PULMONARY IMPEDANCE BRIDGE

• US 3,750,649 A
• Filed: 06/25/1971
• Issued: 08/07/1973
• Est. Priority Date: 06/25/1971
• Status: Expired due to Term

• Current Assignee: John W. Severinghaus
• Original Assignee: John W. Severinghaus
• Inventors: Severinghaus, John W.
• Primary Examiner(s): Howell, Kyle L.
• Application Number:
  US05/156,667
• Time in Patent Office: 774 Days
• Field of Search: 128/2.1Z,2.1R,2.1E,2R,2.5V
• US Class Current: 600/529
• CPC Class Codes: A61B 5/0535 Impedance plethysmography for measuring blood flow A61B5/0295
• CPC Class Codes: A61B 5/0809 by impedance pneumography

Abstract

Apparatus for measurement of lung resistance includes a low voltage and high frequency power supply connected to a driver electrode contacting one side of a chest with a detector electrode contacting the opposite side of the chest and a pickup electrode engaging the chest therebetween. A variable resistor is connected with other resistors between the detector and pickup electrodes to form a bridge circuit with a portion of the lung resistance and a meter connected to the detector electrode indicates bridge balance whereat the resistance of the variable resistor is equal to the resistance of a portion of the lung. A guard ring about the detector electrode has segments thereof driven by operational amplifiers from the detector electrode to substantially eliminate skin potential gradients laterally of the detector.

Claims

1. A pulmonary impedance bridge for measurement of lung impedance comprising a driver electrode adapted for connection to a power supply and to one lateral side of the chest of a torso including a lung, a detector electrode adapted for connection to the other lateral side of said chest, an electrically conducting guard ring adapted for disposition about said detector on said chest, a pickup electrode adapted for disposition on the mediastinum of said torso, a variable resistor connected to said detector electrode, first and second resistors connected in series between said pickup electrode and said variable resistor, an inverter connected across said second resistor, and a meter connected to the junction of said detector electrode and said variable resistor for indicating balance of a bridge formed by said resistors and the resistance of the lung between the mediastinum and detector electrode as established by varying the value of said variable resistor, whereby the adjusted value of said variable resistor at balance of said bridge is equal to the resistance of said lung between the mediastinum and detector.

2. Apparatus for measuring and monitoring resistance of a lung in vivo comprising a. a driver electrode adapted for connection to a power supply and engagement with a first lateral side of a chest wall, b. a detector electrode adapted for engagement with the other lateral side of said chest wall, c. a high frequency and low voltage power supply connected between said driver and detector electrodes, d. an electrically conducting guard ring adapted for engagement with said chest wall about said detector electrode and out of contact therewith, e. a pickup electrode adapted for engagement with said chest on the mediastinum thereof, f. a variable balance resistor connected to said detector electrode, g. first and second bridge resistors connected in series between said pickup electrode and balance resistor to form a bridge with said balance resistor and the lung between said pickup electrode and detector electrode, h. an inverter connected across said second bridge resistor for energizing said bridge with substantially equal voltages of opposite phase, and i. means indicating current flow from said detector electrode to said power supply as an indication of bridge unbalance whereby the resistance value of said balance resistor at zero current flow is the resistance of a lung between said mediastinum and detector electrode.

3. Apparatus as set forth in claim 2 further defined by said guard ring being divided circumferentially into a plurality of segments, a plurality of guard pickup electrodes disposed one between each guard ring segment and said detector electrode and adapted to contact with the chest wall, and amplifier means connected between said detector electrode and guard ring segments and controlled by the potentials of said guard pickup electrodes for eliminating potential gradient between detector electrode and guard ring segments.

4. In apparatUs for measurement of lung resistance including a detector electrode adapted to engage a first side of a chest wall and a driver electrode energized by a low voltage high frequency power supply and adapted to engage a second opposite side of said chest wall, the improvement comprising a guard ring divided into circumferential segments disposed about said detector electrode in engagement with said chest wall, a plurality of feedback amplifiers separately connected between said detector electrode and guard ring segments, and pickup electrodes adapted to engage the chest wall between said detector electrode and respective guard ring segments and separately connected to feedback inputs of said amplifiers for matching the segment currents to chest wall currents.

5. In apparatus for measuring lung resistance including a detector electrode adapted to engage one side of a chest wall and a driver electrode adapted to engage an opposite side of a chest wall and connected to a power supply, the improvement comprising a pickup electrode adapted to engage the chest wall intermediate the detector and driver electrodes, resistors including a variable balance resistor connected between said pickup and detector electrodes to form a bridge circuit with the resistance of tissue underlying said detector electrode, an inverter coupled between said pickup electrode and balance resistor, and a meter coupled to said detector electrode for indicating balance of said bridge by variation of said balance resistor as a measurement of the resistance of a part of the lungs.