1. Field of the Invention
The present invention relates to a blood pressure measuring apparatus including a surface-pressure sensor adapted to be pressed against an artery of a living body or subject via a body surface of the subject.
2. Related Art Statement
There is known a blood pressure (BP) measuring device which non-invasively measures a BP value of a living subject based on a pulse-sound signal or a pulse-wave signal which is continuously obtained while an inflatable cuff wound around subject's body portion such as an upper arm is inflated, or is deflated after being inflated, to press the body portion. The non-invasively measured BP value is an approximation of an intra-arterial BP value directly or invasively measured from inside an artery of the subject.
In the conventional BP measuring device, however, the cuff presses the subject's body portion all around with a considerably great force, so that the subject may suffer the discomfort due to the use of the cuff.
Meanwhile, Unexamined Japanese Utility Model Application laid open under Publication No. 1(1989)-161707 discloses a blood pressure (BP) monitor including (a) an inflatable cuff, (b) a fluid supply which supplies a pressurized fluid to the cuff, (c) a control device which changes the fluid pressure in the cuff, (d) a surface-pressure sensor adapted to be pressed on subject's body surface to detect a pressure pulse wave produced from subject's artery and generate a pressure signal representing the detected pulse wave, and (e) BP determining means for determining a BP value of the subject, based on each of successive pulses contained in the pressure signal, according to a relationship between blood pressure (BP) and pressure signal (PS). In the BP monitor, the BP-PS relationship is determined, and updated, based on the standard BP values periodically measured using the cuff. The cuff is necessary to measure the standard BP values used for calibrating the pressure signal of the surface-pressure sensor, because the accuracy of the BP measurement using the surface-pressure sensor is not satisfactorily high.