Xenon transit through the oliguric human kidney: analysis by maximum likelihood

Profound hypotension and sodium retention with the ovarian hyperstimulation syndrome

A 34-year-old woman developed profound hypotension and sodium retention following hormonal induction of ovulation. There was a transient response to infusion of albumin, but hypotension and hyponatremia persisted for 5 days. Nevertheless, acute renal failure did not develop. Available information indicates that this syndrome can occur with exogenous administration of gonadotrophic hormones or with a successful pregnancy.

The management of acute renal failure in the intensive therapy unit

The intensive care setting is well recognised as a highly technical area, and intensive care nurses are regularly introduced to new and increasingly more sophisticated and complicated equipment. The aim of this article is to eliminate some of the confusion surrounding the choice of dialysis treatment in acute renal failure by reviewing the different types of continuous renal replacement therapy (CRRT). Explanation of the principles behind CRRT is expanded by identification of the main differences between continuous haemofiltration and continuous haemodialysis. Some of the more common problems encountered are discussed and suggestions for nursing practice included.

Noninvasive monitoring of renal blood flow characteristics during acute renal failure in man

Duplex Doppler ultrasound (DDU) was used to study the blood flow characteristics of the renal interlobar artery in 20 subjects with acute renal failure (ARF), 14 subjects with transient impairment of renal function and 23 control subjects with normal function. Renovascular resistance was assessed by pulsatility index (PI) and change in flow velocity by change in mean frequency shift (delta f). The 99% confidence intervals for PI in the three groups were 3.32-5.46, 1.58-2.34 and 0.99-1.33 respectively. Values for delta f were 0.2-0.38, 0.5-0.62 and 0.7-1.02 kHz respectively. Ten ARF patients recovered function, 99% confidence intervals for PI just prior to recovery were 0.9-1.48 and for delta f 0.52-1.02 kHz. There was increased renovascular resistance and reduced intrarenal blood flow velocity at the onset of ARF. These changes persisted during ARF; recovery of function occurred after they returned to normal. Similar, but less marked, changes were found in patients with a transient impairment of function.

Application of the maximum likelihood principle to separate exponential terms in T2 relaxation of nuclear magnetic resonance

The method of maximum likelihood has been implemented for the estimation of multiple exponential components of T2 decay curves in spin echo NMR measurements on biologic tissues. Each Each component contributes an exponential term described by two parameters (initial amplitude and T2) to the T2 decay curve. The maximum likelihood method estimates the parameters and their standard errors for all terms simultaneously, avoiding the subjectivity inherent in methods such as graphical peeling. In the model used, it was assumed that water protons are compartmentalized and that the measured spin echo signals from the protons undergoing relaxation obey the Poisson distribution. A system of non-linear equations was derived and solved iteratively for the values of the exponential parameters which maximize the likelihood of obtaining the observed data under these assumptions. The approach was implemented for bi- and tri-exponential models on a MicroVAX II computer (Digital Equipment Corporation, Maynard, MA). Simulations of bi- and tri-exponential data, with and without system noise, were analyzed to assess the accuracy and reproducibility of the method. A subset of the simulations was repeated with non-linear least squares techniques and was compared to the results obtained with maximum likelihood. Rabbit muscle and gerbil brain samples were measured and analyzed with the maximum likelihood method. The simulations showed that within specific limits on relative sizes and relaxation rates of components, these parameters can be estimated with errors less than 5%. The comparison to non-linear least squares analysis showed that the maximum likelihood method is generally superior in estimating the parameters in difficult cases. The results from tissue measurements demonstrate that the method is effective even in cases where graphical peeling would clearly not yield reliable results.

Role of the medullary perfusion defect in the pathogenesis of ischemic renal failure

Experiments were performed on rats to investigate the significance of the medullary hyperemia known to follow renal ischemia. To this end, its frequency was determined, its severity was quantified, and its relation to renal function was examined early (1 to 3 hr) and later (18 hr) after 45 min of warm ischemia. All kidneys were found to have a hyperemic outer medulla early after ischemia, which was shown to develop during the period of ischemia itself, but which was found to be highly variable in its severity. The degree of hyperemia was assessed both subjectively by grading and by histometric determinations of inner stripe capillary volume. One to hours after ischemia, the severity of medullary hyperemia was reflected in all indices of renal function, the least congested kidneys showing the best function. Eighteen hours after ischemia, the degree of medullary hyperemia was reflected in all indices of renal function, except urine flow rate; the non-congested kidneys showed functional recovery and the still-congested kidneys showed worsening function. Glomerular blood flow, known to be preferentially reduced in deep nephrons 1 to 3 hr after ischemia, had normalized 18 hr after ischemia in the non-congested kidneys but was still severely and unevenly depressed in the congested kidneys. It is concluded that congestion of the outer medulla is a key event in ischemic renal failure, its occurrence is coincidental with the reduction in deep nephron perfusion and urinary concentrating power in the early and maintenance phase and its disappearance heralds the restoration of deep nephron perfusion and urinary concentrating ability in the recovery phase.

[Toxic nephropathies (author's transl)]

Direct tubular damage, hypersensitivity reaction, metabolically mediated kidney disturbances, and chronic nephropathies are important sequelae of several drugs or their metabolites. In this review the drug-induced kidney disease is discussed from a clinical, histological, and pathogenetic point of view. The knowledge of possible nephrotoxic reactions and their underlying toxins are essential for prevention of this kidney disease.

Synergism of dopamine plus furosemide in preventing acute renal failure in the dog

The protective effects of a combination of dopamine and furosemide were studied in dogs during the initial phase of acute renal failure (ARF) induced by intravenous uranyl nitrate (10 mg/kg). Fifteen minutes after injection of the nephrotoxin, and infusion of dopamine (3 micrograms/kg/min), furosemide (1 mg/kg/bolus followed by 1 mg/kg/hr), or both drugs simultaneously were given for 6 hours. Exogenous creatinine clearance was measured for 6 hours, and the intrarenal blood flow was measured with radioactive microspheres before and 3 hours after the induction of ARF. Treatment with both dopamine and furosemide produced renal vasodilatation, high urine flow rate, and attenuation of the fall in GRF seen in untreated animals. In contrast, single use of dopamine or furosemide was totally ineffective in producing renal vasodilation, a diuresis, or the maintenance of the GFR. These data indicate that dopamine plus furosemide have a synergistic effect in preventing the early pathophysiologic changes associated with ARF in this animal model. Maintenance of a high GFR correlated best with the enhancement of solute excretion and urine flow rate. Potential protective effects of dopamine plus furosemide in other models of ARF deserve careful investigation.

beta-Adrenoceptor-blocking agents and the kidney: effect of nadolol and propranolol on the renal circulation

1 Nadolol was administered intravenously to five hypertensive patients and three healthy volunteers in balance on a 10 mEq sodium intake. 2 Nadolol (0.3-10.0 micrograms/kg) induced a significant, dose-related increase in renal blood flow, measured with radioxenon, with a maximum increase of 72 +/- 4 ml/100g/min (26%) at 3.0 micrograms/kg. 3 Heart rate and plasma renin activity decreased significantly over the same dose range. 4 The renal vascular response to nadolol contrasts sharply with those found with other beta-adrenoceptor-blocking agents. 5 The magnitude of the increase in renal blood flow, its time-course and the parallel fall in plasma renin activity raise the possibility that the renal vasodilation reflects the reversal of angiotensin's influence on the renal arterial bed.

Assessment of intrarenal perfusion with radioxenon: a critical review of analytical factors and their implications in man

Radioxenon has achieved wide use for assessing tissue perfusion. Here we review its application to the kidney for assessing mean blood flow and intrarenal perfusion rates. Correlation with alternative methods in animals suggests that the initial disappearance slope provides an adequate measure of mean renal blood flow despite the theoretical limitations of this approach. The stochastic method and compartmental analysis can also provide an acceptable measure fo mean renal blood flow, but only after the slowest flow components have been removed. Compartmental analysis does, however, provide an index of cortical perfusion not available from other methods. The evidence that the rapid component of xenon washout provides an index of cortical perfusion in man is reviewed, along with insights gained from the application of this approach to human disease.

Studies of the mechanism of oliguria in a model of unilateral acute renal failure

To further evaluate the mechanism of the oliguria of acute renal failure, a model was utilized in which intense and prolonged vasoconstriction produced the unilateral cessation of urine flow. The radioactive microsphere method was used to measure total and regional blood flow before and after the intrarenal infusion of norepinephrine, 0.75 mug/kg/min, for 2 h in the dog. In the control kidney, renal blood flow increased 32% 48 h after norepinephrine in association with a fall in the fractional distribution of flow to the outer cortex. In the experimental kidney, total renal blood flow fell from 190 ml/min before norepinephrine to 116 ml/min at 48 h (P < 0.025) with a uniform reduction in cortical blood flow. After the administration of 10% body wt Ringer's solution, there was a marked redistribution of flow to inner cortical nephrons in both the control and experimental kidney. In addition, there was a marked increase in total blood flow in both kidneys. On the experimental side, flow rose to 235 ml/min, a value greater than in either the control period (P < 0.05) or at 48 h after norepinephrine (P < 0.001). However, in spite of this marked increase in blood flow, there was essentially no urine flow from the experimental kidney. In separate studies, the animals were prepared for micropuncture. In all studies, the surface tubules were collapsed, and there was no evidence of tubular obstruction or leakage of filtrate. Over 99% of the 15-muM spheres were extracted in one pass through the experimental kidney. An analysis of the forces affecting filtration suggested that an alteration in the ultrafiltration coefficient may be responsible, at least in part, for the anuria in this model. In this regard, transmission and scanning electron microscopy revealed a marked abnormality in the epithelial structure of the glomerulus. It is suggested that a decrease in glomerular capillary permeability may be present in this model of acute renal failure.