The Effect of an Arteriovenous Fistula on Renal Hemodynamics and Electrolyte Excretion 1

A B S T R A C T Studies were carried out in anesthetized dogs to characterize the increase in cation excretion which occurs after acute unilateral nephrectomy (AUN). 60 min after AUN, cation excretion had increased from 31.5±2.7 to 66.3±12.0 ueq/min (P < 0.005) and fractional cation excretion had increased from 0.56±0.05 to 1.03±0.14% (P < 0.005), as the glomerular filtration rate was unchanged and renal blood flow fell. The increased cation excretion was accompanied by an increase in fractional phosphate excretion, no change in chloride excretion, and a fall in renin secretion. These alterations in renal function were associated with marked changes in systemic hemodynamics: cardiac output fell from 2.52±0.24 to 1.85+0.16 liters/min (P < 0.001), as diastolic pressure rose without an overall increase in mean arterial pressure, and heart rate fell.To assess the importance of these hemodynamic changes in the renal response, AUN in a separate group of dogs was accompanied by the simultaneous opening of a surgically created femoral artery-to-vein fistula at flow matching the blood flow to the removed kidney. When this was done, no alterations in systemic or renal hemodynamics were observed, and cation excretion did not differ from control. Subsequent closure of the fistula then caused a fall in cardiac output from 2.15±0.25 to 1.77±0.20 liters/min (P < 0.05), and an increase in cation excretion from 34.6±9.5 to This work was presented in part at

Section: Resultsmentioning

confidence: 65%

“…Food was withheld for 18 h before surgery but the dogs were allowed free access to water. They were anesthetized with intravenous sodium pentobarbital (30( mg/kg) and were ventilated via a cuffed endotracheal tube attached to a Harvard respirator (Harvard Apparatus Co., Inc., Millis, Mass.).…”

Section: Introductionmentioning

confidence: 99%

Role of Hemodynamic Changes in the Increased Cation Excretion after Acute Unilateral Nephrectomy in the Anesthetized Dog

Humphreys¹,

Ayus²

1978

“…These include changes in ureteral pressure (43)(44)(45) and in uterine blood flow induced by supine recumbency. The latter is of interest since the uterineplacental circulation has been likened to an arteriovenous shunt (45)(46)(47). Also, postural changes may affect the autonomic nervous system (48)(49)(50).…”

Section: Discussionmentioning

confidence: 99%

Effect of hypotonic expansion on sodium, water, and urea excretion in late pregnancy: the influence of posture on these results

Lindheimer¹,

Weston²

1969

A B S T R A C T Mineralocorticoid-treated, normotensive third trimester subjects positioned in lateral recumbency were studied before and during the infusion of 300 mEq of hypotonic saline. Urinary sodium excretion increased in all subjects from a mean value of 199 to 416 IAEq/min.In 12 maximally hydrated subjects free water clearance (CH2o) and urine flow (V) increased from means of 7.54 and 9.50 to 11.6 and 14.5 ml/100 ml of glomerular filtrate (GFR) Also the ratio of urea to inulin clearance (Curen/Cinuiln) increased from 0.59 to 0.64. The changes in the renal handling of water and urea suggest that fractional sodium reabsorption decreased at proximal nephron sites.The subjects then assumed a supine position, and the results were compared to those obtained during the lateral recumbent control periods. Filtered sodium decreased in 11 experiments, but in five studies it remained up to 2.6 mEq/min above control values. There was only one instance in which a significant increase in sodium excretion occurred. It was concluded that supine recumbency blunts natriuresis despite volume expansion or an increase in the filtered load of sodium.Finally, in the 12 hydrated subjects supine recumbency reduced CH2o and V from a mean of 11.6 and 14.5 to 6.2 and 8.2 ml/100 ml of GFR. In eight of these experiPreliminary reports of this work have been published in abstract form:

“…Some of these reports have been concerned with the excretion of electrolytes which accompany a change in blood volume or in its distribution (24)(25)(26)(27)(28)(29). It is pertinent to this discussion and the concept presented to point out the situations in which an increase in blood volume in the cardiovascular system in the thorax is associated with a water diuresis.…”

Section: Discussionmentioning

confidence: 99%

The Effect of Continuous Negative Pressure Breathing on Water and Electrolyte Excretion by the Human Kidney

Sieker¹,

Gauer²,

Henry³

1954

The effects of decreased intrathoracic pressure on arterial blood pressure (1), venous pressure (2, 3), cardiac output (4), and pulmonary pressure and volume (5) have been investigated in the past. The present study was prompted by the association of marked diuresis with continuous negative pressure breathing in anesthetized animals (6) and the observation that in unanesthetized man continuous positive pressure breathing leads to an oliguria (7). The purpose of this investigation was to demonstrate that human subjects like anesthetized animals have an increased urine flow in response to continuous negative pressure breathing. Observations were made on the renal excretion of water, sodium and potassium, urinary pH, and endogenous creatinine clearance in the hope that the mechanism of the diuresis might be elucidated. METHODSSixteen experiments and six control studies were done with eight normal males who ranged in age from 18 years to 43 years. The subjects received their usual breakfast without added salt on the morning of the experiment. The study was carried out with the subject in the recumbent position in a constant temperature environment In order to obtain an adequate urine volume and a steady state, each subject was maintained on 50 cc. and in some cases 100 cc. of 0.14 per cent saline by mouth (8) and expiration was applied through a standard U. S. Air Force pressure breathing oxygen mask attached by a short tubing to a 40 liter cylinder. This cylinder was ventilated by a suction pump with fresh air at the rate of 100 to 160 liters per minute and rebreathing was prevented by means of a two-way valve in the face mask. The desired negative pressure, which in these experiments was a mean pressure of 15 to 18 centimeters of water, was obtained by varying the air inlet to the container. Control studies duplicated the procedure exactly except that the negative pressure breathing was omitted. Repeat studies were done in all but two subjects.The urine volume for each 15-minute interval was noted and the pH of each sample was determined by means of a glass-calomel electrode pH meter which had an accuracy of 0.1 pH units. Sodium and potassium determinations were made on each urine specimen with an internal standard Perkin Elmer flame photometer. The endogenous creatinine content of the blood and urine was measured by the method of Bonsnes and Taussky (9). The creatinine clearance was used for convenience in these studies with an awareness of both its accuracy and its limitations. The pulse and respiratory rates were followed and periodic observations of the blood pressure were made with a standard sphygmomanometer. RESULTS