Air bubble detecting and discriminating circuit arrangement and method

• US 4,565,500 A
• Filed: 02/24/1983
• Issued: 01/21/1986
• Est. Priority Date: 02/24/1983
• Status: Expired due to Fees

• Current Assignee: Stewart-Riess Laboratories, Inc.
• Original Assignee: Stewart-Riess Laboratories, Inc.
• Inventors: Chakkaw, Somkiat, Jeensalute, Thipthep
• Primary Examiner(s): Freeh, William L.
• Assistant Examiner(s): Neils, Paul F.
• Application Number:
  US06/469,412
• Time in Patent Office: 1,062 Days
• Field of Search: 417/12, 417/45, 417/53, 417/63, 417/474-477, 417/412, 604/65, 604/67, 604/123, 604/153, 604/245, 128/DIG. 12, 128/DIG. 13, 340/632
• US Class Current: 417/53
• CPC Class Codes: A61M 5/365 Air detectors A61M5/1684 takes precedence; in extracorporeal blood circuits A61M1/3626
• CPC Class Codes: Y10S 128/13 Infusion monitoring

Abstract

An air bubble detecting and discriminating circuit arrangement especially suitable for use in a peristaltic infusion pump assembly is disclosed herein. This arrangement not only detects air bubbles in the fluid flowing through the tubing forming part of the assembly, but distinguishes between those bubbles which are sufficiently large to create a problem and smaller, micro bubbles which need not be detected. The arrangement also automatically compensates for changes in the flow rate of the fluid through the pump assemblies tubing without requiring any modifications at the time the flow rate is changed.

Claims

1. A peristaltic infusion pump, assembly, comprising:

(a) means including a continuous length of tubing adapted for connection at one end to a supply of fluid and at its opposite end to a patient;

(b) means including a variable speed motor acting on said tubing for peristaltically pumping said fluid therethrough at a flow rate proportionate to the speed of said motor, whereby any air bubbles in said fluid will move with the latter at the same flow rate;

(c) means for detecting the presence of said air bubbles, if any, as they pass through a fixed point along the path of movement through said tubing, said detecting means being capable of producing a first signal in response to the presence of an air bubble at said fixed point and for the duration that the detected bubble passes through said point, the length of said first signal corresponding to the length of the detected bubble; and

(d) means including said motor responsive to said detecting means for distinguishing between detected bubbles of at least a predetermined size which can cause problems from smaller nuisance bubbles which do not, regradless of the flow rate of the fluid, said distinguishing means including means for producing an alarm signal only if problem bubbles are detected, said distinguishing means being capable of producing a second signal for a predetermined period of time after initiation of said first signal, said second period of time being inversely proportionate to the speed of said motor, and said distinguishing means being capable of producing said alarm signal only during the presence of both said first and second signals, said time delay distinguishing between the larger problem bubbles and the smaller nuisance bubbles regardless of the flow rate of the fluid and bubbles.

2. An assembly according to claim 1 wherein said detecting means includes means for detecting air bubbles in either clear or opaque fluid without requiring any modification thereof.

3. In an infusion pump or like apparatus in which a liquid is caused to flow in a continuous stream through a continuous length of tubing by means of a motor such that the flow rate of the liquid is directly proportionate to the speed of said motor, an assembly for detecting air bubbles in said liquid stream and for distinguishing between problem bubbles of at least a predetermined size from smaller nuisance bubbles regardless of the flow rate of the stream, said assembly comprising:

(a) means for detecting the presence of air bubbles regardless of their size, as they pass through a fixed point along their path of movement through said tubing, said detecting means including means for producing a first signal in immediate response to the presence of an air bubble at said fixed point and for the duration that the detected bubble passes through said point, whereby the length of said first signal corresponds to the length of the detected bubble;

(b) means using said motor as a timing clock for producing a second signal a predetermined period of time after initiation of said first signal and for the duration of the latter, said period of time being inversely proportionate to the speed of said motor; and

(c) means for producing an alarm signal in response to the simultaneous presence of said first and second signals, whereby said delay in the production of said second signal after the production of said first signal distinguishes between problem bubbles and smaller nuisance bubbles, regardless of the flow rate of fluid and bubbles through said tubing.

4. An assembly according to claim 3 wherein said motor is a stepping motor and wherein said second signal is produced a predetermined, fixed number of steps of stepping motor after initiation of said first signal.

5. A peristaltic infusion pump assembly, comprising:

(a) means including a continuous length of tubing adapted for connection at one end to a supply of fluid and at its opposite end to a patient;

(b) means including a variable speed motor acting on said tubing for peristaltically pumping said fluid therethrough at a flow rate proportionate to the speed of said motor, whereby any air bubbles in said fluid will move with the latter at the same flow rate, wherein said motor is a stepping motor;

(c) means for detecting the presence of said air bubbles, if any, as they pass through a fixed point along the path of movement through said tubing wherein said detecting means produces a first signal in response to the presence of an air bubble at said fixed point and for the duration that the detected bubble passes through said point, whereby the length of said first signal corresponds to the length of the detected bubble; and

(d) means including said motor responsive to said detecting means for distinguishing between detected bubbles of at least a predetermined size which can cause problems from smaller nuisance bubbles which do not, regardless of the flow rate of the fluid, said distinguishing means including means for producing an alarm signal only if problem bubbles are detected, wherein said distinguishing means produces a second signal a predetermined period of time after initiation of said first signal, said period of time being inersely proportionate to the speed of said motor, and wherein said distinguishing means produces said alarm signal only during the presence of both said first and second signals, whereby said time delay distinguishes between the larger problem bubbles and the smaller nuisance bubbles regardless of the flow rate of the fluid and bubbles, said second signal being produced by a predetermined, fixed number of steps of said stepping motor after initiation of said first signal.

6. A peristaltic infusion pump assembly comprising:

(a) means including a continuous length of tubing adapted for connection at one end to a supply of fluid and at its opposite end to a patient;

(b) means including a variable speed stepping motor and a peristaltic pump head driven by said motor, said head acting on said tubing for peristaltically pumping said fluid therethrough at a flow rate proportionate to the speed of said stepping motor, whereby any air bubbles or dry sections in said tubing will move with said fluid at the same flow rate as the latter;

(c) means for detecting the presence of said air bubbles or dry sections, if any, as they pass through a fixed point along their path of movement through said tubing, said detecting means including means for producing a first electrical signal in response to the immediate presence of an air bubble or dry section at said first point and for the duration that the detected bubble or dry section passes through said point, whereby the length of said first signal corresponds to the length of said detected bubble or dry section;

(d) means for producing a second signal during a predetermined, fixed number of steps of said stepping motor after initiation of said first signal; and

(e) means for producing an alarm signal only in response to the presence of both said first and second signals, whereby an alarm signal is produced upon detection of air bubbles of at least a predetermined size regardless of the flow rate of the fluid and bubbles through the tubing.

7. An assembly according to claim 6 wherein said detecting means includes a photoelectric arrangement located adjacent said tubing at said fixed point for directing a predetermined amount of light through the tubing on one side thereof and for detecting any light passing through the tubing on the other side thereof, said detecting means also including electric circuit means responsive to the amount of detected light passing through said tubing for distinguishing between clear fluid at said fixed point, opaque fluid at said fixed point, or no fluid at said fixed point within said tubing and for producing said first signal only if no fluid is at said fixed point and whereby said detecting means requires no modification for detecting air bubbles in either clear or opaque fluid.

8. A method of detecting air bubbles of at least a predetermined size from smaller bubbles in a peristaltic infusion pump or like apparatus in which a liquid is caused to flow in a continuous stream through a tube by means of a motor such that the flow rate of said fluid is directly proportionate to the speed of said motor, said method comprising the steps of:

(a) detecting the presence of said air bubbles, if any, as they pass through a fixed point along their path of movement through said tubing and producing a first signal as soon as an air bubble is detected at said point and for the duration that the detected bubble passes through said point whereby the length of said first signal corresponds to the length of the detected bubble;

(b) using said motor as a clock, producing a second signal a predetermined period of time after initiation of said first signal and for the duration of the latter, said period of time being inversely proportionate to the speed of said motor and therefore inversely proportionate to the flow rate of said fluid; and

(c) producing an alarm signal in response to the simultaneous presence of said first and second signals, whereby said delay in the production of said second signal after production of said first signal distinguished between larger problem air bubbles and smaller nuisance air bubbles, regardless of the flow rate of fluid and bubbles through said tubing.