United States Patent 
Millay et al.
Patent Number: Date of Patent:
 METHOD AND APPARATUS FOR
DISTINGUISHING BETWEEN ACCURATE
AND INACCURATE BLOOD PRESSURE
MEASUREMENTS IN THE PRESENCE OF
 Inventors: Jack M. Millay; Richard A. Walloch, both of Beaverton, Oreg.
 Assignee: SpaceLabs, Inc., Redmond, Wash.
 Appl. No.: 383,207
 Filed: Jul. 19,1989
 Int.C1.5 A61B5/02
 U.S. CI 128/672; 128/680;
 Field of Search 128/672, 677-686
 References Cited
U.S. PATENT DOCUMENTS
4,360,029 11/1982 Ramsey, III 128/681
4,543,962 10/1985 Medero et al 128/682
4,638,810 1/1987 Ramsey, III et al 128/682 X
4,754,761 7/1988 Ramsey, III et al 128/683
Primary Examiner—Ruth S. Smith
Assistant Examiner—J. P. Lacyk
Attorney, Agent, or Firm—Seed and Berry
A system for determining if a blood pressure measurement made by an automatic blood pressure monitor has been adversely affected by artifact. The system first compares the diastolic, mean arterial and systolic pressures to respective average diastolic, mean arterial and systolic pressures. If all three of these pressures are within a predetermined range of their corresponding average pressures and if the relationship between these pressures conforms to a physiologically realistic model, then the diastolic, mean arterial and systolic pressures obtained from a measurement are considered valid. If more than one of these pressures is outside the predetermined range of its corresponding average pressure, then the measurement is considered to be adversely affected by artifact and is rejected. If only one of these pressures is outside the predetermined range of its corresponding average pressure, then a replacement pressure is calculated for that pressure. The replacement pressure is calculated based on the pressures that are within the predetermined range and on an average of pressures from previous measurements.
30 Claims, 7 Drawing Sheets