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Bubble Detector for Blood Circulating Devices

IP.com Disclosure Number: IPCOM000086180D
Original Publication Date: 1976-Aug-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 3 page(s) / 51K

Publishing Venue

IBM

Related People

Bigbie, SE: AUTHOR [+4]

Abstract

In medical procedures where blood or blood substitute fluids are circulated for injection into a patient, it is necessary to prevent the injection of more than a minimum amount of bubbles into the patient along with the fluid. The diagrammed instrument can be used to warn when bubbles of a dangerous size pass through a sensing station.

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Bubble Detector for Blood Circulating Devices

In medical procedures where blood or blood substitute fluids are circulated for injection into a patient, it is necessary to prevent the injection of more than a minimum amount of bubbles into the patient along with the fluid. The diagrammed instrument can be used to warn when bubbles of a dangerous size pass through a sensing station.

As indicated in Fig. 1, the blood or other ionic fluid will be passed downward through a tube past four electrodes, 2, 3, 4, and 5. Since current will be conducted by ions rather than electrons, to prevent ion buildup on the electrodes the outer pair 2 and 5 are connected to an oscillator 6 which will apply an AC voltage across them. The inner pair 3 and 4 are connected to a differential amplifier 7 whose AC output will be rectified in a rectifier 8 and applied to a meter
9.

Under normal conditions, the tubing 1 will be full of fluid and the voltage detected across the electrodes 3 and 4 will be of substantially uniform magnitude, so that the indication on meter 9 will be constant. However, when a bubble or a group of bubbles pass between the electrodes 3 and 4, the resistance of the path from 3 to 4 increases and a larger voltage difference will be detected. This will increase the meter reading and signal a possible dangerous condition. If desired, meter 9 can be provided with contacts to give an alarm or change flow conditions when bubbles are detected.

With somewhat more equipment it is possible to determine the size of bubbles in the fluid and to integrate bubble sizes into a total bubble volume, to insure that a patient being treated does not receive a dangerous volume of air along with the blood or other fluid. In general, the resistivity of the fluid will not change appreciably over the time of treatment and the flow velocity will be uniform, so the volume of a bubble will be calculated as:

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V is the bubble volume. A(B) is the tubing diameter. P(B) is the blood...