Methods for measuring blood pressure with automatic compensations

A method for measuring an arterial blood pressure of a subject, comprising:

• a) detecting pulse-wave-related signals of the subject with a sensor;
• b) extracting a feature from the signals;
• c) determining factors that can affect the feature;
• and
• d) determining the arterial blood pressure based on the feature with an automatic compensation for the factors,
• wherein the feature is a pulse transit time and the factors comprise a contacting force to the sensor, nervous activities and/or cardiac outputs of the subject, and ambient temperatures,
• and wherein the step d) further comprises:
• 1) obtaining coefficients from a calibration process;
• 2) counterbalancing effects of the factors on the pulse transit time with a first compensation term;
• 3) determining an estimated value of the arterial blood pressure according to the result of the counterbalancing;
• 4) counterbalancing the effects of the nervous activities and/or cardiac outputs on the estimated value with a second compensation term;
• and
• 5) counterbalancing the effects of the ambient temperatures on the estimated value of the arterial blood pressure with a third compensation term.