Apparatus and method for processing korotkov sounds

Claim 1

A Korotkov sound processor for use in a noninvasive blood pressure measuring system which includes an inflatable cuff for encircling a portion of the human body, means for alternately inflating and deflating said cuff for selectively occluding an arterial vessel, means for recording the arm cuff pressure values, and an electromechanical auscultatory transducer for monitoring the sounds of arterial flow past the cuff and for producing electrical signals containing frequency components representative of said sounds, said Korotkov sound processor comprising: filter means including a bandpass filter adapted to be coupled to the auscultatory transducer for selecting from said electrical signals the certain band of frequency components in the range of 18 to 26 Hz; detecting means coupled to said bandpass filter means for detecting the occurrence of the first significant increase in amplitude values of said selected signals for determining the systolic event as the pressure in said cuff is gradually reduced from a pressure sufficient to occlude the arterial vessel to a lower pressure which permits arterial flow, said detecting means including means coupled to said filter means for deriving first absolute value signals from said filtered signals, absolute value circuit means coupled to said auscultatory transducer for receiving the electrical signals from said transducer and for deriving second absolute value signals therefrom, means coupled to said absolute value circuit means for deriving peak amplitude value signals from said second absolute value signals; comparator means for comparing such derived first absolute value signals to said peak value signals to provide an output electrical signal whenever the amplitude ratio of said first absolute value signals and said peak value signals exceeds a value of 0.45; and means coupled to said comparator means for controlling said recording means.

Claim 4

A method of measuring systolic and diastolic blood pressures in a human body comprising the steps of: applying an external pressure to an artery of said body sufficient to occlude arterial flow; diminishing said pressure over a period of time sufficiently to permit the systolic and diastolic events to occur; sensing the occurrence of arterial Korotkov sounds while the pressure is being reduced through said systolic and diastolic events, and producing first electrical signals containing frequency components representative of said sounds; selecting and filtering a band of frequency components in the range of 18 to 26 Hz from said first electrical signals; normalizing the amplitude values for said frequency band by the peak amplitudes of the unfiltered first electrical signals, said normalizing step including producing first absolute value voltage signals from said selected band of signals, a. producing second Absolute value voltage signals from said first electrical signals representative of the arterial sounds, b. deriving peak value signals from said second absolute value voltage signals, and for each Korotkov sound, c. comparing the first absolute value signals to said peak value signals and producing an output electrical signal whenever the amplitude ratio thereof exceeds a value of 0.45 to thereby indicate the occurrence of the systolic event, selecting a second band of frequency components in the range of 40 to 60 Hz from said first electrical signals, for each successive Korotkov sound, normalizing the amplitude values for said second band of frequency components by the mean amplitude of the largest amplitude sound occurring in said second band, said last mentioned normalizing step including, a. producing third absolute value signals from said second selected band of electrical signals, b. producing second peak value signals from said third absolute value signals, c. comparing successive ones of said last mentioned absolute value signals to the largest amplitude peak value signal of said second peak value signals and producing a second output electrical signal whenever the comparison ratio thereof drops below a vlaue of 0.17 to thereby indicate the occurrence of the diastolic event, and recording said first and second output electrical signals and the pressures applied to the artery while diminishing said pressures over said period of time to thereby provide an indication of arterial blood pressures at the time of occurrence of the systolic and diastolic events.

Claim 5

A method of measuring systolic and diastolic blood pressures in a human body comprising the steps of: applying an external pressure to an artery of said body sufficient to occlude arterial flow; diminishing said pressure over a period of time sufficiently to permit the systolic and diastolic events to occur; sensing the occurrence of arterial Korotkov sounds while the pressure is being reduced through said systolic and diastolic events, and producing first electrical signals containing frequency components representative of said sounds; selecting and filtering a band of frequency components in the range of 18 to 26 Hz from said first electrical signals; normalizing the amplitude values for said frequency band by the peak amplitudes of the unfiltered first electrical signals, said normalizing step including producing first absolute value voltage signals from said selected band of signals, a. producing second Absolute value voltage signals from said first electrical signals representative of the arterial sounds, b. deriving peak value signals from said second absolute value voltage signals, and for each Korotkov sound, c. comparing the first absolute value signals to said peak value signals and producing an output electrical signal whenever the amplitude ratio thereof exceeds a value of 0.45 to thereby indicate the occurrence of the systolic event, selecting a second band of frequency components in the range of 40 to 60 Hz from said first electrical signals, for each successive Korotkov sound, normalizing the amplitude values for said second band of frequency components by the mean amplitude of the largest amplitude sound occurring in said second band, said last mentioned normalizing step including, a. producing third absolute value signals from said second selected band of electrical signals, b. producing second peak value signals from said third absolute value signals, c. comparing successive ones of said last mentioned absolute value signals to the largest amplitude peak value signal of said second peak value signals and producing a second output electrical signal whenever the comparison ratio thereof drops below a vlaue of 0.17 to thereby indicate the occurrence of the diastolic event, and recording said first and second output electrical signals and the pressures applied to the artery while diminishing said pressures over said period of time to thereby provide an indication of arterial blood pressures at the time of occurrence of the systolic and diastolic events.