Solid tissue impedance estimating method, cardiac output calculating method, pulmonary artery wedge pressure calculating method, cardiac output monitoring device, cardiac output monitoring system, pulmonary artery wedge pressure monitoring device, and pulmonary artery wedge pressure monitoring system

A solid tissue impedance estimating method for estimating a solid tissue impedance arising from a solid tissue, the method comprising:

• infusing a hypertonic saline solution into pulmonary circulation of a patient;
• measuring a minimum impedance value and a maximum impedance value for each of a predetermined number of cardiac cycles, after the hypertonic saline solution is infused, wherein the measured minimum impedance values and measured maximum impedance values form data sets, wherein each of the data sets contains the measured maximum impedance value and the measured minimum impedance value of the impedance signal during each of the cardiac cycles, and wherein the minimum and maximum impedance signals are obtained between a can electrode implanted in a left thoracic wall and an electrode inserted into a coronary vein;
• plotting the measured maximum impedance values and the measured minimum impedance values against each other and performing a linear regression to create a linear regression line;
• determining an impedance at an intersection between a line of identity and the linear regression line, wherein the impedance is a solid tissue impedance, and wherein the line of identity is a line where the minimum impedance values divided by the maximum impedance values is 1;
• and
• outputting the solid tissue impedance value based on the intersection between the line of identity and the linear regression line.