United States Patent im
Passafaro
[ii] Patent Number: 4,651,741 [45] Date of Patent: Mar. 24,1987
[54] METHOD AND APPARATUS FOR
DETERMINING OXYGEN SATURATION IN
VIVO
[75] Inventor: James D. Passafaro, Santa Ana,
Calif.
[73] Assignee: Baxter Travenol Laboratories, Inc., Deerfield, 111.
[21] Appl. No.: 739,546
[22] Filed: May 30,1985
[51] Int. Q." A61B5/00
[52] U.S. CI 128/633; 128/637;
356/41
[58] Field of Search 128/633, 634, 632, 637;
356/39, 40, 41, 309
[56] References Cited
U.S. PATENT DOCUMENTS
3,825,342 7/1974 Lubbers et al 356/41
3,847,483 11/1974 Shaw et al 356/41
4,114,604 9/1978 Shaw et al 128/634
4,266,554 5/1981 Hamaguri 356/41 X
OTHER PUBLICATIONS
"Effects of Multiple Scattering and Peripheral Circulation on Arterial Oxygen Saturation Measured with a
Pulse-Type Oximeter", Medical & Biological Engineering & Computing, Y. Shimada et al, pp. 475-479, Sep. 1984.
Primary Examiner—Stephen F. Husar
Attorney, Agent, or Firm—Weissenberger and Peterson
[57] ABSTRACT
Accurate in vivo measurement of blood oxygen saturation by fiberoptical means is made possible throughout a wide range of hematocrit or total hemoglobin values by using a single R/IR ratio I and calculating the SO2 value therefrom through the use of a second-order polynomial of the form
SOi=Ak2fi+BkI+C
in which A, B and C are hematocrit or total hemoglobin-dependent coefficients. These values may be contained in a lookup table accessed by a hematocrit or total hemoglobin value selection, and k is a purely multiplicative calibration constant which can be readily determined for any individual fiberoptic system.
9 Claims, 6 Drawing Figures
