Korotkoff sound filtering for automated three-phase measurement of blood pressure.

Under rest conditions, changes in the Korotkoff sounds at phases I, IV, and V can be correlated with specific frequencies within the bandpass of the stethoscope. A filter capable of detecting the changes in Korotkoff sounds at phases I, IV, and V is described together with the frequency changes that characterize these phases. The importance of frequency components outside the bandpass of the stethoscope is stressed, especially in terms of the possibility of yielding more clinical information and, perhaps, additional clues above the origin of the Korotkoff sounds themselves.