Bioelectrical impedance vector analysis in haemodialysis patients: relation between oedema and mortality

Whole-body and thoracic bioimpedance measurement: hypertension and hyperhydration in hemodialysis patients

Mono-frequency (50 kHz) and multi-frequency (3 kHz - 1 MHz) whole-body and thoracic segment bioimpedance measurement were doing before and after hemodialysis session in 20 patients. The patients were classified in hypertensive or non-hypertensive according to the mean blood pressure, BPmean. The relation between hyper-hydration in thorax segment through real part of impedance and mean blood pressure was analyzed. Also the bioelectrical impedance vector analysis method was used to analyze the displacement of Z/H vector in order to establish the relation with hyper-hydration (edema). Finally we made multi-frequency measurements with the objective to find a significative change in high and low frequency. We obtained a significant difference (P < 0.05) in impedance parameters before and after HD session. Some patients are located in hyper-hydration zone, below the inferior pole of the 75% tolerance ellipse, whereas others patients were within the tolerance ellipses. The real part of the impedance in thorax region can identify over-hydrated patients with an increased risk for cardiovascular disease associate to hypertension. Multi-frequency bioimpedance measurement show an important change at low and high frequency and indicate that is possible to obtain more information about extra-cellular or intra-cellular fluid status, to find the relation between fluid loads, bioimpedance parameters, extra-cellular water, and blood pressure.

Is bioelectrical impedance vector analysis of value in the elderly with malnutrition and impaired functionality?

OBJECTIVE

The calculation of body composition using bioelectrical impedance analysis is difficult in the elderly because most equations have been found to be inadequate, especially in the malnourished elderly. We therefore evaluated the use of bioelectrical impedance vector analysis in elderly nursing home residents.

METHODS

One hundred twelve nursing home residents were included in the study (34 men, 78 women, age 85.1 y, age range 79.1-91.4 y). Nutritional status was determined by the Mini Nutritional Assessment (MNA), functional status was assessed by handgrip strength, knee extension strength, and Barthel's index, and bioelectrical impedance analysis was performed using Nutriguard M (Data Input, Darmstadt, Germany).

RESULTS

Twenty-two nursing home residents were classified as well nourished (MNA I), 80 were considered to be at nutritional risk (MNA II), and 10 were classified as malnourished (MNA III). Handgrip strength, knee extension strength, and Barthel's index were lower in MNA II and MNA III than in MNA I. Phase angle also decreased significantly with the MNA (4.0, 3.8-4.7 degrees; 3.7, 3.3-4.3 degrees; and 2.9, 2.6-3.5 degrees). There was a significant displacement of the mean vector in MNA II and MNA III compared with MNA I.

CONCLUSION

The bioelectrical impedance vector analysis resistance/reactance graph could represent a valuable tool to assess changes in body cell mass and hydration status in elderly nursing home residents.

Bioelectrical impedance and strength measurements in patients with heart failure: comparison with functional class

OBJECTIVE

Patients with chronic heart failure (HF) develop important changes in body composition. Nevertheless, the usual methods of body composition assessment can be misleading in patients with HF because tissue hydration is altered. Bioelectrical impedance vector analysis (BIVA) works without making any assumption about constant soft tissue hydration. In this study, patients with HF and systolic dysfunction (HFS) and preserved systolic function (HFPSF) underwent a body composition evaluation by the BIVA method; the comparison was done between New York Heart Association (NYHA) functional classes I-II and III-IV.

METHODS

We studied 243 patients with HF, 140 (101 in NYHA I-II and 39 in III-IV) with HFS and 103 (67 in NYHA I-II and 36 in II-IV) with HFPSF. Whole-body bioelectrical impedance was measured using BodyStat QuadScan 4000, which is tetrapolar and multiple-frequency equipment.

RESULTS

In both HF categories, reactance and phase angle were significantly lower, the impedance ratio of 200 kHz to that at 5 kHz was higher, and had significantly shorter and downsloping impedance vector in the NYHA III-IV group compared with the NYHA I-II group by gender.

CONCLUSION

Bioelectrical impedance analysis allows an easier evaluation of body composition and this might be particularly useful to stratify the severity of HF.

Thoracic versus whole body bioimpedance measurements: the relation to hydration status and hypertension in peritoneal dialysis patients

The whole body bioimpedance technique is a highly promising non-invasive, reproducible, fast and inexpensive bed-side method for monitoring hydration status. Using segmental bioimpedance measurements, it is possible to obtain information about the fluid change in each body segment (Song, Lee, Kim and Kim 1999 Perit. Dial. Int. 19 386-90). In this pilot study we have measured 25 male patients (30-65 yr, BMI 20-32 kg m(-2)) undergoing continuous ambulatory peritoneal dialysis (CAPD). Tetrapolar impedance measurements were obtained using the right-side technique (whole body), and a segmental impedance method focused in the thorax region. Blood pressure (BP) measurements were taken manually with a sphygmomanometer. Patients were classified as either stable (group 0) or unstable (group 1) using clinical parameters of overall cardiovascular risk. The Mahalanobis distance (dM2) was calculated for the mean blood pressure (BP(mean)), and the impedance parameter R normalized by body height H for the right-side (R(RS)/H) and the thorax segment (R(TH)/H). Differences between groups were significant (p < 0.0001) for R(TH)/H and for BP(mean), and less significant (p = 0.016) for R(RS)/H. Group 1 patients showed a small dM2 as compared with a reference patient (a critical patient with acute lung edema) with high BP(mean) and low values of R(TH)/H and R(RS)/H. Moreover, Group 0 patients showed a larger dM2 with respect to the reference patient, with lower BP(mean) and higher values of R(TH)/H and R(RS)/H. All patients classified as unstable by clinical assessment were correctly classified using R(TH)/H in conjunction with BP(mean) using dM2. Segmental-monofrequency non-invasive bioimpedance of the thoracic region could provide a simple, objective non-invasive method of support for facilitating the clinical assessment of CAPD patients.

Bioelectrical impedance analysis in clinical practice: a new perspective on its use beyond body composition equations

PURPOSE OF REVIEW

The bioelectrical impedance analysis is not a direct method for estimating body composition. Its accuracy depends on regression equations, and recent papers have suggested that this approach should not be used in several clinical situations. Another option is to obtain information about the electrical properties of tissues by using raw bioelectrical impedance measurements, resistance and reactance. They can be expressed as a ratio (phase angle) or as a plot (bioelectrical impedance vector analysis). This review describes their use in clinical practice.

RECENT FINDINGS

The phase angle changes with sex and age. It is described as a prognostic tool in many clinical situations. There are some controversies about considering it as a nutritional marker. Studies in burn victims and sickle-cell disease corroborate its ability to evaluate cell membrane function. Bioelectrical impedance vector analysis allows a semi-quantitative estimation of body composition from information from tissue hydration and soft-tissue mass in a plot. It can be used in healthy individuals or patients, for a population or individual evaluation of fluid imbalance or an assessment of soft-tissue mass. It has also been used as a prognostic tool in dialysis and cancer patients.

SUMMARY

The phase angle can be considered a global marker of health, and future studies are needed to prove its utility in intervention studies. Bioelectrical impedance vector analysis has increased its utility in clinical practice, even when the equations may be inaccurate for body composition analysis.