Both while the subjects were sitting and while they were standing, the AIM yielded measures of cardiac function, including heart rate, preejection period, left ventricular ejection time, and stroke volume, that were similar to those acquired by using the reference Minnesota 304B system (all Pearson R correlations > +0.87, all P < 0.001). Orthostatic challenge was used to systematically alter cardiac function in a laboratory setting in 11 healthy men and women.
The objective of the present study was to provide a preliminary evaluation of AIM comparability with the widely validated Minnesota model 304B impedance cardiograph with standard tetrapolar band electrodes. The AIM system was developed for use with a new hybrid tetrapolar spot-band electrode configuration and was designed to be comfortable and inconspicuous. To make the application of ICG even more simple the 4 TECT Sensor-Application has been developed whereby only 4 sensors instead of previously used 8 sensors are necessary.A wearable, ambulatory impedance monitor (AIM) has been developed to permit impedance cardiographic measurements while patients and volunteers engage in normal daily activities. In the result the accuracy of stroke volume calculation can be greatly increased. For this purpose the arterial pulse waves taken from the ear lobe and/or the upper arm are used in addition to the standard ICG signal to detect the true X-point (closing of the aortic valve). Therefore, the new and unique ACM (Arterial Compliance Modulation) - technology has been developed. This is a general methodical problem of impedance technology (including velocimetry, bio-reactance and other derived methods) which can be solved only by using an additional signal. These influences often result in the appearance of curve points in the ICG wave form which could be, falsely, interpreted as the closing of the aortic valve so that the X-point is not detected correctly and the calculation of the stroke volume is inaccurate.
In the result an impedance pulse wave (IMP) is recorded.įor the determination of the stroke volume the first mathematical derivative of the impedance pulse wave (IMP) is used. This voltage corresponds with impedance changes caused by pulse synchronous variations of the blood volume in the thoracic aorta and the alignment of the orientation of the erythrocytes when the blood is pumped out of the left ventricle of the heart into the aorta. The 4 inner electrodes (called measuring electrodes) are placed between the current electrodes and measure the voltage which is caused when the current flows through the thorax. The 4 outer electrodes (called current electrodes) are used to pass a very low constant and alternating current (1.5 mA, 86 kHz) through the thorax which is imperceptible to the patient and does not cause any physiological reaction. For this purpose usually 8 electrodes are placed on neck and thorax.
In case of Impedance Cardiography (ICG) – often also named Thoracic Electrical Bio-impedance (TEB) – changes of electrical impedance of the thorax are measured. It is 100% non-invasive, easy to apply and operator independent. This examination method allows a real beat-to-beat measurement of the stroke volume and is, therefore, very suitable for haemodynamic monitoring, fluid management and cardio-vascular function tests.