Improving the accuracy of 99Tcm-mercaptoacetyltriglycine clearance by using two blood samples instead of one? Paediatric Task Group of the EANM

From a database of 133 patients (98 children and 35 adults) who underwent multiple blood sampling for 99Tcm-mercaptoacetyltriglycine (MAG3) clearance, we determined simplified algorithms allowing the estimation of clearance. A one-compartment model with two blood samples was applied. The best choices for the adult population were the 12 and 90 min blood samples, giving a standard error of the estimate (S.E.E.) of less than 10 ml min-1 1.73 m-2; for the children, the 10 and 80 min blood samples gave a S.E.E. of 20 ml min-1 1.73 m-2; for both the adults and the children, the 10 and 70 min blood samples gave the best results with, however, a S.E.E. of 19 ml min-1 1.73 m-2. The use of such a combined algorithm will therefore result in a degradation of the results in adults, suggesting that a separate algorithm for each group is preferable. We compared the accuracy of the two blood sample method to the one blood sample method based on previously published algorithms for children and adults, respectively. The S.E.E. was significantly lower, in adults as well as in children, using the empirical two blood sample method. This two blood sample method seems potentially useful for routine practice in adult patients. The advantages of using such a method in children is balanced by the practical problems inherent in the need to take a second blood sample during the first 10 min, at a time when the plasma activity is rapidly decreasing.

Compartment-oriented microdissection of regional lymph nodes in medullary thyroid carcinoma

Lymph node metastases have been proven to be the main prognostic factor in medullary thyroid carcinoma (MTC). This retrospective study was undertaken to evaluate the efficiency of two surgical techniques of regional lymph node dissection with regard to the normalization of pentagastrin-stimulated serum calcitonin level and patient survival: selective lymphadenectomy, i.e., the excision of macroscopically or microscopically involved lymph nodes, versus a systematic lymphadenectomy performed by the new technique of a compartment-oriented microdissection. From 1970 to 1990, 82 patients with sporadic (n = 57) and hereditary (n = 25) MTC underwent a total of 142 operations including 63 selective lymphadenectomies and, since 1986, 35 systematic lymphadenectomies. The study revealed that in node-positive MTC the rate of interventions with a postoperative normalization of pentagastrin-stimulated serum calcitonin was higher after systematic lymphadenectomy (29.2%) than after selective lymphadenectomy (8.5%) (P < 0.01). The rate of patients undergoing repeat surgery due to a recurrence of MTC was 48% after selective lymphadenectomy and 10% after systematic lymphadenectomy. Survival was significantly better for patients after systematic versus selective lymphadenectomy (P < 0.005). This study thus emphasizes that systematic lymphadenectomy, using the technique of a compartment-oriented microdissection of cervicomediastinal lymph nodes, represents the preferred surgical treatment as well as the optimum technique in primary as well as secondary node-positive MTC.

Improvement of tracheal autograft revascularization by means of fibroblast growth factor

Ischemic airway complications after lung transplantation remain a significant problem despite the use of bronchial omentopexy. Clinical observations suggest that enhancement of vascular ingrowth could possibly increase the efficacy of a bronchial omental flap. This study was therefore designed to investigate whether basic fibroblast growth factor can enhance blood supply of an ischemic airway by acceleration of vascular ingrowth in a rabbit autotransplant model. Segments of the trachea were harvested and transplanted into a subcutaneous pouch. The animals were randomly assigned to one of four groups: group I, no omentopexy; group II, omentopexy; group III, omentopexy and fibrin glue; or group IV, omentopexy and fibrin glue enriched with 2.5 micrograms basic fibroblast growth factor. After 14 days the animals were sacrificed. The extent of perfusion was investigated by means of radioactive microspheres. The morphology of the tracheal segments was investigated in a blinded fashion macroscopically, by means of light microscopy, and by means of scanning electron microscopy. The radioactivity measurements revealed a significantly increased perfusion of group IV (77% +/- 42%) as compared with groups I (17% +/- 13%) and III (20% +/- 16%). By macroscopic and light microscopic assessment, the epithelial integrity of group IV was significantly improved compared with groups I and II. At electron microscopy the integrity of group IV was significantly superior to all remaining groups. We conclude that a deposit of basic fibroblast growth factor and fibrin glue appears to increase revascularization of an ischemic airway from omentum and thus results in improved epithelial preservation of a tracheal autograft.

Determination of the technetium-99m mercaptoacetyltriglycine plasma clearance in children by means of a single blood sample: a multicentre study. The Paediatric Task Group of the EANM

A multicentre European study was undertaken in order to determine a reasonable algorithm allowing the determination of overall technetium-99m mercaptoacetyltriglycine clearance using a single blood sample. Employing multiple blood sample clearance as a reference method, it was shown that an acceptable estimation of the MAG3 renal clearance could be obtained using a blood sample taken at any time between 30 and 40 min after tracer injection. After correction for body surface area, comparison of clearance determined using (a) the single blood sample and (b) the multiple blood samples provided a coefficient of correlation of 0.949 and an SEE of 27 ml/min. This algorithm is valid for clearance values higher than 100 ml/min/1.73 m2 and for children older than 1 year of age.

[Determination of renal clearance with only a single access for injection and blood extraction]

An injection technique was developed to administer radioactivity to children and adults and to withdraw plasma samples through the same venous line. The error in clearance estimation due to "contamination" was smaller than that caused by the timing of blood sampling or the type of algorithm used for clearance calculation.

Bestimmung der renalen Clearance mit nur einem Zugang für Injektion und Blutentnahme

An Kindern und Erwachsenen wurde eine Injektionstechnik entwickelt, die die Injektion eines Radiotracers und die Blutentnahmen zur Clearance-Bestimmung über den selben Zugang ermöglicht. Der Fehler in der Clearance- Bestimmung durch eine »Kontamination« ist deutlich geringer als jener durch den Einfluß des Blutentnahme-Zeitpunktes oder des zur Berechnung der Clearance verwendeten Algorithmus.

Prognostic factors in medullary thyroid carcinoma: evaluation of 741 patients from the German Medullary Thyroid Carcinoma Register

A retrospective study of 741 patients with medullary thyroid carcinoma diagnosed between 1967 and 1991 was carried out by members of the German Medullary Thyroid Carcinoma Study Group to evaluate prognostic factors. A total of 559 patients (75%) were considered to have sporadic disease, and 182 (25%) had the familial type. The sex ratio (male to female) was 1:1.4 in sporadic disease patients, and the mean age at diagnosis was 45.9 years (range 5-81 years). For familial disease patients the sex ratio was 1:1.1, and the mean age at diagnosis was 33.4 (range 5-77 years). The follow-up time for 630 patients ranged from 1 month to 20.8 years (mean 13.0 years). The overall adjusted survival rate was 86.7% at 5 years and 64.2% at 10 years. In a univariate analysis the stage of disease at diagnosis, age, sex, and type of disease (sporadic, familial) were relevant prognostic factors, with a better prognosis for young female patients with familial disease and diagnosed at an early stage. In a multivariate proportional hazards analysis, the difference in the survival rate of patients with familial disease versus those with the sporadic form disappeared, while prognostic information provided by age and sex was still significant. The poorer prognosis of patients with sporadic medullary thyroid carcinoma may be related to the patients' older age at detection and more advanced tumor stage at diagnosis. There seems to be no difference in biological behavior between tumors of the sporadic and those of the familial type.

Postprandial release of glucagon-like peptide-1, pancreatic glucagon, and insulin after esophageal resection

Postprandial concentrations of glucose and the immunoreactivity of insulin, glucagon-like peptide-1 (GLP-1), and pancreatic glucagon were measured in 10 patients who had undergone esophageal resection (ER) and replacement by the stomach. Emptying of the esophageal substitute was assessed by scintigraphy using a 99Tc-labeled solid test meal. The data were compared with measurements performed in 14 controls, in 7 of whom gastric emptying was measured. The gastric emptying half time was 6.8 +/- 6.2 min (median 144 s) in ER cases, significantly shorter than in controls: 70 +/- 29 min (median 51 min). The early integrated (first 30 min) and total integrated insulin and GLP-1 concentrations were significantly higher than in controls. In 3 of 10 esophagectomy patients the blood glucose concentration fell below 3.8 mmol/l postprandially. High GLP-1 concentrations in the first 30 min were associated with low serum glucose during the 2nd h postprandially when all the hypoglycemic episodes occurred. It is concluded that rapid emptying of the esophageal substitute induces the exaggerated GLP-1 response, which is a main factor for reactive hypoglycemia.

[Mucociliary clearance in childhood]

AIM OF THE STUDY

A new, nearly monodisperse human serum albumin particle produced by air-pressure-nebulization was inhaled by children and lung-transplant patients.

METHOD

After inhalation of the particles obtained with an air-pressure nebulizer, the initial deposition pattern showed a marked tracheobronchial deposition which could be reproducibly obtained without a special breathing technique, the alveolar deposition being not higher than 10%. With the use of 99mTc, the radiation exposure is limited to a level which is low enough for children, but images can be taken up to 24 hrs later. Further parameters for in vivo characterization of the mucociliary function are the 24 h retention pattern and the velocity of particle motion in the trachea.

RESULTS

Within the first 45 minutes, the global clearance rate was 51% in healthy children, which is rather high in comparison with the literature, most likely due to size of particles and the selection of patients with a mean age of 10.7 years. In ciliary dysfunction, the initial clearance rate was 16% and 46% within 24 h.

CONCLUSIONS

With simplification of the preparation, application, and examination technique, this method is to be used in children, so that a wider use can be anticipated. The normally fast initial elimination of particles allows quick differentiation of normal and impaired ciliary function.

[Unilateral renal artery stenosis. Color-coded Doppler sonography and captopril scintigraphy in a 13-year-old patient]

Modern noninvasive techniques, such as doppler sonography or color-encoded doppler sonography, have only rarely been used for diagnosis of renovascular hypertension in children. In the following case report, we describe the successful diagnosis of renovascular hypertension in a 13-year-old girl by using color-encoded doppler sonography and Captopril renal scintigraphy. The patient was admitted with hypertension of 180/130 mmHg. Laboratory findings showed elevated plasma renin and aldosterone concentrations. No abnormalities were found by abdominal sonography, isotope renography, intravenous pyelography, or in venous digital subtraction angiography. However, subsequent color-encoded doppler sonography clearly showed evidence of an artery stenosis of the right kidney. Furthermore, isotope renography one hour after oral administration of captopril revealed an almost complete loss of glomerular filtration rate of the right kidney. Based on these findings, arterial digital subtraction angiography, including transluminal angioplasty, was performed. During this treatment procedure, the right renal artery stenosis could be confirmed and was subsequently dilated without complication. In the following twelve months the patient remained normotensive and required no further antihypertensive drug treatment.

Limitations of clearance determination using the single sample distribution volume method. An error analysis on the basis of compartment models

To investigate the error possibly contained in the single sample distribution volume method for the determination of renal clearance, a mathematical model was applied to describe the effect of changes in distribution volume, clearance, intravascular space, intracompartmental exchange and the time point of blood sampling. The method was found to be valid only under well-defined circumstances (Topt = 45 +/- 5 min, Cl = 390 +/- 50 ml/min, Vd = 16.7 +/- 4 l, alpha = 0.05.V1 ml/min, V1/Vd = 0.5 +/- 0.05) as shown in sample calculations. Two-compartment model-based error calculations demonstrate that this technique implies at best an uncertainty of +/- 10% or more. Whilst it can be used preferably in healthy, normal-weight adults, it is not applicable, without error, under all other circumstances.

Frequency and significance of cervicomediastinal lymph node metastases in medullary thyroid carcinoma: results of a compartment-oriented microdissection method

The frequency and significance of cervicomediastinal lymph node metastases have been investigated in 82 medullary thyroid carcinoma (MTC) patients retrospectively comparing two surgical techniques of lymph node dissection: selective lymphadenectomy (n = 63) versus compartment-oriented microdissection (n = 35). No positive correlation was observed between primary tumor size and the number of lymph node metastases. In patients with lymph node metastases proven histologically, 42% showed only cervical involvement (35% unilateral--type A, 7% bilateral--type B) and 22% cervicomediastinal lymph node involvement (15% cervico-unilateral and mediastinal--type C, 7% cervicobilateral and mediastinal--type D). Biochemical cure was 83% in node-negative patients but only 21% in node-positive patients. In node-positive MTC, calcitonin normalization was achieved in none with bilateral lymph node involvement but only in those unilateral lymph node metastases (31% in type A, 17% in type C). Survival and biochemical cure are significantly improved by application of the compartment-oriented microdissection method more so at primary surgery than at reoperation.

Emptying of the gastric substitute, glucagon-like peptide-1 (GLP-1), and reactive hypoglycemia after total gastrectomy

Postprandial glucagon-like peptide-1 (GLP-1), pancreatic glucagon, and insulin were measured in 27 tumor-free patients 43 months (median) after total gastrectomy and in four controls using a 99technetium-labeled 100-g carbohydrate solid test meal. Emptying of the gastric substitute was measured by scintigraphy. Fourteen patients suffered from early dumping symptoms, and five of them also reported symptoms suggestive of reactive hypoglycemia (late dumping). The median emptying half-time (T1/2) of the gastric substitute was 480 sec. Sigstad's dumping score was 8.5 +/- 1.6 (mean +/- SE) in patients with rapid emptying (T1/2 less than 480 sec), and 3.0 +/- 1.5 in patients with slow emptying of the gastric substitute (P = 0.02). The peak postprandial concentration of GLP-1 was 44 +/- 20 pmol/liter in controls, 172 +/- 50 in patients without reactive hypoglycemia, and 502 +/- 116 in patients whose glucose fell below 3.8 mmol/liter during the second postprandial hour. Plasma GLP-1 concentrations peaked at 15 min, and insulin concentrations at 30 min after the end of the meal. A close correlation between integrated GLP-1 responses and integrated insulin responses (r = 0.68) was observed. Multiple regression revealed that three factors were significantly associated with the integrated glucose concentrations during the second hour (60-120 min): Early (first 30 min) integrated GLP-1 (inverse correlation; P = 0.006), age (P = 0.006), and early integrated pancreatic glucagon (P = 0.005). There was a close (inverse) relationship of T1/2 with early integrated GLP-1 and pancreatic glucagon, but not with insulin. Gel filtration of pooled postprandial plasma of gastrectomized individuals revealed that all glucagon-like immunoreactivity eluted at Kd 0.30 (Kd, coefficient of distribution), the elution position of glicentin. Almost all of the GLP-1 like immunoreactivity eluted at Kd 0.60, the elution position of gut GLP-1. The authors contend that GLP-1-induced insulin release and inhibition of pancreatic glucagon both contribute to the reactive hypoglycemia encountered in some patients following gastric surgery. Rapid emptying seems to be one causative factor for the exaggerated GLP-1 release in these subjects.

[Unilateral lung transplantation in terminal pulmonary emphysema]

Early attempts of single lung transplantation for end-stage chronic obstructive pulmonary disease mostly failed due to a ventilation-perfusion mismatch between the allograft and the contralateral native lung. We performed unilateral lung transplantation in a 39-year-old female with severe pulmonary emphysema and could demonstrate in a one year follow-up that the transplanted lung will be given preference for both--ventilation and perfusion in approximately the same ratio (80%/90%). With improvement of pulmonary preservation, individual adjustment of immunosuppression and detailed monitoring of the transplanted lung unilateral lung transplantation becomes a therapeutical option in patients with severe emphysema.

[Effect of reconstruction method on nutritional status after gastrectomy. Comparison of Roux-Y esophagojejunostomy and jejunum interposition]

Body composition, postprandial symptoms and social performance were studied in 61 tumor-free patients after total gastrectomy and Roux-Y esophagojejunostomy (n = 30) or jejunal interposition (n = 31). Emptying of the gastric substitute and small bowel transit of a 99mTc-labeled solid test meal were measured by scintigraphy. Serum glucose levels, and immunoreactive insulin were measured simultaneously. The lowest postoperative weight was 73 +/- 2% of the pre-morbid weight in Roux-Y cases, and 77 +/- 2% after jejunal interposition, the weight at study was 82 +/- 2% respectively 87 +/- 1% of the premorbid weight (p less than 0.05). Of the patients younger than 60 years at operation only one third of the twelve Roux-Y cases had resumed their work, as compared to two thirds of the eighteen interposition cases (p = 0.056). The incidences of the postprandial symptoms were not different among the modes of reconstruction, except for a slightly higher incidence of late dumping in Roux-Y (17% vs. 10%). After correction for gender higher mean values of fat-free mass, total body water, and intracellular water were measured in interposition cases (bioelectric impedance analysis). The emptying half-time of the gastric substitute was 488 s in the Roux-Y group, and 378 s after interposition (p = 0.05), whereas the small bowel transit (median: 200 min) showed no differences between the groups. There was no correlation between t1/2 or small bowel transit and the nutritional data. Early dumping (p = 0.01) was the only symptom significantly associated with rapid emptying of the gastric substitute.(ABSTRACT TRUNCATED AT 250 WORDS)

Bronchial circulation after experimental lung transplantation: the effect of direct revascularization of a bronchial artery

Direct revascularization of a bronchial artery has been proposed as a measure to alleviate the problem of bronchial ischemia after lung transplantation. To assess the effect of restoration of arterial blood flow to the transplanted bronchus, bronchial mucosal blood flow was measured in a model of modified unilateral lung transplantation in pigs. Laser Doppler velocimetry (LDV) and radioisotope studies using radio-labeled erythrocytes (RI) were used to measure blood flow at the donor main carina (DC) and upper lobe carina (DUC) after 3 h of reperfusion. The recipient carina was used as a reference point; values obtained by LDV and RI were expressed as percentage of blood flow at the recipient carina. Two groups of animals were studied. In group 1 (n = 6) standard unilateral transplantation was performed; in group 2 (n = 6) a left bronchial artery was reimplanted into the descending thoracic aorta of the recipient. No differences were observed between the two groups with respect to preoperative or postoperative gas exchange or hemodynamics. In group 1, bronchial blood flow at the DC was 37.6 +/- 2.2% (LDV) and 44.1 +/- 14.8% (RI) of reference blood flow. At the DUC, blood flow was 54.9 +/- 7.7% (LDV) and 61.6 +/- 25.7% (RI) of normal flow. In group 2, blood flow was increased at the DC as measured by LDV (55.3 +/- 17.1%; p less than 0.05) and by RI (60.8 +/- 25.3%; p less than 0.2). A similar increase was found at the DUC (LDV: 81.8 +/- 19.3%; p less than 0.05; RI: 88.6 +/- 31.0%; p less than 0.2). It is concluded that there is a significant gradient of blood flow from intra- to extrapulmonary airways after lung transplantation. Reimplantation of a bronchial artery results in significant improvement of graft bronchial blood flow. Restoration of bronchial perfusion to normal levels, however, cannot be achieved, suggesting a possible defect in the microcirculation of the donor airways.

[Fat emulsions in parenteral feeding following liver transplantation. I. Effect on the recovery of RES function in the transplant]

Following liver transplantation, the effect of postoperative parenteral nutrition with MCT/LCT fatty emulsions on the recovery of RES function in the allograft was investigated in a randomised prospective study of three groups of patients (group I: 50 g MCT/LCT fats twice weekly, group II: 0.7 g/kg body weight per day MCT/LCT fats, group III: 1.5 g/kg body weight per day MCT/LCT fats). RES function was assessed using 99mTc-HSA-MM clearance. There were no statistically significant differences in the recovery of RES function after transplantation between the three groups. A negative effect on RES function as a result of the administration of MCT/LCT fats up to 1.5 g/kg body weight per day can therefore be excluded.

Three-dimensional assessment of myocardial oxidative metabolism: a new approach for regional determination of PET-derived carbon-11-acetate kinetics

We have developed a new analysis algorithm which generates polar coordinate maps of myocardial carbon-11-(11C) acetate kinetics. In 10 normal subjects (n = 20 studies), myocardial 11C clearance rate constants (k) averaged 0.057 +/- 0.009 (per minute). Regional k-values varied only 10.6 +/- 2.4% in the normal left ventricle. However, there was a small but significant segmental variation with increased 11C clearance in the septal, anterior, and basal regions (p less than 0.05). Since 11C clearance rates reflect tri-carboxylic acid cycle flux, these results suggest that myocardial oxidative metabolism is relatively homogeneous in the normal human heart at rest with minor regional variations, which possibly reflect varying regional wall stresses or substrate utilization. The proposed approach provides three-dimensional evaluation of regional oxidative metabolism which will permit characterization of the location, extent, and severity of myocardial disease.

Extracellular space, blood volume, and the early dumping syndrome after total gastrectomy

Extracellular space and blood volume were measured using 82Br dilution and 51Cr-tagged erythrocytes in 24 tumor-free patients after total gastrectomy. Eleven of the patients suffered from early dumping. Age, blood volume, and extracellular space were significantly smaller in dumpers (P less than 0.05). The dumping score could be predicted by a multiple regression model considering blood volume per lean body mass and extracellular space (r = 0.637; P = 0.0039). Rapid (t1/2 less than 360 seconds) emptying of the gastric substitute, assessed using a 99Tc-labeled solid test meal, was significantly associated with dumping in addition to extracellular space and blood volume (r = 0.876; P = 0.0018). Both rapid emptying and a narrow extracellular space seem to contribute to the early dumping syndrome.

[A comparison of two algorithms for determining renal whole body clearance following simultaneous acquisition with a partially shielded whole-body counter and a gamma camera]

The influence of instrumentation, algorithm, and the time of blood sampling on whole-body renal clearance as defined by effective renal plasma flow (ERPF) was investigated. The study involved simultaneous sampling with a partially shielded whole-body counter (WBC) and a gamma camera to assess ERPF. The results obtained using two different analysis algorithms for each modality are compared. Although ERPF as determined by the Oberhausen technique was significantly higher than that obtained using an algorithm developed by the authors, for each algorithm there was no significant difference between the WBC and gamma camera-derived values within the range of 100 to 800 ml/min. Furthermore, positioning of the ROI was not critical for gamma camera-derived ERPF (SD less than 1% for multiple crescentic ROIs and approximately 4% for multiple rectangular ROIs). However, the time of blood sampling did appear more important since the average ERPF derived from the 10- and 20-min samples compared with that from the 15- and 25-min samples differed significantly for both analysis algorithms. The methodology which we have validated provides a more precise tool for further investigations of the influence of medication, posture, and exercise stress on renal function.

Renal elimination of beta-2-microglobulin and myoglobin in patients with normal and impaired renal function

Since the demonstration that beta 2-microglobulin (beta 2M) is an amyloidogenic protein in man, the excretion of this low-molecular-weight protein under conditions with normal and reduced renal function has received increased interest. The renal arteriovenous extraction of beta 2M, polyfructosan (an inulin analogue), and a second low-molecular-weight protein, myoglobin, was measured in vivo in 16 human kidneys with normal renal function/gross morphology and in 22 kidneys with reduced function. In kidneys with normal function, the extraction of beta 2M significantly exceeded that of polyfructosan (0.198 +/- 0.037 vs. 0.182 +/- 0.05; p = 0.04), while that of myoglobin (0.177 +/- 0.068) was not different from that of polyfructosan. In kidneys with reduced function, the extraction of polyfructosan or myoglobin was not significantly altered. In contrast, the beta 2M extraction decreased to 0.110 +/- 0.060 (p less than 0.01 vs. extraction of polyfructosan or myoglobin). This decrease was significantly correlated with the decrease of the endogenous creatinine clearance or the total or unilateral 131I-hippuran clearance. These results indicate that in normal renal function the glomerular filtration of beta 2M may be supplemented by a peritubular mode of removal. The mechanism(s) underlying the selective decrease of beta 2M extraction in kidneys with reduced function remain speculative. However, this decrease will lead to a further augmentation of the retention of beta 2M in renal failure.

Vergleich zweier Algorithmen zur Bestimmung der renalen Ganzkörper-Clearance nach simultaner Akquisition mit dem teilabgeschirmten Ganzkörperzähler und der Gammakamera

The influence of instrumentation, algorithm, and the time of blood sampling on whole-body renal clearance as defined by effective renal plasma flow (ERPF) was investigated. The study involved simultaneous sampling with a partially shielded whole-body counter (WBC) and a gamma camera to assess ERPF. The results obtained using two different analysis algorithms for each modality are compared. Although ERPF as determined by the Oberhausen technique was significantly higher than that obtained using an algorithm developed by the authors, for each algorithm there was no significant difference between the WBC and gamma camera-derived values within the range of 100 to 800 ml/ min. Furthermore, positioning of the ROI was not critical for gamma cameraderived ERPF (SD <1 % for multiple crescentic ROIs and approximately 4% for multiple rectangular ROIs). However, the time of blood sampling did appear more important since the average ERPF derived from the 10- and 20-min samples compared with that from the 15- and 25-min samples differed significantly for both analysis algorithms. The methodology which we have validated provides a more precise tool for further investigations of the influence of medication, posture, and exercise stress on renal function.