Clinicians and healthcare decision-makers conduct their clinical practice based on the results of clinical trials. However, some health problems remain unresolved; in such cases, further research is required. To ensure reliable research results, it is important to understand the study design and conduct well-designed clinical trials. Many study designs can be chosen within the two broad categories of observational and interventional. Clinical studies have a variety of designs, including case series, case-control, cross-sectional, and prospective and retrospective cohort studies. Well-designed clinical studies can clarify important differences between treatment options and provide data on long-term drug efficacy and safety. Interpreting the results of clinical trials can be difficult because weaknesses in research design, data collection methods, analytic methods, and reporting can compromise their value and usefulness. However, although randomized controlled trials are limited owing to ethical and practical issues, they are optimal for investigating the effects of therapy and establishing causality. Here we present an overview of different clinical research designs and review their advantages and limitations.

Unlike most secretory cells, high extra cellular calcium inhibits rather than stimulates hormonal secretion in several cells such as parathyroid cells, Juxtaglomerular cells and osteoclast. To gain further insight into the common but unique stimulus-secretion coupling mechanism in these cells, bovine parathyroid slices were incubated in various conditions of Krebs-Ringer (KR) solution containing essential amino acids. Parathyroid cells showed the inverse dependency of secretion on extra cellular calcium concentration as we expected. Ammonium acetate overcame the inhibitory effect of 2.5 mM of calcium and the maximum effect was as much as the five times of the basal value, while there was a little additive effect under 0 mM CaCl2. PTH secretion was biphasic according to the change of extra cellular osmolarity and the lowest response was observed at 300 mOsm/l. In Na-rich KR solution, high concentration of nigericin (> 10(-4)M) completely overcame the inhibitory effect of 2.5 mM CaCl2 and the maximum stimulatory effect was 8 times greater whereas it was only 2 times greater without CaCl2. In K-rich KR solution that abolished the K-gradient between the extra cellular solution and the cytoplasm, the rate of PTH secretion increased, and furthermore the addition of nigericin increased the rate of secretion significantly. The results above suggested that the osmotic swelling of the secretory vesicle in parathyroid cells might promote exocytosis as in Juxtaglomerular cells. We propose that the swelling of the vesicle is also prerequisite for secretion in several cells inhibited paradoxically by Ca++, whatever the signal transduction pathway for swelling of the secretory granules induced by the lowering of Ca++ in cytoplasm are.
Acetates/pharmacology ; Animal ; Body Fluids/*metabolism ; Cattle ; Cell Membrane Permeability ; Ionophores/pharmacology ; Mannitol/pharmacology ; Nigericin/pharmacology ; Osmosis ; Parathyroid Glands/drug effects/*secretion ; Parathyroid Hormones/*secretion ; Support, Non-U.S. Gov't

BACKGROUND: As cardiac disorders, especially coronary artery disease is increasing in end-stage renal disease patients, the indications for coronary artery bypass surgery are increasing now. They have high risks for postoperative morbidity and mortality after coronary artery bypass surgery. MATERIAL AND METHOD: Between March of 1996 and May of 2000, medical records of 25 patients with end-stage renal disease who underwent coronary artery bypass surgery at Asan medical center were reviewed retrospectively. We reviewed the short-term results of preoperative risk factors, preoperative renal function, perative methods, operation results, hospital course, postoperative morbidity and mortality. RESULT: Preoperative creatinine clearance was 12.68+/-5 ml/min and serum creatinine level was 6.18+/-3 mg/dL(range 1.7-14. 4). Preoperatively, 11 patients(44%) received dialysis and the others(14 patients, 56%) were not supported by dialysis due to adequate urine output. Of the non-dialysis patients(14 cases), 8 patients were newly supported by dialysis, perioperatively. Of the preoperative hemodialysis patients(9 cases), two patients changed dialysis method postoperatively to peritoneal dialysis. Operative mortality occured in 2 patients(8%) and the causes of death were sepsis from aspiration pneumonia and mediastinitis, and postoperative bleeding and mediastinitis, respectively. Postoperative complications were developed in 14 patients(56%). There were 2 cases(8%) late mortalities and the cause of death was catheter-induced peritonitis. The actuarial survival rates in hospital survivals at 4 years was 82+/-13%. CONCLUSION: The coronary artery bypass surgery of end-stage renal disease patients were performed with acceptable mortality(8%). However , because the morbidity and mortality from morbidity were very frequent, perioperative prevention of infectious complications and careful patient management are very important.
Cause of Death ; Chungcheongnam-do ; Coronary Artery Bypass* ; Coronary Artery Disease ; Coronary Vessels* ; Creatinine ; Dialysis ; Hemorrhage ; Humans ; Kidney Failure, Chronic* ; Mediastinitis ; Medical Records ; Mortality ; Peritoneal Dialysis ; Peritonitis ; Pneumonia, Aspiration ; Postoperative Complications ; Renal Dialysis ; Retrospective Studies ; Risk Factors ; Sepsis ; Survival Rate