Clinical measurement of body composition using in vivo neutron activation analysis

Relationship Between Total Body Protein and Cross-Sectional Skeletal Muscle Area in Liver Cirrhosis Is Influenced by Overhydration

Sarcopenia as defined by reduced skeletal muscle area (SMA) on cross-sectional abdominal imaging has been proposed as an objective measure of malnutrition, and it is associated with both wait-list mortality and posttransplant complications in patients with cirrhosis. SMA, however, has never been validated against the gold standard measurement of total body protein (TBP) by in vivo neutron activation analysis (IVNAA). Furthermore, overhydration is common in cirrhosis, and its effect on muscle area measurement remains unknown. We aimed to examine the relationship between SMA and TBP in patients with cirrhosis and to assess the impact of overhydration on this relationship. Patients with cirrhosis who had undergone IVNAA and cross-sectional imaging within 30 days were retrospectively identified. Patients with significant clinical events between measurements were excluded. Psoas muscle area (PMA) and SMA at the level of the third lumbar vertebrae were determined. Total body water was estimated from a multicompartment model and expressed as a fraction of fat-free mass (FFM), as determined by dual-energy X-ray absorptiometry, to provide an index of hydration status. In total, 107 patients underwent 109 cross-sectional imaging studies (87 computed tomography; 22 magnetic resonance imaging) within 30 days of IVNAA. Median time between measurements was 1 day (IQR, -1 to 3 days). Between 43% and 69% of the cohort was identified as sarcopenic, depending on muscle area cutoff values used. TBP was strongly correlated with SMA (r = 0.78; P < 0.001) and weakly correlated with PMA (r = 0.49; P < 0.001). Multiple linear regression showed SMA was significantly and positively associated with FFM hydration (P < 0.001) independently of TBP. In conclusion, SMA is more closely related to TBP than is PMA, and it should be preferred as a measure of sarcopenia. Overhydration significantly affects the measurement of cross-sectional muscle area.

From chemical analysis of the body...to metabolic insights provided by the new methodology

It is by no means an exaggeration to say that Dr Widdowson is one of the pioneers of body composition research and her studies in the 1940s and 1950s have laid the foundations of body composition science today. These have included both animal and human studies, although this paper will focus only on the latter. Together with Professor McCance and Christine Spray she was responsible for the analysis of three entire adult human cadavers and that of a 4-year-old child (Widdowson et al. 1951). Further work with Dr Dickerson explored the composition of specific tissues and organs of the body (Widdowson & Dickerson, 1964). These studies provide some of the best direct data on human body composition. Moreover the findings from this work form the basis of the indirect techniques which are used so widely today.

Monte Carlo simulation of neutron irradiation facility developed for accelerator based in vivo neutron activation measurements in human hand bones

The neutron irradiation facility developed at the McMaster University 3 MV Van de Graaff accelerator was employed to assess in vivo elemental content of aluminum and manganese in human hands. These measurements were carried out to monitor the long-term exposure of these potentially toxic trace elements through hand bone levels. The dose equivalent delivered to a patient during irradiation procedure is the limiting factor for IVNAA measurements. This article describes a method to estimate the average radiation dose equivalent delivered to the patient's hand during irradiation. The computational method described in this work augments the dose measurements carried out earlier [Arnold et al., 2002. Med. Phys. 29(11), 2718-2724]. This method employs the Monte Carlo simulation of hand irradiation facility using MCNP4B. Based on the estimated dose equivalents received by the patient hand, the proposed irradiation procedure for the IVNAA measurement of manganese in human hands [Arnold et al., 2002. Med. Phys. 29(11), 2718-2724] with normal (1 ppm) and elevated manganese content can be carried out with a reasonably low dose of 31 mSv to the hand. Sixty-three percent of the total dose equivalent is delivered by non-useful fast group (> 10 keV); the filtration of this neutron group from the beam will further decrease the dose equivalent to the patient's hand.

A simple prediction of total body water to aid quality control in isotope dilution studies in subjects 3-87 years of age

The principal method of measuring total body water (TBW) is by isotope dilution. Also, the doubly labelled water method, which is the method of choice for measuring total energy expenditure (TEE) in free-living individuals, includes calculation of TBW as the dilution space of the tracer. TBW was measured in 261 subjects (135 males and 126 females), aged 3-87, including healthy children, children with HIV and adults with non-insulin dependent diabetes mellitus (type 2 diabetes), mild hypertension, pancreatic cancer and lung cancer, either in studies of body composition or TEE. A linear relationship was found between TBW and height in all subjects. When TBW is plotted against height cubed (Ht3, m3) the regression line can be forced through the origin. Considering only adults with 18.5>body mass index <29.9 and all children (n=220), this yielded TBW (l)=7.40 x Ht3, R2=0.95. This simple linear relationship between measured TBW and Ht3 compared favourably with other prediction methods, assuming TBW is a constant proportion (55%) of body weight and TBW predicted from height and weight (mean difference between measured and predicted TBW 0.55 l compared with -1.95 and -1.20 l, respectively). Absolute errors were greater at higher TBW, but use of a log10 transformation reduced this effect. This simple relationship of TBW with Ht3 is too crude to be used as a body composition predictor in individual subjects as it ignores, for instance, body shape. However, it can be used as a quality control tool. Here, use of a log10 transformation and residual plot can serve to identify outliers, which can be checked for gross errors in data input and if necessary samples are re-analysed.

Measurement of nitrogen in the body using a commercial PGNAA system—phantom experiments

An industrial prompt-gamma neutron activation analysis (PGNAA) system, originally designed for the real-time elemental analyses of bulk coal on a conveyor belt, has been studied to examine the feasibility of using such a system for body composition analysis. Experiments were conducted to measure nitrogen in a simple, tissue equivalent phantom comprised of 2.7 wt% of nitrogen. The neutron source for these experiments was 365 MBq (18.38 microg) of 252Cf located within an engineered low Z moderator and it yielded a dose rate in the measurement position of 3.91 mSv/h; data were collected using a 2780 cm(3) NaI(Tl) cylindrical detector with a digital signal processor and a 512 channel MCA. Source, moderator and detector geometries were unaltered from the system's standard configuration, where they have been optimized for considerations such as neutron thermalization, measurement sensitivity and uniformity, background radiation and external dose minimization. Based on net counts in the 10.8 MeV PGNAA nitrogen photopeak and its escape peaks the dose dependent nitrogen count rate was 11,600 counts/mSv with an uncertainty of 3.0% after 0.32 mSv (4.9 min), 2.0% after 0.74 mSv (11.4 min) and 1.0% after 3.02 mSv (46.4 min).

Lithium target performance evaluation for low-energy accelerator-based in vivo measurements using gamma spectroscopy

The operating conditions at McMaster KN Van de Graaf accelerator have been optimized to produce neutrons via the (7)Li(p, n)(7)Be reaction for in vivo neutron activation analysis. In a number of earlier studies (development of an accelerator based system for in vivo neutron activation analysis measurements of manganese in humans, Ph.D. Thesis, McMaster University, Hamilton, ON, Canada; Appl. Radiat. Isot. 53 (2000) 657; in vivo measurement of some trace elements in human Bone, Ph.D. Thesis. McMaster University, Hamilton, ON, Canada), a significant discrepancy between the experimental and the calculated neutron doses has been pointed out. The hypotheses formulated in the above references to explain the deviation of the experimental results from analytical calculations, have been tested experimentally. The performance of the lithium target for neutron production has been evaluated by measuring the (7)Be activity produced as a result of (p, n) interaction with (7)Li. In contradiction to the formulated hypotheses, lithium target performance was found to be mainly affected by inefficient target cooling and the presence of oxides layer on target surface. An appropriate choice of these parameters resulted in neutron yields same as predicated by analytical calculations.

Of mermaids and mountains. Three decades of prompt activation in vivo

During 1966 to 1972, several laboratories demonstrated the feasibility of measuring the major body elements H, N, Ca, and Cl by prompt gamma in vivo neutron activation analysis (PGIVNA). The MERMAID facility in Birmingham, England used a cyclotron-produced pulsed neutron beam, but other groups in the United Kingdom, United States, Canada, and New Zealand subsequently developed systems based on radioisotope neutron sources that could measure body nitrogen with a precision of a margin of error of a few percentage points. The accuracy of N measurement was greatly enhanced by Vartsky's internal standardization, using prompt-gamma H as the marker and total body hydrogen (based on total body water and skinfolds) as the reference. Chlorine and extracellular water volume were used in a similar way by the Swansea group to calibrate the prompt-gamma analysis of total body calcium. The PGIVNA technique is most valuable in assessing nutritional status, particularly in relation to body protein.

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.

Prospects of imaging by associated particle timing with D + D and D + T neutrons

The optimum parameters and limits are predicted for the performance of an associated particle imaging system on the basis of recently completed projects studying the use of timing with neutrons for elemental analysis of bulk samples such as the human body or traveling trunks.

Effect of sex and age on bone mass, body composition and fuel metabolism in humans

The mechanism(s) governing the gain of upper-body fat and its relationship to the decrease in bone mass with age is still unclear. Therefore, four groups of subjects matched for weight, height, and body mass index (n = 119; 60 women, 59 men), but differing in age (above and below 50 y) and sex were investigated using dual energy x-ray absorptiometry (DXA) to assess body composition (bone, lean, and fat mass as well as its distribution) and indirect calorimetry to determine resting fuel metabolism. Fat mass of trunk and arms (P < 0.01), but not legs, increased with advancing age in males, resulting in a continuous increase in the ratio of upper- to lower-body fat (r = 0.45, P < 0.001). In contrast, total fat mass remained stable in women, irrespective of menopause, but a redistribution of fat occurred with advancing age (r = 0.43, P < 0.001), resulting in a higher upper- to lower-body fat ratio (P < 0.05) in older than in younger women. Total lean soft-tissue mass of all segments of the body was greater in men than in women irrespective of age (P < 0.001), and lower in the older groups than in the younger ones irrespective of sex. In males, but not females, lean soft-tissue mass in arms and legs decreased (r = 0.57, P < 0.001), whereas the ratio of total fat to lean soft-tissue mass increased (r = 0.53, P < 0.001) with age. Bone mineral content correlated with total body fat in both groups of women and in young males (r > 0.5, P < 0.001), but not in older males. With advancing age, the proportion of lean soft-tissue mass occupied by total skeleton declined in women (n = 59, P < 0.001), but remained stable in males. Resting energy expenditure decreased with age in both sexes. Protein and carbohydrate oxidation were similar in all four groups of subjects. Total fat oxidation and fat oxidation per kilogram of lean soft-tissue mass decreased with age (r > 0.36, P < 0.01) in males, but not in females, whereas it increased with increasing fat mass in females (r > 0.32, P < 0.03), but not in males. In contrast, fat oxidation per kilogram of fat mass decreased with fat mass in males (r = 0.61, P < 0.001), but not in females. Our results suggest that aging affects body composition and fuel metabolism differently in each gender, leading to reduced fat oxidation and accumulation of upper-body fat with loss of striated muscle in men, and to an increased ratio of upper- to lower-body fat and bone loss in women, the latter depending on fat mass.

Human body composition: advances in models and methods

The field of human body composition research is reaching a mature stage in its development: The three interconnected areas that define body composition research--models and their rules, methodology, and biological effects--are well-defined and are actively investigated by scientists in diverse disciplines from many different nations; and methods are available for measuring all major atomic, molecular, cellular, and tissue-system level body composition components in research, clinical, and epidemiological settings. This review summarizes main body composition research concepts, examines new component-measurement methodologies, and identifies potential areas of future research.

Reliability of in vivo neutron activation analysis for measuring body composition: comparisons with tracer dilution and dual-energy x-ray absorptiometry

In vivo neutron activation (IVNA) analysis has the capacity to measure several total body elements in human subjects. Although it has been considered a criterion method for the past 3 decades, the reliability of IVNA analysis has been tested only in phantom calibrations. In 5 male weight-stable patients with AIDS, total body N, Ca, Cl, Na, P, and C were measured three times in 16 weeks at Brookhaven National Laboratory. With tracer dilution methods for total body water (TBW) by 3H2O and for extracellular water (ECW) by 35SO4 and NaBr, and dual-energy x-ray absorptiometry (DXA), total body calcium (TBCa) and fat percentage were measured within 2 weeks of IVNA measurements. For comparison, tracer dilution for TBW by D2O and ECW by NaBr, plus DXA measurements, were performed three times in 5 weight-stable healthy volunteers. The reliability of the IVNA technique was very high in patients with AIDS; it ranged from 0.99 for total body chloride (TBCI) to 0.84 for total body phosphorus (TBP), and it agreed with phantom calibration results in the literature. The reliability for measuring fat percentage and TBCa by DXA was similar in patients with AIDS and in healthy volunteers. Tracer dilution for measuring TBW by 3H2O in patients with AIDS and by D2O in healthy volunteers had a reliability score similar to those found with IVNA and DXA. The reliability scores for measuring ECW in patients with AIDS by 35SO4 and NaBr, 0.66 and 0.68, respectively, were the lowest among all measurements, whereas the reliability score for NaBr in healthy volunteers was 0.96, as with the other measurements.

A review of in vivo experimental methods to determine the composition of the human body

This review of experimental methods employed in the measurement of the composition of the human body covers the developments that have occurred over the past 30 years. Early methods such as hydrodensitometry and skinfold anthropometry have been superseded by dual-energy x-ray absorptiometry and bioelectrical impedance spectroscopy. The measurement of the whole-body abundance of certain elements by isotopic dilution, neutron activation analysis and x-ray fluorescence can give important information of clinical significance, but neutron activation facilities remain available in only a few centres worldwide. The relatively simple, rapid and risk-free electrical methods such as multifrequency bioelectrical impedance analysis, which can be employed at the bedside, have been found to be more complicated in their interpretation. Electromagnetic methods may only measure the composition of the human body at its surface. X-ray computed tomography and magnetic resonance imaging have not yet been employed much in body composition measurements. Some models for the composition of the human body are reviewed.

The assessment of body composition in patients with cirrhosis

Very little information is available on body composition in patients with cirrhosis. Difficulties arise in studying these patients because they tend to retain fluid and this results in changes in tissue density and in the hydration fraction of fat-free mass. As the classic body composition techniques rely on the assumption that these variables remain constant, use of these methods will result in either under- or overestimates of body composition variables. Use of multi-component models, employing two or more measurement techniques, will obviate the need for some of the assumptions inherent in the use of single techniques, thereby increasing the accuracy of the assessments, without loss of precision.

Application of the associated particle technique for the whole-body measurement of protein, fat and water by 14 MeV neutron activation analysis--a feasibility study

A small and compact sealed tube neutron generator with an integral alpha particle detector has been used for applying the associated particle technique for prompt-gamma 14 MeV neutron activation analysis of total body carbon (TBC), total body nitrogen (TBN) and total body oxygen (TBO). Ground sheep meat samples in the weight range 20-40 kg and of varying composition have been scanned using two 12.5 cm diameter x 10 cm Nal(Tl) crystals for gamma-ray detection. The content of protein, fat and water was calculated from their fractional content of C, N and O using a four-compartment model of body composition, which included minerals. The precision for measuring TBC, TBN and TBO has been obtained from the mean count rates of ten repeat irradiations of the same sample. The accuracy has been confirmed by comparison against chemical analysis. The reproducibilities for measuring TBN have been found to be comparable to those obtained when the same samples were analysed using prompt-gamma thermal-neutron activation analysis in an existing body composition facility. Based on the results obtained, we conclude that an instrument comprising the neutron generator and four 15 cm x 15 cm x 45 cm NaI(Tl) gamma ray detectors can be assembled to determine, in vivo, protein, fat and water in an approximately 41 kg sample with precisions of 4.4%, 5.0% and 2.1% (CV) respectively within a 15 min scan. The radiation dose equivalent delivered due to neutrons would be approximately 0.03 mSv.

Reliability of clinical judgement in evaluation of the nutritional status of surgical patients

The ability of surgeons to make a reproducible and reliable evaluation of the nutritional status of patients was assessed. Three independent observers assigned 64 patients to one of four nutritional states--normal nourishment, and mild, moderate and severe malnutrition--using a questionnaire and clinical examination. Interobserver variability was analysed using the kappa statistic and reliability by assessing the correlation between the assigned class and total serum protein, haemoglobin, albumin, transferrin and cholesterol levels, weight loss and the results of immunological skin tests. Concordance was observed in 49 of the 64 judgements (77 per cent) and partial agreement in the remainder (kappa = 0.74, P < 0.001). Clinical judgement correlated significantly with albumin, transferrin and cholesterol levels and weight loss (R2 = 0.73, P < 0.001). Surgeons are able to assess nutritional status using clinical judgement.

Biological homogeneity and precision of measurement: the boundary conditions for normal in body composition

For compartments most urgently important to clinical medicine we have satisfactory levels of measurement precision, and the clinical considerations now are the availability of the methods, and the collection of data for normal subjects. Our colleagues in physics and imaging will improve measurement precisions, but the work most needed is to refine the biological side of the measurement equation. Large numbers of measurements, carefully done with carefully calibrated and unchanging systems, exist only for the special case of measuring body calcium in women, in the large cohort of approximately 2,500 women, studied by Aloia and Cohn with neutron activation, and for body potassium, in these women, and in the larger numbers of diverse age, sex, race, and size in the Rosetta study in our laboratory. Can we benefit from the "orthogonal measurements" and "orthogonal physiologic constraints" approaches, in which triangulation is used to combine measurements from several techniques to establish upper-lower bounds estimates by different techniques, with convergence on a "best fit" result? We have noted that the intrinsic homeostatic mechanisms of the body function with great precision to control body temperature, osmotic and ionic concentrations in the water phase, hypertrophy of muscle with exercise, and remodeling of bone by stress. We consider it unlikely that the control mechanisms are more loosely hinged for such secondary parameters as K/FFM and bone density.(ABSTRACT TRUNCATED AT 250 WORDS)

Design studies related to an in vivo neutron activation analysis facility for measuring total body nitrogen

Design studies relating to an in vivo prompt capture neutron activation analysis facility measuring total body nitrogen are presented. The basis of the design is a beryllium-graphite neutron collimator and reflector configuration for (alpha, n) type radionuclide neutron sources (238PuBe or 241AmBe), so as to reflect leaking, or out-scattered, neutrons towards the subject. This improves the ratio of thermal neutron flux to dose and the spatial distribution of thermal flux achieved with these sources, whilst retaining their advantage of long half-lives as compared to 252Cf based systems. The common problem of high count-rate at the detector, and therefore high nitrogen region of interest background due to pile-up, is decreased by using a set of smaller (5.1 cm diameter x 10.2 cm long) NaI(Tl) detectors instead of large ones. The facility described presents a relative error of nitrogen measurement of 3.6% and a nitrogen to background ratio of 2.3 for 0.45 mSv skin dose (assuming ten 5.1 cm x 10.2 cm NaI(Tl) detectors).

Protein status and metabolic expenditure determine the response to intravenous nutrition--a new classification of surgical malnutrition

To determine whether nutritional and metabolic factors affect the response to intravenous nutrition (IVN) 146 surgical patients were classified according to their protein and metabolic status using direct measurements of body protein and metabolic expenditure. The patients were grouped into four categories: category I, moderate to severe protein depletion without raised metabolic expenditure; category II, moderate to severe protein depletion with raised metabolic expenditure; category III, mild protein depletion without raised metabolic expenditure; and category IV, mild protein depletion with raised metabolic expenditure. After 2 weeks of IVN patients in category I gained a mean(s.e.m.) of 0.43(0.06) kg of body protein (P less than 0.001) and had significant rises in both plasma transferrin and prealbumin (P less than 0.05); patients in category II gained 0.30(0.11) kg of protein (P less than 0.005) and also had significant rises in transferrin and prealbumin (P less than 0.05). Patients in category III lost 0.24(0.11) kg protein (P less than 0.05) and had no changes in either transferrin or prealbumin and patients in category IV lost 0.51(0.13) kg of body protein (P less than 0.001) and although there was a significant rise in plasma prealbumin there was no significant change in plasma transferrin. When postoperative patients were examined separately, they did not differ significantly from preoperative patients except in category I, where their protein gain was only 0.19(0.10) kg, an amount not significantly different from that gained by patients in category II. In each of the four categories described, the changes in total body protein occurring with 2 weeks of IVN were determined by the relative effects of two competing processes; protein depletion and raised metabolic expenditure. With moderate to severe protein depletion (approximately 30 per cent depletion of body protein stores) there was a marked tendency to gain protein with IVN. When the patient had a raised metabolic expenditure or was postoperative this tendency of depleted patients to gain protein was still present but it was less. With only mild protein depletion (approximately 10 per cent depletion) increases in metabolic expenditure made it difficult, if not impossible, to prevent continuing protein loss in spite of aggressive nutritional support. The patient categories we have described determine the response to IVN and form the basis of a new clinical classification of surgical malnutrition.

A proposed three-phase counting system for the in vivo measurement of the major elements using pulsed 14 MeV neutrons

It is proposed to employ a pulsed source of 14 MeV neutrons for in vivo activation analysis. This would permit the differentiation, with time, of the resulting gamma ray emission into three separate spectra, according to the type of nuclear reaction and mode of decay. The three-phase counting has been divided into approximately 10 microseconds during "beam-on," and 200 and 800 microseconds during "beam-off." Measurements of the major elements, C, N, O, Cl, and P, to give nutritionally-important body compartments of total body fat, protein, water, minerals, and extracellular water, thus is expected with a single scan.

An introduction to body composition models used in nutritional studies

Chemical analysis of cadavers has led to the definition of 'reference' man but diseases may result in significant changes in body composition. By measuring body composition in patient groups the nature of disease progression can be followed and management regimens evaluated. Various techniques are available which attempt to measure body composition in vivo. Several models of body composition have evolved with the introduction of new measurement techniques. A description of these models is presented. The limitations of the models and the techniques adopted for their measurement are discussed.

Calibration and evaluation of a 252Cf-based neutron activation analysis instrument for the determination of nitrogen in vivo

A novel clinical instrument for multi-element in vivo neutron activation analysis has been recently constructed in Swansea. The instrument is intended primarily for prompt gamma measurement of total and partial body calcium, total body nitrogen and partial body cadmium. For the measurement of nitrogen the subject is scanned both prone and supine across a vertical collimated neutron beam from a 4 GBq 252Cf source. Two shielded Nal(TI) detectors, each of volume 2760 cm3, are placed above the subject on the opposite side to that irradiated. The prompt gamma ray spectrum contains prominent peaks from hydrogen, nitrogen, chlorine and carbon. The optimisation, calibration and evaluation of the instrument for the measurement of nitrogen, by the reaction 14N(n, gamma)15N, is described. The calibration corrects the ratio of nitrogen-to-hydrogen counts measured from the subject for background gamma rays and the effects of body habitus. Body hydrogen is use as as internal standard. Repeated measurements of a homogeneous anthropomorphic phantom indicate that the ratio of nitrogen-to-hydrogen counts may be determined by a coefficient of variation of 1.6% for a neutron dose equivalent incident on the phantom of 0.45 mSv (QF = 10). The accuracy of the calibration was assessed by measuring three anthropomorphic phantoms (weight range: 41.4-110 kg) containing simulated skeletons and the major organs of the body. For these phantoms the mean discrepancy of the measured to the known nitrogen content was +4.9%. The simultaneous measurement of chlorine and carbon is discussed.

A simple calibration of a shadow shield counter for the measurement of total body potassium in critically ill patients

A shadow shield counter has been built for the determination of total body potassium (TBK), based on the detection of the 1.46 MeV gamma rays emitted by the naturally occurring radioisotope (0.01%) 40K. Simple calibration procedures have been adopted which do not require administration of 42K to the subject. Self-absorption effects of gamma rays have been taken into account by monitoring the activity of 40K per gram of potassium as a function of weight. All activity measurements, either during calibration or of a subject, include background in the spectral band covering the full width at half maximum (FWHM) of the 40K photopeak. The overall precision for determining the TBK was in the range of 1.8-3.0%.

Identification and assessment of the malnourished patient

The assessment of protein-energy malnutrition has become important for identifying patients whose nutritional status increases their risk of an adverse outcome during hospitalization. Anthropometric, biochemical and immunological measurements, used either alone or in combination are not sensitive or specific enough for monitoring short-term nutritional changes, although some of these variables are associated with an increased incidence of postoperative complications after surgical procedures. The sensitivity of clinical assessment is dependent on the training of the clinician and the outcome variable being sought. For most clinicians, objective measurements are needed to raise their awareness to potential nutritional problems. The relationship of nutritional status to clinical events, particularly stress events during hospitalization, is critical to the interpretation of nutritional measurements and relating them to outcome variables. A classification based on the concepts of nutritional depletion and stress is presented. The prevalence of PEM has been shown to be between 20 and 30% in western hospitals, depending on the population studied and the criteria used to define PEM. In studies which have claimed an association between nutritional status and outcome, the contribution of nutritional variables to the development of postoperative complications has been overestimated and the relevance of technical factors underestimated.

Body composition research at the University of Auckland--some implications for modern surgical practice

The fundamental changes in body composition which accompany surgical illness are loss of body protein, gain in extracellular water, and erosion of body fat stores. The rate at which each of these processes occurs and the balance between them determine the clinical picture observed and an understanding of them opens the door to intelligent management of many complex disorders. Recent advances in technology have lent impetus to body composition research and a number of new findings have major implications for clinical practice. In this review, some of the work from the body composition laboratories in the University Department of Surgery at Auckland Hospital will be described with special emphasis on that which is directly relevant to the practising surgeon.

A clinical instrument for multi-element in vivo analysis by prompt, delayed and cyclic neutron activation using 252Cf

The design and construction of a versatile clinical instrument for multi-element in vivo neutron activation analysis of major and minor body elements is described. A 200 micrograms (4 GBq) 252Cf neutron source is stored below ground level and pneumatically propelled to one of two irradiation ports. These deliver collimated beams of fast neutrons either to a localised volume such as the liver or kidney, or across the width of a patient for a head-to-toe scanning whole-body measurement. The source control system allows selection of either a continuous or cyclic mode of activation. The instrument is intended primarily for measurement, by the prompt-gamma technique, of total and partial body calcium, total body nitrogen and partial body cadmium. The potential of the instrument for determination of these three elements has been established. Phantom results suggest that total body calcium can be measured with a precision of +/- 2.6% (CV) for an average whole-body skin dose equivalent of 6.4 mSv; total body nitrogen with a precision of +/- 2.0% for an average whole-body skin dose equivalent of less than 0.4 mSv; and a detection limit (2 SD of the background) of 2.4 mg of cadmium in the kidney has been obtained for a radiation dose equivalent to the skin of 3 mSv (QF = 10). The suitability of this instrument for the measurement of other elements is also discussed.

The immediate and long-term effects of postoperative total parenteral nutrition on body composition

The short and long-term effects of postoperative total parenteral nutrition (TPN) on body composition were studied in a randomised series of patients undergoing major colorectal surgery. Ninety-two patients (colorectal cancer: 50, ulcerative colitis or Crohn's disease: 42) were grouped according to diagnosis and clinical inflammatory activity. TPN was given for 9.7 +/- 1.1 days. The complication rate was not changed by the TPN. Nitrogen balance was studied during the first week. Body weight, total body potassium, triceps skinfold, serum albumin and body water were measured before and at intervals up to 24 weeks after the operation. Cumulative nitrogen balance in control patients at 7 days after surgery was -47.3 g. Patients given TPN balanced nitrogen intake and output (cancer patients and patients with quiescent inflammatory bowel disease, IBD) or were in positive balance (patients with active IBD). Weight loss at 1 week after surgery was less in TPN patients compared to controls and this difference remained statistically significant up to 6 months after termination of the nutritional treatment. A similar, although not statistically significant, difference was noted in total body potassium and triceps skinfold. Patients with active IBD regained pre-operative body composition earlier than cancer patients and patients with quiescent IBD. It is concluded that TPN after major colorectal surgery reduces postoperative weight loss and that this effect lasts after termination of the nutritional treatment. In the absence of increased body potassium and increased body water, we conclude that the long-term effect of TPN on body weight is most likely due to preservation of fat.(ABSTRACT TRUNCATED AT 250 WORDS)

Body composition changes in marrow transplant recipients receiving total parenteral nutrition

Nine patients with acute lymphocytic leukemia in remission, aged 12-35 years, undergoing allogeneic bone marrow transplantation (BMT) were studied for changes in body fluid balance and body composition. Body composition and fluids were assessed the first 4 weeks following BMT, using isotope dilution and anthropometry. Oral and parenteral nutrient intakes were recorded daily. Tracer dilution techniques were used to assess body fluid volumes and estimate body cell, lean body, and body fat masses. Body cell mass was lost (mean -1.62 kg, P less than 0.05) without significant changes in body fat or lean body masses. There was an expansion of the extracellular fluid compartment (mean +0.8 l, P less than 0.05) and a loss in the intracellular fluid compartment (mean -1.3 l, P less than 0.05) with little change in total body water volume. Changes in body weight correlated poorly with body cell mass or fluid volume changes. Change in arm muscle area correlated well with changes in body cell mass (r = 0.61, P less than 0.05) and lean body mass (r = 0.68, P less than 0.05), while that of arm fat area did not reflect its isotope dilution-derived counterpart. Instead, the change in arm fat area was related to shifts in fluid compartments. Prealbumin decreased significantly (mean -9.3 mg/dl, P less than 0.05), while albumin decreased slightly (mean -0.1 mg/dl), and both were related to changes in body cell mass. Nitrogen balance was negative throughout the study and the overall mean was related to the change in body cell mass (r = 0.60, P less than 0.05). Calorie and protein intakes were not associated with the changes in body composition, implying other causal factors.

Total parenteral nutrition prevents further nutritional deterioration in patients with cancer cachexia

The effects of total parenteral nutrition (TPN) on some nutritional variables were prospectively investigated in 12 severely cachectic patients with advanced cancer. The following variables were determined before and at 5-day intervals during the 20-day administration of TPN: anthropometric indices (body weight, arm circumference, triceps skinfold, arm muscle circumference, arm muscle area, arm fat area, total body muscle mass); biochemical indices (total protein, albumin, cholinesterase, total iron binding capacity, thyroxin-binding prealbumin, retinol binding protein, urinary 3-methylhistidine and creatinine excretion, nitrogen balance); and peripheral lymphocyte count. TPN was delivered at 49.5 nonprotein kcal/kg-1/day-1 (80% as dextrose and 20% as fat) and amino acids 1.9 g/kg-1/day-1. A significant increase was obtained in body weight, triceps skinfold, arm fat area, and retinol binding protein. All remaining anthropometric and biochemical parameters did not show any significant positive or negative change, although nitrogen balance remained positive. No significant liver toxicity was apparent after the TPN period. It was concluded that although TPN is unable to completely reverse some nutrition-related variables in cachectic patients with cancer, most patients were kept within a normal range and some improved. Therefore, further deterioration of the nutritional state, which is characteristic of this phase of disease, was at least prevented.

Body composition of two human cadavers by neutron activation and chemical analysis

In vivo neutron activation analysis (NAA) is currently used to measure body composition in metabolic and nutritional studies in many clinical situations, but has not previously been validated by comparison with chemical analysis of human cadavers. Total body nitrogen (TBN) and chlorine (TBCl) were measured in two human cadavers by NAA before homogenization and chemical analysis (CHEM) after (cadaver 1: TBN, 1.47 NAA, 1.51 CHEM; TBCl, 0.144 NAA, 0.147 CHEM; cadaver 2: TBN, 0.576 NAA, 0.572 CHEM; TBCl, 0.0227 NAA, 0.0250 CHEM). The homogenates were also analyzed by NAA, and no significant differences were found, indicating that the effects of elemental inhomogeneity on the measurement of TBN and TBCl are insignificant. Total body water, fat, protein, minerals, and carbohydrates were measured chemically for each cadaver and compared with estimates for these compartments obtained from a body composition model, which when used in vivo involves NAA and tritium dilution. The agreement found justifies the use of the model for the measurement of changes in total body protein, water, and fat in sequential studies in groups of patients.