Apparatus and method for monitoring air emboli during extracorporeal circulation

• US 4,014,206 A
• Filed: 03/31/1975
• Issued: 03/29/1977
• Est. Priority Date: 03/31/1975
• Status: Expired due to Term

• Current Assignee: Akron City Hospital
• Original Assignee: Akron City Hospital
• Inventors: Taylor, Bruce C.
• Primary Examiner(s): Queisser, Richard C.
• Assistant Examiner(s): Kreitman, Stephen A.
• Application Number:
  US05/563,856
• Time in Patent Office: 729 Days
• Field of Search: 73/19, 73/23, 324/61 R, 324/65 R, 128/2 R, 128/2.05 R, 128/2.1 R, 128/2.05 E, 128/2.05 F, 128/214 E, 128/DIG. 13, 340/237 R, 340/239 R
• US Class Current: 73/19.1
• CPC Class Codes: G01N 33/4915 using flow cells flow cytometry G01N15/14

Abstract

Disclosed is a method and apparatus for detecting the presence of an embolism, such as air, during extracorporeal circulation in tubing carrying blood or other fluid such as would be present in the use of an artificial kidney machine. Electrodes are placed near the tubing to monitor the impedance thereof as well as the impedance of the fluid passing therethrough. An oscillator is attached to the electrodes and puts out a signal, the frequency of which is proportional to the basic impedance of the tubing and fluid. When an air bubble or the like passes the electrodes, the impedance will change causing a change in the frequency of the signal of the oscillator. The difference between the normal frequency and the changed frequency is indicative of the size of the embolism. Means are provided so that if a single embolism is large enough to cause damage to the patient or if a number of smaller emboli accumulate to the point of potentially causing damage to the patient, an alarm may be sounded or other remedial measures, such as system shutdown, could be taken. In addition, should the basic impedance of the fluid change, means are provided to prevent a false indication of an embolism.

Claims

1. Apparatus for detecting at least one embolism contained in a fluid during extracorporeal circulation of the fluid in a tubing comprising:

means to monitor the electrical impedance of the tubing, fluid and any emboli contained therein having an output signal whose voltage is proportional to the electrical impedance of the tubing, fluid and any emboli contained therein,

first oscillator means receiving the output signal from said means to monitor and providing at least one output signal whose frequency is proportional to the electrical impedance of the tubing, fluid and any emboli contained therein,

second oscillator means having an output signal whose frequency is proportional to the electrical impedance of the fluid and tubing,

detector means receiving the output signals from said first and second oscillator means and providing an output signal the duration of which is indicative of the difference between the frequencies of the output signals of said first and second oscillator means,

said detector means having an electrical feedback loop, said second oscillator means being in said feedback loop, integrator means in said feedback loop and proviging an output signal which is the time integral of the input thereto, said integrator means receiving the output signal of said detector means and providing said output signal to said second oscillator means, the output of said second oscillator means being fed back to said detector means to complete the feedback loop, and

control means for providing an actuation signal indicative of the presence of at least one embolism including

counter means receiving the output signal of said detector means and a frequency signal of said first oscillator means and providing a plurality of output signals, said frequency signal incrementing said counter means only when said counter means receives a signal from said detector means,

accumulation circuit means including multivibrator means receiving a first signal of said counter means and providing a periodic output signal as long as it is receiving the first output signal, and second counter means having a predetermined accumulation of emboli stored therein and counting each periodic signal from said multivibrator means to provide an output signal when said predetermined accumulation is reached, and

gate means receiving the output signal of said second counter means and a second signal from said counter means being indicative of the presence of a single embolism of predetermined size, said gate means providing the actuation signal.

2. Apparatus according to claim 1, wherein said accumulation circuit means further includes third counter means receiving the periodic output signal from said multivibrator means and providing an output signal indicative of the accumulation of emboli, and display means receiving the output of said third counter means and visually displaying the same.

3. Apparatus for detecting at least one embolism contained in a fluid during extracorporeal circulation of the fluid in a tubing comprising:

means to monitor the electrical impedance of the tubing, fluid and any emboli contained therein having an output signal whose voltage is proportional to the electrical impedance of the tubing, fluid and any emboli contained therein,

first oscillator means receiving the output signal from said means to monitor and providing at least one output signal whose frequency is proportional to the electrical impedance of the tubing, fluid and any emboli contained therein,

second oscillator means having an output signal whose frequency is proportional to the electrical impedance of the fluid and tubing,

detector means receiving the output signals from said first and second oscillator means and providing an output signal the duration of which is indicative of the difference between the frequencies of the output signals of said first and second oscillator means,

said detector means having an electrical feedback loop, said second oscillator means being in said feedback loop, integrator means in said feedback loop and providing an output signal which is the time integral of the input thereto, said integrator means receiving the output signal of said detector means and providing said output signal to said second oscillator means, said integrator means having a time constant, the output of said second oscillator means being fed back to said detector means to complete the feedback loop, and control means for providing an actuation signal indicative of the presence of at least one embolism including

counter means receiving the output signal of said detector means, said counter means being incremented when receiving the output of said detector means and providing an output signal indicative of said incrementation, and

multivibrator means receiving the output signal of said counter means, said multivibrator means having a time constant substantially less then the time constant of said integrator means.

4. Apparatus for detecting at least one embolism contained in a fluid during extracorporeal circulation of the fluid in a tubing comprising:

means to monitor the electrical impedance of the tubing, fluid and any emboli contained therein having an output signal whose voltage is proportional to the electrical impedance of the tubing, fluid and any emboli contained therein,

first oscillator means receiving the output signal from said means to monitor and providing at least one output signal whose frequency is proportional to the electrical impedance of the tubing, fluid and any emboli contained therein,

second oscillator means having an output signal whose frequency is proportional to the electrical impedance of the fluid and tubing,

detector means receiving the output signals from said first and second oscillator means and providing an output signal the duration of which is indicative of the difference between the frequencies of the output signals of said first and second oscillator means, and

control means receiving the output signal of said detector means and providing a plurality of output signals including an actuation signal indicative of the presence of at least one embolism, said control means including counter means and accumulation circuit means,

said counter means receiving an output signal of said detector means and a frequency signal of said first oscillator means, said frequency signal incrementing said counter means only when said counter means receives a signal from said detector means,

said accumulation circuit means including multivibrator means receiving a first signal of said counter means and providing a periodic output signal as long as it is receiving the first output signal, and second counter means having a predetermined accumulation of emboli stored therein and counting each periodic signal from said multivibrator means to provide an output signal when said predetermined accumulation is reached indicative of said predetermined accumulation,

said counter means providing a second signal being indicative of the presence of a single embolism of predetermined size, and

gate means receiving the output signal of said second counter means and said second signal from said counter means and selectively providing the actuation signal.

5. Apparatus according to claim 4, said control means further including means to select the predetermined accumulation of emboli.

6. Apparatus according to claim 4, wherein said accumulation circuit means further includes third counter means receiving the periodic output signal from said multivibrator means and providing an output signal indicative of the accumulation of emboli, and display means receiving the output of said third counter means and visually displaying the same.

7. Apparatus for detecting at least one embolism contained in a fluid during extracorporeal circulation of the fluid in a tubing comprising:

means to monitor the electrical impedance of the tubing, fluid and any emboli contained therein having an output signal whose voltage is proportional to the electrical impedance of the tubing, fluid and any emboli contained therein,

first oscillator means receiving the output signal from said means to monitor and providing at least one output signal whose frequency is proportional to the electrical impedance of the tubing, fluid and any emboli contained therein,

second oscillator means having an output signal whose frequency is proportional to the electrical impedance of the fluid and tubing,

detector means receiving the output signals from said first and second oscillator means and providing an output signal the duration of which is indicative of the difference between the frequencies of the output signals of said first and second oscillator means,

integrator means receiving the output of said detector means and providing and output which is the time integral of its input, said second oscillator means receiving the output of said integrator means, said integrator means having a time constant,

control means for providing a plurality of output signals including an actuation signal indicative of the presence of at least one embolism, said control means including

counter means receiving the output signal of said detector means and a frequency signal of said first oscillator means, said frequency signal incrementing said counter means only when said counter means receives a signal from said detector means, and providing a plurality of output signals including a first output signal indicative of the presence of at least one embolism,

accumulation circuit means for providing an output signal indicative of a predetermined accumulation of emboli including multivibrator means receiving a second signal of said counter means, said multivibrator means having a time constant substantially less then the time constant of said integrator means, and

gate means receiving the output signal of said accumulation circuit means and said first signal from said counter means and selectively providing said actuation signal.