APPLICATION OF IMPEDANCE CARDIOGRAPHY DURING EXERCISE

Impedance cardiography has been used over the last 30 years to measure stroke volume on a beat-by-beat basis. Cardiac output has been succes sfully measured with either upper or lower body exercise during light or moderate workloads. With strenuous exercise, movement artifacts sev erely limit the acquisition of a quality impedance cardiogram. Advance s in computer technology and signal conditioning techniques have creat ed the next generation of impedance cardiograph systems. The purpose o f this study was to evaluate such a system, the noninvasive continuous cardiac output monitor (NCCOM3-R7), at rest and during submaximal upr ight cycle exercise. In addition, the relationships between thoracic i mpedance (Z(o)), first derivative of the change in thoracic impedance (dZ/dt) and posture were evaluated using the NCCOM3-R7 and the Minneso ta impedance cardiograph 304B (MIC). Twenty-eight healthy men and wome n participated. The Z(o) progressively increased when moving from the supine to seated to standing position with both instruments. However, the NCCOM3-R7 yielded lower Z(o) values and higher dZ/dt values compar ed with the MIC for all postures. Z(o) and dZ/dt values appear to be d ependent upon factors such as posture, gender, electrical current, and characteristics of the instrumentation. Exercise cardiac output value s seemed reasonable for most subjects, although population subsets exi st where the accuracy must be questioned. The general consensus suppor ted by the impedance literature and reaffirmed by the present observat ions is that impedance cardiography provides a reasonable estimate of the directional changes in stroke volume and cardiac output during exe rcise and can be used to monitor changes in thoracic fluid balance. As this technology evolves and is further refined, it will undoubtedly p lay an increasing role in environmental medicine, exercise stress test ing, cardiac rehabilitation, and sports medicine.