Bio-electrical impedance spectroscopy: alternatives for the conventional hand-to-foot measurements.

BACKGROUND AND AIMS: Bio-impedance spectroscopy (BIS) is a very attractive method for measuring body composition. The standard method measures impedance from hand to foot. However, in patients a hand or foot is not always accessible. In these cases alternative methods would be helpful. The objective of this study was to compare BIS measurements from hand to foot (HF) with foot to foot (FF) and hand to hand (HH) measurements as alternatives. Aims were firstly, to assess the relationship between resistance (R) values measured by the different methods, secondly, to study the influence of body geometry on this relationship and lastly, to assess the predictive capacity of the methods for measuring body fluid volumes. METHODS: In 53 subjects with different degrees of obesity (mean BMI = 38; SD = 9 kg/m(2)) three BIS measurements were performed from HF, HH and FF with a Xitron 4000B machine. Resistances of extracellular (Recw) and intracellular water (Ricw) were extrapolated by fitting the data to a Cole-Cole plot. Total body water (TBW) and extracellular water (ECW) were measured by deuterium and bromide dilution respectively. Intracellular water (ICW) was calculated as TBW-ECW. Anthropometric measurements, including length and circumference of limbs and trunk, were performed as measures for body geometry. RESULTS: The Recw, Ricw and R50 values of HF measurements could be accurately described as a function of the Recw, Ricw and R50 values of HH or FF measurements. The relative circumference of arms and legs and the length of the trunk influenced the relationship between R values of the three different measurements. The degree of overweight did not affect this relationship. The precision of the predictions of TBW, ECW and ICW based on R values of the HH measurements were comparable with the traditional HF measurements while the FF measurements gave slightly less accurate results. CONCLUSIONS: Under circumstances where total body BIS measurements cannot be performed, FF or HH measurements may be used as alternatives. However, for clinical use the effect of changes in fluid distribution on the accuracy of these methods needs to be studied further.

Multi-frequency bioimpedance measurements of children in intensive care.

Bioimpedance spectroscopy is used to monitor the condition of the tissues of children staying in intensive care for the treatment of meningitis. The results are significant, with the angular frequency at maximum reactance lying between 1500 and 6400 x 10(3) rads(-1), whereas in a control group, this value does not exceed 900 x 10(3) rads(-1). The ratio between the specific conductance at zero and that at infinite frequency (this ratio is proportional to total body volume/volume of extracellular space) remains constant at 1.4 and equal to the ratio in the control group, despite infusions with physiological saline. The electrical parameters are associated with physiological ones and indicate that the membrane 'capacitance' decreases, as a result of the illness, from approximately 0.4 in the control group to 0.05 in the patient group. However, there is a time-delay between the onset of illness and the change in membrane capacitance. It is also found that the ratio between extracellular and intracellular specific conductivity in the group of patients and controls remains constant at approximately 4.3. The changes in the physiological and electrical parameters were compared with chemical parameters that were measured during the stay in intensive care.

Effects of therapy with lansoprazole on intestinal permeability and inflammation in young cystic fibrosis patients.

BACKGROUND: Defective pancreatic bicarbonate secretion with low intestinal pH or intestinal inflammation of any origin increase intestinal permeability in cystic fibrosis (CF). METHODS: In this open study, the authors evaluated the effect of a proton-pump inhibitor on intestinal permeability and inflammation in 14 young, pancreatic-insufficient CF patients. Permeability was measured by a three-sugar permeability test before and after 1 year of lansoprazole use, and urinary nitric oxide (NO) oxidation products were assessed before and during that year as a marker of inflammation. RESULTS: After 1 year of lansoprazole use, median urinary recovery percentages changed from 2.5% to 1.7% (P = 0.064), from 24.9% to 24.5% (no significance), and from 10.5% to 11.1% (no significance) for lactulose, mannitol, and L-rhamnose, respectively. Despite the fact that the median urinary excretion ratios decreased from 0.108 to 0.083 (P = 0.03) and from 0.246 to 0.176 (P = 0.016) for lactulose and mannitol and for lactulose and rhamnose, respectively, they both remained increased. Median urinary NO products-to-creatinine ratios were 0.287 for CF patients before lansoprazole and 0.130 for healthy control participants (P = 0.002). Although there was a tendency toward a decrease in the NO products-to-creatinine ratio during treatment, this was not significant at the end point. CONCLUSIONS: Intestinal permeability is considerably increased in CF patients and is partly corrected after the use of a proton-pump inhibitor for 1 year, which may point to a harmful effect of the acid luminal contents on the tight junctional related paracellular permeability pathway. The start and end values for the NO products-to-creatinine ratio in CF patients were not significantly different, but were considerably increased when compared with control participants (P = 0.002).

Measurement of total body water in children using bioelectrical impedance: a comparison of several prediction equations.

BACKGROUND: Body composition evaluation by bioelectrical impedance analysis in children makes use of different group-specific population-derived equations. The present study was conducted to attempt to validate the use of population-independent physical model-derived equations in children. METHODS: The validity of bioelectrical impedance analysis for the measurement of total body water in children was evaluated by comparing results of two physical model-derived and two population-derived equations with those of deuterium dilution as reference method in a group of 38 heterogeneous children. RESULTS: Means +/- standard deviation (in liters) for total body water measured with deuterium dilution and the physical model 1-derived equation were 18.4 +/- 4.7 L and 18.1 +/- 4.4 L, respectively. This difference is not significant, whereas significant differences were found for all other tested equations. Significant smaller absolute differences between the model 1 equation and deuterium reference results were found when compared with the results of the other three tested equations. CONCLUSION: When compared with results of the reference deuterium method the physical model 1-derived equation was the only one that provided reliable total body water results by bioelectrical impedance analysis in children.

The value of dextran 12,000 in ischemically damaged canine kidneys during machine perfusion.

The use of non-heartbeating (NHB) donor kidneys has led to the search for new methods of viability-testing. We investigated, in a canine model, the relationship between the filtration of dextran 12, 000 into urine and a certain period of warm ischemic time (WIT) during machine perfusion. Twenty-four canine kidneys were divided into three groups, sustaining 0 min, 30 min or 60 min of WIT. After cooling and flushing, the kidneys were perfused on a perfusion machine for 8 h. Three hundred milligrams of dextran 12,000 was added to the perfusate. In the perfusate, dextran and lactate dehydrogenase (LDH) concentrations were measured. Dextran concentrations were also analysed in urine. Intrarenal vascular resistance (IRR) was calculated from pressure and flow characteristics. The 30WIT group showed a higher dextran excretion rate than the other two groups. IRR and LDH measurements showed lower levels in the ischemic groups compared with the control group. Dextran 12,000 is not suitable as a viability test but does show interesting results regarding the low LDH and IRR levels in the ischemic groups.

Glutamine: the pivot of our nitrogen economy?

Glutamine serves as a shuttle of useful nontoxic nitrogen, supplying nitrogen from glutamine-producing (eg, muscle) to glutamine-consuming tissues. True production rates of glutamine are difficult to measure, but probably are less than 60 to 100 g/d for a 70-kg man. During catabolic stress increased amounts of glutamine are released from muscle, consisting of protein derived glutamine, newly synthesized glutamine, and glutamine losses from the intramuscular free pool. The large and rapid losses of free muscle glutamine are difficult to restore, presumably as a result of disturbances in the Na+ electrochemical gradient across the cell membrane. Whereas increased amounts of glutamine are released from muscle, glutamine consumption by the immune system (liver, spleen) also is enhanced. Thus, during catabolic stress changes occur in the flow of glutamine between organs. These changes are not necessarily reflected by alterations in the whole-body appearance rate of glutamine. In contrast with the gut, where glutamine is taken up in a concentration dependent manner, the immune system actively takes up glutamine despite decreased plasma concentrations. Supplementation with glutamine influences uptake by both the gut and the immune system, as evidenced by increased mucosal glutamine concentrations and gut glutathione production. There is evidence suggesting that this improves gut barrier function. Although the benefit of glutamine supplementation is most evident from experimental studies, clinical studies on the effect of glutamine do exist and suggest that glutamine supplementation has beneficial effects with regard to patient outcome.

Body composition in renal transplant patients: bioimpedance analysis compared to isotope dilution, dual energy X-ray absorptiometry, and anthropometry.

Whether multifrequency bioelectrical impedance analysis (MF-BIA), a relatively new method for measuring body composition, is also applicable for accurate body composition measurements in renal transplant (RTx) patients is not known. Therefore, the use of MF-BIA is validated in 77 RTx patients with a stable renal function at least 2 yr posttransplantation. MF-BIA is compared to isotope dilution techniques for measurement of body water compartments, and to dual energy x-ray absorptiometry (DEXA) and anthropometry for measurement of fat and fat free mass. Finally, DEXA and anthropometry are compared to each other. Method agreement is assessed by intraclass correlation coefficients (ICC) and plotted by Bland and Altman analysis. MF-BIA significantly underestimates total body water (TBW, 0.7+/-2.1 L) and overestimates the extracellular water (ECW, 3.3+/-1.8 L) compared to isotope dilution; the ICC between both techniques is 0.943 for TBW and 0.846 for ECW. The percentage body fat (BF) measured by MF-BIA is significantly higher than both BF measured by DEXA (3.4+/-4.7%) or by anthropometry (5.5+/-5.2%). The ICC between MF-BIA and DEXA is 0.887 and between MF-BIA and anthropometry 0.856. BF measured by DEXA is significantly higher than BF measured by anthropometry (2.1+/-4.4%); their ICC is 0.913. In conclusion, MF-BIA seems to be suitable for measurement of TBW in RTx patients; however, method agreement between isotope dilution and MF-BIA for the measurement of ECW is not satisfactory. In the assessment of fat and fat free mass, the reliability of MF-BIA appears to be questionable. Method agreement between DEXA and anthropometry seems to be slightly better.

Determination of total body water by multifrequency bio-electric impedance: development of several models.

Multifrequency bio-electronic impedance analysis (MF BIA) measurements are taken from a heterogeneous group of patients, varying in size between obese and slim. The measuring system uses four electrodes: two current and two potential electrodes. Three new models are developed to calculate total body water (TBW) from the BIA data, and the resulting TBW values are compared with TBW determined by D2O dilution. The results demonstrate that the most simple model provides the best TBW values. For individual patients, TBW can be determined by means of bioimpedance measurement with an accuracy of 3 litres. In the most simple model (model 1), the body is electrically represented by a cylinder, and corrections are made for the amount of fat. This is an extension of the model used by Xitron. In the more advanced models (2 and 3), the body is represented by a cylinder for the trunk, and truncated cones represent the arms and legs. In model 2, delta TBW amounts to 3 litres. It is shown that the resistance of the trunk is proportional to the square root of the length. In model 3, it is assumed that subcutaneous fat is a poor conductor of electric current. An equation is developed that describes the partition of subcutaneous fat, and the fat layer is then removed from the cones representing arms and legs and from the cylinder that models the trunk.

Absence of glutamine isotopic steady state: implications for the assessment of whole-body glutamine production rate.

1. During infusion of [5-15N]glutamine in patients with gastrointestinal cancer we unexpectedly observed a gradual decrease in time of the appearance rate (Ra) of glutamine in plasma. Here we investigate whether the failure to achieve a plateau isotopic enrichment in plasma is, among other factors, due to incomplete equilibration of the glutamine tracer with the large intramuscular free glutamine pool.2. Plasma and intramuscular glutamine enrichment were measured during 6-11 h infusions of L-[5-15N]glutamine and L-[1-13C]glutamine in post-absorptive patients admitted to hospital for elective abdominal surgery. L-[1-13C]Leucine and L-[ring-2H5]phenylalanine were infused to measure the proportion of glutamine appearing in plasma directly due to its release from protein.3. The glutamine tracer entered muscle, but the rise in intramuscular glutamine enrichment was small, presumably as a result of the enormous size of the intramuscular glutamine pool and the limited speed of entry of glutamine into muscle. In each patient the intramuscular glutamine enrichment was lower than that in plasma (P<0.001), and both increased with tracer infusion time (P<0.001), indicating incomplete equilibration of the glutamine tracer.4.A comparison of the results obtained by the two glutamine tracers indicated that recycling of the nitrogen label contributed to about 15% of the decrease in Ra.5. There was a gradual reduction in the glutamine release from proteolysis, which contributed to 16-21% of the decline in Ra.6. We conclude that slow equilibration of the glutamine tracer with the large muscle glutamine pool significantly contributes to the absence of isotopic steady state. Consequently, the appearance rate of glutamine in plasma measured during short tracer infusion periods (hours) considerably overestimates the whole-body glutamine flux.

A new method for plasma volume measurements with unlabeled dextran-70 instead of 125I-labeled albumin as an indicator.

A method has been developed to determine plasma volume with dextran-70 without the use of a fluorescent label. The results obtained are compared to those found using the 125I-labeled albumin method, which is taken as the gold standard. The CV of the method is about 5%, compared to 3% with the gold standard. It is shown to be of use for the determination of an increase in plasma volume during pregnancy.

Mechanism of volume adaptation in the awake early pregnant rat.

The objective of the present study was to determine whether the increase in plasma volume (PV) during pregnancy is established by fluid retention or by a shift within the extracellular fluid volume (ECFV) from the interstitium toward the intravascular compartment. To this end, we simultaneously, measured total body water, (TBW), ECFV, and PV together with the hematocrit (Hct) and plasma osmolality 4, 8, and 12 days postsurgery in chronically instrumented pregnant (P) and nonpregnant (NP) rats. The P rats were instrumented with a catheter in the femoral artery on day 1 postconception. In the NP group, neither TBW nor ECFV and PV had changed consistently on days 8 and 12 postsurgery relative to day 4. In contrast, in the P animals, TBW, ECFV, and PV had increased by 16, 24, and 20%, respectively, by day 12 relative to day 4. To evaluate whether PV had increased in concert with an overall rise in TBW or as a result of a fluid shift at the cost of the interstitial fluid volume, we calculated the relative size of each fluid compartment on three consecutive measurement sessions. In the NP group, TBW, presented as percentage of maternal weight (%MW) as well as ECFV (%TBW) and PV (%ECFV) had not changed consistently throughout the measurement period. In the P animals, TBW (%MW) was slightly higher on day 12 compared with day 4, but ECFV (%TBW) and PV (%ECFV) had not changed significantly. Finally, in the NP group, Hct had not changed, whereas, in the P animals, Hct was 10% lower on days 8 and 12 compared with day 4. Plasma osmolality did not change consistently in either group during the course of the experimental period. The gradual synchronous increase in all fluid compartments, without consistent change in their relative distribution, suggests that, in normal rat pregnancy, PV expansion is primarily achieved by fluid retention rather than by a redistribution of the ECFV.

Gut permeability, intestinal morphology, and nutritional depletion.

Nutritional depletion increases the risk for postoperative complications. The intestinal barrier may be important in the underlying pathophysiologic mechanism. In this study, 26 patients were evaluated to determine whether nutritional depletion was related to gut integrity and intestinal morphology. Nutritional depletion was estimated by calculating percentage ideal body weight (PIB) or percentage ideal fat free mass (PIFFM). To assess gut integrity, a lactulose/mannitol (L/M) test was performed. Duodenal biopsies were taken, and villous height, crypt depth, number of IgA-producing plasma cells, intraepithelial lymphocytes (IELs), and proliferating index were determined. The L/M ratio was increased, and villous height was decreased in depleted patients. Depletion was not associated with differences in the number of immune cells or proliferating index. The number of IgA-producing plasma cells was positively correlated with the L/M ratio. This study shows that nutritional depletion is associated with increased intestinal permeability and a decrease in villous height.

Glutathione S-transferase as predictor of functional outcome in transplantation of machine-preserved non-heart-beating donor kidneys.

Non-heart-beating (NHB) donors are a valuable source of kidneys for transplantation. The organs, however, sustain substantial warm ischemic damage that may jeopardize the transplantability and result in nonfunction of the grafts. Quantification of warm ischemic time (WIT) and prediction of transplant outcome are essential for the use of NHB donor organs. During machine preservation (MP) the viability of NHB donor kidneys was evaluated through calculating intrarenal vascular resistance and determining lactate dehydrogenase and alpha-glutathione S-transferase (alphaGST) in the perfusate. Thirty-seven functioning (F) and nine nonfunctioning kidneys (NF) were compared. WIT was longer in NF; serum creatinine, donor age, and preservation time were not different. WIT correlated well with alphaGST after 4 and 8 hr of MP (r=0.353, P=0.009, and r=0.346, P=0.011, respectively). When compared with F, intrarenal vascular resistance was increased in NF after 4 and 8 hr of perfusion (P<0.05); at all time points, alphaGST levels were elevated in NF (P<0.05). Lactate dehydrogenase activity was not different between the groups, but could identify immediate functioning grafts within the F group. In conclusion, alphaGST levels correlated strongly with WIT and were also able to distinguish NF from F grafts. alphaGST can adequately predict the functional outcome of NHB donor grafts before transplantation; levels of alphaGST can be used to define reliable safety margins for viability. Therefore, MP is useful in evaluating the viability of NHB donor kidneys, and the parameters discussed will help to select nonviable grafts from this valuable pool of kidneys for transplantation.

Acid steatocrit during infancy.

The faecal acid steatocrit is an improved steatocrit method for the evaluation of faecal fat. The present study was set up in order to establish reference values during the first year of life. Faecal acid steatocrit values were determined in 58 healthy full term and in 16 healthy prematurely born infants. Very high acid steatocrit results (above 60%) were found in all premature and many formula-fed term infants during the first 6 months of age, thereafter with values below 10%. In 40- to 120-day-old infants acid steatocrit results of human milk-fed infants were significantly lower than those of formula-fed infants (p < 0.01). We conclude that high acid steatocrit results after the age of 6 months are indicative of fat malabsorption, while before this age high values can be due to "physiological steatorrhoea". The acid steatocrit should be useful for the evaluation of milk fat absorption in infants.

Improved steatocrit results obtained by acidification of fecal homogenates are due to improved fat extraction.

Conflicting results have been reported on the value of the steatocrit as a screening test for steatorrhea. We recently modified the test procedure by fecal acidification with the hope of improving fat extraction and consequently the sensitivity of the test. The aim of the present study was to ascertain whether or not fecal acidification led to improved fat extraction by comparing the fat content of both fatty and solid layers obtained by centrifugation of 12 acidified (acid steatocrit) and unacidified (classical steatocrit) steatorrheal stool samples. The fat content of fatty and solid layers was evaluated using the semiquantitative (+ = 1, +2 = 2, +3 = 3) scoring system described by Drummey for the interpretation of the Sudan microscopic method for fecal fat. The fatty layers sum of scores for the 12 samples examined was 31 and 16 for the acid and classical steatocrit, respectively. The solid layers sum of scores for the 12 samples was 13 and 24 for the acid and classical steatocrit, respectively. Fat extraction from stool samples was significantly improved after fecal sample acidification (p < 0.005). Acid steatocrit results agreed better with chemically measured fecal fat than classical steatocrit results. We conclude that fecal acidification, by improving fat extraction, increases the reliability of the steatocrit method for the detection of steatorrhea.

Determination of total body water by a simple and rapid mass spectrometric method.

A rapid and inexpensive method was developed to determine deuterium enrichment in body fluids. This is achieved by converting water into acetylene. To vacutainer tubes a small amount of calcium carbide is added. The tubes are evacuated and 25 microliters of sample are injected through the stopper. The reaction takes place spontaneously at room temperature in a few seconds. Enrichment at mass 27 compared with mass 26 can be determined by continuous flow isotope ratio mass spectrometry without any interference from the carrier gas helium. A series of D2O samples diluted with increasing amounts of H2O is prepared at the time of measurement of the biological samples and the measured ratios are used to calculate the isotope dilution of the unknown. The relative error of the method is 1.6% when a dose of 25 ml kg-1 is administered to the patient. The method was compared with two different methods in use in other laboratories, by a published method The means of the differences were -0.1 and 0.08 1, respectively, with standard deviations of 0.63 and 3.0.

An improved bromide assay for the estimation of extracellular water volume by capillary gas chromatography.

A sensitive bromide determination has been developed that consists of the following steps: isolation (purification) of bromide; oxidation of bromide to bromine with potassium permanganate and subsequent reaction with acetone, to give the volatile bromoacetone; quantification of bromoacetone by capillary gas chromatography. The method can also be used with small sample volumes appropriate for paediatric applications. Thermodynamic arguments are used to calculate the equilibria involved. The accuracy and reproducibility of the method have been determined. Finally, the bromide space of six volunteers was determined and the clearance of the bromide by the kidneys was investigated.

The acid steatocrit: a much improved method.

The steatocrit method has recently been introduced as a simple screening test for steatorrhea. As it seemed likely that separation of fecal homogenate by centrifugation into a lipid phase, a watery phase, and a solid phase would be pH-dependent, we evaluated the effect of fecal acidification on steatocrit results. We also compared classical and acid steatocrit results in healthy children and in patients with cystic fibrosis and studied the relationship between two steatocrit methods and fecal fat content as measured by a reference chemical method. Steatocrit results increased with the degree of fecal acidification, and maximal results were obtained at the lowest fecal pH values. Means and SEM for classical and acid steatocrit values were 1.1 +/- 0.4% (classical) versus 3.8 +/- 1% (acid) in controls (n = 6) and 5.4 +/- 1.9% (classical) versus 26.9 +/- 4.3% (acid) in cystic fibrosis patients (n = 9). The correlations between fecal fat content measured chemically and steatocrit results were 0.18 (p = 0.35) and 0.81 (p < 0.0001) for classical and acid steatocrit, respectively. We conclude that acidification of fecal homogenates leads to a marked improvement in the steatocrit method.

Glutamine and the preservation of gut integrity.

Parenteral glutamine dipeptide improves nitrogen balance in postoperative patients on total parenteral nutrition (TPM). Animal studies show that the structure and function of the gut is preserved by glutamine. It is not known if this is the case in human beings. 20 patients admitted to hospital for total parenteral nutrition were randomly allocated to receive parenteral nutrition enriched with glycyl-L-glutamine (Gln TPN), or standard parenteral nutrition (STPN). Mucosal biopsy specimens were taken from the second part of the duodenum before starting parenteral nutrition, and after two weeks. The ratio between the urine concentrations of lactulose and mannitol after enteral administration was used to measure intestinal permeability. After two weeks of parenteral nutrition in the GlnTPN group, intestinal permeability was unchanged, whereas permeability in the STPN group increased. Villus height was unaltered in the GlnTPN group but in the STPN group it decreased. The addition of glutamine to parenteral nutrition prevents deterioration of gut permeability and preserves mucosal structure.