Angiographic injector with pump motor starting control

BACKGROUND OF THE INVENTION

This invention relates to an angiographic injector and more ³particularly to such an injector providing an injection pressure which rises relatively gradually thereby to prevent whipping of the catheter tip.

Angiographic injectors are employed in studying the functioning of a patient’s arterial system. The purpose of the injector is to introduce, through a long, thin, hollow catheter, materials which are radio-opaque, that is, which will provide contrast for X-ray photography. Typically, the catheter is introduced into the arterial system through a vessel which passes । relatively close to the patients’s skin so as to minimize the insertion wound. The catheter is then threaded by the surgeon to that part of the arterial system under study. Typically, it is desirable that the injection of material be relatively precisely controlled in time so that synchronization of the injection with the X-ray photography or with the patient’s heart beat can be provided. Accordingly, in certain circumstances it may be necessary to employ relatively high injection pressures. In various applications, however, a rapid onset of a relatively high injection pressure will cause the tip of the catheter to whip, that is, to move violently sideways in an oscillatory motion which continues for the duration of the injection. This motion is objectionable and may itself cause injury.

According to one aspect of the present invention, it has been found that the occurrence of this whipping motion can be eliminated by a relatively gradual application of pressure, even though relatively high pressures are ultimately reached. This progressive application of the pressure causes the tip of the catheter to move relatively slowly against the wall of the cavity or vessel in which it is positioned and to then be held there as the pressure increases.

Among the several objects of the present invention may be noted the provision of an angiographic injector in which injection pressure builds up relatively gradually; the provision of such an injector in which the rate of pressure build-up may be controlled and adjusted; the provision of such an injector in which the ultimate pressure level is readily adjustable; the provision of such an injector which prevents catheter whipping; the provision of such apparatus which is highly reliable and which is relatively simple and inexpensive. Other objects and features will be in part apparent and in part pointed out hereinafter.

SUMMARY OF THE INVENTION

The angiographic injector of the present invention employs an electric motor to pump radio-opaque material through a catheter which is adapted to be inserted into a patient’s vascular system. Whipping of the tip of the catheter is prevented by gradually and progressively energizing the motor at the start of an injection cycle. The motor is connected to an a.c. power source through a triggerable semiconductor current switching device so that the energization of the motor is variable as a function of the phase angle of triggering of the switching device. A control signal voltage is generated which rises gradually over a plurality of cycles of the a.c. source frequency, starting at a preselectable time. Further, means are provided for repetitively triggering the switching device at a phase angle which varies as a function of the amplitude of the control signal voltage, the phase angle being progressively advanced. Accordingly, the motor is progressively energized and whipping of the catheter tip is prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. I is a somewhat diagrammatic illustration of an angiographic injector according to the present invention;

FIG. 2 is a schematic circuit diagram of motor control apparatus employed in the FIG. 1 injector; and

FIG. 3 is a graphical representation of various waveforms occurring in the circuit of FIG. 2.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1, there is indicated at 11 generally, the mechanical injector assembly employed in the illustrative embodiment of apparatus constructed in accordance with the present invention. This assembly may, for example, be essentially the same as that disclosed in my earlier U.S. Pat. No. 3,156,236. For the purposes of the present invention it may be briefly noted that this assembly comprises a piston pump 13, an electric motor 15 for driving the pump, and a low friction ball-nut assembly 17 for converting the rotary motion of motor 15 to a linear motion suitable for operating the piston of the pump. The pump 13 provides radio-opaque contrast material to an elongate catheter 14 for injection into a patient’s vascular system in conventional manner.

As is disclosed in the aforementioned patent, motor 15 is preferably of the permanent split capacitor type, although other motors adaptable to this kind of operation can be used. At speeds substantially below synchronous speed, the permanent split type of motor provides a substantially constant output torque for a given level of energization. Thus, the injection pressure may be controlled as a predictable and controllable function of energization of the motor 15. While an electric motor has been illustrated as a preferred means of providing an electrically controllable force, an electrically operated clutch or solenoid may also be used as a force control, e.g. in conjunction with a separate mechanical or hydraulic power source. Thus, as used herein, the term motor means should be understood in its broad sense to include such equivalents.

In accordance with the present invention, the energization of motor 15 is controlled by means of a substantially conventional solid-state motor power controller 19. Motor control 19 is of the type which employs a triggerable semiconductor current-switching device, e.g. a silicon-controlled rectifier (SCR) or a triac. Such power controls are known in the art and, accordingly, ate not described in detail herein. As is understood in the art, the level of energization of motor 15 can be controlled as a function of the phase angle of firing of the triggerable current-switching device. Triggering pulses suitable for firing such a current-switching device are applied to the motor controller 19 through a pulse transformer T1 from a programmable firing-angle control 21. As will be described in greater detail hereinafter, control 21 includes a switch SI whose operation controls the duration of an injection cycle and a variable resistance R8 for controlling the rate at which pressure is built up in the injector pump 13. Control 21 may also include various timers and reversing switches (not shown) for controlling the operation of motor 15 as is conventional in this art.

In the firing angle control 21 illustrated in FIG. 2, a.c. power is applied to a bridge rectifier DI through the switch SI. The pulsating d.c. voltage provided by the bridge DI is applied, through a pair of dropping resistors R1 and R2, to a Zener diode D2 so as to provide, between a pair of leads L3 and L4, a clipped waveform substantially as illustrated at A in FIG. 3.

The firing angle control employs a relaxation oscillator which comprises a unijunction transistor Q2. The base-one circuit of this transistor is connected to the primary winding of pulse transformer Tl, as illustrated. The base-two terminal of unijunction transistor Q2 is connected, through a load resistor R3, to the junction between dropping resistors R1 and R2. This intermediate connection of the unijunction transistor somewhat spoils the regulation to transistor Q2 provided by the Zener diode D2, with regard to the operation of the relaxation oscillator, in a manner tending to compensate for the effect of line voltage variation upon the operation of the motor 15.

The relaxation oscillator also comprises a timing capacitor C2 which receives charging current from two sources, a resistor R4 which is connected to the positive supply lead L3

3,674,009 and the emitter output terminal of a Darlington pair amplifier QI. The collectors of the Darlington pair are connected to the positive supply lead through a common load resistor R5. As is understood by those skilled in the art, the unijunction transistor Q2 is a form of voltage breakdown device and when the voltage on capacitor C2 reaches the firing threshold which is determined by the transistor's intrinsic standoff ratio, the transistor fires, discharging the timing capacitor and delivering a pulse to the primary winding of transformer T1.

A voltage divider comprising a pair of resistors R6 and RIO and a potentiometer R9 is connected across the supply leads L3 and L4 for providing a voltage which is a preselectable portion of the total pulsating d.c. voltage. A current which is proportional to this preselected voltage portion is applied, through the variable resistance R8, to a capacitor Cl. As is described hereinafter, the rate of charging of capacitor Cl determines the rate at which pressure builds up in the injector. The voltage on capacitor Cl is applied, through a currentlimiting resistor R7, to the input terminal of the Darlington pair amplifierQl.

The operation of this apparatus is substantially as follows. It is assumed initially that switch SI is open and has been open long enough so that the timing capacitors Cl and C2 are substantially discharged. Upon closing the switch SI, the a.c. supply voltage is applied to the motor and motor power controller but no current flows through the motor circuit until triggering pulses are applied to the motor power controller 19. Since the capacitor Cl is initially discharged, substantially the only current available to charge capacitor C2 during the first a.c. half-cycle will be that provided through resistor R4. Accordingly, the voltage on capacitor C2 will reach the firing potential of the unijunction transistor Q2 only toward the end of each a.c. half-cycle and thus the level of energization of motor IS will be relatively low.

Gradually, however, the voltage on capacitor Cl will rise, turning on the Darlington pair and causing it to provide a component of charging current to the capacitor C2 during a portion of each half cycle. The value of this component is determined essentially by the value of resistor R5, the Darlington amplifier being operated in saturation. This added component of charging current is provided, during each half cycle, until the voltage on capacitor C2 substantially reaches the level of the voltage on capacitor Cl, the base-emitter offset voltages being ignored, since at this point the Darlington pair turns off. From this point on until the unijunction transistor fires, the charging current is provided substantially only by the resistor R4. The waveform generated across capacitor C2 is represented at B in FIG. 3 and it can be seen that this waveform has a break or knee at a point which varies from cycle to cycle as capacitor Cl charges. From FIG. 3 it can further be seen that, as capacitor Cl charges, the unijunction transistor Q2 reaches its firing point, designated E_F, earlier in each a.c. half-cycle. Accordingly, the motor power controller 19 is progressively fired at earlier phase angles. As the energization of the motor 15 is thus gradually and progressively increased, following the closing of switch SI, it can also be seen that the pressure in the injector will gradually and progressively rise starting from the initiation of an injection cycle. After the unijunction transistor fires in each half cycle, it is kept in conduction for the rest of the half cycle by current provided through the Darlington pair QI and then turned off at the end of the half cycle when the pulsating voltage provided by the bridge rectifier DI drops to zero. In this way, the charging of capacitor C2 starts from a repeatable starting point for each half cycle.

Since the charging current provided to capacitor Cl is variable as a function of the setting of rheostat R8, the rate at which pressure increases following initiation can be adjusted by varying the setting of this rheostat. If only a predetermined rate of rise is needed, a fixed resistance may be used in place of rheostat R8.

In view of the foregoing, it may be seen that several objects of the present invention are achieved and other advantageous results have been attained.

As various changes could be made in the above construction without departing from the scope of the invention, it should be understood that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.