Blood pressure and renal blood flow responses to dietary calcium and sodium intake in humans.

This study was designed to determine the interaction between salt and calcium intake on blood pressure (BP) and renal blood flow (RBF) in a predominantly white population. We measured BP and RBF (P-aminohippurate [PAH] clearance) in hypertensive patients after 7 days on a low salt/low calcium diet and again after either a high salt/high calcium diet (HS/HC) or a high salt/low calcium (HS/LC) diet for another 7 days. Compared to low salt BP, both high salt diets increased BP, but the increase with high salt/low calcium was significantly greater than with high salt/high calcium (+14.6 +/- 3.9/+8.2 +/- 1.7 mm Hg v +7.5 +/- 1.9/+2.5 +/- 1.4 mm Hg; systolic/diastolic, both P less than or equal to .05). PAH clearance increased 26 +/- 13 mL/min/1.73 m2 on the HS/HC diet but only 10 +/- 17 mL/min/1.73 m2 on HS/LC (P = .05 between groups). These data suggest that a low calcium diet may contribute to the phenomenon of salt sensitivity in a white population. The low calcium intake appears to affect both the systemic and renal vasculature.

Salt restriction lowers resting blood pressure but not 24-h ambulatory blood pressure.

Dietary salt restriction is the most common therapeutic recommendation given to hypertensives, but past studies have assessed the effect of salt restriction using resting blood pressure (BP) measurements not with the newer technique of 24-h ambulatory BP monitoring. We compared the effect of high (250 mEq Na/day) and low (10 mEq Na/day) salt diets on resting versus ambulatory BP in 12 normal and 15 hypertensive subjects. Each diet was given for 7 days. Ambulatory BP was monitored from day 6 to day 7 of each diet; resting supine BP was measured on the morning of day 8. In normal subjects, neither resting nor ambulatory BP changed with sodium restriction. In hypertensives, resting BP fell 14 +/- 3/6 +/- 2 mm Hg (systolic/diastolic; P less than .01 for both) with sodium restriction while ambulatory BP fell only 4 +/- 2/2 +/- 2 (P = NS). The resting BP fall was significantly greater than the ambulatory BP fall (P less than .05) for both systolic and diastolic pressure. Ambulatory heart rates were also significantly greater during sodium restriction, suggesting that the low salt diet activated the sympathetic nervous system. This may, in turn, have partially offset the hypotensive effect of sodium restriction. We conclude that using resting BP to assess the effect of sodium restriction may overestimate the efficacy of this therapy. Ambulatory BP monitoring should be employed in future studies of sodium restriction.

Feasibility of outpatient electrolyte balance studies.

Clinical studies requiring controlled electrolyte balance have traditionally been conducted in an inpatient (IP), metabolic ward setting. The purpose of this study was to test the feasibility of performing such studies in an outpatient (OP) clinical research setting. Focusing on sodium (Na) and potassium (K) balance, we retrospectively compared 28 subjects studied as OP vs 25 studied as IP on our metabolic ward. We assessed their adherence to our metabolic diets and their compliance with serial 24-hr urine collections. Dietary compliance was assessed by checksheet and urinary Na excretion; urine collection accuracy was determined by serial 24-hr creatinine excretion. The diets for both studies contained a low Na phase (10 mEq) and a high Na phase (200 mEq for IP and 250 mEq for OP), each lasting 1 week. When in balance on the low Na diet, 24-hr Na excretion was 4.6 +/- 0.7 mEq for OP and 13.4 +/- 2.2 mEq for IP, indicating excellent compliance with the low salt diet. Na excretion on the high Na diet was 184.5 +/- 7.4 mEq for OP and 195.3 +/- 9.6 mEq for IP. These values were not significantly different from each other; however, the OP were significantly less than their diet of 250 mEq Na (p less than 0.05). This difference may have been due to dermal Na losses. K excretion was also similar in the two groups. There was no significant difference in the reproducibility of individual multiple urinary creatinine measurements in OP vs IP.(ABSTRACT TRUNCATED AT 250 WORDS)

Nephrotoxicity from angiographic contrast material. A prospective study.

Three hundred and seventy-eight hospitalized patients undergoing nonrenal angiography were evaluated for subsequent changes in renal function. Acute renal failure was defined as a rise in the serum creatinine level of 1.0 mg/dl or more. Several factors that appeared to play no significant role in causing acute renal failure included: the volume of contrast material injected, the anatomic site of injection and the presence of a prior history of cardiovascular disease or diabetes mellitus. The single risk factor identified was the presence of preexistent azotemia (blood urea nitrogen of 30 mg/dl and serum creatinine of 1.5 mg/dl). Whereas nonazotemic patients had a 2 percent incidence of definite acute renal failure, patients with chronic azotemia (mean blood urea nitrogen/creatinine = 47/2.3 mg/dl) had a 33 percent incidence. Three patients required short-term dialysis, and two required potassium-exchange resin therapy. No patient required permanent dialysis, and no patient died of acute renal failure. The persistence of a positive nephrogram 24 hours after angiography was a sensitive detector of a rise in the serum creatinine level although more expensive than the creatinine determination. While urine sediment analysis confirmed the diagnosis in many cases, it was relatively insensitive. Monitoring of urine volume proved to be of little value. We recommend a screening serum creatinine determination 24 to 48 hours after infusion of angiographic contrast material in azotemic patients.

Psychosocial crisis in diabetic renal failure.

Twenty-nine diabetic renal failure patients suffered a psychosocial crisis at the time when chronic dialysis or renal transplantation was required. These patients could be classified into groups as to the impact of the crisis in terms of participation in life-support therapy. Group 1 consisted of potentially lethal mechanism (9 patients): discontinued dialysis (5); refused to start dialysis (3); overt act to cause personal harm (1). Group 2 contained probably nonlethal mechanism (11 patients): threatened to discontinue dialysis or to never start dialysis if not given a chance for a transplant (5); threatened to discontinue dialysis or to never start dialysis (5); threatened to cause personal harm (1). Group 3 consisted of a combination of mechanisms (9 patients): with drug abuse (4); without drug abuse (5). Important similarities between the groups were easier to document than were subtle differences in the kinds of options in family and employment relationships; in the degree of objective and subjective handicap due to impaired vision; in the level of expectation and/or disappointment following renal transplantation; and in the capacity to cope with changing personal relationships produced by the complications of diabetes.