Assessment of body composition in dialysis patients by arm bioimpedance compared to MRI and 40K measurements

This study used multi-frequency bioimpedance spectroscopy (BIS) of the arm and whole body to estimate muscle mass (MM) and subcutaneous adipose tissue (SAT) in 31 hemodialysis (HD) patients comparing these results with magnetic resonance imaging (MRI) and body potassium ((40)K) as gold standards. Total body and arm MM (MM(MRI)) and SAT (SAT(MRI)) were measured by MRI. All measurements were made before dialysis treatment. Regression models with the arm (aBIS) and whole body (wBIS) resistances were established. Correlations between gold standards and the BIS model were high for the arm SAT (r(2) = 0.93, standard error of estimate (SEE) = 3.6 kg), and whole body SAT (r(2) = 0.92, SEE = 3.5 kg), and for arm MM (r(2) = 0.84, SEE = 2.28 kg) and whole body MM (r(2) = 0.86, SEE = 2.28 kg). Total body MM and SAT can be accurately predicted by arm BIS models with advantages of convenience and portability, and it should be useful to assess nutritional status in HD patients.

Consequences of overhydration and the need for dry weight assessment

Despite significant progress in the fields of dialysis technology and medical therapy, mortality of hemodialysis (HD) patients remains high. Chronic overhydration is a major contributor to the high cardiovascular morbidity and mortality observed in HD patients. The difficulty of measuring excess fluid accurately and the determination of 'dry weight' are reflected in the abundant literature on overhydration. Data indicate that a significant proportion of HD patients are not at 'dry weight'. Considering its impact on cardiovascular diseases, the relation between excess fluid, sodium, interdialytic weight gain, hypertension and cardiac diseases needs more attention. Clearly the reduction of sodium intake is of prime importance. This can be achieved by a reduction of dietary sodium intake, individualized dialysate sodium concentration, avoidance of sodium profiling and use of hypertonic saline during dialysis. These measures are expected to result in less thirst and consecutive water intake, thereby facilitating achieving dry weight (DW). In concert, the application of new tools for DW assessment such as continuous intradialytic bioimpedance spectroscopy measurement, means to prevent intradialytic symptoms (e.g. glucose bolus instead of hypertonic saline; improved hemodynamic stability by reduced dialysate temperature) may be operative in reducing morbidity and mortality in HD patients.

A mathematical model comparing solute kinetics in low- and high-BMI hemodialysis patients

BACKGROUND

Patients with low Body Mass Index (BMI) on maintenance hemodialysis have a higher mortality risk than patients with elevated BMI. We investigated the use of kinetic modeling to test different hypotheses which have been advanced to explain this relationship.

METHODS

Equations from a three-pool urea-kinetic mathematical model (hepatic mass, extracellular fluid, muscle mass and adipose tissue) were solved to yield predictive profiles of solute and putative toxin concentrations versus time for patients of different body weights.

RESULTS

For the interdialytic interval, our mathematic model suggests that extracellular solute/toxin concentration increases more rapidly in small patients. Additionally, time average concentration (TAC) is higher for this cohort. A lower value of the muscle mass and adipose tissue mass-transfer coefficient (K(MMAT)), which determines the rate of solute release into the extracellular fluid, exacerbates this difference.

CONCLUSION

These results suggest that higher mortality for smaller dialysis patients may be mediated by higher time average toxin concentration, especially for solutes with a low mass-transfer coefficient value.

Evaluation of treatment adherence in type 1 diabetes: a novel approach

BACKGROUND

Intensified insulin therapy requires outstanding compliance but no measure of therapy adherence has been agreed upon. The aim of the current study was to test the hypothesis that treatment adherence, as described by a novel multiple regression model, relates to glycosylated haemoglobin and hypoglycaemia frequency in type 1 diabetes. Furthermore, we sought to analyse the complex diurnal patterns of therapy adherence.

MATERIALS AND METHODS

Thirty type 1 diabetes patients (20 females and 10 males), treated with intensified insulin therapy, were studied in a retrospective manner. Patients were trained to follow treatment algorithms for adjusting regular insulin dosage which took into account the actual blood glucose, food intake and the time of the day. By means of multiple linear regression analysis, with regular insulin dosage as the dependent variable, blood glucose and food intake as the independent variables, the insulin treatment algorithms actually used by the individual patient were retrieved. The correlation between prescribed and implemented insulin therapy served as a measure of adherence. Metabolic control was assessed by glycosylated haemoglobin and hypoglycaemia frequency.

RESULTS

Median glycosylated haemoglobin was 7.7% (range: 6.3-10.8); median monthly hypoglycaemia frequency was 3.8 (range: 0-9.8). Patients with good metabolic control (glycosylated haemoglobin < 7.7 and/or hypoglycaemia frequency < 3.8 per month) adhered to prescribed insulin dosing algorithms more frequently than those with poor metabolic control.

CONCLUSIONS

In patients with type 1 diabetes on intensified therapy a positive relationship between adherence to the therapy prescribed and metabolic control exists.

A Kinetic Model of Calcium Mass Balance during Dialysis Therapy

A kinetic model of Ca mass balance during dialysis has been developed. It is a single-compartment, variable-volume model to compute Ca mass balance during dialysis in its volume of distribution, the extracellular fluid. The model was used to analyze literature data which were suitable for the assessment of Ca mass balance over the course of dialysis. The modeled analyses predicted the serial plasma Ca concentrations very well. The mass balance analyses revealed a pool of rapidly diffusible Ca beyond the extracellular fluid distribution volume where Ca could be mobilized (M+(Ca)) or sequestered (M-(Ca)) very rapidly at rate equal but opposite in sign to dialyzer flux and thus effectively maintain near constant plasma Ca in the face of dialyzer Ca concentration gradients. This pool is likely the large pool of diffusible (miscible) Ca in connective tissue and on bone surfaces. Analysis of net Ca flux during dialysis with Cdi(Ca) = 2.50 mEq/l suggests that 80% of patients are in positive Ca balance during dialysis. Further studies are required to verify the model and to develop a model of interdialytic Ca mass balance.

Metabolic consequences of body size and body composition in hemodialysis patients

Small body mass index is associated with increased mortality in chronic hemodialysis patients. The reasons for this observation are unclear but may be related to body composition. This study aimed to investigate the body composition in chronic hemodialysis patients. The difference between body mass and the sum of muscle, bone, subcutaneous, and visceral adipose tissue masses, measured by whole body magnetic resonance imaging, was defined as the high metabolic rate compartment representing the visceral mass. Protein catabolic rate was calculated from urea kinetics. Forty chronic hemodialysis patients (mean age 54.7 years; 87.5% African Americans; 45% females) were studied. High metabolic rate compartment expressed in percent of body weight was inversely related to body weight (r=-0.475; P=0.002) and body mass index (r=-0.530; P<0.001). In a multiple linear regression model, protein catabolic rate was significantly correlated only with high metabolic rate compartment (r=0.616; P<0.001). Assuming that protein catabolic rate in addition to protein intake reflects urea and uremic toxin generation, it follows that high metabolic rate compartment is the major compartment involved in their generation. Consequently, uremic toxin production rate may be relatively higher in patients with low body weight and low body mass index as compared to their heavier counterparts. The poorer survival observed in smaller dialysis patients may be related to these relative differences.

The role of nuclear factor-kappa B in bacterial translocation in cholestatic rats

Xanthinoxidase (XO) derived radical species are involved in bacterial translocation (BT) in cholestatic rats. The mechanism by which XO influences remains unclear. It has been shown recently that nuclear factor-kappa B (NF-kappaB), a ubiquitous transcription factor, can be activated by oxidative stress and thereby promote the process of BT. We investigated the effects of NF-kappaB inactivation on the incidence of BT in cholestatic rats. Sprague-Dawley rats were randomly assigned to one of eight groups: groups 1-4 were sham laparotomized rats either untreated (S1) or treated for 5 days with thalidomide (S2), curcumin (S3), or Inchin-ko (ICK; S4); groups 5-8 underwent common bile duct ligation (CBDL) for 5 days and were either untreated (C1) or treated with thalidomide (C2), curcumin (C3), or ICK (C4). After 5 days bacteriological cultures were performed from portal blood and V. cava, from the central mesenteric lymph node complex (MLN), spleen, and liver. The intensity of the activated NF-kappaB-subunit p65/p50 in the ileum mucosa was estimated by light microscopy and a scoring system from 1 to 20. Malondialdehyde (MDA) and myeloperoxidase activity (MPO) in the ileum were evaluated and expressed as U/g dry weight. Thalidomide and ICK reduced in CBDL-rats significantly the BT rate (63% vs. 18%, 63% vs. 30%, P<0.01). Enzyme estimations (MDA, MPO, and GSH) in sham operated animals showed no significant changes in the untreated groups compared with the treated groups. CBDL-rats pre-treatment with all three compounds caused a significant increase of MDA levels if groups were compared with the untreated C1-group (C1 31.6+/-7.7, C2 54.5+/-12.2, C3 53.3+/-11.2, and C4 47.2+/-9.4). GSH was reduced after the pre-treatment by all compounds but only significantly after curcumin pre-treatment (C1 vs. C3: 13.9+/-1.8 vs. 7.1+/-1.8; P<0.05). MPO estimations were significantly higher in the untreated C1-group if compared with groups C2, C3, and C4 (C1 1036.4+/-340.9, C2 709.9+/-125.9, C3 545.2+/-136.6, and C4 556.7+/-247.4; P<0.05). Thalidomide inhibited significantly the activation of NF-kappaB (C2 vs. C1: 6.0+/-4.5 vs. 12.7+/-5.3; P<0.01). Likewise, Curcumin and ICK suppressed NF-kappaB activation, but this did not reach significance in this experiment. NF-kappaB is involved in the process of BT in cholestatic rats and may be activated by XO derived ROS. We assume that the activated NF-kappaB initiates transcription of target genes inducing cytokine production, which in turn disrupts the tight junctions leading to BT from the intestinal lumen to the MLNs and circulation.

Application of Bioimpedance Techniques to Peritoneal Dialysis

Peritoneal dialysis (PD) has been used as a home dialysis therapy for renal replacement for more than 30 years. In a recent assessment of treatment quality, the mortality of patients on PD was referenced as being higher than of those on hemodialysis. Several reports suggest that a high proportion of PD patients are overhydrated. Clinical assessment of dry weight in PD patients is difficult and further complicated by the paucity of signs and symptoms indicative of dehydration (such as intradialytic hypotension or muscle cramps). Monitoring tools used for fluid status estimation during hemodialysis, e.g. online blood volume and blood pressure measurement, are not readily available in PD patients. Bioimpedance analysis technique has been considered as a potential tool to measure body fluid non-invasively, inexpensively and simply. Although Bioimpedance analysis has been used in clinical studies for more than 20 years, the knowledge of the electrical properties of body tissues is still evolving. In this review we aim to clarify the principles of different bioimpedance techniques and to introduce their applications in PD patients.

Gender, age and seasonal effects on IgA deficiency: a study of 7293 Caucasians

BACKGROUND

The frequency of serum IgA deficiency (SIgAD) differs between populations. We examined the prevalence of SIgAD in healthy Caucasians.

MATERIALS AND METHODS

Serum immunoglobulin A (SIgA) was measured in 7293 volunteers (2264 women, 5029 men) aged 30 +/- 14.2 years (mean +/- SD; range: 12-66). Serum immunoglobulin A and subnormal SIgA levels were defined by a SIgA level < 0.07 g L(-1), and between 0.07 and 0.7 g L(-1), respectively. Means were compared by analysis of variance (anova) and analysis of covariance (ancova); frequencies by the chi(2) test.

RESULTS

Fifteen subjects (0.21%; one woman, 14 men) had SIgAD. Subnormal SIgA levels were found in 155 persons (2.13%): 21 females (0.93% of the females) and 134 males (2.66% of the males; difference: 1.74%; 95% CI: 1.12-2.33%; P < 0.001). Males were more likely to have subnormal SIgA levels or SIgAD (odds ratio 3.09, 95% CI: 1.97-4.85). The prevalence of SIgAD and subnormal SIgA was lowest in winter (chi(2) = 14.8; P = 0.002; 3 d.f.; and chi(2) = 43.2; P < 0.001; 3 d.f., respectively). Serum immunoglobulin A concentrations were significantly higher during winter. Serum immunoglobulin A levels increased with age on average by 0.2 +/- 0.06 g L(-1) per decade of life (P < 0.001). Taking into account the influence of age, SIgA concentration was lower in females as compared with males.

CONCLUSION

The prevalence of SIgAD and subnormal SIgA levels is increased in males. There exists a significant influence of gender, age and seasons on SIgA levels.

UROMODULIN mutations cause familial juvenile hyperuricemic nephropathy

Gout, which is commonly associated with hyperuricemia, affects 0.2% of the population. Hyperuricemia has a heterogeneous etiology that may be due to either over production and/or reduced renal clearance, of urate. In order to identify the mechanisms underlying reduced excretion of urate, we undertook positional cloning studies of familial juvenile hyperuricaemic nephropathy (FJHN), which is an autosomal dominant disorder characterized by hyperuricaemia, a low fractional renal excretion of urate, and chronic renal failure that is associated with interstitial fibrosis. The FJHN locus has been previously localized to a 22 centiMorgan interval flanked centromerically by D16S401 and telomerically by D16S3069, on chromosome 16p11-p13. This interval contains over 120 genes and we selected 13 renal expressed sequences to search for mutations in 5 unrelated FJHN families that contained 21 affected and 24 unaffected members. This revealed 5 heterozygous missense mutations (Cys77Tyr, Cys126Arg, Asn128Ser, Cys255Tyr and Cys300Gly) that altered evolutionary conserved residues in the gene encoding UROMODULIN. UROMODULIN, which is an 85 Kda glycoprotein, has roles in renal stone formation, the modulation of immune responses, and urothelial cytoprotection. The results of our studies, which have identified the gene causing FJHN, now indicate a further, novel role for UROMODULIN in urate metabolism.

A novel 6 bp insertion in exon 7 associated with an unusual phenotype in a family with Fabry disease

A male patient presented with oligosymptomatic Fabry disease (end stage renal failure and non-obstructive cardiomyopathy) at around 30 years of age. His leukocyte alpha-galactosidase activity (alpha-gal) was 2.6% of controls. A 50-year-old sister had similar cardiac symptoms and her asymptomatic heterozygous daughter (33 years) had normal enzyme activity. All three patients carried a novel, 6bp insertion on exon 7 of the AGAL gene. The majority of male Fabry patients carrying mutations in exon 7 have residual alpha-gal below 1% and suffer from neuropathic pain. Comparable oligosymptomatic phenotypes in Caucasian patients carry a common mutation on exon 6 (R301Q) and have a significantly later onset. The course of the disease is likely to be altered by recombinant enzyme therapy in the future. Therefore, a thorough documentation of phenotypes, residual activities and underlying genotypes is of current interest.

Coronary anatomy predicts presence or absence of renal artery stenosis. A prospective study in patients undergoing cardiac catheterization for suspected coronary artery disease

AIMS

This study aimed to determine the prevalence of renal artery stenosis (RAS) and associated risk factors in patients undergoing cardiac catheterization for suspected coronary artery disease (CAD).

METHODS

One hundred and seventy-seven consecutive patients (62 females) with a serum creatinine concentration <2.0mg.dl(-1) were studied. Abdominal aortography followed cardiac catheterization to screen for RAS.

RESULTS

In 110 patients (62%) CAD and in 19 patients (11%) significant RAS (luminal narrowing of >or=50%) were detected, 12 of whom had high grade (>or=70%) RAS, and two subjects had significant RAS without CAD. Patients with RAS were older (67+/-8 vs 61+/-11 years, mean+/-SD;P =0.004), had higher systolic blood pressure (150+/-15 vs 138+/-20 mmHg;P =0.005), a lower glomerular filtration rate (GFR; 61+/-16 vs 80+/-22 ml.min(-1), P<0.001) and more often diabetes mellitus (69% vs 30%; P=0.004). In multivariate analysis a low GFR and the extent of CAD were independent predictors of RAS. The presence of >2 significant coronary lesions predicted RAS (sensitivity 0.84, specificity 0.77, positive predictive value 0.30, negative predictive value 0.98).

CONCLUSION

Screening for RAS in patients with >2 diseased coronary segments has a high diagnostic yield, which is even greater in the presence of a reduced GFR, diabetes mellitus, and elevated systolic blood pressure.

Search for occult secondary osteoporosis: impact of identified possible risk factors on bone mineral density

OBJECTIVES

To determine whether the use of more elaborate diagnostic tests can identify possible risk factors for secondary osteoporosis and to evaluate the impact of these possible risk factors on the severity of bone disease in the study population.

DESIGN

Cross-sectional study.

SETTING AND PARTICIPANTS

We have investigated 377 subjects (285 females, 92 males) with osteoporosis (T-score less than -2.5 in dual energy X-ray absorption) or nontraumatic lumbar vertebral fractures; these patients were referred to our hospital, a secondary care centre, for evaluation and treatment of osteoporosis.

RESULTS

Osteoporosis without attributable risk factor was diagnosed in 106 women (37%) and 30 men (33%). In 241 patients (179 women, 62 men) one or more possible risk factors for osteoporosis (in this paper also called subclinical disease) were revealed. The most common were lactose malabsorption, disturbed exocrine pancreatic function and renal tubular disturbances, including renal hypercalciuria, incomplete renal tubular acidosis and mild phosphate diabetes. The number of possible risk factors in the individual patient was significantly related to the severity of osteoporosis as assessed by Z-scores (Spearman correlation r = -0.43, P < 0.001, n = 172 for females; r = -0.28, P < 0.05, n = 65 for males).

CONCLUSIONS

All the identified subclinical diseases would have remained undetected if the currently accepted guidelines for the investigation of patients with osteoporosis were applied. The statistically significant correlation between the number of identified possible risk factors and the severity of bone disease in the individual patient strongly suggests the pathogenetic significance of the identified subclinical diseases. It is yet to be shown, whether specific treatment of these subclinical diseases yields additional improvement of bone mass as compared with standard treatment of osteoporosis.

Prevalence and characterization of renal tubular acidosis in patients with osteopenia and osteoporosis and in non-porotic controls

BACKGROUND

Chronic metabolic acidosis may increase alkali mobilization from the bone and thus promote the development of osteoporosis. The objective of the current study was to compare urinary acidification in patients with reduced bone mineral content with that in control subjects with normal bone density.

METHODS

Forty-six subjects (41 females, 5 males) with osteopenia or osteoporosis were studied. In none of the subjects were overt metabolic acidosis, derangement of potassium homeostasis, or renal insufficiency present. Distal tubular acidification was studied by means of oral ammonium chloride loading test (0.1 g/kg body weight) and the oral frusemide test (40 mg). In addition the frusemide test was performed in 20 healthy age- and sex-matched controls (17 females, 3 males).

RESULTS

In all control subjects a urinary pH <5. 5 was observed following the ingestion of 40 mg frusemide. In contrast, in patients with reduced bone mineral density incomplete renal tubular acidosis type I (RTA I) was diagnosed in 10 of 46 subjects (22%) by oral ammonium chloride loading test. Disorders possibly related to RTA I were detected in eight of these 10 patients. Thirty-six patients had a normal urinary pH response following oral ammonium chloride loading. Oral frusemide, 40 mg, failed to lower urinary pH <5.5 in sixteen patients (35%), these included 10 subjects with incomplete RTA I, and six subjects with a normal oral ammonium chloride loading test. An abnormal frusemide test was found in 35% of patients with reduced bone mass and in none of the normal controls (chi(2)=7.39; P<0.01). With the ammonium chloride test as the gold standard for diagnosis of distal RTA, the frusemide test showed a sensitivity of 1.0 (95% CI, 0.69-1.0) and a specificity of 0.89 (95% CI, 0.78-0.96) for the diagnosis of distal RTA. Patients with incomplete RTA I were younger than those without incomplete RTA I (42+/-16 vs 54+/-14 years; P=0.025; mean+/-SD). Basal serum bicarbonate concentrations and capillary pH did not differ between the groups.

CONCLUSION

Incomplete RTA I may be prevalent in a significant proportion of patients suffering from osteopenia or osteoporosis. The outcome of the frusemide test suggests either a defect of the H(+)ATPase in the cortical collecting tubule (CCT) or a defective Na(+) reabsorption in the CCT. Prospective studies are needed to further elucidate the impact of incomplete RTA I on the development of reduced bone mineral content.

Urinary N-acetyl-beta-D-glucosaminidase and neopterin aid in the diagnosis of rejection and acute tubular necrosis in initially nonfunctioning kidney grafts

AIM

The study aimed at investigating urinary neopterin, a marker of cellular immune response, and urinary N-acetyl-beta-D-glucosaminidase (NAG), a marker of tubular damage, as noninvasive means to differentiate between acute tubular necrosis (ATN) and rejection in initially nonfunctioning (INF) human renal transplants.

METHODS

Seventy-two renal transplant patients were studied. Forty-five of them experienced an uncomplicated early posttransplant course, 27 patients suffered from INF. Twenty-two patients experienced ATN, 5 patients had a total of six biopsy-proven rejections. The NAG activity was measured by a colorimetric assay, neopterin by high-performance liquid chromatography. Receiver operating characteristics (ROC) analysis was applied to compute diagnostic performance and an optimal discriminating threshold.

RESULTS

Demographic characteristics (age, gender, cold and warm ischemia periods, HLA mismatches) and posttransplant urinary NAG and neopterin excretions did not differ between ATN and rejection groups. Both urinary NAG and neopterin excretions were lower in the control group (NAG 1.8 +/- 1.0 U/mmol urinary creatinine; neopterin 270 +/- 126 nmol/mmol urinary creatinine; mean +/- SD) as compared with the ATN group (NAG 12 +/- 10 U/mmol, p < 0.001 vs. control group; neopterin 303 +/- 195 nmol/mmol, n.s.) and the rejection group (NAG 7 +/- 8 U/mmol, p < 0. 01; neopterin 508 +/- 419 nmol/mmol, p < 0.01). The ratio of urinary neopterin to NAG excretion (uNNR; dimension nmol neopterin/U NAG activity) increased during rejections as compared with ATN (139 +/- 74 vs. 50 +/- 38 nmol/U, p < 0.01). The area under the ROC curve for uNNR was 0.88 +/- 0.07 (p < 0.001). Applying a ROC-estimated optimal discriminator of uNNR (80 nmol/U), 16 patients with ATN and all six rejection episodes were classified correctly.

CONCLUSION

The uNNR provides a noninvasive means to aid in the differential diagnosis of rejection and ATN in INF human renal transplants.

Effects of postprandial walking on delayed gastric emptying and intragastric meal distribution in longstanding diabetics

OBJECTIVE

We investigated the influence of standardized postprandial walking on the rates of gastric emptying and of intragastric meal distribution in 50 consecutive patients with longstanding insulin-dependent diabetes mellitus.

METHODS

Gastric emptying of a semisolid meal labeled with 99mTc was continuously recorded with a dual-head gamma camera with patients in the supine position for 90 min before and 20 min after a 30-min postprandial walk. Regions of interest enclosing total stomach, and proximal and distal gastric compartments were calculated to determine gastric emptying rates and intragastric meal distribution.

RESULTS

The evaluation of gastric emptying rates before and after postprandial walking demonstrated two variants of delayed gastric emptying: one variant that was counteracted by postprandial walking in seven patients (14%, Group I) and another variant that was not influenced by postprandial walking in 11 patients (22%, Group II). In addition, the emptying rates of 28 patients (56%) were within the range of controls and in four patients the emptying was accelerated (8%). The filling of the proximal gastric compartment was predominant and remained dominant after walking in Groups I and II. In controls and in diabetics with normal gastric emptying, the preliminary predominant filling of the proximal compartment was equalized after walking and the proximal compartment regained predominance thereafter. The changes in gastric emptying characteristics from delayed to accelerated gastric emptying may be related to the duration of diabetes (r = -0.47, p<0.03) and were not indicated by symptoms of upper GI discomfort or by secondary diabetic manifestations.

CONCLUSION

Postprandial walking may improve gastric emptying in 14% of patients with longstanding insulin-dependent diabetes mellitus.

beta-2 Adrenergic receptor variants affect resting blood pressure and agonist-induced vasodilation in young adult Caucasians

Recent evidence suggests that the prodownregulatory Gly16 allele of the beta-2 adrenergic receptor (beta-2 AR) is associated with essential hypertension in African Caribbeans. To further investigate the effect of the glycine (Gly)16 and arginine (Arg)16 beta-2 AR variants on hemodynamics, we investigated the agonist-mediated in vivo vasodilation in normotensive Austrian Caucasians and analyzed the results with respect to the Gly16/Arg16 polymorphism. Fifty-seven normotensive men, 20 to 32 years of age with body mass index of 18.7 to 29.9 kg/m2, were genotyped for the Arg16/Gly16 beta-2 AR alleles. All 15 Gly16/Gly16 subjects, all 12 Arg16/Arg/16 subjects, and 27 of 30 heterozygous subjects underwent hemodynamic measurements while supine after an overnight fast. The observers were unaware of the subjects' genotypes. The subjects received a graded infusion of the selective beta-2 AR agonist salbutamol (0.07, 0.14, and 0.21 microgram/kg per minute, respectively), each dose over 8 minutes. Stroke volume and blood pressure were determined continuously by means of impedance cardiography and oscillometry, respectively. The last 4 minutes of each infusion were evaluated statistically. Basal mean blood pressure was higher in the Gly16/Gly16 subjects compared with Arg16/Arg16 subjects (mean+/-SD: 81.6+/-6.14 versus 75.2+/-4.93 mm Hg, P<0.01). Homozygous Gly16 subjects showed a significantly decreased vasodilation during the first dose of salbutamol infusion compared with Arg16/Arg16 subjects (Deltatotal peripheral resistance index -17.9+/-14.4 versus -30. 6+/-8.3%, P<0.01) despite increased sympathetic counterregulation in the Arg16/Arg16 group (Deltaheart rate +16.9+/-7.0% versus +8.6+/-7. 0%, P<0.01; Deltacardiac index +39.5+/-18.5% versus 21.4+/-18.8%, P<0.05). Our results provide additional evidence that the Gly16/Arg16 alleles of the beta-2 AR are intimately related to blood pressure regulation and deserve further studies in the pathogenesis of essential hypertension.

Incomplete renal tubular acidosis in 'primary' osteoporosis

Chronic metabolic acidosis may increase alkali mobilization from bone and thus promote the development of osteoporosis. While it is undisputed that overt metabolic acidosis is associated with metabolic bone disease, renal acidification in patients with idiopathic osteoporosis has not been studied systematically. The purpose of this study was to investigate the prevalence of renal acidification defects in patients with 'primary' osteoporosis. Thirty-two women (including 10 premenopausal women) and 16 men who were referred to our department for investigation of osteoporosis were enrolled in this study. Patients with obvious or possible secondary osteoporosis were excluded. None of the patients had overt metabolic acidosis. In random urine samples 12 of the 48 patients had pH levels below 5.5 and were therefore considered to have normal renal acidification. The remaining 36 patients underwent further testing by a short-course oral ammonium chloride load. In this test nine of these 36 patients (7 men and 2 premenopausal women) failed to lower urinary pH below 5.5 despite the induction of systemic metabolic acidosis. In these patients, therefore, the diagnosis of incomplete distal renal tubular acidosis was made (RTA I). Patients with incomplete RTA I had significantly lower spontaneous plasma pH (7.38 +/- 0.0081 vs 7.41 +/- 0.004, mean +/- SEM, p = 0.002), a lower serum bicarbonate concentration (21.9 +/- 0.49 mmol/l vs 23.1 +/- 0.24 mmol/l, p = 0.034), a lower base excess (-2.33 +/- 0.42 mmol/l vs -0.55 +/- 0.21 mmol/l, p = 0.001) and lower Z-scores in bone densitometry (-2.18 +/- 0.27 vs -1.40 +/- 0.15, p = 0.028) than patients with normal renal acidification. In conclusion, a high prevalence of incomplete RTA I (in 44% of the male patients, 20% of the premenopausal female patients and 6% of all female patients) was found in patients with osteoporosis who, without testing, would have been diagnosed as having 'primary' osteoporosis. The mild metabolic acidosis observed in these patients may have contributed to loss of bone mass by a compensatory mobilization of alkali and calcium from bone. Because of possible therapeutic consequences (e.g., administration of alkali salts and high doses of vitamin D) we propose that measurements of urinary pH and, if necessary, ammonium chloride testing should be included in the diagnostic investigation especially of male and of premenopausal female patients with osteoporosis. Since referral bias, although unlikely, cannot be excluded in our study, the prevalence of RTA I in unselected patients with osteoporosis needs to be determined at primary screening institutions.

A software package for non-invasive, real-time beat-to-beat monitoring of stroke volume, blood pressure, total peripheral resistance and for assessment of autonomic function

The goal of the present study was to develop and evaluate algorithms for non-invasive, real-time, beat-to-beat monitoring of stroke index (SI), blood pressure (BP) and total peripheral resistance index (TPRI) which has a menu-driven interface, suitable for routine use by unskilled staff. In addition, it was our aim to include a meta-analysis for the evaluation of autonomic function derived from the above haemodynamic data. This includes spectral analysis of heart rate (HR), BP, SI and TPRI and the automatic calculation of baroreceptor reflex sensitivity. Impedance cardiography was used for beat-to-beat SI determination, Finapres corrected by an oscillometric blood pressure measurement (Dinamap) on the upper arm for beat-to-beat BP measurement. We demonstrate noise free recordings during physiological (head up tilt) and pharmacological intervention (alpha 1-, beta 2-adrenoreceptor agonists, insulin induced hypoglycemia). The newly developed software should prove valuable for physiological, pharmacological and clinical studies.

Graft ischemia correlates with urinary excretion of the proximal marker enzyme fructose-1,6-bisphosphatase in human kidney transplantation

This study was undertaken to test the hypothesis that ischemia prior to transplantation causes tubular damage without clinical evidence of graft dysfunction. The urinary excretion of fructose-1,6-bisphosphatase (EC 3.1.3.11, FBPase), a cytosolic enzyme located exclusively in the proximal tubules, and the lysosomal enzyme N-acetyl-beta-D-glucosaminidase (EC 3.2.1.30) were measured daily between postoperative days 1 and 4 in 25 renal cadaveric graft recipients who enjoyed an entirely uncomplicated first postoperative month. During the first 4 posttransplant days urinary FBPase excretion was 0.9 +/- 0.5 U/g (0.1 +/- 0.06 U/mmol) urinary creatinine [+/-SD; range 0.2-2.1 U/g (0.02-0.24 U/mmol)]. Cold ischemia time was 20.6 +/- 8.4 h (median 22 h, range: 3-32 h). Multiple regression revealed a significant correlation between cold ischemia time and posttransplant urinary FBPase excretion (multiple R = 0.65, p < 0.001). There were no confounding effects of recipient's age and gender, number of previous transplants, cyclosporin A levels, warm ischemia time, anastomosis time, donor age and gender. Urinary FBPase excretion was significantly lower in grafts stored for a shorter time than the median cold ischemia time of 22 hours (0.69 +/- 0.42 U/g, n = 13) as compared to those stored for a longer period of time (1.13 +/- 0.56 U/g; n = 12; p = 0.035). These results indicate that graft injuries occur even in the absence of graft dysfunction and that the duration of cold ischemia itself correlates with a degree of tubular cell damage as defined by urinary FBPase excretion.

Essential hypertension in African Caribbeans associates with a variant of the beta2-adrenoceptor

Populations of West African ancestry dwelling in Western communities exhibit greater prevalence of human essential hypertension and higher rates of end-organ damage. The sympathetic nervous system influences cardiac output, vascular tone, renal sodium reabsorption, and renin release and could be implicated in enhanced vascular responsiveness observed in African hypertensives. Such an effect could arise from genetic variants that alter agonist response of alpha-adrenoceptors, leading to enhanced vasoconstriction, or attenuate beta2-adrenoceptor-mediated vasodilatation. Indeed, there is evidence of a blunted vasodilator response to the beta-agonist isoprenaline in African Americans. A variant of the beta2-adrenoceptor gene that encodes glycine rather than arginine at position 16 (Arg16-->Gly) has been shown to confer exaggerated agonist-mediated receptor downregulation, which might attenuate vasodilator response. One hundred thirty-six unrelated hypertensives and 81 unrelated normotensives of African Caribbean origin were identified from primary care on the island of St Vincent. Genomic DNA from these subjects was analyzed for the presence of the Gly16 and Arg16 alleles by using an allele-specific polymerase chain reaction method. We report strong support for association of the prodownregulatory glycine 16 variant of the beta2-adrenoceptor gene with hypertension in African Caribbeans from St Vincent and the Grenadines (chi2=18.9, P=.000014, 1 df). This observation, coupled with reports of attenuated vasodilator responses to beta-agonists among people of West African ancestry, may provide a mechanism for enhanced vascular reactivity and identify a candidate gene for hypertension in this ethnic group.

Open-flow microperfusion of subcutaneous adipose tissue for on-line continuous ex vivo measurement of glucose concentration

OBJECTIVE

To evaluate a novel technique for on-line continuous glucose measurement in subcutaneous adipose tissue, and to investigate its accuracy for detection of hypoglycemia.

RESEARCH DESIGN AND METHODS

The method combined an open-flow microperfusion of subcutaneous adipose tissue using a double lumen catheter and an extracorporeal sensor cell. An isotonic ion-free solution was perfused through the inner lumen of the catheter, equilibrated with the subcutaneous tissue fluid, and sampled through the outer lumen. The recovery was continuously monitored as the ratio between the measured sampled fluid conductivity and the subcutaneous tissue fluid conductivity (assumed to have a constant value of 1.28 S/m at 25 degrees C). Glucose concentration was calculated on-line from the measured glucose in the sampled fluid and the measured recovery in healthy volunteers during hyperglycemic glucose loads (n = 8), hypoglycemic hyperinsulinemic clamp (n = 6), and a 24-h monitoring period (n = 7).

RESULTS

Subcutaneous glucose concentrations in the fasting state were 94% of the plasma glucose concentrations in arterialized venous samples. According to the error grid analysis, 96.9% of the on-line measured subcutaneous glucose concentrations during hyperglycemia and 96.3% during hypoglycemia were in accurate or acceptable zones. The mean differences between the measured subcutaneous glucose and the actual plasma glucose concentration were -0.06-3.3 mmol/l (hyperglycemia), and -0.6-1.1 mmol/l (hypoglycemia).

CONCLUSIONS

By combining open-flow microperfusion, glucose sensor, and conductivity measurement, glucose concentration in the subcutaneous adipose tissue can be monitored on-line, extracorporeally, and continuously without any in vivo calibration, and gives accurate measurements during hyper- and hypoglycemia.