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Query: UMLS:C0015672 (fatigue)
 51,768 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The functional origin of atrioventricular nodal hysteresis was studied in isolated rabbit heart preparations. This hysteresis is characterized by asymmetric changes in nodal conduction time (NCT) occurring for symmetric changes in cycle length. The respective contribution of the nodal properties of recovery, facilitation, and fatigue to the beat-to-beat changes in NCT observed during paired symmetric ramps of decreasing and increasing cycle length was determined with specifically design stimulation protocols. Nodal hysteresis was found to be entirely accounted for by variations in the contribution of nodal recovery and fatigue properties observed at corresponding cycle lengths. The study establishes how this contribution varies on a beat-to-beat basis as a result of cycle length history. This holds true for the numerous changes in hysteresis observed in response to changes in the sequence and slope of the ramps. Facilitation clearly affected NCT during these responses but did not contribute to the hysteresis. Moreover, the study demonstrates that there is no inherent change in the characteristics of nodal function with the direction of the ramp that could account for the hysteresis. Thus nodal hysteresis arises from nodal functional properties of recovery and fatigue but does not constitute a distinct independent intrinsic property of the node.
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PMID:Mechanisms of conduction time hysteresis in rabbit atrioventricular node. 748 56

It is important for women to understand the risk of first onset and symptomatic exacerbation of paroxysmal supraventricular tachycardia (SVT) during pregnancy. Reports regarding the effects of pregnancy on first onset and symptomatic exacerbation of paroxysmal SVT have been controversial, and have not been conducted in a systematic fashion. Two hundred seven consecutive female patients diagnosed with symptomatic paroxysmal SVT were requested to respond to multiple questionnaires before electrophysiologic study and catheter ablation. A person-years data method was used to estimate risk of first onset of paroxysmal SVT during pregnancy. Exacerbation of paroxysmal SVT was assessed by a score scale including each of the following symptoms: palpitation, fatigue, rest dyspnea, effort dyspnea, dizziness, chest oppression, blurred vision, and syncope (total score change > 2 points). In the 107 patients with accessory pathway-mediated tachycardia, 7 patients had had a first onset of tachycardia during pregnancy (relative risk ratio 0.86, confidence interval 0.4 to 1.9, p = 0.35). In the 100 patients with atrioventricular nodal reentrant tachycardia, 1 patient had had the first onset of tachycardia during pregnancy (relative risk ratio 0.11, confidence interval 0.02 to 0.56, p = 0.004). Otherwise, 14 of the 63 patients (22%) with tachycardia in the pregnant and nonpregnant periods had exacerbation of symptoms during pregnancy. Thus, first onset of paroxysmal SVT during pregnancy was rare (3.9%), and pregnancy was associated with a low risk of first onset of paroxysmal SVT. However, symptoms of paroxysmal SVT were exacerbated during pregnancy in some patients.
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PMID:Effects of pregnancy on first onset and symptoms of paroxysmal supraventricular tachycardia. 757 23

The functional origin of the changes in atrioventricular (AV) nodal function with the atrial pacing site was studied in isolated rabbit heart preparations. The rate-dependent AV nodal properties of recovery, facilitation, and fatigue were characterized with premature stimulation protocols repeated for each of three atrial pacing sites (upper atrium, low crista terminalis, and low interatrial septum). The effects of the atrial pacing site, reference site from which the beginning of nodal activation is measured (low crista and low septum) and stimulation protocol on nodal conduction and refractory parameters, were assessed with multifactorial analyses of variance. The changes in nodal parameters with the stimulation protocol did not differ significantly with the pacing site, indicating that the rate-dependent nodal properties are not affected by the atrial origin of the impulse. Only the baseline value of nodal parameters varied with the atrial pacing and reference site. However, the comparison of data obtained while the low crista was the pacing and reference site to those obtained while the low septum was the pacing and reference site yield no statistically significant differences, thus indicating that changes in perinodal activation were largely responsible for the observed changes in baseline. Upper atrial and low crista pacing yielded very similar data. We conclude that 1) the atrial pacing site affects perinodal activation but not rate-dependent nodal function, 2) the two inputs are equally effective in activating the AV node, and 3) input summation is a minor factor in rate-dependent nodal function.
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PMID:Effects of atrial pacing site on rate-dependent AV nodal function in rabbit hearts. 757 37

A theoretical model, formulated as a finite difference equation is proposed for rate-dependent conduction properties of the atrioventricular (AV) node. The AV nodal conduction time, which is defined as the time interval from the atrial activation to the activation of the bundle of His, depends on the history of activation of the node. The theoretical model, which incorporates physiological concepts of recovery, facilitation and fatigue, accurately predicts a variety of experimentally observed complex rhythms of nodal conduction. In particular, alternans rhythms, in which there is an alternation in conduction time from beat to beat, are associated with period-doubling bifurcations in the theoretical model.
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PMID:Alternans and period-doubling bifurcations in atrioventricular nodal conduction. 773 14

The wide variety of delays that the atrioventricular node can generate in response to an increased rate are explained by dynamic interactions between the three intrinsic properties of recovery, facilitation, and fatigue. The functional model presented suggests that any deviation of nodal conduction time from its minimum basal value represents, at any given time, the net sum of the effects produced by these properties. When a constant fast atrial rate is suddenly initiated, the node first "sees" a shortening in recovery time and responds by an increase in conduction time. This increase further shortens the recovery time of the ensuing beat, which is accordingly further delayed, and so on until a steady state is reached or a block occurs. However, these events do not occur alone. The second beat at the fast rate is conducted with a shorter conduction time than expected from the recovery time alone, and is therefore facilitated. These facilitatory effects develop within one short cycle and dissipate within one long cycle. They affect increasingly the conduction time of beats occurring with shorter cycle lengths. While steady-state effects of recovery and facilitation occur within seconds, nodal conduction time continues to increase slowly over several minutes when a rapid rate is maintained. This effect is attributed to fatigue, which develops and dissipates with a slow, symmetric time course. The dynamics of these properties can now be directly studied with selective stimulation protocols, and have many implications for the understanding of nodal behavior in the context of supraventricular tachyarrhythmias.
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PMID:Dynamic behavior of the atrioventricular node: a functional model of interaction between recovery, facilitation, and fatigue. 818 79

While rate-dependent atrioventricular (AV) nodal functional properties play a major role in determining antegrade AV nodal conduction, their existence and characteristics have not been assessed during retrograde AV nodal impulse propagation. Pacing protocols were used to study selectively AV nodal recovery, facilitation, and fatigue in 6 isolated, superfused rabbit AV nodal preparations and in 11 morphine-chloralose anesthetized dogs. All three properties were identifiable during retrograde AV nodal activation in rabbits. Retrograde recovery and fatigue were clearly demonstrated in dogs, but facilitation could not be evaluated because of echo beats during retrograde premature stimulation. Functional properties were qualitatively similar during retrograde and antegrade propagation; however, important quantitative differences were noted. The time constant for recovery from activation was significantly greater in the retrograde [rabbits, 69 +/- 8 (SE) ms; dogs, 93 +/- 11 ms] compared with the antegrade direction (rabbits, 50 +/- 5 ms; dogs, 58 +/- 4 ms; P < 0.05 vs. retrograde for each species). The magnitude of fatigue resulting from sustained increases in rate was also substantially greater in the retrograde direction in both rabbits (17 +/- 2 vs. 10 +/- 1 ms antegrade, P = 0.01) and dogs (20 +/- 4 vs. 6 +/- 1 ms antegrade, P < 0.01). Conduction time and refractory period were both greater in the retrograde compared with antegrade direction, and directional differences in conduction properties were magnified as activation rate increased.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Rate-dependent functional properties of retrograde atrioventricular nodal conduction in experimental animals. 823 13

A multicenter, phase II trial of continuous-infusion interleukin 2 (IL-2) was done in the Southwest Oncology Group to evaluate the efficacy and safety of this treatment in a broad-based population of patients with metastatic renal-cell carcinoma. Forty-seven patients from 11 different institutions were entered in this study, with 43 eligible. Two technically ineligible patients who received treatment and for whom records are available are included in the data analysis. Thus, there are 45 analyzable patients. Of these patients, performance status was 0 in 58% and 1 in 42%. Thirty-one patients had a prior nephrectomy, and 12 patients had received prior therapy. IL-2 was initially given at a dose of 4.5 x 10(6) Roche U/m2/day, 4 days a week, for 4 weeks in a row, followed by a 3-week rest period. Because of the difficulty in obtaining reimbursement for the hospitalization required on the days of IL-2 administration, after 10 patients had been entered, the treatment regimen was changed to 6 x 10(6) Roche U/m2/day for 4 days as an inpatient, followed by 2 weeks of potential outpatient treatment at a dose of 3 x 10(6) Roche U/m2/day for 4 days each week. This was followed by a 2-week rest period. Within the 45 analyzable patients, there were 0 complete responses and 6 partial responses, for a response rate of 13% (95% confidence interval 5.1-27%). Responses occurred in lung metastases, nodal disease, and in one patient with bone metastases and the primary kidney tumor. Response durations were 1 month, 1 month, 14+ months, 19 months, 26+ months, and 27 months. Of 12 patients with a nephrectomy and only lung metastases, 4 showed partial responses. Medial survival for all analyzable patients is 15 months (95% confidence interval 8-20 months). Toxicity was significant, with nausea and vomiting, diarrhea, fever and chills, dermatologic changes, and fatigue the most frequent. There were 18 instances of grade 4 toxicity, with the most common grade 4 toxicity, respiratory, found in 8 patients. There were two early deaths of probable heart-related causes while receiving treatment. A continuous-infusion IL-2 regimen that allows some potential outpatient treatment shows effectiveness and toxicity similar to that in other multicenter IL-2 infusion trials and high-dose intravenous bolus regimens.
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PMID:A phase II trial of continuous-infusion recombinant interleukin-2 in patients with advanced renal cell carcinoma: a Southwest Oncology Group study. 857 65

The characteristics and functional origin of the changes in transient atrioventricular (AV) nodal responses with heart rate history were studied in isolated rabbit heart preparations. For this purpose, ramp stimulation sequences were applied to the atrium from different initial conditions. A ramp decrease and increase in the His-stimulus interval and a reverse sequence consisting of a ramp increase and decrease were performed starting from a control basic cycle length, after 5 min of fast rate, or with 5 min of fast rate inserted between the two ramps. The nodal conduction times (NCT) obtained during the ramp stimulations formed hysteresis loops, the direction, shape, and magnitude of which varied markedly with the nodal history. That is, the nodal response to a given ramp took a variety of forms, depending on the initial condition. The effects of the initial condition also depended on ramp direction and sequence. A paradoxical NCT-recovery relationship (decrease in NCT with shortening His-atrial interval) was consistently observed at the onset of any ramp decrease performed after 5 min of fast rate. These effects also varied with the rate used to change the nodal history. The insertion of a control cycle at every 20th beat during repeated ramp protocols allowed the determination of the contribution of the nodal property of fatigue to these effects. Fatigue was found to account for all observed hysteresis patterns. In conclusion, heart rate history can, by modulating beat-to-beat changes in fatigue, transform transient nodal responses and hysteresis observed during stimulation ramps. Interpretation of transient nodal responses thus requires exact knowledge of previous nodal history.
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PMID:Characteristics and mechanisms of the effects of heart rate history on transient AV nodal responses. 876 58

The clinicopathological and immunohistochemical findings in 25 cases of inflammatory pseudotumor of lymph nodes (IPT) are presented. The patients were 13 women and 12 men between 8 and 81 years of age. Clinically, symptoms of prior infection, fatigue, abdominal pain, weight loss, fever of unknown origin, pelvic inflammatory disease, or nausea and night sweats were obtained in 15 patients, whereas six patients presented with asymptomatic lymphadenopathy. In four additional patients, no clinical information was obtained. The involved nodes included cervical, supraclavicular, inguinal, mesenteric, and mediastinal lymph nodes. In two cases, there was synchronous involvement of separate lymph node groups (inguinal and cervical in one case and cervical and mediastinal in another case), whereas in a third patient there was synchronous involvement of the spleen and a paraaortic lymph node. Histologically, the lesions were characterized by a fibrosing/inflammatory process that showed marked heterogeneity and striking variation from case to case. Based on their histological features, the lesions could be classified into three different groups: Stage I was characterized by the appearance of single or multiple small foci containing a spindle cell proliferation admixed with a prominent inflammatory background, with complete preservation of the remainder of the nodal architecture; stage II was characterized by more diffuse involvement of the lymph node with a marked inflammatory response admixed with a prominent myofibroblastic proliferation leading to subtotal effacement of the nodal architecture, often with extension of the process beyond the capsule into perinodal fat; and stage III was characterized by almost complete replacement of the lymph node by diffuse sclerosis with scant residual inflammatory elements and total loss of the normal nodal architecture. Immunohistochemical studies in 20 cases showed a striking number of vimentin- and actin-positive myofibroblastic cells with moderate increase in CD20/CD45+ small lymphocytes and polyclonal plasma cells in the stage I lesions, the emergence of numerous CD68+ histiocytes admixed with lymphocytes, plasma cells, and abundant fibromyofibroblastic cells in the stage II lesions, and only few remaining scattered CD68+ histiocytes and fibroblasts in the stage III lesions. Our findings suggest that inflammatory pseudotumor of lymph node represents an evolving, dynamic process that may adopt different morphological appearances depending on its stage of evolution. Recognition of the various stages of this process may be of importance for differential diagnosis with other fibrosing/inflammatory conditions of lymph nodes.
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PMID:Inflammatory pseudotumor of lymph nodes: a study of 25 cases with emphasis on morphological heterogeneity. 904 98

A previously healthy 64-year-old woman attended our hospital with chest pain, facial edema, and general fatigue. A chest radiograph revealed cardiomegaly, small bilateral pleural effusions, and hilar congestion--findings that improved after early therapy with furosemide and methyldigoxin. A chest radiograph recorded 7 years earlier had revealed no dilation of cardiac shadow. There were no findings suggesting atrial septal defect (ASD) or valvular heart disease. Echocardiography revealed a tumor-like mass adhering to the posterior wall of the left atrium. Color-flow Doppler echocardiography revealed a left-to-right shunt at the atrial level. The Qp/Qs ratio as measured by cardiac catheterization was 2.0. Coronary angiography revealed abnormal dilated arteries from the atrioventricular nodal branch and several feeding arteries from the left circumflex branch. We hypothesized that the left-to-right shunt could be due to the tumor, which extended to the rim of the patent foramen ovale, or to the very small, previously unrecognized, ASD. This patient died 6 months after her first admission and an autopsy was performed. Light microscopic examination of the tumor revealed spindle-shaped fibroblast-like cells arranged in a storiform or fascicular pattern. The immunohistochemical findings were consistent with malignant fibrous histiocytoma (MFH). In the literature, left-to-right shunt at the atrial level has not been reported in patients with cardiac MFH.
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PMID:A case of primary malignant fibrous histiocytoma of the heart with a left-to-right atrial shunt. 939 62


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