Low-temperature properties of magnetically frustrated rare-earth zirconatesA2Zr2O7.

Rare-earthA2Zr2O7zirconates have attracted considerable attention of the scientific community for their complex magnetic, electronic and material properties applicable in modern technologies. The light rare-earth members of the series, crystallising in the pyrochlore variant of cubic crystal structure, have been studied in detail. The heavierA2Zr2O7compounds have been investigated mainly from the material properties viewpoint, focussing on their thermal properties and stability at high temperature and pressure. Low-temperature studies were mostly missing until recently. We present the low-temperature magnetic and thermodynamic properties ofA2Zr2O7withA= Y, La, Nd, Eu, Gd, Tb, Dy, Ho, Tm, Yb, and Lu, well covering the whole series, newly synthesised by high-temperature sintering and melting methods. X-ray diffraction reveals and confirms the ordered pyrochlore structure in the light members, the disordered cubic structure of the defect-fluorite type inA2Zr2O7withA= Y, Gd-Yb, and finally the lower symmetry rhombohedral structure in the end-member Lu2Zr2O7. The specific heat of the investigated compounds is dominated by a low-temperature anomaly associated with magnetic ordering: long-range in light rare-earth zirconates; and short-range in heavier members. The effective magnetic moment in the studied compounds, determined by fitting the magnetisation data to the Curie-Weiss formula, is in good agreement with the expected value of theA3+free ion. The magnetic properties have been revealed to be strongly influenced by the geometric frustration of the magnetic moments of both the pyrochlore structure, as well as the face centred cubic lattice created by the cations of the defect-fluorite structure, but connected also to intrinsic atomic disorder. The experimental results are discussed in the framework of previous studies onA2Zr2O7zirconates, as well as otherA2B2O7compounds.

Hysteretic structural changes within five-layered modulated 10M martensite of Ni-Mn-Ga(-Fe).

Modulated structure of Ni-Mn-Ga-based alloys is decisive in their magnetic shape memory (MSM) functionality. However, the precise nature of their five-layered modulated 10M martensite is still an open question. We used x-ray and neutron diffraction experiments on single crystals to investigate structural changes within 10M-modulated martensite of the Ni50Mn27Ga22Fe1MSM alloy. The modulation vector gradually increases upon cooling from commensurateq= (2/5)g110, whereg110is the reciprocal lattice vector, to incommensurate withqup to pseudo-commensurateq= (3/7)g110. Upon heating, reverse changes are observed with a thermal hysteresis of ≈60 K. The same hysteretic behaviour was detected in the electrical resistivity and the effective elastic modulus. Scanning electron microscopy showed that the changes are accompanied by the refinement of thea/blaminate. These observations indicate that the commensurate state is a metastable form of 10M martensite. Upon cooling, this phase evolves through nanotwinning into a more irregular and more stable incommensurate structure.

Impact of isoelectronic substitution and hydrostatic pressure on the quantum critical properties of CeRhSi3.

There is an ongoing dispute in the community about the absence of a magnetic quantum critical point (QCP) in the noncentrosymmetric heavy fermion compound CeRhSi3. In order to explore this question we prepared single crystals of CeRh(Si1-x Ge x )3 with x = 0.05 and 0.15 and determined the temperature-pressure (T-p) phase diagram by means of measurements of the electrical resistivity. The substitution of isoelectronic but large Ge enforces a lattice volume increase resulting in a weakening of the Kondo interaction. As a result, the x = 0.05 and x = 0.15 compound exhibit a transition into the antiferromagnetic (AFM) at higher temperatures being T N = 4.7 K and T N1 = 19.7 K, respectively. Application of pressure suppresses T N (T N1) monotonically and pressure induced superconductivity is observed in both Ge-substituted compounds above p ⩾ 2.16 GPa (x = 0.05) and p ⩾ 2.93 GPa (x = 0.15). Extrapolation of T N(p) → 0 of CeRh(Si0.95Ge0.05)3 yields a critical pressure of p c ≈ 3.4 GPa (in CeRh(Si0.85Ge0.15)3 p c ≈ 3.5 GPa) pointing to the presence of an AFM QCP located deep inside the superconducting state.

The development of specific heat and electrical resistivity in the CeNi(x)Pd(1-x)In series.

Our report describes the anomalous electronic behavior of CeNi(x)Pd(1-x)In compounds studied by specific heat and electrical resistivity measurements. These compounds belong to the large and relatively thoroughly studied group of ternary rare-earth intermetallics crystallizing in the ZrNiAl-type structure. The investigated series shows a transition from the heavy fermion antiferromagnetic system of CePdIn to the valence fluctuating state observed in CeNiIn. The isostructural and isoelectronic substitution of Pd by Ni leads to a change in the character of the d-electrons and the lattice parameters of the system because of the smaller radius of Ni atoms. These changes have a great impact on the magnetic properties of the studied compounds. The antiferromagnetic transition shifts first to lower temperatures, from T(N) = 1.7 K for CePdIn to T(N) = 1.3 K for CeNi0.2Pd0.8In. For a Ni content ≥40%, there is no sign of a magnetic phase transition in the specific heat and electrical resistivity data. Moreover, the data indicate anomalous non-Fermi-liquid behavior for concentrations with 0.4 ≤ x ≤ 0.6, which is clearly seen in both types of measurements. The rest of series behaves similarly to the second parent compound CeNiIn. Besides the cerium compounds, superconductivity in LaNi0.2Pd0.8In is also presented.

24 hours electrocardiographic monitoring in obese children and adolescents during a 3 weeks low calorie diet (500 kcal).

Twenty-four hour electrographic recordings were made on 36 grossly obese children and adolescents during a 3-week weight reduction regimen with a 525 kcal (2196 kj) mixed diet at weekly intervals. One hundred and ten Holter ECGs were analysed. Weight loss during the treatment was calculated to be 5.7 +/- 1.6 kg. Average and minimal heart rate decreased constantly throughout the study period from 83.9 +/- 9 to 75 +/- 9/min and 53 +/- 6 to 45 +/- 6/min, respectively (P less than 0.01, P less than 0.005). During the second week maximal heart rate increased significantly but returned to baseline values in the third week. Neither before nor during the period of therapy were any dysrhythmias monitored. Dietary regimens containing 500-700 kcal, based on a mixed composition of foods with sufficient amounts of minerals, can be regarded as a safe therapeutic tool in the treatment of obese children and adolescents.

[The effect of concomitant aortic valve insufficiency on the values of Doppler sonographic gradient determination in patients with aortic stenosis]. / Einfluss der begleitenden Aorteninsuffizienz auf das Ergebnis der dopplersonographischen Gradientenbestimmung bei Patienten mit Aortenstenose.

We examined the influence of concomitant significant aortic incompetence (AI) on Doppler-gradient measurements in valvular aortic stenosis (AS) by comparing catheter and Doppler gradients of 51 patients with isolated AS and of 24 patients with additional AI. In patients with additional AI there was a significantly greater overestimation of the peak-to-peak gradient by the maximal instantaneous Doppler gradient (AS + AI: overestimation 31.0 +/- 17.6 mm Hg, AS: overestimation 10.5 +/- 20.2 mm Hg; p less than 0.01) and also by the maximal instantaneous catheter gradient (AS + AI: overestimation 32.8 +/- 11.8 mm Hg, AS: overestimation 20.4 +/- 14.0 mm Hg; p less than 0.01). Comparison of the respective catheter-derived and Doppler-sonographically measured instantaneous and mean gradients showed no differences between the two patient subgroups. Higher instantaneous gradients in patients with additional AI are mainly explained by the lower end-diastolic aortic pressure. However, Doppler-sonographic overestimation of the severity of stenosis in patients with combined AS + AI, due to the sole measurement of the instantaneous gradient in clinical practice, should be of limited importance because in these patients significant AI already sufficiently indicates aortic valve replacement.

Prognostic value of supine scintigraphic heart function and simultaneous conventional exercise response in patients after myocardial infarction.

A total of 240 survivors of one or more myocardial infarctions were consecutively admitted to perform supine exercise radionuclide ventriculography. Within 3 years after the test, 22 died; this group was compared to an age-matched control group of 22 survivors for left and right ventricular function during rest, exercise, and simultaneously assessed exercise performance as well as ECG variables. Evaluation of 3-year survival by linear discriminant analysis revealed an accuracy of 82% for discriminant models using ECG and exercise performance variables. Implementation of resting left ventricular ejection fraction and change of right ventricular ejection fraction during exercise, as well as scintigraphic presence or absence of dyskinesia, improved the accuracy of the model to 91% of correctly classified patients.

Radionuclide detection of mild valvular regurgitation: its significance as assessed by Doppler sonography.

Radionuclide ventriculography (RNV) indices of regurgitation, Fourier amplitude ratio (FAR) and additional RNV variables were prospectively compared to Doppler echocardiography (DE) in 108 consecutive patients with no or mild left ventricular regurgitation, to assess RNV accuracy in detecting regurgitation in patients with different cardiac disorders. Exclusion of left ventricular or tricuspid regurgitation allowed investigation of the FAR range at rest and during exercise in a sufficiently large appropriate reference group without regurgitation. FAR, as well as other RNV variables, failed to provide more information for the diagnosis of mild (clinically irrelevant) left ventricular regurgitation than the diagnosis upon admission alone. Despite the superiority of DE as a gold standard in the detection of mild regurgitation, at present evaluation of RNV regurgitation indices might be the only method to discover regurgitation arising during dynamic exercise.

[Vasodilator therapy in pulmonary hypertension and chronic obstructive lung disease (COPD). Hemodynamic studies exemplified by nifedipine and nitroglycerin]. / Vasodilatatorentherapie bei pulmonaler Hypertonie und chronisch obstruktiver Lungenerkrankung (COPD). Hämodynamische Untersuchungen am Beispiel von Nifedipin und Nitroglycerin.

In 41 patients with chronic obstructive pulmonary disease (COPD) and pulmonary hypertension, the effects of sublingual administration of 20 mg nifedipine and 0.8 mg nitroglycerin on the hemodynamics were assessed at rest and during bicycle ergometry. Additionally, in six patients, the effects of nifedipine during longterm treatment were analyzed. On acute testing, at rest and during exercise nifedipine led to decreases in mean pulmonary artery pressure of 16% and 23% and pulmonary arteriolar resistance of 23 and 35%, respectively, in 81% (17/21) of the patients. The reduction in the pulmonary vascular resistance was greater than that of the systemic resistance. In all patients, cardiac output increased. There was a similar number of responders to nitroglycerin (16/20). The reductions in mean pulmonary artery pressure and pulmonary arteriolar resistance ranging between 20 and 25% at rest and during exercise were comparable to those affected by nifedipine. In addition to the right ventricular afterload reduction, there was a decrease in cardiac output of 17%. During longterm treatment with nifedipine (average 18 months), the reduction in mean pulmonary artery pressure and pulmonary arteriolar resistance was not of the same magnitude as seen on acute testing. This may be due primarily to progression of the underlying disease since pulmonary function studies demonstrated an increase in the obstructive component. With the intention of circumventing or postponing the onset of right ventricular failure, the individual patient should undergo hemodynamic studies to delineate the optimal medication.

Dynamic 123I-HDA myocardial scintigraphy after aortocoronary bypass grafting.

In an attempt to evaluate the dynamics of fatty acid metabolism after aortocoronary bypass grafting (ACBG), ten patients were investigated after ACBG by 123I-HDA myocardial scintigraphy. Tracer kinetics were followed for 90 min and compared to those of 36 nongrafted patients with different underlying heart diseases, including healthy volunteers. Regional analysis and monoexponential curve fitting were used to evaluate t1/2 (half-life of the early period of tracer elimination); biexponential curve analysis was used to calculate Ca/Cb, the ratio of a fast and a slow component of tracer elimination. Rest and stress MUGA-RNV served as discriminating parameters to discern between patient groups with normal and abnormal ventricular function. Group I (normal controls) encompassed ten patients with normal ventricular function, including three after ACBG, and group II seven patients after ACBG and with abnormal ventricular function. Group III had coronary artery disease (CAD) documented by angiography, and group IV by prior myocardial infarction (MI). Group V included patients with cardiomyopathy (CMP). Regional analysis of group II revealed no significant differences to control regions (Gr I) for t1/2 or Ca/Cb, but showed for Ca/Cb a nonsignificant shift toward group III values. However, group II differed significantly from group III and V. Three patients with normal ventricular function after ACBG showed elimination values that were all well within the range of completely normal individuals. Thus our data support the assumption that a normal function is indicative of a normal metabolism. Following myocardial fatty acid metabolism during rest might be a helpful noninvasive tool for etiologic differentiation of disturbed ventricular function.

Two years' experience with the duromedics bileaflet heart valve prosthesis.

The new Duromedics Bileaflet Cardiac Valve prosthesis has a special moving hinge mechanism for its two leaflets to wash the critical articulation area and thus reduce thrombus formation. Between October 1983 and June 1985, we implanted 278 of these prostheses in 254 patients. We did 114 aortic valve replacements, 109 mitral valve replacements, 34 double valve replacements, and two tricuspid valve replacements. Nearly 20% of the patients had had previous cardiac procedures. The hospital mortality was 5.9%. Follow-up was started with 214 surviving Austrian patients, and up to the present time, we have a follow-up period of 1704 patient months. Five patients died late after the operation (3.5 per 100 patient years). We observed 10 valve-related complications in nine patients (7 per 100 patient years). There were three cases of prosthetic endocarditis (2.1 per 100 patient years), two paravalvular leaks, and four bleeding episodes (2.8 per 100 patient years). The mechanical hemolysis was minimal, and the postoperative hemoglobin value averaged 15 g%. The LDH increased from 230 IU to 307 in the aortic valve replacements, 406 in the mitral valve replacements, and 435 in the double valve replacements. Intraoperative pressure gradients and postoperative Doppler echocardiography showed good hemodynamic performance. We conclude that good clinical results and a low complication rate can be achieved with the Duromedics Valve.

Functional tricuspid insufficiency: conservative or operative management.

Between 1978 and 1982 mitral valve replacement was performed in a total of 43 patients with mitral valve disease in the presence of functional tricuspid insufficiency (TI). The concomitant tricuspid valve regurgitation was treated conservatively in 17 patients, a Carpentier ring prosthesis was implanted in 9 patients. De Vega annuloplasty was performed in 13 patients and 4 times the valve was replaced with a Hancock bioprosthesis. The hospital mortality of 26% (11 patients) was high, due to the poor clinical condition of the patients. In a mean follow-up of 43.1 +/- 18,0 months, 20 patients could be restudied by clinical and echocardiographical investigation. Tricuspid insufficiency was found in all of the 9 patients who had been treated conservatively. Seven out of 11 patients operated showed no signs of TI, 3 had mild TI and 1 patient had severe TI. In the conservatively treated group, the preoperative mean pulmonary vascular resistance (PVR = 296 +/- 161 dynes x sex x cm-5), pulmonary artery pressure (PAP = 46.1 +/- 16.2 mmHg) and rise of right atrial V-wave (15.8 +/- 3.6 mmHg) were only slightly higher than n the operatively treated group (PVR - 274 +/- 146 dynes x sex x cm-5), PAP = 43.2 +/- 13.6 mmHg, V-wave = 18.5 +/- 6.4 mmHg) with no statistically significant difference. Preoperative hemodynamic findings in patients with and without TI a follow-up were also not significantly different. These results indicate that the recurrence of functional TI depends on the method of treatment, rather than preoperative increased PVR, PAP or V-wave rise.

[Rare cause of a left ventricular aneurysm in a 10-year-old boy]. / Seltene Ursache eines linksventrikulären Aneurysmas bei einem 10 jährigen Knaben.

A 3-year-old boy had an accident with a blunt chest trauma, 9 years later a left ventricular aneurysm was diagnosed by echocardiography and angiography. The 12-year-old-boy was operated successfully. The pathogenesis of cardiac lesions in association with blunt chest traumas is described, and frequent control examinations in the affected patients are recommended.

Effects in elderly people 67-76 years of age of three-month endurance training on a bicycle ergometer.

Eight women and 4 men, mean age 71.1 years, examined by a clinical check-up participated in a bicycle ergometer training program (12 weeks with 3 training sessions per week). Symptom limited ergometric bicycle tests were performed before and after the training period. The training work load was continuously controlled by maintaining the training heart rate according to 60% of the maximum work load of the first test. To hold the training heart rate (HR) on a constant level the work load had to be increased systematically during the whole training period up to 180% of the level at the beginning. The working time in each training session was increased from 2 X 10 mm at the beginning up to 2 X 20 min after the sixth week. The maximum work load (+ 16%) and the maximum oxygen uptake (+ 11%) increased significantly. The submaximal HR decreased significantly. In contrast there was no significant difference in maximum HR and maximal change of base excess between the initial exercise test and the control study at the end of the training program. This indicates that the increased exercise capacity represents a real endurance training effect and not only an increase in the degree of exhaustion. We conclude that also in healthy people between 67-76 years a significant endurance effect is possible when the training work load and training time is increased systematically according to the rules of training sciences.

Chylopericardium: a rare cause of pericardial effusion.

A 21 year old man presented with asymptomatic, isolated chylopericardium. Despite echocardiography, radionuclide-angiography, computer tomography, and chemical analysis of the chylous effusion, the etiology remained obscure. After patent blue dye infusion into peripheral soft tissues, the appearance of coloring material in the effusion at 4 hours suggested direct communication of the pericardium with an apparently large thoracic duct. Fifteen months later, cardiomegaly persists in site of medium-chain triglyceride dietary restriction.

[Results of 3 months' endurance training on a bicycle ergometer in people between 67 and 76]. / Ergebnisse eines 3monatigen Ausdauertrainings auf einem Fahrradergometer bei alten Menschen zwischen 67 und 76 Jahren.

8 healthy women and 4 men, examined by a clinical check-up, mean age 71.1 years, took part in a bicycle ergometer training, 3 times a week, for 12 weeks. Symptom limited ergometric bicycle tests were done before and after the training period. The training work load was continuously controlled by maintaining the training heart rate according to 60% of the maximum work load of the first test. In order to hold the training heart rate (HR) on a constant level the work load had to be increased systematically during the whole training period up to 180% of the level at the beginning. The working time in each training session was increased from 2 X 10 minutes in the beginning up to 2 X 20 minutes from the 7. week on. The maximum work load (+ 15%) and the maximum oxygen uptake (+ 14%) increased significantly. The submaximal HR decreased significantly. In maximum HR and maximum decrease of the base excess were no significant changes, indicating a real endurance training effect and not only an increase in the degree of exhaustion. We conclude that also in healthy people between 67-76 years a significant endurance effect is possible when the training is systematically increased in work load and working time, according to the rules of training science.

[Value of sonography in cardiologic diagnosis]. / Stellenwert der Sonographie in der kardiologischen Diagnostik.

Echocardiography offers a non-invasive method ideal for the patient and the observer. It improved the diagnostic possibilities during the past few years significantly and reached highest diagnostic sensitivity in certain cardiovascular diseases. It is ideally suited for follow-up examinations and for the evaluation of medical or surgical interventions. In addition it can be helpful as screening method for invasive diagnostic procedures. Despite all advantages one has to keep in mind that it is only one single diagnostic step within the whole diagnostic framework. For the management of patients it is decisive to know the information which can be gained and to know the possibilities and limitations of the method.

Echographic method for the estimation of cardiac output from mitral-valve area, heart rate, and diastolic-filling period in conditions of mitral stenosis: correlation with cardiac catheterization.

An orifice equation for the non-invasive measurement of mitral-valve area is demonstrated. It is shown that by combining this expression with the assumption of mitral-valve area invariance an orifice equation for the non-invasive assessment of cardiac output in conditions of mitral stenosis using simple echographically measureable variables can be developed. This equation is V = (21)-1 R X A X T2, where V = cardiac output in ml, R = heart frequency, A = mitral-valve area in cm2 and T = diastolic-filling period in sec X min-1. These results suggest that when mitral-valve area is accurately measured at one point in time, cardiac output may be measured at subsequent times at a clinically useful level from a knowledge of the echographically measurable variables of heart rate and diastolic-filling period.