William M Dormont

US Patent:

53947320, Mar 7, 1995

Filed:

Sep 10, 1993

Appl. No.:

8/119790

Inventors:

David A. Johnson - Littleton CO
Douglas P. Miller - Broomfield CO
Keith J. Manica - Lakewood CO
William M. Dormont - Boulder CO
Christopher J. Welsh - Fort Collins CO
William R. Mandel - Harlem MT

Assignee:

COBE Laboratories, Inc. - Lakewood CO

International Classification:

G01N 2902

US Classification:

73 191

Abstract:

Inclusions in a liquid flow, such as air bubbles in a blood flow, are detected by transmitting a signal through the fluid and receiving and interpreting the received signal based on the expected degree of attenuation for the liquid and the inclusions. The amplitude of the transmitted signal is automatically adjusted to maintain a constant average amplitude of the detected signal, thus compensating for changes in the detection environment. The average amplitude of the transmitted signal is controlled by integrating the received signal using an integrator with a time constant longer than the time constant of the expected inclusion signals, and comparing the integrated signal to a constant reference level. The presence of microbubbles is detected and a signal comprising a string of high frequency pulses is generated while the microbubbles are present. By counting the pulses, in conjunction with knowledge about the flow of liquid and the anticipated size of the microbubbles, an estimate of the total amount of air infused into the patient within a given time period is calculated.