Automated Constant Cuff-Pressure System to Measure Average Systolic and Diastolic Blood Pressure in Man

An automated constant cuff-pressure system to remotely determine average human blood pressure levels was developed to overcome problems in measurement caused by natural beat-to-beat fluctuations in arterial pressure. A standard blood pressure cuff is inflated to approximately systolic pressure for a prescribed number of heart cycles. Korotkoff (K) sounds are picked up by a crystal microphone over the brachial artery. The EKG is recorded and an electronic coincidence circuit detects the number of R waves followed by a AT sound. Cuff pressure is automatically adjusted until there is a 50 percent coincidence of R-K sounds. This cuff pressure is now by definition the median systolic pressure. The same procedure is followed to determine median diastolic pressure. A change of 2 mmHg in cuff pressure alters the R-K coincidence by 25 percent, insuring an accuracy of measurement of ±2 mmHg. Average measures of pressure obtained by the constant cuff-pressure method were demonstrated to be as accurate as averages based on intra-arterial readings. Application of this system in epidemiological screening is discussed.