US 3590809 A
Description (OCR text may contain errors)
I Umted States Patent 1 1 3,590,809
[72} Inventor Seymour 8. London  References Cited 35 East Dilido Drive, Mlllltti Bench. Flt]. UNITED STATES PATENTS 33l39 2.l49,690 3ll939 Snyder l28/21O5 gffi g g 5,105,490 l0/l963 Schoenfeld... 1. l28/2l4 d J 3,242,920 3/1966 Andersen 12812.05 Y 3.455.019 4/1969 Reynolds... l28/2.05 3.456.,648 7/1969 Lee et al. 128/205 Primary Examiner-William E Kamm 541 METHOD FOR CENTRAL venous PRESSURE MONITORING 2 Drum! Figs ABSTRACT: Method of central venous pressure monitoring [52I [1.8. CI 128/205 D, including inserting a catheter in the right atrial cardiac l28/2l4. l28/DIG. l3 chamber, supporting a vertical column of liquid above said [5| 1 Int. Cl 6. A6lb 5/02 chamber, transmitting light through the column and the liquid,  Field at Search 128/205 D, discriminately sensing that light which has been transmitted 2.05 F, 2.05 V, 2.05 R, 2.05. DIG. l3. 2 l4, 2.05 through the liquid and monitoring central venous pressure as a MS function of liquid level in the column.
PATENTEU L IQYI 3.590.809
sum 1 or 3 INVEN'T OR BY ,S'emmesmsemmes ATTORNEYS PATENTEUJUL mam 3590309 INVENT( )R M 553770? a how/30m BY semmesandsemmes ATTORNEYS METHOD FOR CENTRAL VENOUS PRESSURE MONITORING BACKGROUN D OF TH E INV ENTION I. Field of the Invention The veins form a large volume, low-pressure collecting system, containing about 65 percent the circulating blood volume. The pumping action of the heart provides the pressure and by emptying the large veins, creates a dropping pres' sure gradient, propelling blood centrally. The veins also function as a reservoir and respond to the homeostatic needs of the body by distension or tension. The pressure at any one point in the venous system reflects two factors: (I) the amount of blood contained which acts to mechanically distend the walls of the veins, and (2) the state of tension of the walls due to reflex tone. Regulatory mechanisms adjust heart rate, stroke volume, arterial tone, capillary bed size, and venous tone to maintain effective circulation of the blood.
The central venous pressure (CVP) measured at vena caval and at right atrial levels, is an index of the effectiveness of the heart in handling the venous blood flow presented at the right atrium. A higher than normal CVP suggests that the central veins are relatively overdistended and that the heart cannot effectively keep them empty." A low CVP indicates simply that the heart is effectively maintaining a forward flow and that the veins are relatively undistended. The CVP may range from 20 to I mm. of water in normal individuals. This wide variation is only partly due to differences in a common zero reference point and may also be due to subtle regulatory mechanisms. Clinically, however, despite this wide range of normal values, in a given individual, information as to a change in the monitored CVP is recognized as being of real value in acute problems involving massive fluid loss and replacement. Hypovolemic shock and heart ofpump" failure may be present with clinically confusing similarities, but this important distinction is simply made by CVP measurement. In other conditions such as obliguria secondary to renal shutdown and coronary occlusion with circulatory collapse, the CVP can be a diagnostic aid as well as of therapeutic importance.
While the indications for CVP monitoring are increasing, the presently available techniques, simple in principle, are time consuming and laboriously accomplished. A plastic catheter or tube is introduced through a brachial, subclavian, or jugular vein into the vena cava or right atrium. By referring the level of the miniscus within the tube to an external zero reference at right atrial level, the vertical pressure in millimeters of water within the right atrium can reasonably and consistently be measured. To prevent clotting within the catheter, the latter can be connected to a vertical tubing and intermit tently flushed with saline, which is then allowed to empty into the right atrium. The vertical distance from the external zero reference point to the top of the stabilized saline column represents the central venous pressure in millimeters of water. These measurements are usually made periodically by a nurse or technician manually manipulating a stop cock, saline reservoir and clamp system. The attendant must first fill the vertical column with saline, then wait to allow the slowly emptying column to stabilize and finally record the level of the miniscus. After this reading the saline reservoir to the manometer catheter is opened and saline is flushed through to prevent clotting at the tip of the catheter. An electronic version of this method substitutes a strain gauge or other pressure transducer for the vertical saline gravometric column. The gauge pressure can be recorded by an oscilloscope and the data can be taped for future reference. While these methods are reasonably ac curate, both require a similar continuous manipulation of the CVPrescrvoir system as well as direct observation of the pressures.
2. Description ofthe Prior Art THe prior art devices have been directed principally to the provision of blood flow meters of the type employed in heartlung pumping systems. Robicsek (U.S. Pat. No. 3,017,885) is a typical blood flow meter.
Other prior art devices have provided catheter probe devices for blood sample withdrawal (Still, U.S. Pat. No. 3,043,303). Also, one prior art device (Baehr, U.S. Pat. No. 3,287,72l has addressed itself to the gravity feeding of prescribed amounts of fluid by means of a catheter tube pinching clamp and an electronic signal circuit. Most of these devices have been extraordinarily complex, as well as expensive to manufacture and difficult to operate.
London, U.S. Pat. Nos. 3,202, 148 and 3,319,623 concern method and apparatus for measuring blood pressure by means of a sound detecting pressurized cuff, while energizing a mercury column and related blood pressure visual display panel, as Korotkow sounds are detected. In London, U.S. Pat. No. 3,3 l9,623 an aneroid manometer is used instead ofa mercury column.
None of the prior art devices have been capable of transmitting light through a vertically positioned plastic manometer tube and discriminately sensing that light which has been transmitted through the liquid and monitoring central venous pressure as a function of the liquid level in said column. None of the prior art devices have been capable of varying the sensing of light relatively to the type of liquid being supported in the vertical manometer tube and none of the prior art devices have embodied high and low level alarms or visual display capabilities of applicant's method.
SUMMARY OF THE INVENTION Applicants studies of the problem of monitoring central venous pressure have evolved a method for simplifying the obtaining of this information so that a continuous visual readout of the central venous pressure presented by means of a photocell circuit and light source positioned astride the conventional intravenous tubing, as illustrated in FIG. I. When the preselected levels have been exceeded or desirable levels are not attained, i.e., either the pressure is too high or too low, both audial and visual alarm signals are given. The recognition of an undesirable physiologic state of the CVP can be utilized optionally in automatic programming of treatment during the alarm state. By a simple external clamps arrangement coor dinated electronically with the alarm recognition system, fluids and medications can be started, stopped, or rate of flow changed automatically. When correction of the preselected alarm state has been achieved, the programming system reverts back to the monitoring state.
Applicant has provided a method and device for digital readout to automatically measure and monitor directly the level of the central venous pressure. The height of a column of physiologic saline solution vertical to the right atrial chamber of the heart and in direct continuity by catheter or other tubing with the lumen of the right atrium or superior vena cava is measured electronically. The level of this fluid column is sensed by a vertical series of photocells, each coupled with a regulated light source on the other side of a clear plastic intravenous tube. An electronically triggered and electrically connected corresponding column of indicator lamps appears as an illuminated numerical "readout of the CVP.
Alarms and/or a programming device are automatically initiated by the use of a selector switch that places the alarmprogramming circuits in parallel with the specific indicator lamp preselected as appropriate for alarm notification.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a perspective view of a proposed central venous pressure monitor, embodying a cardiac catheter positioned in the right atrium and a vertical manometer tube positioned within the monitor housing;
FIG. 2 is a fragmentary circuit diagram of the vertical manometer tube positioned in the vertical chamber defined by opposed series of exciter lamps and photocells and additionally showing the photocell lamps gated to individual SCR indicator lamps which appear on the exterior of the housing as a visual display of central venous pressure (CVP), housing; and
FIG. 3 is a circuit diagram, showing the high alarm, low alarm, and audio alarm switching mechanisms, as well as the leads to the high programmer solenoids and the low programmer solenoids.
DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an illustration of the function of the CVP monitor (without the valve for automatic programming). The tubing connection 104 from the saline flaslt I26 (the reservoir for the slow flush and the saline filled vertical manometer column 132) and the manometer tubing I04 are joined by a Y-tube connection, 136. Termination of this connection 136, leads to the cardiac catheter tip 124. The latter enters the right atrial cardiac chamber via a large vein, the superior vena cava. The zero level (shown in phantom) of the central venous pressure monitor is adjusted by moving the housing 108 vertically on an adjustable stand 138, so that the zero of the monitor scale is fixed at the right atrial level. (The external reference for the right atrium is considered to be about 5 centimeters below the sternum, at the second interspace of the rib cage.) The flow from the flask I26 containing the saline is regulated to run continuously at a rate of about l cc. per hour. This serves to maintain saline in the vertical manometer column 132 and to prevent blood from entering the catheter which might clot and plug the lumen of the cardiac catheter.
In FIG. 2 there is illustrated a vertical column I00 of photocells 0', 2. 4', 6', 26, 28', 30' and 32', each 2 cm. apart and a matching vertical column of corresponding incandescent exciter lamps 102 are arranged directly opposite to each other, separated only by a vertical plastic intravenous tubing I32, supported in vertical chamber I06 of housing I08. As each exciter lamp is directly opposite its corresponding photocell, each pair of lamp and photocell forms a separate sending circuit, sensitive only to change in light transmission, since ambient light is excluded from the chamber. Increased transmission of light drops the internal resistance of the photocell and allows more current to flow. Light transmission through plastic manometer tubing 132 will be varied by the content of the tubing, either increased as by a clear fluid such as saline, or decreased by any denser fluid which obstructs light transmission. Normal saline is well tolerated, available, simple and since a satisfactory end point can be obtained between a filled and nonfilled column, is the fluid of choice for the suggested manometer. The increased current flow through the photocells such as 32' when the column is filled, is used to close a sensitive electronic switch 116, illuminating indicator lamps such as 32" corresponding to the height of each photocell as illustrated in FIG. 3.
Each photocell (PC), e.g., 32' is connected by one terminal 110 to a positive voltage source H2, (l6) and by the other terminal I14 to of an indicator silic0n-contr0llcd rectifier ("SCR"), as at and a solid-state switch 116. The increased current through the photocell 32' that occurs in the presence of increased light transmission is used to trigger these switches. Precise regulation in the amount of current flow in the standby" condition is further controlled by a small reverse bias of negative current applied through line I18 to the SCR and by a potentiometer 120, reducing the current optimally to the SCR. This ensures that each indicator lamp circuit is triggered only if the transilluminated plastic column I32 is filled by saline to the vertical height of the paired photocelbexciter lamp circuit. As the central venous pressure fluctuates, the saline column will rise and fall and, ac cordingly, the indicator lamps will be illuminated or extin guished because of this changing bias produced by the in crease or decrease in light transmission through the saline filled column.
Standard commercially available intravenous tubing I04 and venous pressure sets are used to connect to the venous catheter I22 and for the manometer transillumination chamber 106. To prevent plugging of the catheter tip I24 during continuous central venous pressure pressure monitoring, saline solution in flask 126 is slowly flushed through the catheter tip 124. A microdrip regulator (not illustrated) controls the flow from saline reservoir I26 to the manometer tubing to the vein. A flow of IO cc. per hour is adequate to prevent clotting at the tip and slow enough not to raise or al' feet the level of the saline column in the venous pressure monitor.
ALARMS The indicator lamp circuits also provide signal sources for alarm or therapy programming as illustrated in FIG. 3. An alarm state can be detected for venous pressures higher or lower than desirable. Sensing of the alarm state for high venous pressures is provided by a simple circuit. An NPN transistor 03 (controlling a sensitive relay, K1), is put in parallel with one of the numbered indicator lamps by high alarm selector switch 128. When the SCR indicator lamps circuit conducts and the lamp 32", for example, is illuminated, the alarm transistor 0,, whose base is biased positive by the indicator SCR "6 circuits output, conducts, closing the contacts of the three-pole relay Kl. On the other hand, by substituting a PNP transistor, 0 a low alarm sensing circuit is created (i.e., the absence of a positive bias). Now if the CV? should drop below a point preselected by low alarm selector switch U0, and the selected indicator lamp eg 2" is not illuminated or becomes extinguished, then the absence of positive bias causes the transistor 0 to conduct. The three-pole relay K, contacts are closed when 0, conducts and the low alarmprogramming circuits are activated. Therefore, the alarm condition, high or low, is made dependent on whether or not the selected indicator lamp is illuminated. The venous pressure may fluctuate, the indicator lamps will correspondingly be illuminated or extinguished, and thus the alarm system similarly will be activated or turned off during periods of monitoring.
Memory circuits (not illustrated) can record the height or level of pressure fluctuations for a given period by the use of parallel direct current circuits with SCR switches. A write out or tape recording for data review is also feasible.
PROGRAMMING In critical clinical situations, shock or congestive failure may be incipient and the time between discovery of this change and the institution of therapy may be reflected in the outcome of the case. The venous pressure monitor can be so programmed that if an alarm condition exists, a preselected medication of fluid administration change is automatically instituted. The control of flow from the saline, slow flow manometer reservoir flask 126, to an alternate emergency fluid administration, is by means of an external electronically controlled valve (not illustrated). The latter by external compression of the plastic tubing can open or close flow through the plastic tubing I32. A rocker arm arrangement (not illus trated ).electronically controlled, when placed in parallel with the alarm circuit, at a preselected level by means of switches 128 and 130, pinches shut one or more tubes, simultaneously opening other tubes. The level of operation for automatic programming is preselected through switches 128 and 130 by the physician for medication and/or fluid replacement on an emergency basis, depending on the venous pressure level. The programming circuits are simple. If an alarm condition exists, the circuit I44, 146 to a high programmer or a low programmer solenoid is closed, pulling in the rocker arm clamp; the slow flow from the flask I26 and the manometer column 134 is stopped; and the alternate therapy solution is opened to continuity with the right atrial chamber. Programming as herein illustrated, is designed to be manually interrupted or can be automatically interrupted. This latter is accomplished by a timing device (not illustrated) that opens the circuit to high programmer or low programmer solenoid for about I minute at intervals of 2- l minutes. This permits the monitor to revert to the standby condition and scan the CV? and to prevent overcorrection.
Manifestly, various changes in circuitry may be empioyed without departing from the scope of invention.
1. Method of central venous pressure monitoring compris- A. Introducing the lower end of a liquid column into the venous area of the patient so that the level of liquid in said column indicates venous pressure;
B. Supporting said liquid in vertical column by means of central venous pressure;
C. Transmitting light through said column and said liquid by a plurality of independent light sources vertically superposed adjacent one side of said column;
D. Discriminately sensing that light which has been transmitted through the liquid via a plurality of independent light sensing elements vertically superposed on the other side of said column;
B. Indexing the height of said liquid in vertical column to the right atrial cardiac chamber; and
F. Monitoring venous pressure as a function of the level of liquid in said column through which light is transmitting by electrically energizing a visual display of liquid level as a function of venous pressure, said display comprising a plurality of independent lamps superposed in vertical column corresponding to said light sources and light sensing elements.
2. Method of central venous pressure monitoring as in claim 1, including:
K. varying sensing of light relatively to the type of liquid being supported in said column.