INTRAVENOUS PRESSURE MONITOR

• US 3,738,356 A
• Filed: 01/22/1971
• Issued: 06/12/1973
• Est. Priority Date: 01/22/1971
• Status: Expired due to Term

• Current Assignee: Harold W. Workman
• Original Assignee: Harold W. Workman
• Inventors: Workman, Harold W.
• Primary Examiner(s): Howell, Kyle L.
• Application Number:
  US05/108,756
• Time in Patent Office: 872 Days
• Field of Search: 128/2.5D,2.5E,2.5N 73/398R
• US Class Current: 600/488
• CPC Class Codes: A61B 5/0215 by means inserted into the body catheters A61M25/00

Abstract

An air-filled catheter transmits an intravenous blood pressure to a pressure-sensing transducer having a coil connected to a flexible membrane or diaphragm which defines one side of the catheter chamber. A digital feedback signal is generated in response to displacement of the membrane; and this feedback signal is used to energize the coil and drive the membrane back to its original position. A highly sensitive (i.e. compliant) diaphragm is used; and the high repetition rate of the feedback signal limits displacement of the diaphragm within very small tolerances to reduce the compliance error of the diaphram. The average value of the current in the driving coil necessary to displace the diaphragm to offset the catheter pressure is a measure of the intravenous pressure.

Claims

1. In a System for continuously measuring venous pressure, the combination comprising a conduit having an end adapted to be placed in a vein, a flexible diaphragm having one side in fluid communication with the interior of said conduit;

a closed reference volume of air in fluid communication with the other side of said diaphragm;

an electrical coil magnet means associated with said coil to exert a force thereon when said coil is energized;

means attaching one of said coil and said magnet means to said diaphragm;

switch means responsive to the position of said diaphragm for opening a set of contacts when said diaphragm is displaced in one direction from its original position and for closing said contacts when said diaphragm is displaced in the opposite direction;

circuit means in circuit with said switch for energizing said coil to force said diaphragm in a direction opposite to its direction of displacement from said original position, said switch operating at a cycle rate greater than the dominant frequency mode of the pressure being measured whereby the average signal energizing said coil over a number of cycles is a measure of venous pressure, said circuit means, said magnet means and said coil comprising a drive means for displacing said diaphragm over approximately the same distance for all ranges of pressure being measured thereby enabling said diaphragm to be highly sensitive without introducing compliance error.

2. The system of claim 1 wherein said circuit means includes a first circuit means connected to said switch means for generating a first constant signal when said means is open and a second constant signal of opposite polarity when said switch means is closed, and a second integrating circuit means responsive to said first circuit means for energizing said coil with an increasing signal of a first polarity in response to said first constant signal and for energizing said coil with an increasing signal of opposite polarity in response to said second constant signal.

3. The system of claim 1 wherein said switch means includes a first contact mounted on said diaphragm and a second contact mounted adjacent to said first contact and adjustable to balance the system before measuring.

4. A system for continuous intravenous blood pressure measurement comprising:

air-filled catheter means adapted at one end for insertion in a vein and defining at the other end a chamber;

a flexible membrane closing a portion of said chamber;

a closed volume on the other side of said membrane providing a reference pressure;

feedback means associated with said membrane including a switch having contacts adapted to be closed when said membrane is in a first position consisting of an original position or to one side thereof, said contacts being open when said membrane is in a second position to the other side of said original position, said feedback means including circuit means generating a first electrical forcing signal as long as said switch is closed and a second electrical forcing signal as long as said switch is open, said feedback means generating said first and second forcing signals at a cycle rate greater than the dominant mode of the pressure being measured;

force-producing means including an electrical transducer having a coil responsive to said first and second electrical forcing signals and a magnetic member associated with said coil, one of said coil and magnetic member carried by said membrane, said coil receiving said feedback signals for forcing said membrane in a first direction toward said original position in response to said first feedback signal and for forcing said membrane in a direction opposite to said first direction and toward said original position in response to said second feedback signal, whereby the average value of said forcing signals is representative of the pressure being measured thereby enabling said system to measure positive and negative pressures relative to said reference pressure; and

means for measuring the average forcing signal.