Evaluation of Hydration Status by Bioelectrical Impedance Vector Analysis in Patients with Ischemic Heart Disease Undergoing Exercise Stress Test

Summary

Hydration status imbalances can have a short-term effect on direct and indirect determinants of oxygen uptake and pulse, and morbidity and mortality prognostic factors in ischemic heart disease. This protocol describes the technique for assessment of hydration status through bioelectrical impedance vector analysis and cardiopulmonary response during exercise stress test.

Abstract

Ischemic heart disease (IHD) represents a group of clinical syndromes characterized by myocardial ischemia, leading to an impairment in the myocardial blood supply and compromised perfusion. Several clinical variables assessed through a stress test, such as oxygen uptake (VO2) and heart rate oxygen pulse (HR/O2), have been attributed as cardiopulmonary prognostic factors in patients with IHD. However, other factors like hydration status (HS), potentially affecting the cardiopulmonary response, have been barely addressed. Unbalanced HS has a short-term effect on plasma volume and the sympathetic nervous system, which impacts blood volume, and lowers VO2 and HR/O2. Recently, bioelectrical impedance analysis (BIA), a method based on the opposition of body tissues (including fluid volume) to a low electrical current, has been widely used to assess HS by obtaining two components: resistance (R) and reactance (Xc) and using prediction formulas. However, several limitations as chronic illness or abnormal fluid status, may affect the results. In this sense, alternative BIA methods, such as bioelectrical impedance vector analysis (BIVA), have become relevant. R and Xc (adjusted by height) result in a vector plotted on the R/Xc graph, which allows interpreting the HS as normal or abnormal according to the distance of the mean vector. This study aims to describe how to determine HS by BIVA using a single-frequency device and compare the results with the cardiopulmonary response in patients with IHD.

Introduction

Ischemic heart disease (IHD) represents a group of clinical syndromes characterized by myocardial ischemia, a mismatch in the myocardial blood supply and demand. The underlying pathophysiological defect includes inadequate perfusion, mainly due to atherosclerotic disease of epicardial coronary arteries^1,2,3. In general, the presence of cardiovascular disease (CVD) is common, showing poor survival worldwide⁴. Particularly in 2015, IHD contributed to approximately 9 million deaths and more than 160 million disability-adjusted life years, and nowadays, IHD remains one of the main causes of mortality, and it favors the heart disease burden around the world⁵.

To evaluate both the presence and prognosis of IHD, some non-invasive procedures like the exercise stress test (EST) are routinely used. EST provides an assessment of the overall performance of cardiovascular, muscular, pulmonary, hematopoietic, neurosensory, and skeletal systems when the maximum tolerable stress appears under the EST⁶.

Under normal conditions, physiological adaptations would be expected while exercising. During exercise, several changes occur, like a dynamic change of fluid in blood within the vascular compartment, the reduction of plasma and blood volume, and the increase in hematocrit and plasma metabolite concentrations. Reduced plasma volume normalizes approximately 1 h after exercise, which may also vary depending on individual training level and water replenishment⁷.

However, IHD may lead to an acute impaired response to exercise, affecting EST performance in some variables comprising aerobic capacity and exercise tolerance, such as oxygen uptake (VO2) and heart rate/oxygen pulse (HR/O2)⁸. Recently, hydration status (HS), a measure of the water contained in the body¹, has been proposed as a factor linked to plasma volume, able to modify blood flow and viscosity. HS has also been related to systolic volume, heart rate, and arteriovenous oxygen difference, determinants of VO2. Furthermore, some studies describe the relation of HS with a lower cardiopulmonary response (cardiac chronotropic and inotropic, VO2 and HR/O2)⁹.

In addition, several factors like age, environmental conditions, the level of physical activity/exercise, and dietary factors like fluid intake have been described to participate in HS balance¹⁰. Likewise, pathophysiological conditions such as IHD and its progression may influence HS¹¹.

Although HS closely relates to cardiopulmonary, biological-environmental responses or lifestyle factors, the particular association of IHD in population with previous conditions has been scantily addressed; and it represents a significant challenge for clinical research, specifically due to the assessment of early stages, as well as the requirement for reliable and standardized methods to evaluate the HS.

To address this, bioelectrical impedance analysis (BIA), a practical, non-invasive, and cost-effective method, can be used to estimate body composition within a clinical setting but also has been proposed as an alternative method to evaluate HS showing advantages over other methods like biomarkers tests (urinary or plasma osmolality) due to the presence of high variability in the results and even over the gold standard method (isotope dilution) due to the complexity of the technique that requires specific training and highly cost equipment, becoming clinically impractical^12,13,14,15.

The conventional BIA method applies an alternating, low electric current intensity (below the perceptual thresholds), entering the human body and crossing internal tissues. Then, based on the principle that body organs may act as electric conductors or dielectrics, we may obtain a register of electric impedance (or bioelectrical impedance [Z]) that reflects the opposition of the organs to the free applied electric flow (EF), depending on their composition (fat or muscle mass, bone, water, etc.)¹². Here, Z sources are resistance (R) and reactance (Xc). The former is related to the opposition of the EF throughout cellular ionic solutions (intracellular and extracellular), while the latter is a capacitive component of tissue interfaces, cell membranes, and organelles¹².

In addition, bioelectrical impedance vector analysis (BIVA) is an alternative BIA method approach that uses spatial relationships between R and Xc (both adjusted by height) to assess soft tissue hydration. The R and Xc data are plotted on a bivariate resistance-reactance graph, which allows visualizing body composition and HS^12,16.

Considering the less explored field of HS balance associated with cardiopulmonary, as well as the growing interest to characterize new applications of methods like BIVA in the evaluation of HS, this study aims to determine HS by BIVA method and to analyze HS relation with VO2 and HR/O2 in ambulatory patients with IHD.

Protocol

The Institutional Research Ethics Committee from Centro Médico Nacional "20 de Noviembre", ISSSTE, approved this protocol (ID 383.2019). All enrolled patients signed written informed consent. 1. Before bioelectrical impedance analysis (BIA) measurement NOTE: The BIA protocol procedure is measured using a single-frequency bioelectrical impedance device (Table of Materials). This device provides two values (resistance and r…

Representative Results

First, R and Xc (both adjusted by patient´s height) data registered from the single frequency (SF-BIA) device was used to obtain the BIVA R/Xc graph. Second, we classified hydration status as euhydration, hyperhydration, and hypohydration. Representative hydration data from male patients plotted with circle and triangle, aged 66 years and 67 years, weighing 72.2 kg and 72.3 kg, height 169 cm and 163 cm, are shown (Figure 2). In addition, impedance data are shown R/H= 280.7, Xc/H= 23.6 &…

Discussion

Although BIA is considered a safe, practical, and noninvasive method, which overcomes the limitations of other methods to measure body composition and body water^19,23, it is relevant to consider the potential bias occurring regarding the type of bioelectrical impedance (the method described here is specific for a single-frequency bioelectrical impedance device), or the variation in the steps and technique verification methods.

It has b…

Materials

BIVA Tolerance	BIVA SOFTWARE 2002		Piccoli A, Pastori G: BIVA software. Department of Medical and Surgical Sciences, University of Padova, Padova, Italy, 2002 (available at E-mail:apiccoli@unipd.it).
Cardiopoint ECG C600	BTL	407-80MANEN03100	ELECTROCARDIOGRAPH
Cardiopoint Trolley	BTL	40700B000240	TROLLEY
Portable Digital Flat Scale	SECA	813	DIGITAL FLAT SCALE
Portable Stadiometer	SECA	213	STADIOMETER
Quantum IV	RJL SYSTEMS	Q4B-2405	BIOELECTRIC IMPEDANCE ANALYZER
Treadmill Clinical	BTL	216A18	TREADMILL