Expansion and relaxation of magnetic mirror domains in a Pt/Co/Pt/Co/Pt multilayer with antiferromagnetic interlayer coupling.

We detail measurements of field-driven expansion and zero-field relaxation of magnetic mirror domains in antiferromagnetically coupled perpendicularly magnetized ultrathin Co layers. The zero-field stability of aligned ('mirror') domains in such systems results from non-homogeneous dipolar stray fields which exist in the vicinity of the domain walls. During field-driven domain expansion, we evidence a separation of the domain walls which form the mirror domain boundary. However, the walls realign, thereby reforming a mirror domain, if their final separation is below a critical distance at the end of the field pulse. This critical distance marks the point at which the effective net interaction between the walls changes from attractive to repulsive.

Dynamic binding of driven interfaces in coupled ultrathin ferromagnetic layers.

We demonstrate experimentally dynamic interface binding in a system consisting of two coupled ferromagnetic layers. While domain walls in each layer have different velocity-field responses, for two broad ranges of the driving field H, walls in the two layers are bound and move at a common velocity. The bound states have their own velocity-field response and arise when the isolated wall velocities in each layer are close, a condition which always occurs as H→0. Several features of the bound states are reproduced using a one-dimensional model, illustrating their general nature.

Creep and flow regimes of magnetic domain-wall motion in ultrathin Pt/Co/Pt films with perpendicular anisotropy.

We report on magnetic domain-wall velocity measurements in ultrathin Pt/Co(0.5-0.8 nm)/Pt films with perpendicular anisotropy over a large range of applied magnetic fields. The complete velocity-field characteristics are obtained, enabling an examination of the transition between thermally activated creep and viscous flow: motion regimes predicted from general theories for driven elastic interfaces in weakly disordered media. The dissipation limited flow regime is found to be consistent with precessional domain-wall motion, analysis of which yields values for the damping parameter, alpha.

Changes of plasma noradrenaline levels in the renal and systemic circulation after successful percutaneous transluminal angioplasty in renovascular hypertension.

The sympathetic nervous system involvement in the pathogenesis of human renovascular hypertension was studied in 10 hypertensive patients with unilateral renal artery stenosis, who underwent percutaneous transluminal angioplasty (PTA). Before PTA, systolic/diastolic BP readings were 185.3 +/- 7.8/123.2 +/- 5.1 mmHg, peripheral PRA values were 8.63 +/- 2.27 ngAl/ml/h, the ratio RVRR was 2.15 +/- 0.27, the ratio V1-IVC/IVC was 1.00 +/- 0.23 (V1 = PRA from the renal vein of the stenotic side, IVC = PRA from the inferior vena cava) and the ratio V2-IVC/IVC was 0.04 +/- 0.02 (V2 = PRA from the renal vein of the non-stenotic side); 30 min after successful PTA the respective values of the above measured parameters were: 144.2 +/- 6.7/98.2 +/- 3.1 mmHg (p less than 0.01), 8.13 +/- 2.21 ngAl/ml/h (p less than 0.005), 1.79 +/- 0.19 (p less than 0.01), 0.68 +/- 0.18 (p less than 0.001) and 0.06 +/- 0.02 (p less than 0.005). Peripheral plasma noradrenaline levels (plNA) were 0.694 +/- 0.058 ng/ml, plNA levels from the renal vein of the stenotic side were 0.962 +/- 0.108 ng/ml and plNA levels from the renal vein of the non-stenotic side were 0.759 +/- 0.092 ng/ml; 30 min after successful PTA the respective values were 0.518 +/- 0.055 ng/ml (p less than 0.01), 0.681 +/- 0.078 ng/ml (p less than 0.005) and 0.510 +/- 0.063 ng/ml (p less than 0.005). It is suggested that the reversal of chronic renal ischaemia by PTA induced statistically significant changes in the sympathetic nervous system activity, parallel to the changes of renin secretion.

The effect of spironolactone in hypertensive patients on regular haemodialysis and after renal allotransplantation.

To determine the role of the renin-angiotensin-aldosterone system in the maintenance of hypertension in patients with end stage renal disease, twenty four hypertensive patients were studied on regular haemodialysis treatment (RDT) and after successful kidney transplantation. The first group consisted of nine patients on RDT with their own kidneys in situ, and the second group consisted of nine kidney transplants. All 18 patients were given spironolactone 300 mg daily for three weeks following a control period of the same duration. In addition, three anephric patients on RDT were studied with the above protocol and three other patients on RDT were given the same dose for only six days. Blood pressure (BP), body weight, plasma K-Na, aldosterone and renin activity in all patients, and Na and aldosterone in urine in the second group were measured. In the first group of patients on RDT plasma potassium and renin activity increased significantly but BP remained unchanged. In the second group of transplanted patients plasma potassium, renin activity, and aldosterone were increased and BP diminished significantly. In the group of three anephric patients plasma potassium increased but plasma renin activity remained very low. Finally, in the patients on dialysis who received spironolactone for only six days there was a parallel increase of serum potassium and plasma renin activity. These findings suggest that in patients on RDT spironolactone stimulates renin secretion and potassium retention possibly by an effect on the remaining nephrons and/or the intestinal wall. On the contrary, in the transplanted patients the effect of spironolactone on the renal tubule is capable of producing sodium depletion and fall in BP.

Effect of hemodialysis on left ventricular performance.

Systolic time intervals (STI) and echocardiograms (Echo) were performed before and 30 min after hemodialysis (H) in 19 stable patients (pts) with chronic renal failure undergoing maintenance H. The % shortening of the internal diameter (% delta D), the mean velocity of circumferential fiber shortening (VCF), and the ratio of the pre-ejection period to the left ventricular (LV) ejection time (PEP/LVET) were used as indices of LV performance; the electromechanical systole corrected for heart rate (QS2I) was used as an index of adrenergic activity. After hemodialysis, LV function was improved in 9 pts, Group (GI) and decreased in 10 pts (GII). Changes due to H are shown. The % delta D and VCF before H were normal in GI but abnormal in GII (31.6 +/- 1.4 vs 24.5 +/- 1.4 and 1.07 +/- 0.06 vs 0.88 +/- 0.04, respectively). Systolic blood pressure remained unchanged in GI but decreased in GII (-9.5 +/- 4 mm Hg, p less than 0.01). Body weight decreased significantly (p less than 0.05) and equally in both Gs (-1.2 +/- 0.03 in GI and -1.6 +/- 0.03 in GII). Serum electrolytes, creatinine, and hemoglobin were identical in both Gs before and after H. LV performance improved in pts with LV dysfunction before H, but decreased in pts with normal LV function before H. The decreased afterload in GII and the different effect of alterations in preload and afterload in the failing and normal LV most likely account for these changes. STI and Echo provide simple techniques to assess changes in LV function due to H and one is complementary to the other.

The effect of preventive administration of verapamil on acute ischaemic renal failure in dogs.

In 15 healthy mongrel dogs the kidneys were exposed bilaterally, the renal pedicle was clamped on one side (control kidneys) and verapamil, 0.5 mg/kg body weight, was given intravenously. Ten minutes later the renal pedicle on the other side was clamped (verapamil group). At the end of a 60-minute ischaemic period, blood flow was re-established. The mean time to initiation of diuresis was shorter in the verapamil group and creatinine clearance was significantly higher. At the end of the two-hour experiment the mean fractional excretion of sodium and the mean urinary excretion of LDH were higher in the control group. CNa, CK, Cosm and Curea were significantly higher in the verapamil group during the two-hour period of study after revascularisation. On a statistical basis 60 minute acute ischaemic renal failure is significantly modified by the administration of verapamil.

Effect of furosemide on acut ischaemic renal failure in the dog.

The effect of furosemide on the development of the acute ischaemic renal failure in the dog was studied. 11 canine kidneys were used as controls (group I) and 12 as a group where furosemide (6-8 mg/kg of body weight) was given (group II) immediately after releasing the clamps. Urine volume and sodium clearance were found significantly higher in the second group of kidneys during a period of 60 min after restoration of the blood flow to the kidney. Urea clearances remained low with no noted difference between the 2 groups. By the end of the first hour osmolar and potassium clearances were found to be significantly higher in the second group. The above findings suggest that furosemide given after an induction of acute ischaemic renal failure in the dog provides, up to the 1st hour after recirculation, some benefit in water and solute excretion but no benefit in urea clearance.

Haemoglobin oxygen dissociation curve in patients on regular haemodialysis.

Changes in the haemoglobin-oxygen dissociation curve (Hb-O2) and the factors which influence its position were studied before and after dialysis in 7 patients on regular haemodialysis during 20 dialyses. Seven normal subjects were used as controls. Haemoglobin showed a lower than normal affinity for O2 in uraemic patients before haemodialysis (p50in vivo = 33.09 +/- 0.92 mmHg and p507.4 = 31.51 +/- 0.73 mmHg, P less than 0.001), and this could be considered as a protection against tissue anoxia. After dialysis Hb-O2 affinity at the patient's pH (p50 in vivo = 27.97 +/- 0.57 mmHg, P less than 0.001). This probably eliminates the benefits of the predialysis balance of tissue oxygenation, producing a degree of hypoxia, and may play a role in the genesis of post-dialysis symptoms. Measures should be taken to improve oxygenation of high risk patients with latent heart failure or respiratory disturbances during and after dialysis.