Abstract: A first input interface receives measured values of non-invasive blood pressure of a subject intermittently at a first frequency. A second input interface receives measured values of pulse wave transit time of the subject at a second frequency higher than the first frequency. A processor executes regression analysis processing based on the measured values received until when a measured value acquired by Nth (N is an integer that is no less than 2) measurement of the non-invasive blood pressure is received to acquire a regression equation in which the measured value is set as an explanatory variable. An information presenting device visibly presents estimated values of the non-invasive blood pressure calculated with the regression equation and the measured values, until a measured value acquired by (N+1)th measurement of the non-invasive blood pressure is received.

Abstract: Method for measuring a blood volume is provided. At least two types of respiratory variation data; for instance, data pertinent to respiratory variations in stroke volume (SVV) data, data pertinent to respiratory variations in an amplitude of a pulse wave (PAV), a pulse wave transit time (PWTT) in a respiratory cycle, and a heart rate (HR) in a predetermined time, are measured, and patient's inherent coefficients ?, ?, and K are calculated, whereby a cardiac output can be determined by an equation CO=K (?*PWTT+?)*HR.

Abstract: Method for measuring a blood volume is provided. At least two types of respiratory variation data; for instance, data pertinent to respiratory variations in stroke volume (SVV) data, data pertinent to respiratory variations in an amplitude of a pulse wave (PAV), a pulse wave transit time (PWTT) in a respiratory cycle, and a heart rate (HR) in a predetermined time, are measured, and patient's inherent coefficients ?, ?, and K are calculated, whereby a cardiac output can be determined by an equation CO=K(?*PWTT+?)*HR.