With nearly 70 percent of our bodies made up of water as well as a variety of dissolved salts, humans are natural conductors of electrical current. However, various elements of the human body restrict or impede the flow of electrical current, a phenomenon termed “bioimpedance.” Variations in restrictiveness to the flow of electrical current through an organism can provide researchers with a wealth of information on a range of physiological conditions.
Bioimpedance can be defined as the response of an organism to an externally applied electrical current. For more than a century, researchers have used bioimpedance as a safe and noninvasive metric for a range of physiological data, from measuring body composition through bioimpedance analysis (BIA) to investigating various biological systems such as cardiovascular function via impedance cardiography.
While not new, breakthroughs in technology and techniques for recording and analyzing bioimpedance have made it increasingly accessible to researchers. Through impedance cardiography and cardiac output, researchers gain access to a wide range of cardiovascular and hemodynamic data, including heart rate (HR), cardiac output (CO), acceleration index (AI), mean blood pressure (MBP), stroke index (IA), stroke volume (SV), and systemic vascular resistance, to name just a few.
The recent development of trans-radial electrical bioimpedance velocimetry (TREV) has provided researchers with a heightened level of accessibility when attempting to record high-quality data. Unlike traditional transthoracic methods of recording impedance cardiography signals, TREV measures blood movement through the radial and ulnar arteries of the forearm. The approach streamlines electrode placement, making it less prone to complications associated with other impedance cardiography methods.
One example of the practical application of impedance cardiography is in research on stress as it relates to coronary health. A 2019 study published by researchers at the University of Illinois at Urbana-Champaign compared the stress response of a group of young participants to that of participants over the age of 55 who had been diagnosed with coronary artery disease (CAD). Researchers recorded physiological signals, including electrocardiogram (ECG), impedance cardiogram (ICG), and continuous BP during rest, stress, and recovery. ECG and ICG signals were collected using BIOPAC BN-NICO wireless amplifiers and BN-EL50-LEAD4 leads. Researchers found ICG provided a reliable metric for stress response.
Recently, a team from the University of California, Santa Barbara (UCSB) employed TREV to demonstrate how this newer bioimpedance metric can be used to track event-related contractility in a maximal grip force experiment. The experiment employed TREV electrodes attached to the participant’s forearm and amplified by a NICO100D smart amplifier. Additionally, ECG electrodes were amplified by an ECG100D while the respiration cycle was recorded via a TSD221-MRI respiration belt. All data signals were acquired and analyzed using an MP160 system running AcqKnowledge software. The experiment confirmed the effectiveness of TREV as a reliable metric for connecting the cardio-sympathetic drive to other physiological conditions, such as force production.
While not new to physiological research, the application of bioimpedance continues to flourish and evolve. To learn more about how bioimpedance is being applied in the research setting as well as new techniques, check out BIOPAC’s webinar on bioimpedance and cardiac output focusing on TREV.
To learn more about incorporating impedance cardiography and TREV in your study, contact your regional BIOPAC sales representative today.
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