Voltage control of ferrimagnetic order and voltage-assisted writing of ferrimagnetic spin textures

Voltage control of magnetic order is desirable for spintronic device applications, but 180° magnetization switching is not straightforward because electric fields do not break time-reversal symmetry. Ferrimagnets are promising candidates for 180° switching owing to a multi-sublattice configuration with opposing magnetic moments of different magnitudes. In this study we used solid-state hydrogen gating to control the ferrimagnetic order in rare earth-transition metal thin films dynamically. Electric field-induced hydrogen loading/unloading in GdCo can shift the magnetic compensation temperature by more than 100 K, which enables control of the dominant magnetic sublattice. X-ray magnetic circular dichroism measurements and ab initio calculations indicate that the magnetization control originates from the weakening of antiferromagnetic exchange coupling that reduces the magnetization of Gd more than that of Co upon hydrogenation. We observed reversible, gate voltage-induced net magnetization switching and full 180° Néel vector reversal in the absence of external magnetic fields. Furthermore, we generated ferrimagnetic spin textures, such as chiral domain walls and skyrmions, in racetrack devices through hydrogen gating. With gating times as short as 50 μs and endurance of more than 10,000 cycles, our method provides a powerful means to tune ferrimagnetic spin textures and dynamics, with broad applicability in the rapidly emerging field of ferrimagnetic spintronics.

[Treatment of essential hypertension with a combination of propranolol, spironolactone-thiabutazide and dihydralazine (author's transl)]

In 61 out-patients with essential hypertension, grade I or II, propranolol was administered alone in increasing doses (3 x 40 mg/d or 3 x 80 mg/d) or, if there was insufficient response, with a double or triple combination consisting additionally of spironolactone (50 mg/d)-thiabutazide (5 mg/d) and dihydralazine (3 x 25 mg/d). This treatment schedule achieved normal pressures in 51 patients, in 22 on 40 mg, in 7 on 80 mg propranolol, in 16 after the addition of the diuretic, and in 6 with the triple combination. Four patients had to be excluded from the study because they developed either marked bradycardia or anxiety states or paraesthesias after propranolol (3 x 40 mg/d). On chronic beta-adrenergic blockade the serum potassium level increased slightly, but remained within normal limits. The initial value of plasma-renin activity was highest in the group of those who responded to the propranolol treatment.

[Glucocorticoid-induced effect of erythropoietin in haemolytic anaemia with uraemia and red cell enzyme deficiency (author's transl)]

The effect of 6-methylprednisolone (GCC) was studied on erythropoietin (ESF) levels and on the metabolic functions of erythrocytes (RBC). GCC (U mg/kg/day for 15 days) was administered to 6 patients with the haemolytic-uraemic syndrome (group B) and to 6 patients with non-spherocytic haemolytic anaemia due to hereditary pyruvate kinase enzyme deficiency (group C). 6 healthy persons served as control (group A). The metabolic functions of RBC were investigated by assaying HMPS activity, GSH/GSSG and lactate/pyruvate ratios, relevant glycolytic intermediates, 2,3-DPG, ATP, and key enzymes. A significant increase in ESF was observed in group B patients after GCC therapy, correlating with an improvement in the haemolytic state, and consequent rectification of the secondary disturbances of RBC metabolism. Group C patients already had raised ESF levels before GCC therapy; no further increase occured in response to treatment and no other clinical or haematological change was recorded. Hence, no harmonal influence of GCC on the disturbed RBC metabolic process was detectable in the cases.

[Coronary artery reserve in patients with hyperlipoproteinemias (author's transl)]

The coronary reserve was measured in 119 patients with different types of primary hyperlipoproteinemia. Cardiovascular diseased with clinical manifestation were excluded. 90 patients of same age with normal serum lipids served as controls. The groups did not differ in other risk factors as blood pressure or overweight (the latter excluded in hyperlipoproteinemia type IV). The controls showed decreased coronary reserve in 8%, type IIa patients in 36%, IIb patients in 18% and type IV patients in 23%. The frequency of restriction in coronary flow increased with age: in hyperlipoproteinemic patients of 50 years and more it was found in nearly 40%. Further interesting results were the significantly higher systolic and diastolic blood pressures reached during exercise in our hyperlipoproteinemic patients.

[Behaviour of plasma renin activity during long-term treatment with propranolol (author's transl)]

17 patients (40 +/- 9 years) with essential hypertension were included in the study. A monotherapy of 120, 160 or 240 mg propranolol per day was administered orally according to the antihypertensive effect. Four weeks after treatment, blood pressure and heart rate showed a statistically significant decrease and remained unchanged over a period of six months. Plasma renin activity decreased significantly from 5.7 +/- 6.3 ng/ml/h at the beginning of the study to 1.8 +/- 1.3 ng/ml/h after 4 weeks. 5 months later however plasma renin activity increased again to 5.0 +/- 0.9 ng/ml/h. The difference was statistically significant. From 17 patients 7 (41%) had lower levels of plasma renin activity after 6 months treatment when compared with pretreatment values. In only 3 patients (18%) was plasma renin activity lower after 6 months than after four weeks. We conclude that the increase in plasma renin activity is a reactive mechanism to the reduced blood pressure under long-term conditions. The decrease of plasma renin activity in short-term treatment of essential hypertension is not a mechanism responsible for the antihypertensive effect of propranolol during long-term treatment.

[Mitral valve and mitral ring movement in mitral stenosis. An ultrasonic study with different valve models (author's transl)]

We constructed three different mitral valve models in order to investigate the different mechanisms which account for the concordant opening and closing movement of the posterior compared to the anterior mitral valve in mitral stenosis. Three different types of movements are possible: a dorso-anterior movement of the mitral ring, opening and closure of the valve itself and a rotation of the entire valve apparatus. Our in-vitro studies showed that the best explanation for the concordant diastolic movement of the posterior valve is given by the assumption that during the early diastolic opening phase of the valves the whole stenotic valve apparatus is rotated upward, i.e. towards the transducer. This rotation, has a higher amplitude compared to the residual downward-oriented opening movement of the posterior valve.

[Cyclic AMP and plasma renin activity in renal vein blood after amitryptiline, theophylline, furosemide and beta adrenergic blocking substances (author's transl)]

The influence of amitryptiline, theophylline and furosemide on the concentration of cyclic-AMP and plasma renin activity (PRA) was investigated in renal vein plasma. Additionally, the stimulating effect of furosemide on the PRA after application of the beta-adrenergic receptor antagonists propranolol and practolol and the cyclic AMP concentration in the plasma were measured. All drugs were given intravenously. After amitryptiline cyclic-AMP concentration increased about 1.5-fold compared with the basal value,PRA was not altered. After theophylline cyclic-AMP concentration increased about 1.2-fold, PRA 2.0-fold compared with the basal value, PRA was not altered. After theophylline cyclic-AMP concentration increased about 1.2-fold, PRA 2.0-fold coa increased within 7 min and no further increase was observed till the 15th min. After practolol cyclic-AMP concentration and PRA decreased about 20% compared with the basal value within 10 min. The stimulating effect of subsequently applied furosemide on PRA was not altered, but the cyclic-AMP concentration was not changed in this time by furosemide. After propranolol cyclic-AMP concentration and PRA decreased about 20% compared with the basal value. The cyclic-AMP concentration was not influenced by the following furosemide application, in agreement with the findings after practolol, however, PRA could be stimulated only in 36% of these patients under beta-receptor blockade. Our results show that changes of the concentrations of cyclic-AMP and of PRA are independent of each other. An elevated intracellular cyclic-AMP level due to the inhibition of phosphodiesterase is as a single factor unable to stimulate renin release. Our results give no evidence of a direct involvement of the adenylcyclase-system in the mechanism of renin release. The effect of propranolol and practolol on the basal value of PRA and cyclic-AMP is equal. The different influence of 10 mg propranolol and 20 mg practolol on the stimulating effect of 40 mg furosemide on the PRA can be interpreted as a dosage problem.

[Effect of an oral contraceptive (ethinylestradiol/D-norgestrel) on growth hormone and insulin secretion]

The growth hormone, insulin and blood glucose values were measured during a glucose tolerance test in 12 women before and after 3 months' use of a contraceptive of the sequential type (11 pills containing 0.05 mg D-norgestrel and 0.05 mg ethinylestradiol and 10 pills containing 0.125 mg D-norgestrel and 0.05 mg ethinylestradiol). Neither fasting blood glucose nor glucose tolerance are altered during administration of the contraceptive steroids. On the other hand, the reactive insulin level is significantly increased in comparison to the basal value, thus showing the signs of hyperinsulinemia. Both the gestagens and the estrogens appear to contribute to this disturbance of insulin secretion. Presumably the hyperinsulinemia is an expression of decreased sensitivity of the peripheral tissue to insulin. The growth hormone, a so-called insulin antagonist, is not responsible for the "insulin resistance" observed. The values measured by us after administration of the contraceptive do not significantly differ from the basal values.

[Treatment of essential hypertension with propranolol (author's transl)]

Effect of long-term administration of propranolol was studied in 90 unselected patients with essential hypertension. At a dose of 180 and 360 mg daily it dropped the blood pressure to at least 155/95 mm Hg in 31 patients (34.4%). Those who responded to propranolol had lower systolic and diastolic blood pre-treatment pressures than those who failed, were younger by an average of eight years, and in no case had decreased plasma-renin activity and demonstrated greater plasma-renin activity after furosemide. After a titration phase with increasing doses of propranolol those who responded were treated in a crossed double-blind test with propranolol or placebo. There was a significant difference in systolic blood pressure (standing and lying) and diastolic pressure (standing) between the two. There was also a highly significant difference in heart rate. During chronic beta blockade the basal and stimulated plasma-renin activity fell. But percentage stimulation of renin secretion was fully maintained. However, aldosterone response was decreased. Serum potassium rose slightly but significantly, cAMP 24-hour urine excretion fell significantly. Electrolyte excretion did not differ between the two treatment periods.

[The influence of saralasine on blood pressure and renal function in Bartter's syndrome and decompensated hepatic cirrhosis (author's transl)]

Infusion of the angiotensin-II-antagonist saralasine led in one patient with Bartter's syndrome and one patient with decompensated hepatic cirrhosis, both of whom had a markedly raised plasma renin activity, to a fall in systolic and diastolic blood pressure. The results indicate that in normotensive patients a raised angiotensin II concentration in blood is haemodynamically important for the level of blood pressure if plasma renin activity is raised. In normotensives with normal plasma renin activity saralasine in the usual dosage (4.2 mug/kg-min) does not influence the blood pressure.

[Fatty acid patterns and glucose tolerance in Huntington's chorea (author's transl)]

Fatty acid patterns of plasma lipids and glucose-tolerance in Huntington's chorea. 25 patients with Huntington's chorea of various manifestation (9 predisposed symptomefree, 5 with light and 11 with severe manifestation) had studies of carbohydrate and lipid metabolism. These studies measured glucose-tolerance tests, insulin-, HGH-secretion, serum lipids and plasma fatty acid conposition of the cholesterylesters, triglycerides and phospholipids. The reactive insulin- but not HGH-levels were significantly raised, 32 % of the patients with Huntington's chorea had abnormal glucose-tolerance tests, compared with 3.2 % in a control group. Duration of symptoms correlated with higher cholesterol levels. Minor deviations were found in the fatty acid patterns in various lipid clases.

[The influence of propranolol, practolol and theophylline on the plasma renin activity (author's transl)]

The stimulating effect of theophylline on the plasma renin activity (PRA) under beta-receptor blockade by propranolol or practolol was investigated in 27 patients with essential hypertension of degree I-II. After propranolol and also practolol PRA decreased about thirty per cent of the basal value, increased however by the factor of 2 to 3 after application of theophylline, in spite of the blockade of the beta-receptors indicated by a slight decrease of systolic blood pressure and heart rate. The effect of propranolol and practolol on the basal PRA was not different. Our results show the possibility, to stimulate renin secretion despite blockade of beta receptors by propranolol or practolol, respectively.

[Spironolactone and thiabutazide in the treatment of essential hypertension (author's transl)]

The anti-hypertensive effect of spironolactone and thiabutazide was tested on 47 unselected patients with primary hypertension. They were divided into two groups according to the change in plasma-renin activity in response to furosemide administration: those with and those without response to stimulation, and sub-groups with low, normal or high plasma-renin activity (low renin hypertension; normal renin hypertension; high renin hypertension). During both 4-week treatment periods there was a distinct fall in systolic blood pressure, most marked in the patients without plasma renin stimulation (after spironolactone of about 26.2 mm Hg, after thiabutazide 29 mm Hg), the diastolic pressure fall being only slight in all groups (about 5-10 mm Hg). The plasma-renin activity and plasma-aldosterone concentration increased in all groups, after both spironolactone and thiabutazide three-to fourfold compared with the basal value, even in patients without change in plasma-renin activity after furosemide injections. Serum sodium content decreased after administration of spironolactone, increasing again after subsequent thiabutazide administration. Serum potassium content increased after spironolactone, decreasing after thiabutazide. There was no significant difference between either individual groups or different treatment periods with spironolactone or thiabutazide as far as weight, urine volume or electrolyte excretion in 24-hour urine was concerned.

[Plasma aldosterone and plasma renin activity in patients with essential and renal hypertension under acute stimulation with saline depletion and acute suppression with saline infusion]

Plasma aldosterone, plasma renin activity, sodium and potassium in the plasma and the urine were determinated under acute stimulation with saline-depletion (furosemide) and under acute suppression with saline infusion in 40 patients with primary hypertension stage I, 19 patients with primary hypertension stages II and III, and 11 patients with renal hypertension (chronic glomerulonephritis and chronic pyelonephritis). The majority of the patients with primary hypertension stage I showed a good stimulation of the plasma aldosterone and the plasma renin activity under acute salt depletion. Three out of the 40 patients with primary hypertension stage I, and 13 of the 19 patients with primary hypertension stages II and III did not show any stimulation of the renin secretion ("low renin hypertension"). In all these patients the plasma aldosterone stimulation remained intact. With infusion of saline all the groups showed suppression of the plasma aldosterone and the plasma renin activity. A good stimulation of the plasma renin activity, demonstrates that in our experiments the renin-angiotensin system cannot be responsible for the increase in aldosterone secretion under salt depletion. Most likely the increase of the plasma aldosterone, in spite of the fixed renin activity, is stimulated by the sodium depletion due to diuretics. In all patients with primary hypertension we did not find an inadequate reaction of the aldosterone secretion under saline infusion. The patients with renal hypertension showed a minimal stimulation and suppression of the plasma renin activity. The plasma aldosterone secretion increased only slightly under sodium depletion and the decrease under saline infusion was statistically not significant. Thus we conclude that these patients show an inadequate reaction of the plasma aldosterone and renin secretion under salt infusion and depletion.

[Ultrasonic cardiographic studies of heart size in atrial septal defect, combined mitral and aortic valve disease]

27 patients with following diagnoses were examined by ultrasound: ASD; Aortic valve disease; Mitral valve disease with predominant insufficiency; Mitral stenosis; right heart failure; patients without evidence of cardiac disease. The right ventricular dimension (RVD Index) was assessed representing the distance between the right ventricular epicardial echoes and echoes from the right side of the interventricular septum divided by the patient's body surface area, analogue measurements were done to obtain the left ventricular dimension (LVD Index). The ratio from LVD to RVD was calculated. The motion of the interventricular septum was classified as Normal, Abnormal A and Abnormal B, according to known criteria. Three groups of patients could be differentiated: Patients without cardiac disease; Patients with right ventricular enlargement and ASD; Patients with left ventricular enlargement with aortic and mitral valve disease. In patients with cardiac enlargement, echocardiography provides better information concerning the ratio of the left ventricular to the right ventricular diameter compared to a routine chest X ray.