Frequently Asked Questions
What is the difference between HCP and Impedance Cardio Graphy?
A principal differnce between the HCP and ICG or bioreactance-based techniques, is that the HCP performs a direct measurement of ventricular volume changes, instead of total heart volume changes. Therfore, the HCP, theoretically provides a better basis for assessment of stroke volume, becauce total heart volume variation is not necessarily a reliable indicator of ventricular stroke volume. The voltage signal measured in ecery ICG system is caused by the combined effect of volume changes in different intrathoracic compartments during the cardiac cycle, such as the intracardiac cavities, aorta, superior and inferior vena cava, and pulmonary circulation. form all the factors, ICG attemps to distill the stroke volume.
The voltage signal measured in ecery ICG system is caused by the combined effect of volume changes in different intrathoracic compartments during the cardiac cycle, such as the intracardiac cavities, aorta, superior and inferior vena cava, and pulmonary circulation. form all the factors, ICG attemps to distill the stroke volume using a single inpute coltage stram. From a mathematical point of view, however, this single voltage input stream is sufficient to balance the many unknown variables inside the thorax. Some ICG-Like techniques use multiple electrode, but - in contrast to our method - still measure only one single voltage, because the leasds of many of these electrodes are interconnected to form a single input channel. In contrast , with this technique (HCP), nine electrodes produce eight independent and simultaneous voltage input streams, connected to eigh independent voltage demodulator units.
How does HCP manage the inter-individual thorax demensions, like thickness if sub-cutaneous fat and muscle layers, and overall thorax sizes?
HCP performes an auto-calibrations procedure, the measuring electrodes are used temprarily for current injection. In an in vitro study and in computer models, we have shown that, invoking the reciprocity theorem of electromagnetic fields, this procedure is capable of assessing the attenuation of singles between the heart and the skin. This auto-calibration takes away the need for an initial calibration using ultrasound. while the auto calibration vannot manage all thorax sizes with a single sized electrode patch, from the smalles new-born to the largest obese, furter trials are expected to leas to 3 or 4 electrode sices that can cover the whole spectrum of the population's thorax sizes.
How has this technology been validated?
In animal research, an Ultrasonic Flow Probe (FP) around the aorta was ued as the gold standard, while cardiac output was manipulated by decrease in venous retur induced by a vena cava obstruction, Increase in hear rate by external cardac pacing, and inptropic stimulation bij administration of dobutamine. The results are reproted in http://ccforum.com/content/15/4/R165.
In order to cause changes in stroke colume in healthy volunteers, and at the same time let other (enviromental) parameters remain the same as much as possible, we used inflatable antishock trousers (known as 'G-suits' to airforce pilots). It has been shon tat, in a standing position, sudden deflation of an inflated G-Suit can cause the stroke volume to drop suddenly. We performed a procedure on healthy volunteers, in which a G-suit was inflated gradually from 0 mmHg to 70 mmHg during 2 minutes and 30 seconds. Subsequently, a constant pressure of 70mmHg pressure was maintained during 2 minutes, after which, finally, a sudden delfation bach to 0 mmHg took place within 5 seconds. Simultaneously, during the entire procedure, contiuous HCP recordings, as well as LVOT (Left Ventricular Outflow Tract) Doppler recordings were performed. Results have been reproterd in: http://www.biomedical-engineering-online.com/content/11/1/51
The results indicate taht teh HCP was able to track the changes in vetnricular stroke colume reliably. Furthermore, the HCP produced ventricular volume-time curves that were consistent with the literature. Further validation to value HCP as a diagnostic tool, is ongoing with miniaturized devices and increased functinality, and will include different patientgroups in a multicentrer trial commencing in 2018.
How does HCP manage interference in measuremetns related to respiration?
In order to exclude artefacts in the measured voltage change pattern on the thoracic skin due to distortions caused by changing air columes inside the lungs, we adopted a 'respiration-gated' approach. By monitoring the respiratory fluctiation in the series of absolute values of measurments from subsequent heartcycles, the HCP automatically selects a subset of cardiac cycles, out of the total set of cardac cycles within a period of 20 seconds, that corresponds to a specific phase in the respiratory cycle as well as the same colume of air inside the lings in this way.