Future lines of research on phase angle: Strengths and limitations

Abstract

Bioelectrical impedance analysis (BIA) is the most widely used technique in body composition analysis. When we focus the use of phase sensitive BIA on its raw parameters Resistance (R), Reactance (Xc) and Phase Angle (PhA), we eliminate the bias of using predictive equations based on reference models. In particular PhA, have demonstrated their prognostic utility in multiple aspects of health and disease. In recent years, as a strong association between prognostic and diagnostic factors has been observed, scientific interest in the utility of PhA has increased. In the different fields of knowledge in biomedical research, there are different ways of assessing the impact of a scientific-technical aspect such as PhA. Single frequency with phase detection bioimpedance analysis (SF-BIA) using a 50 kHz single frequency device and tetrapolar wrist-ankle electrode placement is the most widely used bioimpedance approach for characterization of whole-body composition. However, the incorporation of vector representation of raw bioelectrical parameters and direct mathematical calculations without the need for regression equations for the analysis of body compartments has been one of the most important aspects for the development of research in this area. These results provide new evidence for the validity of phase-sensitive bioelectrical measurements as biomarkers of fluid and nutritional status. To enable the development of clinical research that provides consistent results, it is essential to establish appropriate standardization of PhA measurement techniques. Standardization of test protocols will facilitate the diagnosis and assessment of the risk associated with reduced PhA and the evaluation of changes in response to therapeutic interventions. In this paper, we describe and overview the value of PhA in biomedical research, technical and instrumental aspects of PhA research, analysis of Areas of clinical research (cancer patients, digestive and liver diseases, critical and surgical patients, Respiratory, infectious, and COVID-19, obesity and metabolic diseases, Heart and kidney failure, Malnutrition and sarcopenia), characterisation of the different research outcomes, Morphofunctional assessment in disease-related malnutrition and other metabolic disorders: validation of PhA with reference clinical practice techniques, strengths and limitations. Based on the detailed study of the measurement technique, some of the key issues to be considered in future PhA research. On the other hand, it is important to assess the clinical conditions and the phenotype of the patients, as well as to establish a disease-specific clinical profile. The appropriate selection of the most critical outcomes is another fundamental aspect of research.

Keywords: Bioelectrical impedance vector analysis; Body composition; Morphofunctional assessment; Outcome research; Phase angle; Phase sensitive bioelectrical impedance analysis.

Fig. 1

Overview of the diversity in distribution of peer-reviewed publications in Scopus including phase angle in biomedical research. a Number of publications. b Publication areas. c Geographical distribution of publications. d Type of medical journal. Abbreviations: PhA: phase angle

Fig. 2

Phase angle research areas. Web of Science

Fig. 3

Knowledge Map of "phase angle" of the main areas and the documents (https://openknowledgemaps.org/)

Fig. 4

Bibliometric map of keywords related to phase angle (VOSviewer software). The search was carried out on February 2, 2023

Fig. 5

Generic RXc plot that illustrates the vector distributions with interpretations for fluid status and cell mass. Xc: reactance. Rz: resistance. H: height. Ohm: Ohms. M: meters

Fig. 6

Graphical representation of cell damage and hydration changes in the BIVA model. A Healthy person. Normal values of PhA, BCM and hydration. B Mecanism. Malnutrition, sarcopenia, caquexia. Values: low PhA, low BCM and normal hydration. C Cell damage is represented by the shift of the vector on the X-axis in the direction of cell mass loss and leads to a decrease in PhA. D Mecanism. Inflammatory damage, oxidative stress. E Mecanism. Congestion: heart failure (PRO BNP and CA125) and chronic kidney disease (glomerular filtration rate). F In the hydration mechanism, with no change in cell mass, there is a shift of the vector along the Y-axis, resulting in a decrease in PhA. G Mecanism. Inflammation (CRP and CRP/Prealbumin ratio). Low PhA, normal BCM, hight hydration. H: Disease. Patients. Low PhA, low BCM, high hydration. Legend: Heart failure. Inflammation. Abbreviations: BCM: body cell mass. ECW: extra cellular water. NT-proBNP = N-terminal b-type natriuretic peptide pro. PhA: phase angle. Rz: resistance. TBW: total body water. Xc: reactance

Fig. 7

Illustration of the effects of hydration status and malnutrition on bioimpedance measurements and vector positions on the resistance-reactance graph using bioimpedance vector analysis. Abbreviations: ECW: extracellular water. ICW: intracellular water. abn: abnormal. nl: norma.l PhA: phase angle. R/H: resistance normalized for height. Xc/H: reactance normalized for height

Fig. 8

Graphical abstract: Parameters, Diseases, Cell mass and hydration changes, Outcomes and Morphofunctional assessment