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PubMed1988

Differential mechanism for differentiation into immunoglobulin-secreting cells in human resting B lymphocyte subsets isolated on the basis of cell density.

We have investigated differential mechanism for differentiation of human peripheral blood resting B cells to Ig-secreting cells. Purified resting B cells were further fractionated into subsets by discontinuous density gradients of Percoll, and proliferation and differentiation responses to Staphylococcus aureus Cowan I (SAC) and/or T cell-derived soluble factors were studied. High density resting B cells were stimulated to proliferate vigorously in response to SAC, but were poorly differentiated by SAC in presence of T cell factors. In contrast, low density resting B cells failed to proliferate in response to SAC and/or T cell factors; these cells could, however, be induced by stimulation with SAC plus T cell factors to become cells actively secreting Ig. These results indicate that there may exist heterogeneity in the human resting B cells: one subset of resting B cells (B cells with low density) can differentiate directly into Ig-secreting cells without the need for proliferation, and another subset (B cells with high density) can proliferate actively without subsequent differentiation into Ig-secreting cells. To address whether these resting B cell subsets belong to the same lineage, only high density B cells recovered from circulating resting B cells were first stimulated for 7 d with SAC, refractionated on Percoll gradients, and differentiation response of the refractionated B cells to SAC and T cell factors was examined. B cells shifting toward low density fraction were located in the resting status and could differentiate in response to SAC plus T cell factors. These results indicate that some of B cells with high density belong to the same cell lineage as those with low density and they must first proliferate before differentiation.

Antibody-Producing Cells↗

PubMed1999

Blood glutathione homeostasis as a determinant of resting and exercise-induced oxidative stress in young men.

Although the importance of glutathione in protection against oxidative stress is well recognized, the role of physiological levels of glutathione and other endogenous antioxidants in protecting against exercise-induced oxidative stress is less clear. We evaluated the role of glutathione and selected antioxidant enzymes as determinants of lipid peroxidation at rest and in response to exercise in men (n = 13-14) aged 20-30 years, who cycled for 40 min at 60% of their maximal oxygen consumption (VO2max). Levels of plasma thiobarbituric acid reactive substances (plasma TBARS) and blood oxidised glutathione (GSSG) increased by about 50% in response to exercise. Mean blood reduced glutathione (GSH) decreased by 13% with exercise. Of the measured red blood cell (RBC) antioxidant enzyme activities, only selenium-dependent glutathione peroxidase (Se-GPX) activity rose following exercise. In univariate regression analysis, plasma TBARS levels at rest predicted postexercise plasma TBARS and the exercise-induced change in total glutathione (TGSH). Blood GSSG levels at rest were strongly determinant of postexercise levels. Multiple regression analysis showed blood GSH to be a determinant of plasma TBARS at rest. The relative changes in TGSH were determinant of postexercise plasma TBARS. In summary, higher blood GSH and lower plasma TBARS at rest were associated with lower resting, and exercise-induced, lipid peroxidation. Subjects with a favourable blood glutathione redox status at rest maintained a more favourable redox status in response to exercise-induced oxidative stress. Changes in blood GSH and TGSH in response to exercise were closely associated with both resting and exercise-induced plasma lipid peroxidation. These results underscore the critical role of glutathione homeostasis in modulating exercise-induced oxidative stress and, conversely, the effect of oxidative stress at rest on exercise-induced changes in glutathione redox status.

Adult↗

PubMed2006

Limitation of the resting ankle-brachial index in symptomatic patients with peripheral arterial disease.

Peripheral arterial disease (PAD) has been demonstrated to be prevalent in the primary care setting. However, it has also been shown to be unrecognized and under-treated. Owing to the association with cardiovascular disease it has been recommended to screen high-risk patients for PAD in the primary care setting using the ankle-brachial index (ABI). ABI has been demonstrated to be highly sensitive and specific in diagnosing PAD in patients with significant stenosis. However, the utility in patients with less severe stenosis and calcified vessels is in question. The aims of this study were to determine the diagnostic utility of measuring the ABI at rest in patients referred to the vascular laboratory for evaluation of suspected PAD, and to assess the added value of pulse volume recordings and post-exercise studies in patients with a normal ABI. A computerized vascular diagnostic laboratory database was queried for symptomatic outpatients referred for measurement of segmental blood pressure, the ABI or pulse volume recordings by physicians not specialized in the evaluation and management of patients with peripheral vascular disease. Of 707 patients undergoing outpatient physiologic arterial evaluations between February 1, 2003 and July 31, 2004, 396 met these inclusion criteria. Data recorded included resting ABI, ABI following treadmill exercise test and the presence of abnormal pulse volume recordings. The study population (n = 396) consisted of equal numbers of men and women (mean age 69 years, range 19-100 years). Among 396 studies, resting ABI values were normal in 183 (46.2%) and abnormal in 159 (40.2%). Of the 138 patients who underwent exercise testing, 84 had normal ABI readings at rest. In the 84 patients who had a normal ABI at rest and underwent exercise testing, the ABI fell below 0.9 after exercise in 26 (31%). Arterial non-compressibility was detected in 54 (13.6%) patients, whose average age was 67 years. Thirteen (24%) of those with non-compressible vessels had abnormal pulse volume recording (PVR) results, compared to five with normal resting ABI who had abnormal PVR findings (2.7%). In conclusion, this study demonstrated that nearly half of patients referred to the outpatient vascular laboratory because of suspected arterial disease had a normal resting ABI. While it is recommended that the ABI be measured at rest in patients at risk of PAD in primary care practice, these findings suggest that patients with symptoms of PAD should be more completely evaluated in a vascular laboratory. Furthermore, when the ABI is normal at rest in patients with symptoms of intermittent claudication, exercise testing is recommended to enhance the sensitivity for detection of PAD.

Adult↗

PubMed1997

Prediction of resting cardiovascular functioning in youth with family histories of essential hypertension: a 5-year follow-up.

Two hundred forty-six children (96 Whites, of whom 51 were males; 150 African- Americans, of whom 69 were males) with a familial history of essential hypertension (EH) were re-evaluated 5 years after an initial evaluation. During the initial visit anthropometric, demographic, and resting cardiovascular (CV) parameters (designated initial baseline levels) were assessed. These CV parameters (systolic and diastolic blood pressure [BP], heart rate, cardiac output index [CI], and total peripheral resistance index [TPRI] were also measured during postural challenge, a video game challenge, and a cold pressor task. At follow-up, resting CV parameters were again evaluated, and designated as follow-up resting levels. Moderate temporal stability (r range = .43-.56) was observed for all resting CV parameters. Mean stress responses for each CV parameter for all 3 stressors during the initial visit were positively related to the respective CV follow-up resting level. BP stress responses to postural change and video game challenge to be significant independent predictors of future resting BP after controlling for standard EH risk factors. Follow-up resting CI was not predicted by any stress responses, whereas follow-up resting TPRI was predicted by TPRI responses to the video game after controlling for standard Eh risk factors. These results contrast with those from an earlier 1-year follow-up, where stress responses for neither CI nor TPRI predicted follow-up resting levels. It appears that, as children get older, TPRI stress responses play a stronger role in vasoconstrictive function.

Journal Article↗

PubMed2006

Nuclear retention of multiply spliced HIV-1 RNA in resting CD4+ T cells.

HIV-1 latency in resting CD4+ T cells represents a major barrier to virus eradication in patients on highly active antiretroviral therapy (HAART). We describe here a novel post-transcriptional block in HIV-1 gene expression in resting CD4+ T cells from patients on HAART. This block involves the aberrant localization of multiply spliced (MS) HIV-1 RNAs encoding the critical positive regulators Tat and Rev. Although these RNAs had no previously described export defect, we show that they exhibit strict nuclear localization in resting CD4+ T cells from patients on HAART. Overexpression of the transcriptional activator Tat from non-HIV vectors allowed virus production in these cells. Thus, the nuclear retention of MS HIV-1 RNA interrupts a positive feedback loop and contributes to the non-productive nature of infection of resting CD4+ T cells. To define the mechanism of nuclear retention, proteomic analysis was used to identify proteins that bind MS HIV-1 RNA. Polypyrimidine tract binding protein (PTB) was identified as an HIV-1 RNA-binding protein differentially expressed in resting and activated CD4+ T cells. Overexpression of PTB in resting CD4+ T cells from patients on HAART allowed cytoplasmic accumulation of HIV-1 RNAs. PTB overexpression also induced virus production by resting CD4+ T cells. Virus culture experiments showed that overexpression of PTB in resting CD4+ T cells from patients on HAART allowed release of replication-competent virus, while preserving a resting cellular phenotype. Whether through effects on RNA export or another mechanism, the ability of PTB to reverse latency without inducing cellular activation is a result with therapeutic implications.

Acquired Immunodeficiency Syndrome↗

PubMed1984

Ionic basis of resting membrane potential in frog taste cells.

Intracellular recording of the resting membrane potential was made from taste cells of the bullfrog by replacing the interstitial fluid surrounding the cells by various physiological saline solutions. The resting potential of the taste cell was -28 +/- 4 mV (mean +/- S.E.) after replacement of the interstitial fluid by normal Ringer solution. The resting potential was very much dependent on the interstitial K+ concentration ([K+]). Tenfold increase in [K+]o decreased the resting potential by 18 mV. Total removal of interstitial Na+ increased the resting potential by 40%. Ouabain in a concentration of 0.5 nM decreased the resting potential by 36% possibly due to inhibition of the Na+-K+ exchange pump. Neither total removal nor fourfold increase of interstitial Ca2+ changed the resting potential. Complete elimination of interstitial Cl- did not change the resting potential. The mean permeability ratio PNa/PK was calculated to be 0.41. It is concluded that the resting potential of a frog taste cell consists of ionic and metabolic components, and that the ionic component is due to the permeability of the cell membrane to K+ and Na+.

Animals↗

PubMed1996

Hormonal status, metabolic changes, and resting metabolic rate in beef heifers undergoing compensatory growth.

Twelve recently weaned Hereford crossbred heifers weighing 227 kg (12 kg SD) and aged 230 d (8 d SD) on d 0 were used to investigate physiological responses associated with compensatory growth. Six heifers were allotted to ad libitum intake (ADLIB) and six were restricted to a maintenance diet for 95 d followed by realimentation (REST). Plasma collected from all heifers during feed restriction (d 0, 20, 48) and realimentation (d 104, 125, 153, 195) was analyzed for growth hormone (GH), insulin-like growth factor I (IGF-I), thyroid hormones (thyroxine [T4] and triiodothyronine [T3]), insulin, glucose, nonesterified fatty acids (NEFA), blood urea nitrogen (BUN), and 3-methyl histidine (3-MH). Resting metabolic rate (RMR) was measured 5 d before and 15 and 36 d after the beginning of realimentation. Feed restriction was associated with higher (P < .05) plasma concentrations of GH and NEFA and lower (P < .05) concentrations of IGF-I, T4, T3, insulin, and glucose. The BUN concentration was lower (P = .05) in REST than in ADLIB heifers on d 48, whereas 3-MH was not affected during the first 48 d of feed restriction. The RMR was lower (P < .05) in REST than in ADLIB heifers during feed restriction. During realimentation, the ADG of REST heifers was higher (P = .001) than that of ADLIB heifers. Concentrations of IGF-I, insulin, glucose, and NEFA in REST heifers increased and no differences (P > .05) between treatments were observed on d 104 (d 10 of realimentation) and thereafter. Conversely, GH concentration in REST heifers remained elevated through d 104 but dropped to ADLIB levels by d 125 (d 31 of realimentation). The T4 and T3 concentrations remained lower (P < .05) in REST than in ADLIB heifers after 10 d of realimentation but rose to control levels by d 31 of realimentation. The RMR was lower (P < .05) in REST than in ADLIB heifers 15 d into realimentation; however, no difference was found between treatments by d 36 of realimentation. These results indicate that enhanced growth rates in the early phase of compensatory growth are associated with the physiological response of the GH-IGF-I-insulin axis coupled with reduced maintenance requirement due to slower metabolic rate in restricted-refed heifers.

Animals↗

PubMed2000

[Efficacy of stress-rest myocardial SPET with 99mTc-MIBI in predicting recovery of postrevascularization contractile function. Results of the Spanish multicenter protocol. Working Group of Nuclear Cardiology].

BACKGROUND AND OBJECTIVES: The aim of this study was to evaluate the efficacy of stress-rest 99mTc-MIBI SPET to predict wall motion improvement after revascularization. MATERIAL AND METHODS: A prospective and consecutive series of 82 patients (59 +/- 9 years, 12 women), who had some segment with severe impairment of the contractility and underwent coronary revascularization by surgery (n = 64) or angioplasty (n = 18) were studied with rest 99mTc-MIBI SPET. All patients had a rest 99Tc-MIBI SPET, and an exercise test was also performed on 40 of these patients. Before and within 3-6 months after the revascularization a gated blood pool scintigraphy of three projections was performed. The segmentary contractile recovery after revascularization was assessed in relation to the quantification of the 99mTc-MIBI uptake and to the exercise-rest reversibility (exercise uptake < rest uptake). RESULTS: The mean value of the left ejection fraction did not change after the revascularization (41.1 +/- 14.5% vs 41.8 +/- 15.7%). In the post revascularization control a contractile recovery was observed in 40% (113/282) of the segments with severe hypokinesia, akinesia or dyskinesia. Exercise-rest reversibility and rest uptake > 30% were present in 62% (p = 0.002) and 89% (p < 0.0001) respectively of segments that improved contractility after revascularization. CONCLUSIONS: For the 99mTc-MIBI SPET an exercise-rest reversibility and > 30% uptake at rest are predictive criteria of contractile recovery after revascularization.

Exercise Test↗

PubMed1992

Isometric exercise training lowers resting blood pressure.

Both rhythmic and "resistive" (weight lifting) exercise training can produce modest decreases in resting blood pressure. The next logical point along an exercise continuum consisting of different proportions of rhythmic and isometric efforts is a strictly isometric effort. The purpose of these studies was to assess the effects of isometric, handgrip exercise training on resting blood pressure. To avoid the extreme pressor responses elicited by fatiguing isometric efforts, the isometric exercise training used in this study consisted of brief handgrip contractions separated by rest periods. Modest repeated rises in systolic and diastolic pressures therefore served as the putative stimuli for training adaptations in resting blood pressures. Human subjects in study 1 trained with four, 2-min isometric handgrip contractions with 3-min rests between contractions. The intensity of the contractions was equal to 30% of their maximal effort for each day. The bouts of isometric exercise were performed three times per week for 8 wk. Study 2 training consisted of four contractions of 50% of maximum effort held for a duration of 45 s with 1-min rests. These were performed 5 d.wk-1 for 5 wk. In Study 1, all eight trained subjects had a significant decline in both systolic and diastolic resting blood pressures, with group averages of 12.5 and 14.9 mm Hg, respectively. Seven matched control subjects who did not train had no change in resting pressures. In study 2, subjects were trained in their home or workplace and experienced significant mean declines in resting systolic and diastolic pressures of 9.5 and 8.9 mm Hg.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1989

Cardiovascular regulation in the mudpuppy Necturus maculosus at rest and during short term exercise.

Prebranchial blood pressure (Pva), heart rate (fH) and plasma catecholamine concentration were measured in the mudpuppy Necturus maculosus at rest and during exercise. During exercise, both fH and Pva increased, as did the plasma noradrenaline concentration. There was no significant effect on Pva after injection of the adrenergic neuron blocker, bretylium, in resting animals, neither did bretylium affect the exercise-induced increase in Pva. This suggests that there is no adrenergic nervous tone on the vasculature at rest or during exercise. The alpha-adrenoceptor antagonist yohimbine had no effect on the resting Pva in the bretylium-treated animals, but it abolished the increase in Pva during exercise. This is compatible with the view of no influence on Pva by the plasma catecholamines at rest, while during exercise the increase in plasma noradrenaline concentration is responsible for the increase in Pva. Injection of atropine elevated resting fH, and reduced or abolished cardiac arrythmia, indicating an inhibitory cholinergic tone on the heart at rest, and that variations in this tone are responsible for the intrinsic variation seen in untreated animals. After the atropine treatment, there was still an increase in fH during exercise. The beta-adrenoceptor antagonist sotalol decreased fH in resting atropinized animals, and inhibited the exercise-induced tachycardia, implying that there is an additional beta-adrenoceptor-mediated adrenergic tone, affecting the heart both at rest and during exercise. The cholinergic tone decreased during exercise with a concomitant increase in adrenergic tone. Falck-Hillarp fluorescent histochemistry was used to study the presence of adrenergic nerve fibres and other catecholamine-storing cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1986

Antigen presentation by human dermal fibroblasts: activation of resting T lymphocytes.

We have shown that human dermal fibroblasts, exposed to interferon-gamma (IFN-gamma) to induce surface class II major histocompatibility complex (MHC) antigens, were capable of presenting tetanus toxoid (TT) antigen to human TT-specific T cell clones. Antigen presentation by fibroblasts was antigen dependent, required HLA-DR expression by fibroblasts, and was MHC restricted. In contrast, we now report that IFN-gamma-treated fibroblasts are unable to present TT antigen to purified resting T cells obtained from the peripheral blood of TT-immune donors. In addition, although IFN-gamma-treated fibroblasts were able to stimulate alloreactive T cell clones, they were unable by themselves to stimulate primary allogeneic responses in resting T cells. The failure of fibroblasts to stimulate resting T cells was not due to suppressor effects by fibroblasts, because induction of TT and alloantigen responses in resting T cells by monocytes was not inhibited by the presence of fibroblasts. On the contrary, IFN-treated fibroblasts were synergistic with small numbers of monocytes in activating resting T cells. In addition, the failure of antigen presentation by fibroblasts to resting T cells was reversed by the addition of recombinant human interleukin 2 (rIL 2) to cultures, but not of purified human interleukin 1 (IL 1). These results emphasize that the requirements for activation of resting T cells differ from those of T cell clones. Although fibroblasts can efficiently present antigen to T cell clones, antigen presentation by fibroblasts to resting T cells requires the addition of exogenous IL 2. It is postulated that fibroblasts differ from classical antigen-presenting cells in that fibroblasts are incapable of stimulating the production of IL 2 in resting T cells.

Adult↗

PubMed1997

Action potential duration and contraction after rest at room temperature in guinea pig papillary muscle.

Simultaneous recordings of action potential and isometric tension of right papillary muscles were performed. After regular stimulation at 1 Hz, pauses of 10 min were allowed. In the first beat after rest, we measured action potential duration at the 90% of the repolarization (APD90), maximal twitch tension (T), time to peak of contraction (TTP), and rate of development of tension (+dT/dt) and relaxation (-dT/dt). Values were normalized against pre-rest ones. No significative changes were observed after rest at 35 degrees C. After rest at 25 degrees C APD90 and TTP were prolonged but T was reduced. Post-rest +dT/dt were slower, dT/dt did not show significative changes. Nifedipine 10 microM prevented post-rest APD90 lengthening, and produced a further reduction of mechanical response. Substitution of external Na+ by Li+ shortened APD90, increased T of either regular or post-rest beats and led to calcium overload signs. When pause were allowed during Na+ substitution, calcium overload signs were attenuated. We conclude that the combination of rest and room temperature diminished [Ca++]i mainly by Na+/Ca++ mechanism. The reduction of [Ca++]i in turn could delay the inactivation of iCa. As a consequence, longer APs were obtained, accompanied by weaker and slower mechanical responses. Changes in TTP and + dT/dt could suggest that post-rest contractions in room temperature, are dependent of extracellular Ca++ rather than a deplected RS.

Action Potentials↗

PubMed1998

Problems with post-clipping aneurysmal rests.

The postclipping aneurysmal rest is a uncommon but sometimes dangerous event, that is generally underestimated. We distinguish the aneurysmal rest on the basis of its morphology in: 1) partial neck, 2) whole neck, 3) partial neck + partial sac, 4) whole neck + partial sac; on the basis of the relationship with the clip in: 1) proximal, 2) distal, 3) proximal + distal; on the basis of its size in: 1) small (< 2 mm), 2) medium (2-4 mm), 3) large (> 4 mm). From the surgical point of view the aneurysmal rests in our opinion can be classified as unavoidable, avoidable and intentional. Then we analyze the literature data in regard to the possible evolution and the risk of the rest and emphasize the importance of intraoperative angiography which has shown itself to be useful in avoiding aneurysmal rests. There is no consensus of opinion with regard to the type of treatment of the aneurysmal rest. In our opinion the factors which must be considered when deciding on the surgical treatment of a rest are: the age of the patient, mode of presentation of the previous aneurysm, the expertise of the surgeon and the approaches and the techniques used in the first operation, clinical presentation of the rest and its evolution, the surgeon's experience and the possibility of endovascular therapy. Finally we analyze some of the technical aspects of re-operation in relation to the anatomical relationship among the parent artery, the rest and the old clip.

Humans↗

PubMed2006

Rest during pregnancy for preventing pre-eclampsia and its complications in women with normal blood pressure.

BACKGROUND: Women at risk of pre-eclampsia or gestational hypertension are sometimes advised to rest. Whether this, overall, does more good than harm is unclear. OBJECTIVES: To assess the effects of rest or advice to reduce physical activity during pregnancy for preventing pre-eclampsia and its complications in women with normal blood pressure. SEARCH STRATEGY: We searched the Cochrane Pregnancy and Childbirth Group Trials Register (December 2005), the Cochrane Central Register of Controlled Trials (The Cochrane Library, Issue 3, 2005), and EMBASE (2002 to August 2005). SELECTION CRITERIA: Studies were included if they were randomised trials evaluating the effects of rest or advise to reduce physical activity for preventing pre-eclampsia and its complications in women with normal blood pressure. DATA COLLECTION AND ANALYSIS: Two review authors independently selected trials for inclusion and extracted data. Data were double checked for accuracy. MAIN RESULTS: Two small trials (106 women) of uncertain quality were included. Both recruited women with a singleton pregnancy at moderate risk of pre-eclampsia from 28 to 32 weeks' gestation. There was a statistically significant reduction in the relative risk of pre-eclampsia with four to six hours rest per day (one trial, 32 women; relative risk (RR) 0.05, 95% confidence interval (CI) 0.00 to 0.83), but not of gestational hypertension (RR 0.25, 95% CI 0.03 to 2.00), compared to normal activity. Rest of 30 minutes per day plus nutritional supplementation was associated with a reduction in the risk of pre-eclampsia (one trial, 74 women; RR 0.13, 95% CI 0.03 to 0.51) and also of gestational hypertension (RR 0.15, 95% CI 0.04 to 0.63). The effect on caesarean section was unclear (RR 0.82, 95% CI 0.48 to 1.41). No other outcomes were reported. AUTHORS' CONCLUSIONS: Daily rest, with or without nutrient supplementation, may reduce the risk of pre-eclampsia for women with normal blood pressure, although the reported effect may reflect bias and/or random error rather than a true effect. There is no information about outcomes such as perinatal mortality and morbidity, maternal morbidity, women's views, adverse effects, and costs. Current evidence is insufficient to support recommending rest or reduced activity to women for preventing pre-eclampsia and its complications. Whether women rest during pregnancy should therefore be a matter of personal choice.

Bed Rest↗

PubMed1998

Prognostic value of predischarge radionuclide ventriculography at rest and exercise after acute myocardial infarction treated with thrombolytic therapy or primary coronary angioplasty. The Zwolle Myocardial Infarction Study Group.

BACKGROUND: Previous studies have demonstrated the prognostic value of radionuclide ventriculography at rest and exercise in patients post myocardial infarction (MI). The number of studies in patients treated with modern reperfusion techniques, including thrombolysis or primary angioplasty, however, is limited. HYPOTHESIS: The aim of this study was to evaluate the prognostic significance of predischarge radionuclide ventriculography at rest and exercise in patients with acute MI treated with thrombolysis or primary angioplasty. METHODS: A total of 272 consecutive patients with acute MI who were randomized to thrombolysis or primary coronary angioplasty underwent predischarge resting and exercise radionuclide ventriculography. Left ventricular ejection fraction at rest, decrease in ejection fraction during exercise > 5 units below the resting value, angina pectoris, ST-segment depression, and exercise test ineligibility were related to subsequent cardiac events (cardiac death, nonfatal reinfarction) during follow-up. RESULTS: During a mean follow-up of 30 +/- 10 months, cardiac death occurred in 11 (4%) patients and nonfatal reinfarction in 14 (5%) patients. Resting left ventricular ejection fraction was the major risk factor for cardiac death. In patients with an ejection fraction < 40%, cardiac death occurred in 16% compared with 2% in those with an ejection fraction > or = 40% (p = 0.0004). In addition, cardiac death tended to be higher in patients ineligible than in those eligible for exercise testing (11 vs. 3%, p = 0.08). None of the other exercise variables (decrease in ejection fraction during exercise > 5 units below the resting value, angina pectoris or ST-segment depression) were predictive for cardiac death. When all exercise test variables in each patient were combined and expressed as a risk score, a low risk (n = 185) and a higher risk (n = 87) group of patients could be identified, with cardiac death occurring in 1 and 10%, respectively. As the predictive accuracy of a negative test was high, radionuclide ventriculography was of particular value in identifying patients at low risk for cardiac death. Radionuclide ventriculography was not able to predict recurrent nonfatal MI. CONCLUSION: In patients with MI treated with thrombolysis or primary angioplasty, radionuclide ventriculography may be helpful in identifying patients at low risk for subsequent cardiac death. In this respect, left ventricular ejection fraction at rest was the major determinant. Variables reflecting residual myocardial ischemia were of limited prognostic value. Identification of a large number of patients at low risk allows selective use of medical resources during follow-up in this subgroup and has significant implications for the cost effectiveness of reperfusion therapies.

Aged↗

PubMed1986

Diagnosis of exercise-induced left bundle branch block at rest by scintigraphic phase analysis.

Accurate diagnosis of diseases of the ventricular conducting system is essential for their appropriate therapy. Some conduction abnormalities, such as exercise-induced left bundle branch block (EX-LBBB), are not apparent on resting electrocardiograms. Phase analysis of rest and exercise radionuclide ventriculograms (RVG's) was used to compare four EX-LBBB patients with six normal controls. All patients had normal resting electrocardiograms, ejection fractions, and visually normal wall motion. First harmonic phase images were generated reflecting the timing of ventricular contraction. Dynamic phase displays were reviewed and graded in a blinded fashion by three independent experienced observers. Phase angle histograms of the right and left ventricle were determined for both resting and exercise images. The mean phase angle and standard deviation were also calculated for each ventricle. Visual grading of the resting phase images failed to show a significant difference between normal patients and patients with EX-LBBB. Quantitative analysis, however, revealed a significant difference in mean phase angle differences (LV-RV) in resting studies: 0.8 degrees (+/- 1.9 degrees SEM) in normals versus 9.3 degrees (+/- 2.3 degrees SEM) in EX-LBBB patients (P less than 0.03). Exercise accentuated the phase angle differences: 1.8 degrees in normals vs. 31.2 degrees in EX-LBBB patients (P less than 0.001). Quantitative phase analysis of resting RVG's permits the diagnosis of cardiac conduction disease that is not apparent on the resting EKG and may result in better monitoring and treatment.

Bundle-Branch Block↗

PubMed1992

Effect of haemodynamic pressure overload of the adult ferret right ventricle on inotropic responsiveness to external calcium and rest periods.

The inotropic effects of external calcium concentration ([Ca2+]o] and rest periods have been compared in papillary muscles isolated from control (n = 4) and pressure-overloaded right (n = 5) ventricles of adult ferrets. Hypertrophy was induced by pulmonary artery clipping for 30-45 days. Under control conditions (3 mM [Ca2+]o, 0.1 Hz), the isometric twitch force of hypertrophied muscles was decreased by 75%, time to peak was increased by 30% and time to half-relaxation was increased by 50% compared with non-hypertrophied preparations. The sensitivity of contraction to [Ca2+]o was decreased in hypertrophied muscles compared with control ([Ca2+] required for half-maximal contraction: 4.1 mM vs 1.7 mM) and the maximal contraction reached at high [Ca2+]o was smaller in pressure-overloaded muscles compared with control (8.3 +/- 2.0 mN mm-2 vs 19.0 +/- 2.1 mN mm-2 respectively). In both groups, rest periods longer than the steady-state interval were initially accompanied by a potentiation of the first post-rest contraction compared with steady-state. Peak potentiation occurred after a rest of 120 s in hypertrophied muscles and after a rest of 60 s in control. The maximal relative potentiation, i.e. compared with the steady-state twitch, was higher in hypertrophied muscles (+75%) than in control (+20%). After peak potentiation, the amplitude of the first post-rest contraction progressively decreased with increasing periods of rest, although at a slower rate in hypertrophy compared with control. The time constants of post-rest decay were 1203 +/- 99 s and 528 +/- 24 s respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1997

Rest length and compliance of non-immobilised and immobilised rabbit soleus muscle and tendon.

The first aim of this study was to measure the contributions of muscle and tendon to the total compliance of resting muscle-tendon units. A second aim was to determine whether the decrease in muscle-tendon unit rest length produced by prolonged immobilisation in a shortened position is mediated primarily by adaptations of the muscle or tendon. One ankle joint from each of five rabbits was immobilised in a plantarflexed position for 14 days. The passive length-tension properties of soleus muscle fascicles and tendons from both hindlimbs were measured using a video-based tensile-testing system. In non-immobilised muscles, muscle fascicle strains exceeded tendon strains by up to four times. However, because the rest length of tendon was much greater than that of muscle fascicles, changes in tendon length accounted for nearly half of the total change in muscle-tendon unit length. The rest length of immobilised muscle-tendon units was less than that of non-immobilised muscle-tendon units from contralateral limbs. Most of this difference was attributable to a change in the rest length of the tendon; there was little change in the rest length of muscle fascicles. It is concluded that the tendon is responsible for a large part of the compliance of rabbit soleus muscle-tendon units at physiological resting tensions, and that adaptation of tendon rest length is the primary mechanism by which the rabbit soleus shortens in response to immobilisation at short lengths.

Animals↗