Automated blood pressure monitoring instrument

Abstract

An automated blood pressure monitoring instrument including a noise level detector which enables the instrument to have the sound sensing performance analogous to the human ear. Sounds, including Korotkoff sounds, emitted from the occluded artery of a subject person are transduced into corresponding electric signals to be fed through a filter to the said noise level detector. At the noise level detector, a noise level is calculated from the incoming signals in such a manner as to exclude from this calculation values of expected Korotkoff sound levels and the like which are normally thought to be much higher than an estimated or assumed level of noises associated with the body in the normal blood pressure measurement. The noise level thus detected will vary depending upon the conditions of a subject person as well as varies from person to person, and therefore acts as an effective reference for identifying the Korotkoff sounds. Also included in the instrument is a comparator which discriminates the Korotkoff sounds from the incoming sounds by comparison of their sound levels with a Korotkoff sound reference level which is proportional to said noise level and is naturally a variable level characteristic to the conditions of the subject person. This enables the instrument to discern the differences in the incoming sound signals as the human ear might, thus providing an accurate and effective measurement. When the comparator judges that the incoming sound signals have the level exceeding the above Korotkoff sound reference level, it generates a Korotkoff sound signal representative of the Korotkoff sound. A display is included in the instrument for responding to the appearance and disappearance of the Korotkoff sound signal for providing systolic and diastolic blood pressure indications respectively.