The quantum origins of the free induction decay signal and spin noise.

Experiments are described that elucidate the quantum mechanical origins of the free induction decay voltage and of spin noise. It is shown that the experimentally measured FID voltage induced in a Hertzian loop receiving coil following a 90 degrees pulse is typically two orders of magnitude too large to be accounted for by the current quantum theory of signal reception-coherent spontaneous emission. An experiment is then presented in which spin noise is easily observed in a circuit with a Q-factor of order unity, thereby undermining a popular hypothesis that such noise is due to spontaneous emission and is only observable because of the enhancement in the density of the radiation field in a high Q-factor tuned circuit, the NMR probe. Both the free induction decay and the spin noise are shown to be accurately predicted by near-field Faraday induction, which is described in the theory of quantum electrodynamics by an exchange of virtual photons. A heuristic approach to understanding the nature and role of virtual photons in the signal reception process is then given. Thus current popular statements that observation of the magnetic resonance phenomenon relies on the absorption and emission of radio waves are shown to be wrong.

Body composition assessed by neutron activation analysis in dialysis patients.

Malnutrition is prevalent in end-stage renal disease (ESRD) patients treated with hemodialysis (HD) and peritoneal dialysis (PD). In addition, there is increased incidence of morbidity in this group. Evaluation of nutritional status is important. Application of body composition in the ESRD population to evaluate body compartments and to assess nutritional health has become more common in clinical practice. Neutron activation analysis (NAA) may provide data on metabolically active tissue by quantification of total body potassium (TBK) for body cell mass and assessment of protein by total body nitrogen (TBN). This method may be able to detect changes in body composition before clinical signs of malnutrition are apparent. Ten HD (5 male and 5 female) and 10 PD patients (7 male and 3 female) were evaluated by NAA, TBK, and isotope dilution. Female PD patients had an increased total body water (TBW) and increased intracellular water compared to HD females. Albumin was lower in PD women. There was no significant difference between PD men and laboratory controls in TBW, extracellular water, and TBN. The clinical application of body composition methods for evaluation of dialysis patients by serial assessment and for development of a bedside tool needs further study.

Percentage body fat determination in hemodialysis and peritoneal dialysis patients: a comparison.

OBJECTIVE: To evaluate percentage body fat in hemodialysis (HD) and peritoneal dialysis (PD) patients. DESIGN: A prospective study of 20 HD patients and 20 PD patients. SETTING: Sol Goldman Renal Therapy Center, Lenox Hill Hospital, New York, NY; Baumritter Kidney Center Albert Einstein College of Medicine, Bronx, NY; Body Composition Unit, St Luke's Roosevelt Hospital, Columbia University, New York, NY. PATIENTS: Twenty HD (10 men, 10 women) patients, mean age 41.8 +/- 2.4 years and 20 PD (12 men, 8 women) patients, mean age 48.6 years +/- 3.0 years. INTERVENTION: This is a noninterventional study. PATIENTS signed consent to undergo dual-energy x-ray absorptiometry, total body potassium counting bioelectrical impedance analysis, total body water determination, and anthropmetric evaluation. MAIN OUTCOME MEASURES: Present and compare percentage body fat between HD and PD patients as determined by the methods used. RESULTS: Percentage fat is not different between HD and PD patients. Differences in absolute values of percent fat between techniques exist. CONCLUSION: HD patients and PD patients may be evaluated by the methods of body composition used. Percentage body fat will vary among techniques; therefore the same method should be used to follow a patient over time.

Comparison of five body-composition methods in peritoneal dialysis patients.

Body-composition assessment is an important method of evaluating nutritional status in peritoneal dialysis patients. Because body-composition measurement estimates have not been fully validated in this population, we assessed five body-composition methods in 30 well-dialyzed peritoneal dialysis patients. The techniques studied included bioelectrical impedance analysis, dual-energy X-ray absorptiometry, total-body potassium counting, and anthropometry by two techniques. The dialysis patients were matched for age, race, sex, height, weight, and body mass index with 29 healthy control subjects in our laboratory database. By 5 x 2 x 2 analysis of variance, significant differences were found between results by modality (P < 0.0001) as well as by sex, with women having an increased percentage of fat (P < 0.0001). However, there was no significant intermethod difference by condition (peritoneal dialysis or control). That is, although significantly different percentage fat values were found between the body-composition techniques, this variability was independent of whether the measurement was made on control or peritoneal dialysis patients. Despite the differences between modalities, all techniques were found to correlate significantly with each other (P < 0.01 or better for men and P < 0.001 or better for women). Our experience shows that these routine techniques for measuring body composition can be readily applied to stable peritoneal dialysis patients.

Bioelectrical impedance analysis and dual energy x-ray absorptiometry to monitor nutritional status.

There exists an imperative to monitor changes in body composition in all dialysis patients on a regular basis to avoid overt malnutrition. In this regard, the absolute measurement of the fat-free mass assessment may not be as crucial as the serial measurement of fat-free mass with the same modality. A significant difference in measured fat and fat-free mass should be expected if different techniques are employed. Therefore, when attempting to monitor patients over time or to assess the effects of changes in therapeutic regimens, a single methodology should be employed. Our data validate the use of BIA in the stable PD patient, indicating that BIA can predict the DXA results. Considering the ease with which BIA measurements can be obtained and the lack of dependency on operator interpretation, BIA is an ideal technique for use in the clinical setting. The applicability of this technique for use in monitoring longitudinal changes in body composition has, in fact, been well established (25, 30, 31). BIA appears to be an excellent method for routine fat-free mass measurement in dialysis patients. In as much as malnutrition continues to remain a significant problem in PD patients, measuring and monitoring body composition is strongly recommended.

Determinants of serum creatine kinase activity in dialysis patients.

Elevated creatine kinase (CK) has frequently been described in patients on chronic dialysis, but little is known about its cause and distribution. We, therefore, measured CK in 105 patients on hemodialysis and continuous ambulatory peritoneal dialysis and compared it with biochemical, nutritional, and anthropometric data obtained at the same time. In the entire group, CK was 130.3 +/- (SEM) 15.0 IU/l. Thirty patients had elevated levels of enzyme (greater than 130 IU/l). Isoenzymes determined in patients with elevated CK levels were all more than 97% MM fraction. Men had significantly higher (p less than 0.001) CK values (166.0 +/- 25.8 IU/l) than women (82.4 +/- 9.0 IU/l). Blacks had higher CK values (158.8 +/- 21.7 IU/l; p less than 0.001) than whites (92.6 +/- 12.5 IU/l). Men and blacks had significantly higher weight and midarm muscle circumference than women and whites, respectively. A positive correlation was found between CK and lactic dehydrogenase (p less than 0.001) and between CK and midarm muscle circumference (p less than 0.05), and a negative correlation (p less than 0.01) was found with age. Predialysis and postdialysis CK was measured in 10 patients and did not rise. Three of the patients with elevated CK who have undergone successful renal transplantation showed normalization of CK levels. We conclude that CK is elevated in both hemodialysis and continuous ambulatory peritoneal dialysis patients, particularly in men and blacks, that CK levels are probably related to muscle mass, and that CK declines with advancing age. Although blacks have higher CK values as a whole, normalization of CK values after renal transplantation suggests a contributory role of renal dysfunction.