Impedance plethysmograph

• US 3,882,851 A
• Filed: 08/15/1973
• Issued: 05/13/1975
• Est. Priority Date: 10/20/1971
• Status: Expired due to Term

• Current Assignee: New SD, Inc.
• Original Assignee: Frederick J. Sigworth
• Inventors: Sigworth, Frederick J.
• Primary Examiner(s): Kamm, William E.
• Application Number:
  US05/388,541
• Time in Patent Office: 636 Days
• Field of Search: 128/2.5P,2.5R,2.5V,2.08,2.1M,2.1P,2.1R,2.1Z,145.5-148,419P,419R,421
• US Class Current: 600/506
• CPC Class Codes: A61B 5/0535 Impedance plethysmography for measuring blood flow A61B5/0295

Abstract

Plethysmograph having current and voltage electrodes with a variable current source connected to the current electrodes to supply varying current to a biological segment to provide a voltage which is utilized to provide a signal which represents a percent of change of resistance of the biological segment.

Claims

1. In a plethysmograph first and second current input electrodes, first and second voltage drop measuring electrodes adapted to be applied in pairs across a biological segment with one current electrode adjacent one volTage electrode and the other current electrode adjacent the other voltage electrode, an oscillator having a high frequency output, a variable current source connected to the oscillator and to the first and second current input electrodes for receiving a timing signal from the oscillator so that an oscillatory output current is provided to the current input electrodes, amplifier means coupled to said first and second voltage drop electrodes for receiving the voltage developed across said voltage drop electrodes and producing an output responsive thereto, means for providing a predetermined reference voltage, means coupled to the amplifier means for detecting the output of the amplifier means and providing an output responsive thereto, said means for detecting receiving said predetermined reference voltage, means for supplying the output of the means for detecting to the variable current source to provide a control voltage for the variable current source so that the output from the variable current source provides an output from the amplifier means matching said predetermined reference voltage, the output of said means for detecting providing a percent deviation signal which represents a percent of change of resistance value of the biological segment, indicating means for receiving the percent deviation signal from the means for detecting for indicating the percent of change of resistance, said indicating means also being for indicating conductance of the biological segment, and means for alternately connecting said indicating means for receiving the output of the variable current source.

2. In a plethysmograph first and second current input electrodes, first and second voltage drop measuring electrodes adapted to be applied in pairs across a biological segment with one current electrode adjacent one voltage electrode and the other current electrode being adjacent the other voltage electrode, an oscillator having a high frequency output, a variable current source connected to the oscillator and to the first and second current input electrodes for receiving a timing signal from the oscillator so that an output oscillatory current is provided to the current input electrodes, amplifier means coupled to said first and second voltage drop electrodes for receiving the voltage developed across said voltage drop electrodes and producing an output responsive thereto, means for providing a predetermined reference voltage, means coupled to the amplifier means for detecting the output of the amplifier means and providing an output responsive thereto, said means for detecting receiving said predetermined reference voltage, means for supplying the output of the means for detecting to the variable current source to provide a control voltage for the variable current source so that the output from the variable current source provides an output from the amplifier means matching said predetermined reference voltage, the output of the means for detecting providing a percent deviation signal which represents a percent of change of resistance value of the biological segment, and indicating means calibrated in terms of two quantities, one of said quantities being conductance and the other of said quantities being percent of resistance change, together with means for connecting said indicating means alternately to said variable current source and said means for detecting respectively.

3. In a plethysmograph first and second current input electrodes, first and second voltage drop measuring electrodes adapted to be applied in pairs across a biological segment with one current electrode adjacent one voltage electrode and the other current electrode being adjacent the other voltage electrode, an oscillator having a high frequency output, a variable current source connected to the oscillator and to the first and second current input electrodes for receiving a timing signal from the oscillator so that an output oscillatory current is provided to the current input electrodes, amplifier means coupled tO said first and second voltage drop electrodes for receiving the voltage developed across said voltage drop electrodes and producing an output responsive thereto, means for providing a predetermined reference voltage, means coupled to the amplifier means for detecting the output of the amplifier means and providing an output responsive thereto, said means for detecting receiving said predetermined reference voltage, means for supplying the output of the means for detecting to the variable current source to provide a control voltage for the variable current source so that the output from the variable current source provides an output from the amplifier means matching said predetermined reference voltage, wherein said current source includes a logarithmic function generator electrically coupled between the control voltage input and the oscillatory current output so that the plethysmograph will have a constant response time regardless of the biological segment resistance and the current level supplied to the biological segment, the output of the means for detecting providing a percent deviation signal which represents a percent of change of resistance value of the biological segment, and indicating means for receiving the percent deviation signal from the means for detecting and for indicating the percent change of resistance.

4. In a plethysmograph, first and second current input electrodes, first and second voltage drop measuring electrodes adapted to be applied in pairs across a biological segment with one current electrode adjacent one voltage electrode and the other current electrode being adjacent the other voltage electrode, an oscillator having a high frequency output, a variable current source connected to the oscillator and to the first and second current input electrodes for receiving a timing signal from the current input electrodes, said variable current source including at least two active electronic amplification means connected in series and providing an output impedance which is high with respect to the impedance of the biological segment so that plethysmograph calibration will not be substantially affected by changes in the impedance of the biological segment, amplifier means coupled to said first and second voltage drop electrodes for receiving voltage developed across said voltage drop electrodes and producing an output responsive thereto, means for providing a predetermined reference voltage, detecting means coupled to the amplifier means and to the means for providing a predetermined reference voltage for detecting the output of the amplifier means and providing an output responsive thereto, means for supplying the output of the detecting means to the variable current source to provide a control voltage for the variable current source so that the output from the variable current source develops a voltage across said first and second voltage drop electrodes which provides output from the amplifier means automatically nulling said predetermined reference voltage, the output of the detecting means providing a percent deviation signal which represents a percent of change of the value of resistance of the biological segment, a plurality of serially connected diodes and a plurality of serially connected resistors with one of said resistors connected across each of said diodes included in said variable current source for providing a voltage thereacross which is the logarithm of the current therethrough, whereby a constant system response time is obtained regardless of biological segment resistance or current source output level, and indicating means for receiving the percent deviation signal from the means for detecting and for indicating the percent of change of resistance.

5. In a plethysmograph, first and second current input electrodes, first and second voltage drop measuring electrodes adapted to be applied in pairs across a biological segment with one current electrode adjacent one voltage electrode and the other current electrode being adjaceNt the other voltage electrode, an oscillator having a high frequency output, a variable current source connected to the oscillator and to the first and second current input electrodes for receiving a timing signal from the oscillator so that an oscillator output current is provided to the current input electrodes, amplifier means coupled to the voltage drop electrodes for receiving the voltage developed across the voltage electrodes and producing an output responsive thereto, means coupled to the amplifier means for detecting the output of the amplifier means and providing an output responsive thereto, means for supplying the output of the means for detecting to the variable current source to provide a control voltage for the variable current source so that the variable current source provides an output producing a long term constant voltage across the first and second voltage drop electrodes, said variable current source including a logarithmic function generator for providing a constant output response time over a range of biological segment resistance values covering substantially two orders of magnitude, the output of the means for detecting providing a percent deviation signal which represents a percent of change of resistance value of the biological segment, and means connected to receive the percent deviation signal for indicating the biological segment percent change of resistance.