Susan K. Fellner

Left Ventricular Contractility Varies Directly with Blood Ionized Calcium

STUDY OBJECTIVE To determine the effect of variations in blood ionized calcium (Ca2+) on myocardial contractility independent of changes in loading conditions and other biochemical variables. DESIGN Hemodialysis done in a randomized, double-blind manner with dialysates differing in calcium concentration only. Left ventricular contractility was assessed using the load- and heart rate-independent relationship between end-systolic wall stress (sigma es) and rate-corrected velocity of fiber shortening (Vcfc). SETTING In-hospital dialysis unit and echocardiography laboratory of a university medical center. PATIENTS Seven patients with stable, chronic renal failure maintained on regular hemodialysis. INTERVENTIONS Each patient was hemodialyzed three times within 1 week with dialysates differing in calcium concentration only. Ultrafiltration was adjusted to achieve the same postdialysis weight. Immediately after dialysis, two-dimensionally targeted M-mode echocardiographic and calibrated carotid pulse tracings were recorded over a wide range of left ventricular end-systolic wall stress values (a measure of left ventricular afterload) generated by either methoxamine or nitroprusside. MEASUREMENTS AND MAIN RESULTS After dialysis, three statistically distinct levels of Ca2+ were achieved. When Ca2+ was 1.34 +/- 0.03 mmol/L, Vcfc, calculated at a common level of afterload (sigma es = 50 g/cm2), was 1.01 +/- 0.05 cir/sec; at low Ca2+ (1.02 +/- 0.02 mmol/L), Vcfc fell to 0.89 +/- 0.04 cir/sec (P less than 0.001 compared with medium); at high Ca2+ (1.68 +/- 0.07 mmol/L) Vcfc rose to 1.10 +/- 0.03 circ/sec (P less than 0.001 compared with medium and low). CONCLUSION Variations in Ca2+ are directly correlated with clinically significant changes in myocardial contractility.

An Outbreak of Fatal Fluoride Intoxication in a Long-Term Hemodialysis Unit

Long-term hemodialysis is the most common treatment for end-stage renal disease in the United States and was administered to more than 155 000 patients in 1991 [1]. Technologic developments in dialyzer membranes, dialysis machines, and vascular access have made hemodialysis routine, but the procedure remains potentially hazardous because of mechanical malfunctions and human error [2]. Serious adverse reactions have resulted, particularly from microbiological or chemical contamination of hemodialyzers and dialysate solutions [2-7]. Municipal water used to prepare dialysate must be purified to ensure that no contaminants remain that would be toxic to patients receiving dialysis. Reverse osmosis is the most common procedure to remove ions, but deionization systems, alone or after reverse osmosis, were used by nearly one half of the hemodialysis centers in the United States in 1991 [1]. Paradoxically, these deionization systems pose an additional hazard. When their ion exchange resin becomes exhausted, toxic ions previously removed from municipal water and bound to the resin may be displaced into the effluent stream of purified water [5, 6]. Johnson and Taves [8] found that high concentrations of fluoride could be released in this manner into effluent, but no cases of acute fluoride intoxication attributable to this mechanism have been reported. We recently investigated in a hemodialysis unit an outbreak of acute illness and death caused by fluoride intoxication. We describe the epidemiologic characteristics of the outbreak and the pattern of deionization system use that resulted in massive fluoride efflux from an exhausted resin. The Outbreak On 16 July 1993, several patients treated at a long-term hemodialysis unit became ill during or soon after hemodialysis. The predominant symptoms were severe pruritus, headache, nausea, and chest or back pain. One patient had cardiac arrest immediately after completion of dialysis. Patients continued to receive dialysis treatment until that afternoon, when the unit was notified that two other patients had had cardiac arrests after leaving the unit. Dialysis treatments were stopped during the third shift of patients, and patients who had received hemodialysis on 16 July were brought to the University of Chicago Hospital for evaluation. Those who had any symptoms were admitted to the hospital, and patients whose scheduled treatment had been interrupted resumed dialysis at the hospitals acute care dialysis unit. An investigation was then initiated. Methods Clinical and Epidemiologic Characteristics of the Patients We interviewed patients who received long-term hemodialysis treatment in the unit and reviewed their records to identify symptoms during the period 26 April to 16 July 1993, when a temporary water purification system was used. We considered that patients had severe hemodialysis-associated illness if within 5 hours after the start of dialysis either severe pruritus developed or cardiac arrest ensued, or if at least three of the following symptoms developed: burning or feverish feeling; headache; nausea or vomiting; syncope or near syncope; pain in the chest, back, or abdomen; or diarrhea. We reviewed medical and dialysis unit records to determine patient age, sex, primary underlying illness, results of physical examination and clinical laboratory tests, number of years of long-term hemodialysis, duration of the hemodialysis session on 15 or 16 July, hemodialysis blood flow rate, type of dialyzer, and dialyzer reuse. We considered that patients had cardiac disease if they had coronary artery disease, cardiomyopathy, valvular heart disease, or clinically significant electrocardiographic abnormalities such as bundle-branch block. For statistical analysis, we compared each continuous variable using the t-test and the Wilcoxon test, and proportions were compared using the Fisher exact test [9]. Dialysis Unit Design and Water Supply We surveyed the municipal water supply, dialysis water purification systems, types of dialyzers and dialysis machines, dialysate preparation, and dialyzer reprocessing procedures. We also reviewed records of daily municipal water treatment and periodic chemical analyses by the City of Chicago Department of Water during 7 June to 16 July 1993. Sample Collection and Analysis Blood specimens were collected on 16 July from all surviving patients who had had hemodialysis treatment that day. Complete blood count and routine blood chemistry testing were done. A portion of each sample was stored at 70C and later assayed for fluoride. Samples of purified water used for dialysate preparation were collected on 16 July 1993 for analysis of 18 chemicals for which maximum allowable levels were established by the Association for the Advancement of Medical Instrumentation [10]. Samples of municipal water, purified water used to prepare dialysate, acid concentrate, bicarbonate concentrate, and bicarbonate dialysate also were collected on 16 July and assayed for fluoride concentration using an ion-selective electrode system (Orion Research, Cambridge, Massachusetts) [11]. Additional samples of purified water from each of the two sets of deionization tanks in the room (room 1) where sick patients had received hemodialysis treatment were collected on 17 July after approximately 1000 L of water had flowed through the systems when the dialysis machines were tested. These samples and dialysate collected from room 1 on 16 July were assayed by the Illinois Department of Public Health for fluoride and for toxic organic compounds by gas chromatography-mass spectrometry and by ultraviolet spectrometry. Postmortem serum specimens were obtained and assayed for fluoride by the Cook County Medical Examiners Office. Model Deionization System To confirm that sustained high levels of fluoride in effluent from the deionization system in the dialysis unit could have been released by operating the system after the resin was exhausted, a laboratory model of the system was constructed. An activated carbon tank and four newly regenerated deionization tanks were supplied by the water treatment contractor who maintained the system in the dialysis unit. The four tanks were arranged in series as follows: first, a cation resin tank containing sulfonated polystyrene (Amberlite IR-120 Plus, Rohm and Haas, Philadelphia, Pennsylvania) in position 1; next, an anion resin tank containing a type II quaternary ammonium resin (Amberlite IRA-410) in position 2; then two mixed-bed tanks containing both cation and anion resins in positions 3 and 4. This system was used to treat 27 500 L of municipal water, a volume estimated to be the same as that which flowed through each of the two sets of deionization tanks in room 1 from 26 April to 7 June 1993. A second deionization system was then constructed with newly regenerated tanks in positions 1, 2, and 4; the mixed-bed tank from position 4 in the first deionization system was moved into position 3, as had been done in the dialysis unit. The second deionization system was operated beyond exhaustion of the resins to simulate use from 7 June to 16 July 1993. During operation of the two model deionization systems, effluent was collected to measure fluoride concentration and resistivity, which decreases as electrolyte concentration increases. Results Clinical and Epidemiologic Characteristics of the Patients At the time of the outbreak, 56 patients were receiving long-term, high-flux hemodialysis. One half of the patients were treated on Monday, Wednesday, and Friday, and the other half were treated on Tuesday, Thursday, and Saturday. Twenty-one patients received at least a portion of their scheduled dialysis on 16 July before treatments were stopped. Nine of the 21 patients treated on 16 July and 3 of the 25 patients treated on 15 July were classified as cases. Review of dialysis unit records for the previous 12 weeks identified only 1 additional patient who met the case definition. That patient, who had a cardiac arrest on 9 June, was not considered to be part of this outbreak and thus we did not include him as a case-patient. Table 1 summarizes the characteristics of both the 12 patients classified as case-patients and the 20 patients not considered cases who were treated during the same shifts. Symptoms other than cardiac arrest began 1 to 3 hours after the start of hemodialysis in all cases and resolved by the next morning. Case-patients who reported pruritus described it as the most severe they had ever experienced. Diphenhydramine hydrochloride was taken by 5 patients, none of whom noted any relief. Pruritus lasted more than 6 hours in the surviving patients who became ill on 16 July and less than 3 hours in the three patients who became ill on 15 July. Table 1. Demographic Characteristics and Clinical Features of Patients Receiving Long-Term Hemodialysis Cardiac arrests occurred 4 to 6.5 hours after hemodialysis began. Antecedent symptoms were pruritus, vomiting, and/or chest pain in two patients and leg pain in the third. Emergency medical care records showed fatal ventricular fibrillation in all three patients; one was restored briefly to sinus rhythm by electrical cardioversion. All three had preexisting cardiac abnormalities: left bundle-branch block, right bundle-branch block and coronary artery disease, or mitral stenosis with atrial fibrillation. All six surviving patients who became ill on 16 July were hospitalized that evening. None had new abnormal findings on physical examination or complete blood count, and none had hyperkalemia. Three patients had low serum calcium concentrations of 7.8 to 8.3 mg/dL (1.95 to 2.54 mmol/L). Patients in the dialysis unit received high-flux dialysis in two treatment rooms using individual self-proportioning, volumetrically controlled ultrafiltration machines (COBE Centrysystem 3, COBE Laboratories, Lakewood, Colorado). The 12 patients who became ill received dialysis treatment for a mean of 2.8 0.7 hours (ra

History of the Science of Dialysis

Thomas Graham (1805-1869), who is credited with seminal work on the nature of the diffusion of gases and of osmotic forces in fluids, can properly be called the father of modern dialysis. His apparatus to study the behavior of biological fluids through a semipermeable membrane clearly presaged the artificial kidney in clinical use today. In 1913, John Abel and coworkers reported the first application of the principles of diffusion to remove substances from the blood of living animals. Unaware of Abels work, Georg Haas (1886-1971) performed the first human dialysis in the German town of Giessen in 1924. But it was not until 1945 that Willem Johan Kolff, working under extremely difficult wartime conditions in The Netherlands, achieved the first clinically successful hemodialysis in a human patient.

Capacitative calcium entry in smooth muscle cells from preglomerular vessels.

Calcium entry via voltage-gated L-type channels is responsible for at least half of the increase in cytosolic calcium ([Ca2+]i) in afferent arterioles following agonist stimulation. We sought the presence of capacitative calcium entry in fresh vascular smooth muscle cells (VSMC) derived from rat preglomerular vessels. [Ca2+]iwas measured using fura-2 ratiometric fluorescence. Vasopressin V1 receptor agonist (V1R) (10-7M) increased [Ca2+]iby ∼100 nM. A calcium channel blocker (CCB), nifedipine or verapamil (10-7 M), inhibited the response by ∼50%. V1R in the presence of CCB increased [Ca2+]ifrom 106 to 176 nM, confirming that calcium mobilization and/or entry may occur independent of voltage-gated channels. In nominally Ca2+-free buffer, V1R increased [Ca2+]ifrom 94 to 129 nM, denoting mobilization; addition of CaCl2 (1 mM) further elevated [Ca2+]ito 176 nM, indicating a secondary phase of Ca2+ entry. Similar responses were obtained when CCB was present in calcium-free buffer or when EGTA was present. In nominally Ca2+-free medium, the sarcoplasmic reticulum Ca2+-ATPase inhibitors (SRCAI), thapsigargin and cyclopiazonic acid (CPA), increased [Ca2+]ifrom 97 to 128 and 143 nM, respectively, and to 214 and 220 nM, respectively, when 1 mM extracellular Ca2+ was added. In the presence of verapamil, the results with CPA acid were nearly identical. In Ca2+-free buffer, the stimulatory effect of V1R or SRCAI on the Ca2+/fura signal was quenched by the addition of Mn2+ (1 mM), demonstrating divalent cation entry. These studies provide evidence for capacitative (store- operated) calcium entry in VSMC freshly isolated from rat preglomerular arterioles.

Elevated lipoprotein(a) levels in renal transplantation and hemodialysis patients

Hyperlipidemia poses a risk for cardiovascular disease in both hemodialysis and renal transplantation patients. Although lipid profiles differ between the 2 populations, we evaluated the possibility that both groups have similar abnormalities of lipoprotein(a) [Lp(a)]. Mean serum Lp(a) and standard error of the mean (SEM) in hemodialysis and transplant recipients was 16.6 +/- 4.7 and 18.3 +/- 3.6 mg/dl, respectively, compared with 10.7 +/- 4.1 mg/dl in healthy controls, p less than 0.05. That serum Lp(a) levels are significantly elevated in dialysis and renal transplantation patients suggests at least 1 common pathogenic mechanism for the high incidence of atherosclerosis in both groups.

Laparoscopic bilateral nephrectomy for renin-mediated hypertension

Hypertension arising from retained native kidneys complicates the management of recipients of renal transplants. Reluctance to administer angiotensin-converting enzyme inhibitor (ACEI) drugs to patients taking cyclosporine has reopened the question of performing native nephrectomies for poorly controlled, renin-dependent hypertension. We report the first published cases of simultaneous bilateral laparoscopic nephrectomies in 2 patients: 1 in preparation for living-related donor transplantation and the other ten months following cadaver transplantation in a patient whose end-stage renal disease was from malignant nephrosclerosis. Both had very severe hypertension resistant to multiple drugs and both became normotensive with little or no antihypertensive medication following nephrectomies. A bilateral nephrectomy is currently feasible using a laparoscopic approach.

Improved Lipid Profiles in Patients Undergoing High-Flux Hemodialysis

Hyperlipidemia is one of many atherogenic risk factors encountered by patients undergoing chronic hemodialysis (HD). We have studied lipid profiles in these patients and have found less hypertriglyceridemia in those undergoing high-flux HD than those receiving traditional HD. Mean +/- SEM triglyceride level was 1.62 +/- 0.15 mmol/L (143.3 +/- 13.6 mg/dL) in high-flux dialysis patients, 2.39 +/- 0.27 mmol/L (211.6 +/- 24.1 mg/dL) in conventional dialysis patients, and 1.55 +/- 0.13 mmol/L (137.1 +/- 11.5 mg/dL) in normal age- and sex-matched controls. In addition, we found that in patients undergoing high-flux HD, females had higher high-density lipoprotein2 (HDL2) levels (0.62 +/- 0.03 mmol/L [23.8 +/- 1.3 mg/dL]) than males (0.33 +/- 0.04 mmol/L [12.9 +/- 1.7 mg/dL]) (P < 0.01). The mechanism(s) responsible for divergent lipid profiles in subsets of HD patients deserves further investigation. Whether reductions of hypertriglyceridemia and/or increases of HDL2 will diminish the incidence of cardiovascular disease in dialysis patients is unknown.

Effect of renal transplantation on serum oxalate and urinary oxalate excretion

Serum levels of oxalate are elevated in uremic patients on dialysis. The effect of living related donor kidney transplants on serum and urine oxalate levels was studied in 8 patients. Serum and urine oxalate levels were measured prior to transplant, on the day of transplant and daily for 5 days postoperatively, and the results compared to those in 11 normal subjects. All transplanted kidneys functioned immediately. Serum oxalate fell from 55 +/- 9 mumol/l (484 +/- 79 micrograms/dl) before transplant to 21 +/- 3 mumol/l (185 +/- 26 micrograms/dl) the day after transplant, and to 9 +/- 2 mumol/l (79 +/- 18 micrograms/dl) 72 h after transplant. Serum oxalate in normal subjects was 9 +/- 2 mumol/l (79 +/- 18 micrograms/dl). During the initial 24 h after transplant urine oxalate averaged 1,244 +/- 150 mumol/l (109.5 +/- 13.2 mg), but fell to levels not statistically different from normal by 72 h after transplant. Rapid clearance of oxalate after transplant leads to transient hyperoxaluria until normal levels of serum oxalate are reached.

Parathyroid Hormone and Myocardial Performance in Dialysis Patients

Whether parathyroid hormone (PTH) has a clinically important effect on myocardial performance is unclear. Previous investigations of cardiac function before and after parathyroidectomy have failed to control for ionized calcium, other biochemical parameters, or heart rate and cardiovascular loading conditions. We performed load- and rate-independent measurements of myocardial contractility in seven stable hemodialysis patients before and after surgical parathyroidectomy under identical conditions of blood ionized calcium (Ca2+), electrolytes, pH, PO2, and hematocrit. Mid-molecule PTH decreased from 44 +/- 8 to 2 +/- 1 ng/mL. Aortic systolic and diastolic pressures, left ventricular chamber dimensions, end systolic wall stress, left ventricular contractility at a common level of afterload, and contractile reserve evaluated with dobutamine were similar before and after parathyroidectomy. Thus, PTH appears not to have a direct effect on myocardial contractile state in dialysis patients.

Disparate effects of three types of extracellular acidosis on left ventricular function

Effects of acidosis on muscle contractile function have been studied extensively. However, the relative effects of different types of extracellular acidosis on left ventricular (LV) contractile function, especially the temporal features of contraction, have not been investigated in a single model. We constituted perfusion buffers of identical ionic composition, including Ca2+concentration ([Ca2+]), to mimic physiological control condition (pH 7.40) and three types of acidosis with pH of 7.03: inorganic (IA), respiratory (RA), and lactic (LA). Isolated rabbit hearts ( n = 9) were perfused with acidotic buffers chosen at random, each preceded by the control buffer. Under steady-state conditions, instantaneous LV pressure (Pv) and volume (Vv) were recorded for a range of Vv. The results were as follows. 1) LV passive (end-diastolic) elastance increased with IA and RA. However, this increase may not be a direct effect of acidosis; it can be explained on the basis of myocardial turgor. 2) Although LV inotropic state (peak active Pv and elastance) was depressed by all three acidotic buffers, the magnitude of inotropic depression was significantly less for LA. 3) Temporal features of Pv were altered differently. Whereas IA and RA reduced time to peak Pv( t max) and hastened isovolumic relaxation at a common level of LV wall stress, LA significantly increased t max and retarded relaxation. These results and a model-based interpretation suggest that cooperative feedback (i.e., force-activation interaction) plays an important role in acidosis-induced changes in LV contractile function. Furthermore, it is proposed that LA-induced responses comprise two components, one due to intracellular acidosis and the other due to pH-independent effects of lactate ions.Effects of acidosis on muscle contractile function have been studied extensively. However, the relative effects of different types of extracellular acidosis on left ventricular (LV) contractile function, especially the temporal features of contraction, have not been investigated in a single model. We constituted perfusion buffers of identical ionic composition, including Ca2+ concentration ([Ca2+]), to mimic physiological control condition (pH 7.40) and three types of acidosis with pH of 7.03: inorganic (IA), respiratory (RA), and lactic (LA). Isolated rabbit hearts (n = 9) were perfused with acidotic buffers chosen at random, each preceded by the control buffer. Under steady-state conditions, instantaneous LV pressure (Pv) and volume (Vv) were recorded for a range of Vv. The results were as follows. 1) LV passive (end-diastolic) elastance increased with IA and RA. However, this increase may not be a direct effect of acidosis; it can be explained on the basis of myocardial turgor. 2) Although LV inotropic state (peak active Pv and elastance) was depressed by all three acidotic buffers, the magnitude of inotropic depression was significantly less for LA. 3) Temporal features of Pv were altered differently. Whereas IA and RA reduced time to peak Pv (tmax) and hastened isovolumic relaxation at a common level of LV wall stress, LA significantly increased tmax and retarded relaxation. These results and a model-based interpretation suggest that cooperative feedback (i.e., force-activation interaction) plays an important role in acidosis-induced changes in LV contractile function. Furthermore, it is proposed that LA-induced responses comprise two components, one due to intracellular acidosis and the other due to pH-independent effects of lactate ions.