Monitor for biological volume changes

• US 4,059,169 A
• Filed: 02/09/1976
• Issued: 11/22/1977
• Est. Priority Date: 02/09/1976
• Status: Expired due to Term

• Current Assignee: Winston H. Hagen
• Original Assignee: Winston H. Hagen
• Inventors: Hagen, Winston H.
• Primary Examiner(s): Michell, Robert W.
• Assistant Examiner(s): Cohen, Lee S.
• Application Number:
  US05/656,399
• Time in Patent Office: 652 Days
• Field of Search: 128/2.05 V, 128/2.05 F, 128/2.05 R, 128/2.1 Z, 128/2.1 P, 328/127, 73/194 E, 235/150.51
• US Class Current: 600/481
• CPC Class Codes: A61B 5/0535 Impedance plethysmography for measuring blood flow A61B5/0295

Abstract

A monitor for biological volume changes such as fluid content changes includes a source of constant current oscillations for application to the biological volume, and a receiver adapted to be coupled to the biological volume for producing a direct voltage having an amplitude corresponding to the impedance of the biological volume. A display device provides a display responsive to the D.C. voltage. A filter is provided for filtering the voltage, the filter having a time constant up to 15 seconds.

Claims

1. In a monitor for measuring biological volume changes having means for applying constant A.C. current in a biological volume of a subject, receiver means including means for sensing voltage across said biological volume resulting from said A.C. current, means for rectifying said sensed voltage, display means, and means for applying said rectified voltage to said diplay means to display a value representing the electrical impedance of said biological volume, the improvement wherein said means for applying said rectified voltage to said display means comprises filter means for inhibiting variations of said displayed value due to respiration and movement of said subject, said filter means having a time constant between 2 seconds and 15 minutes, said filter means comprising substantially the only signal modifying means between said rectifying means and display means.

2. The monitor of claim 1 wherein said filter means has a time constant of about 8 seconds.

3. The monitor of claim 1 further comprising means for calibrating said monitor, and means responsive to the calibration of said monitor for reducing the time constant of said filter means.

4. The monitor of claim 1 wherein said filter means comprises an operational amplifier having a feedback path, a capacitor, and means for connecting said capacitor in said feedback path whereby said capacitor determines said time constant.

5. The monitor of claim 4 further comprising a calibration resistor, said means for connecting said capacitor comprising means for selectively connecting said capacitor and resistor in said feedback path, whereby the time constant of said filter means is reduced when said calibration resistor is connected in said feedback path for calibration of said monitor.

6. The monitor of claim 1 wherein said display means comprises a strip chart recorder.

7. The monitor of claim 1 wherein said display means is a digital indicator, and further comprising analog to digital converter means connected between said receiver means and display means.

8. The monitor of claim 1 further comprising an alarm means, a source of a digital signal corresponding to a determined electrical impedance, analog to digital converter means connected to the output of said receiver means, means for comparing the outputs of said converter means and said source, and means for applying the output of said comparing means to said alarm means.

9. In a non-invasive fluid monitor for measuring bio-electric impedance having means for applying constant A.C. current to a biological volume of a subject, receiver means including means for sensing voltage across said biological volume resulting from said A.C. current, means for rectifying said sensed voltage, display means, and means for applying said rectified voltage to said display means whereby said display means indicates a value representing the electrical impedance of said biological volume, the improvement wherein said means for applying said rectified voltage to said display means comprises filter means, and means for varying the time constant of said filter means from about 0 to 15 minutes, said filter means comprising substantially the only signal modifying means in said means for applying said rectified voltage to said display means.

10. The fluid monitor of claim 9 wherein said filter means comprises an operational amplifier having a feedback path, said means for varying said time constant comprising capacitor means, means for connecting said capacitor means in said feedback path for determining the time constant of said filter means, and means for varying the capacity of said capacitor means.

11. The fluid monitor of claim 10 further comprising a calibration resistor, and means for selectively interconnecting said calibration resistor and capacitor means in said feedback path, whereby said time constant is reduced when said calibration resistor is connected in said feedback path.

12. A non-invasive fluid monitor comprising an impedance plethysmograph means for producing a voltage corresponding to electrical impedance of a biological volume, filter means having a time constant between 2 seconds and 15 minutes for filtering said voltage, display means, and means applying the output of said filter means to said display means, whereby the display on said display means corresponds to the fluid content of said biological volume.