Application of total body bioimpedance to the critically ill patient. Brazilian Group for Bioimpedance Study.

In the past several years, considerable interest has developed in the study of total body bioimpedance analysis (TBBIA) and body composition in healthy subjects. This simple and noninvasive technique uses derived and regression equations to validate data comparative to the gold standards of total body water determination and body composition. However, this approach has not proved to be of value in the critically ill patient with distorted body composition under the effects of multiple drugs and interventions. Notwithstanding, in recent years several authors have demonstrated the usefulness of this technique, apart from derived equations, relying solely in the judicious interpretation of the primary impedance parameters: resistance (R, ohms [omega], reactance (Xc, omega) and the derived phase angle (phi, degrees). The principles of bioelectrical impedance postulate that R is the opposition of total body water and electrolytes to the flow of an alternating current of low amplitude and high frequency, typically 800 microA and 50 kHz, and Xc is the capacitance produced by tissue interface and cell membranes. The phase shift is quantified geometrically as the angular transformation of the ratio Xc/R and is designated as phi. Altered cellular membrane function is a common feature of the septic patient and it has been systematically associated with a significant low Xc and phi. On the other hand, the fluid balance can be precisely monitored by the changes in R, and the serial measurements of the relation Xc/R (or the phi) has been utilized to discriminate between normal subjects and patients, and between septic and nonseptic critically ill patient. Some authors have demonstrated that this relation Xc/R is highly correlated with mortality and could be used for the staging of critically ill patients throughout their stay in the ICU. The role of TBBIA as a simple and noninvasive technique, and its implications for the management of critically ill patients are presented and discussed. Areas for future investigations, with single and multiple frequency, have the potential to clarify many aspects of this emergent technology at the bedside.

Systolic and diastolic time intervals in the critically ill patient.

OBJECTIVE: The waveform of the first derivative of thoracic electrical bioimpedance was used to calculate systolic time intervals of the cardiac cycle, preejection period/left ventricular ejection time ratio, and diastolic time intervals, isovolumic relaxation period/filling time ratio. DESIGN: Prospective clinical study. Waveforms were examined from 913 normal and abnormal tracings from a thoracic electrical bioimpedance monitor. This monitor was coupled to a two-channel strip-chart recorder that identified preejection period/LV ejection time and isovolumic relaxation period/filling time in 86% of the tracings. SETTING: Two university-affiliated hospitals and one community hospital. PATIENTS: We assessed 100 subjects (ranging in age from 17 to 93 yrs) under various conditions. MEASUREMENTS AND MAIN RESULTS: Data from 15 normal subjects were used as a reference series to define normative values. Preejection period/left ventricular ejection time ratio was 0.35 +/- 0.1 (SD) and was consistent with data from systolic time intervals derived from simultaneous study of the ECG recording, carotid artery tracing, and phonocardiography. The diastolic time ratio (isovolumic relaxation period/filling time) was 0.4 +/- 0.2, in agreement with normal values derived by echocardiography and angiography. In a subgroup of 17 critically ill patients, a correlative study of simultaneously measured thoracic electrical bioimpedance, nuclear stethoscope, and radionuclide ventriculography was conducted. Systolic functions were compared by the ejection fraction derived by preejection period/left ventricular ejection time ratio displayed on the thoracic electrical bioimpedance monitor and by the radionuclide technique, and were found to be 57 +/- 13.8% and 58 +/- 8.6%, respectively (r2 = .49; y = 4.06x + 0.94; p less than .02; n = 17). Increased diastolic time ratios with normal or near-normal systolic time intervals were documented in nine (53%) of 17 critically ill patients with low systolic index. CONCLUSION: Both systolic and diastolic time intervals can be investigated noninvasively at the bedside by the thoracic electrical bioimpedance technique to provide a better understanding of left heart function.

Hemodynamic changes after an intensive short-term exercise and nutrition program in hypertensive and obese patients with and without coronary artery disease.

PURPOSE: To assess the effectiveness of the Pritikin diet and exercise program on cardiovascular hemodynamics using the noninvasive technique of Thoracic Electrical Bioimpedance (TEB). MATERIAL AND METHODS: Twenty subjects divided in two groups, according to their body habitus and hemodynamic disturbances. These data were compared to a group of 10 healthy individuals not involved in the program. Hemodynamic parameters were collected at admission and at the end of the intensive 26-day program of exercise and nutrition. RESULTS: In obese and hypertensive subjects not on medication we observed that cardiac index increased from 3.27 +/- 0.4 to 3.58 + 0.5 L/min/m2; mean arterial pressure decreased from 100 +/- 8.5 to 94.8 +/- 7.9 mmHg while systemic vascular resistance index decreased from 2362 +/- 391 to 1934 +/- 357 dynes. sec. cm-5/m2; p less than 0.05 (Data obtained in supine position). Also documented was a improvement in ventricular performance after postural changes from upright to supine based on indices of left ventricular performance, uniquely obtained by the TEB technique. From admission to discharge, changes were: Ejection fraction 48% to 53%; Peak flow index 295 to 316 ml/s/m2 and Index of contractility 40 to 47 s-1, explained by a shift on the ascending limb of the Starling curve. CONCLUSION: In a selected population, this rehabilitation program is effective for hemodynamic improvement that can be partially explained by metabolic and biochemical changes already reported from this Center.