantly higher in groups 1 and 2 compared with group 3 (p < 0.05) and in group 1 compared with group 2 (p < 0.05). When 201Tl and 99mTc MIBI uptake values were directly compared, no significant differences in group 1 and 2 were observed. In group 3, 99mTc MIBI uptake (67% +/- 14%) was significantly lower (p < 0.001) than initial (72% +/- 11%) and delayed 201Tl uptake (73% +/- 12%). CONCLUSION: Thus rest-redistribution 201Tl and resting 99mTc MIBI cardiac imaging reflect the severity of left ventricular dysfunction in coronary artery disease. However, in segments with severely impaired regional ventricular function, 201Tl uptake is significantly higher than 99mTc MIBI uptake.

Adult↗
PubMed1989

Controlled trial of hydration and bed rest versus bed rest alone in the evaluation of preterm uterine contractions.

Patients who are seen with uterine contractions but without documented change in cervical dilation or effacement are often treated with intravenous hydration before the initiation of intravenous tocolytic therapy. This is done with the intention of stopping uterine activity in patients with false preterm labor. A prospective randomized study was conducted to evaluate the effect of hydration on preterm uterine contractions in patients without proved preterm labor. A total of 28 patients were treated with bed rest and an intravenous bolus and subsequent continuous infusion of 5% dextrose in lactated Ringer's solution. A control group of 20 patients were treated with bed rest alone. Uterine activity and arrest of uterine contractions were compared between the two groups. Contractions stopped in 54% of the patients treated with hydration, whereas contractions stopped in 40% of the patients in the control group. This difference was not statistically significant. As a crossover study, those in the control group with contractions that continued after the initial observation period were subsequently treated with intravenous fluids. Only one patient in this group stopped contracting. Of all patients whose contractions with either therapy, 18% eventually were delivered of preterm infants. This included 20% of the hydration group and 14% of the control group. The use of hydration as a pretherapy indicator to differentiate true preterm labor from false preterm labor could not be supported by this study. In addition, patients whose contractions stopped with either hydration or bed rest are at increased risk of subsequent preterm delivery.

Bed Rest↗
PubMed1992

A randomized prospective comparison of nifedipine and bed rest versus bed rest alone in the management of preeclampsia remote from term.

OBJECTIVE: The objective of our study was to test the hypothesis that treatment with nifedipine for mild preeclampsia remote from term reduces the number of days of maternal hospitalization and improves pregnancy outcome. STUDY DESIGN: A total of 200 patients at 26 to 36 weeks' gestation were randomly allocated to treatment with either bed rest alone (n = 100) or bed rest in combination with nifedipine (n = 100). RESULTS: Patients receiving nifedipine had significantly lower systolic (p < 0.0001) and diastolic (p < 0.0001) blood pressures during therapy. Severe hypertension as an indication for delivery was significantly (p < 0.05) more frequent in the bed-rest-alone group. The two study groups had similar average days of maternal hospitalization (12.6 +/- 7.9 vs 12.3 +/- 10.3) and pregnancy prolongation (22.3 +/- 13.5 vs 22.5 +/- 15.7). There were no differences between groups with respect to birth weight, incidences of small-for-gestational-age infants and preterm birth, number of days spent in special care unit, or cord blood gas measurement. CONCLUSION: Nifedipine therapy for preeclampsia reduces maternal blood pressure but does not reduce number of days of maternal hospitalization or improve perinatal outcome.

Bed Rest↗
PubMed1998

Tc-99m tetrofosmin myocardial SPECT perfusion imaging: comparison of rest-stress and stress-rest protocols.

AIM: The purpose of this study was to evaluate the diagnostic value of Tc-99m tetrofosmin SPECT myocardial perfusion scintigraphy rest/stress and stress/rest protocols for the assessment of coronary artery disease (CAD). METHODS: 65 patients underwent both rest and stress SPECT imaging in a one-day protocol and coronary angiography within 2 months before or after scintigraphy. Scintigraphic data was obtained according to two different protocols; 1) rest-stress (n = 18) and 2) stress-rest (n = 47). RESULTS: Scintigraphic evidence for myocardial ischaemia was found in 36 patients (55%). The overall sensitivity to detect CAD (> 50% luminal stenosis) was 94% (34/36), specificity 66% (19/24), positive predictive value 77%, negative predictive value 90%. The sensitivity to detect CAD for protocols 1 and 2 were 100% and 93%, specificity 56% and 70%, positive predictive value 69% and 81% and negative predictive value 100% and 88%, respectively. The left anterior descending coronary artery showed a sensitivity (overall, protocol 1 & 2) of 78%, 75% (3/4) and 79% (15/19) and a specificity of 71%, 64% (9/14) and 75% (21/28). The right coronary artery showed a sensitivity (overall, protocol 1 & 2) of 91%, 100% (6/6) and 88% (14/16) and a specificity of 70%, 92% (11/12) and 61% (19/31). The left circumflex coronary artery showed a sensitivity (overall, protocol 1 & 2) of 50%, 67% (2/3) and 46% (6/13) and a specificity of 94%, 100% (15/15) and 91% (31/34). CONCLUSION: Tc-99m tetrofosmin appears to be a valuable tool in predicting significant CAD. The sensitivity and the positive predictive value are high, making this test highly appropriate for the diagnosis of CAD. The diagnostic value of the individual coronary arteries is high to moderate. No significant differences were found between both protocols.

Adult↗
PubMed1991

Arterial and venous measurement in resting forearm of metabolic indicators during rest and leg exercise.

We compared the levels of various metabolic indicators in arterial and venous forearm blood during maximal treadmill leg exercise, and the subsequent 9 min in nine volunteers aged 31-56 years. At maximal exercise plasma lactate was 13.2 +/- 3.1 mmol l-1 arterially, while venous was 41% lower, but increased more than arterial after exercise. There was a linear relationship between arterial and venous samples during and after exercise, but not at baseline. Plasma pyruvate increased on the arterial side from 49 +/- 8 to 172 +/- 30 mumol l-1 at maximal exercise, maximal venous was 21% lower. Free fatty acids were not different at rest, but decreased during exercise by 52 and 38% on the arterial and venous side. There was no relationship between arterial and venous levels. Changes in these three variables occurred significantly earlier on the arterial side. Arterial cyclic AMP rose from 97.3 +/- 28.4 to 262.7 +/- 67.5 nmol l-1 from rest to exercise, and was linearly inversely related to the decrease in free fatty acids. The mean venous pH was lower than arterial at rest, but was the same as arterial at maximal exercise and after. Thus, venous plasma lactate and pyruvate, but not free fatty acids, are linearly related to arterial measurements during maximal exercise, while pH is identical. Non-working muscle modifies exercise-induced changes, and therefore venous and arterial forearm blood sampling give more information than either alone.

Adult↗
PubMed1985

A comparative study of the effects of tetrodotoxin and the removal of external Na+ on the resting potential: evidence of separate pathways for the resting and excitable Na currents in squid axon.

To investigate whether the Na permeability of the resting membrane is determined predominantly by the excitable Na channel, we examined the effects of tetrodotoxin (TTX) and the complete removal of external Na+ on the resting potential. In the intact squid axon bathed in K-free artificial seawater, both TTX and the removal of Na+ produced small hyperpolarizations. The effect of Na removal, however, was larger than that of TTX. In the perfused squid axon, the hyperpolarization produced by the removal of external Na+ was greatly enhanced when the internal K concentration ([K+]i) was reduced. The effect of TTX, on the other hand, was not sensitive to the [K+]i or to the membrane potential. For [K+]i = 50 mM and [K+]o = 0, the average hyperpolarization produced by TTX was 1.2 mV, while the hyperpolarization produced by Na removal was approximately 21 mV. The difference between these two effects suggests that the majority of the resting Na current passes through pathways other than the excitable Na channel.

Animals↗
PubMed1984

Thallium-201 myocardial scintigraphy and left ventricular function at rest in patients with rest angina pectoris.

The purpose of this study was to examine the rest thallium-201 perfusion pattern during angina-free periods in 40 patients with rest angina pectoris secondary to coronary artery disease (greater than or equal to 70% diameter narrowing). Seventeen patients had previous Q wave myocardial infarction. The perfusion defects were considered fixed or reversible, depending on the absence or presence of redistribution in the 4-hour delayed images. There were 40 perfusion defects (26 fixed and 14 reversible) in 27 patients whereas 13 patients had normal scans. Reversible perfusion defects were present in 10 patients (25%). Of the 26 fixed perfusion defects, 17 did not have corresponding Q waves. Occluded vessels (63%) had more perfusion defects than vessels with subtotal occlusion (30%) (p less than 0.01). The perfusion defect size was larger in patients with lower ejection fraction than in patients with higher ejection fraction. We conclude: (1) perfusion defects are common in patients with rest angina and are reversible in 25% of patients indicating reduced regional coronary blood flow; (2) the degree of stenosis affects the presence of perfusion defect; (3) fixed defects may be present without corresponding Q waves; and (4) global left ventricular function is related to the size of perfusion defects.

Adult↗
PubMed1988

Studies in REST. I. Reduced Environmental Stimulation Therapy (REST) and reduced alcohol consumption.

Reduced Environmental Stimulation Therapy (REST), formerly known as "sensory deprivation," was used in conjunction with pre-recorded anti-alcohol messages to reduce alcohol consumption. Subjects were college students of both sexes who were "heavy social drinkers," that is, early prodromal alcoholics. There were two studies. In the pilot study experimental subjects had two and a half hours of REST, during which they heard one of two differently worded anti-alcohol messages. After two weeks their alcohol intake dropped significantly from baseline levels (33% and 29%); control subjects showed no significant changes. In a replication and follow-up study experimental subjects had two and a half hours of REST, during which they heard a revised version of the most effective anti-alcohol message used in the pilot study. Two weeks later their alcohol consumption dropped 55% from baseline levels. These reductions in alcohol intake were fully sustained on follow-up three months and six months later. Untreated control subjects showed increased alcohol intake on follow-up.

Adult↗
PubMed2005

Many human medulloblastoma tumors overexpress repressor element-1 silencing transcription (REST)/neuron-restrictive silencer factor, which can be functionally countered by REST-VP16.

Medulloblastoma, one of the most malignant pediatric brain tumors, is believed to arise from the undifferentiated external granule-layer cells in the cerebellum. It is a heterogeneous cancer, and the mechanism of tumorigenesis for the majority of types is unknown. Repressor element-1 silencing transcription/neuron-restrictive silencer factor (REST/NRSF) is a transcriptional repressor that can block transcription of a battery of neuronal differentiation genes by binding to a specific consensus DNA sequence present in their regulatory region. Previously, we found that some medulloblastoma cell lines express REST/NRSF at high levels compared with either neuronal progenitor cells or fully differentiated neurons. However, it is not known if REST/NRSF is indeed overexpressed in human medulloblastoma tumor specimens and in what frequency. Here, we did an immunohistochemical analysis of such tumor specimens using an anti-REST antibody. We show that among 21 human medulloblastoma tumors, 17 expressed REST/NRSF (6 strongly and 11 weakly). In contrast, adjacent normal cerebellum tissue sections and four of the tumor specimens did not express REST/NRSF, indicating that abnormal expression of REST/NRSF is observed in the majority of human medulloblastoma tumors. To determine whether countering REST/NRSF activity blocks tumorigenicity of medulloblastoma cells, especially in the intracranial (i.c.) environment, we found that adenovirus-mediated expression of REST-VP16, a recombinant transcription factor that can compete with REST/NRSF and activate REST/NRSF target genes instead of repressing them, blocked the i.c. tumorigenic potential of medulloblastoma cells and inhibited growth of established tumors in nude mice, suggesting that REST/NRSF may serve as a therapeutic target for medulloblastoma and that forced expression of neuronal differentiation genes in medulloblastoma cells through agents, such as REST-VP16, can interfere with their tumorigenicity.

Adenoviridae↗
PubMed2004

Clinical status of carbon-monoxide-poisoned patients and the results of rest 99mTc-MIBI and 99mTc-Amiscan heart scintigraphy performed in the acute phase of intoxication and stress-rest 99mTc-MIBI scintigraphy six month later.

The double tracer (99mTc-MIBI and 99mTc-Amiscan) scintigraphy is an useful technique to imagine cardiac injury due to CO intoxication. Accumulation (retention) of 99mTc-MIBI is dependent on blood flow and cellular and mitochondrial electrical potential of myocytes. The lower tracer accumulation is seen not only in necrotic heart tissue regions, but also in ischemic area of worse metabolic rate and perfusion. 99mTc-Amiscan contrary to 99mTc-MIBI, is accumulated only in regions of early necrosis so it can be can distinguished from transitory ischemia. Mechanisms of cardiac injury due to CO toxicity is different than due to coronary occlusion and the process of the heart damage is usually much longer. Results of control stress-rest 99mTcMIBI scintigraphy, performed after 6 months from CO exposure in relation to the clinical state on admission and results of 99mTc-MIBI and 99mTc-Amiscans scans obtained in acute phase of poisoning are presented in the study. Initial 99mTc-MIBI SPET examination had confirmed transitory myocardial ischemia of different degree in all the examined patients. The mutual dependence between degree of scintigraphic changes and blood lactate level and CK activity was found. 99mTc-Amiscan scintigraphy demonstrated areas of necrosis in myocardium of some patients; they had statistically higher COHb and blood lactate concentration compared to the rest. A control stress-rest 99mTc-MIBI SPET performed 6 months after CO intoxication, confirmed a late consequences of metabolic abnormalities and a necessity of cardiovascular system follow-up controlling.

Acute Disease↗
PubMedDate not supplied

[The mandibular rest position: relation to the rest vertical dimension].

The concept of the mandibular rest position and the clinical significance of the mandibular resting posture with respect to dental treatment are discussed. The controversy regarding the belief that mandibular resting posture is constant and inviolate is considered on the basis of clinical observations and scientific investigations.

Dental Occlusion↗
PubMed1997

Rest-redistribution thallium-201 and rest technetium-99m-sestamibi SPECT in patients with stable coronary artery disease and ventricular dysfunction.

UNLABELLED: Resting sestamibi uptake was compared with 201Tl rest-redistribution uptake in 48 patients with ischemic heart disease and regional ventricular asynergies. METHODS: In 48 patients, rest/4-hr redistribution 201Tl and resting sestamibi tomography were closely performed on separate days. Segmental tracer uptake was quantified. Wall motion in corresponding segments was also assessed by two-dimensional echocardiography in 17 patients. RESULTS: Quantitative analysis indicates that the uptake of the two tracers was comparable in normal segments as well as in segments with fixed 201Tl defects. In contrast, in segments with reversible 201Tl defects, sestamibi uptake was significantly lower than redistribution 201Tl uptake. CONCLUSION: In patients with chronic ischemic heart disease and regional asynergies, quantified sestamibi activity parallels 201Tl redistribution activity in normal segments and in those with fixed 201Tl defects. In segments showing reversible 201Tl defects, whether or not dysfunctioning, sestamibi uptake is significantly lower than 201Tl redistribution.

Aged↗
PubMed1978

Effect of inhibitors of slow calcium current on rested state contraction of papillary muscles and post rest contractions of atrial muscle of the cat and rabbit hearts.

Effect of Ni, Co and Mn ions and of D-600 on rested state contractions (RSCs) of cat and rabbit papillary muscles and on post rest contractions (PRCs) of cat and rabbit atrial muscle was investigated. Ni and Co in concentration 2 mmol/l reduced the force of RSCs in papillary muscles by 78%, increased the dip between the phase 1 and 2 of respective action potentials (APs), lowered the level of plateau and decreased the total duration of AP. Strong PRCs in atrial muscle were reduced by Ni only by 25%, while the subsequent beats were strongly inhibited. Ni completely inhibited RSCs in papillary muscles increased by caffeine (10 mmol/1) or by reduction in Na concentration by 50%. Mn ions in concentration 1--2 mmol/l inhibited strongly both RSCs in papillary muscles and strong PRCs in atrial muscle, increased the dip between phase 1 and 2 and increased total duration of AP. Mn ions stimulated 45Ca efflux from papillary muscles and atrial strips. D-600 did not affect RSCs nor the shape of respective APs. It is concluded that RSCs in papillary muscles are directly activated by Ca inflow during the respective excitation while strong PRCs in atrial muscle are activated mostly by Ca released from intracellular stores.

Action Potentials↗
PubMed1996

Exercise thermoregulation after 6 h of chair rest, 6 degrees head-down bed-rest, and water immersion deconditioning in men.

The purpose was to investigate the mechanism for the excessive exercise hyperthermia following deconditioning (reduction of physical fitness). Rectal (Tre) and mean skin (Tsk) temperatures and thermoregulatory responses were measured in six men [mean (SD) age, 32 (6) years; mass, 78.26 (5.80) kg; surface area, 1.95 (0.11) m2; maximum oxygen uptake (VO2max), 48 (6) ml.min-1.kg-1; whilst supine in air at dry bulb temperature 23.2 (0.6) degree C, relative humidity 31.1 (11.1)% and air speed 5.6 (0.1) m.min-1] during 70 min of leg cycle exercise [51 (4)% VO2max] in ambulatory control (AC), or following 6 h of chair rest (CR), 6 degree head-down bed rest (BR), and 20 degree (WI20) and 80 degree (WI80) foot-down water immersion [water temperature, 35.0 (0.1) degree C]. Compared with the AC exercise delta Tre [mean (SD) 0.77 (0.13) degree C (*P < 0.05), after WI80 0.96 (0.13) degree C*, and after WI20 1.03 (0.09) degree C*. All Tsk responded similarly to exercise: they decreased (NS) by 0.5-0.7 degree C in minutes 4-8 and equilibrated at +0.1 to +0.5 degree C at 60-70. Skin heat conductance was not different among the five conditions (range = 147-159 kJ.m-2.h-1.degree C-1). Results from an intercorrelation matrix suggested that total body sweat rate was more closely related to Tre at 70 min (Tre70) than limb sweat rate or blood flow. Only 36% of the variability in Tre70 could be accounted for by total sweating, and less than 10% from total body dehydration. It would appear that multiple factors are involved which may include change in sensitivity of thermo- and osmoreceptors.

Adult↗
PubMed1987

The resting spine. A conceptual approach to the avoidance of spinal reinjury during rest.

During periods of rest, the human spine assumes many different postures. This article examines the patterns of stress exerted on the lumbar spine by the more commonplace reclining postures. It proposes a rationale for choosing an optimal resting posture. In the event that the spine is injured, this study suggests that a sleeping posture that will minimize the stress at the level of injury should be adopted.

Back Pain↗
PubMed1973

Problems of determination of rest allowances Part 2: determining rest allowances in different human tasks.

Within a task analysis related to strain on the individual, human tasks can be ordered into five steps differentiated by the various strains on human organs using different capabilities. For these five categories, examples of rest allowances based on laboratory as well as field study research using physiologically oriented methods are given. Different types of breaks are discussed and suitable measures for optimizing rest allowances are mentioned.

Journal Article↗