US 3595221 A
Description (OCR text may contain errors)
United States Patent i 72] inventor John Harold Blackett London, England ] Appl. No. 804,075  Filed Mar. 4, I969  Patented July 27, I971 [73) Assignee Matburn (Holdings) Limited London, England  ENDOSCOPIC HAVING ILLUMINATION SUPPLY UNIT 5 Claims, 2 Drawing Figs.
 US. Cl. 128/6  lnt.Cl A6lb 1/06'  Field of Search ...l28/6,7,8, 9, l l, l3, l6, l8,22
 References Cited I UNITED STATES PATENTS 3,127,115 3/1964 Yellott et al 128/23 UX 3,244,167 4/1966 Ferris et al .7 128/6 FOREIGN PATENTS 975,373 7/1962 Great Britain l28/2.06
2,003,235 1 l/ 1969 France 128/6 Primary Examiner-Channing L. Pace Attomey-William R. Liberman ABSTRACT: The disclosure relates to endoscopic instruments. The instrument is supplied through a circuit including a stepdown output transformer. A secondary winding of the transformer is connected with a light source of the endoscope. A push-pull oscillator circuit is connected with the primary winding of the output holdup oscillator circuit is connected to a current source and is arranged to supply current to the primary at a frequency of not less than 15 kHz.
PATENTEU JULZ'I ls'n SHEET 1 [1f 2 INVENTOR 7'06! Bark AT TORNEY ENDOSCOPIC HAVING ILLUMINATION SUPPLY UNIT This invention relates to endoscopic instruments and to means for supplying such instruments with electric current.
Endoscopes are instruments which are used for the examination of body cavities and are of many different types; for example, oesophagoscopes, bronchoscopes, gastroscopes and cystoscopes for viewing the oesophagus, bronchi, stomach and bladder respectively. I
A conventional endoscope includes a rigid or slightly flexible tube, which can be inserted in a body cavity and which is illuminated by a small lamp at the distal tip of the tube. The tube contains a series of lenses which form an image of the illuminated cavity at the eyepiece fitted to the proximal end of the instrument. The lampis supplied with an electric current at a low voltage (about 4.5 v.) by means of a wire passing through the instrument tube. The tube of the instrument also forms a conductor to complete the circuit to the lamp. The source of electric current is either a battery, which supplies direct current, or a transformer providing a low voltage at the frequency of the mains supply, normally 50 Hz.
Endoscopic instruments of this type, in particular cystoscopes, can, under certain conditions, cause the patient undergoing endoscopic examination to receive an electric shock. While this shock is unlikely to be serious, the violent muscular contraction produced can be very disturbing to the surgeon and the theatre staff, particularly as they are often uncertain of the cause of the electric shock and this may, in some cases, result in the endoscopic examination being abandoned. The cause of such an electric shock is often an open circuit, or high resistance at the junction between the tip of the tube and the lamp cap which allows supply voltage to appear between the patients body and any nerve in the tissues with which the tip may be in contact. Although the low voltages used in endoscopy do not normally produce an electric shock when applied to the skin, which has a fairly high resistance to the flow of electric current comparatively small voltages are sufficient to stimulate muscle contraction when contact is made with an internal organ, for example a nerve within the bladder. Stimulation of this nature may occur whether the endoscopic instrument is supplied from a battery box or from the mains supply via a transformer.
An object of this invention is to provide an endoscopic instrument with which there is no risk of the patient receiving a stimulating electric shock during the examination.
Accordingly, this invention provides an endoscope with a light source; a stepdown output transformer having primary and secondary windings, the secondary being connected with the light source; and the push-pull oscillator circuit which is connected with the primary of the transformer and also has means by which it can be connected to a source of electric current, the said circuit being arranged to supply currentto the primary at a frequency of not less than 1 5 kHz.
It is well known that a high frequency current above kHz. will not produce any sense of electric stimulation in the body tissues.
This invention is not applicable to endoscopes which employ light conducting fibers to transmit light from an external source to the tip of the instrument, but is only applicable to instruments having a bulb at the tip of the instrument.
The oscillator circuit can be supplied from either an electric battery or from an electric mains.
The supply generator of an endoscope according to this invention avoids any electric shock hazard. In addition, it has several other safety factors. Thus, it preferably operates at 100 kHz. to provide a power output of 3.5 watts at 6 v. The light obtained is therefore brighter than that normally obtained from endoscopic lamps, at 4.5 v. if the normally permitted maximum safe voltage with a 50 Hz. supply.
In the accompanying drawings,
FIG. I is a diagram of an endoscope with a mains operated generator or supply unit,
FIG. 2 is a diagram of a battery-operated generator or supply unit.
In the embodiment illustrated in FIG. 1 an endoscope 1 has a light source 2 supplied by a generator which includes a pushpull oscillator circuit with a high frequency output. The circuit includes a pair of low-power silicon transistors Q1 and Q2 and supplies current to the primary SI of a stepdown output transformer T2. The secondary S2 of the output transformer is connected to the electric lamp 2 of the endoscope. The output is preferably at a frequency of kHz. with a power of 3.5 watts at 5 v.
The oscillator circuit includes rectifier DI and D2, low power silicon transistors Q1 and Q2, resistors R1. R2, R3 and R4 and a capacitor C2. The circuit is supplied from a supply circuit which includes the secondary S1 of a supply transformer Tl, a full wave rectifier MR1 and an intensity control RVl for varying the voltage of the supply current. The supply voltage is conveniently 15 v. DC The primary P1 of the supply transformer T1 can be connected to a mains supply.
The intensity control RVl is arranged to control the power input to the oscillator and thus avoid the power loss which would occur if the control was in the output of the oscillator circuit.
With this arrangement there is double electrical isolation between the mains supply and secondary winding S2 of the output transformer T2 by reason of the normal electrical isolation between the primary and secondary of each transformer thereby eliminating any possibility of a dangerous voltage occurring at the output even under fault conditions. With conventional transformers used for providing low voltage current at the mains frequency, there is only one insulation between the mains voltage and the output.
lt is important that the secondary S2 of the output transformer T2 has a very low capacitance to earth, when the generator supplies an endoscope used in combination with diathermy apparatus, such as a resectoscope used particularly for carrying out surgery in the bladder. With a high frequency supply this is simply achieved by the small size and small number of turns in the secondary S2.
The tissues of a human body are cut by means of a high frequency current passed through a diathermy electrode, and the surgeon can observe the progress of the operation by means of the associated endoscope. In such instruments, the diathermy current passes through a conductor very close to the lamp 2 of the endoscope and therefore has a high capacity to it. Sufficient diathermy current can be passed via this capacity and through the liquid in which both the electrode and the lamp are immersed to cause failure of the lamp. When this happens, as is frequent with resectoscopes, it is necessary to remove the instrument from the patient, and change the lamp, which is very time consuming and inconvenient during the examination procedure. As the secondary of the output transformer in this invention has a very low capacitance to earth there is a high impedance to the diathermy current in the lamp circuit sufficient to reduce the current well below that required to blow the lamp. This safety factor is difficult to incorporate into a direct mains powered circuit.
A pilot lamp PL] in the supply circuit indicates when the instrument is switched on. The supply circuit includes an inductance L1 in series and a capacitor C1 connected across the circuit.
Means are provided for reducing the output current to zero if a short circuit occurs within the endoscope. As is inherent in the present oscillator circuit such a short circuit causes the oscillator to stop immediately by reason of the excessive load across the resonant circuit and therefore the output to fall to zero. Such short circuits occur because endoscopic instruments have only small clearances between the inner conductor and the body tube. Therefore damage or misalignment can readily cause such a short circuit. Under these circumstances quite a high current may flow through the instrument, which can produce local heating. This may cause burns inside the body, especially as the patient is usually anesthetized, and
therefore the burning may be undetected for some time. Normally, there is a current limiting lamp in the circuit if the current is provided from the mains via a transformer, but this invention provides greater safety as the current limiting is more effective. Another danger associated with the occurrence ofa short circuit is that a spark may be produced which may cause an explosion if a flammable anesthetic gas is being used. The results of this explosion may be extremely serious to the patient, particularly if an endoscopic examination of the lungs is being carried out when the explosion occurs.
PK]. 2 illustrates a modification intended for battery operation. In this arrangement an onoff switch SW1 is connected in series with the terminals ofa battery and the pilot lamp FL] is connected across the circuit.
What we claim is:
1. An endoscope with a light source; a stepdown output transformer having primary and secondary windings, the secondary being connected with the light source; and a pushpull oscillator circuit of a frequency not less than kHz. which is connected with the primary of the transformer and also has means by which it can be connected to a source of electric current.
2. An endoscope as claimed in claim 1 wherein the oscillator circuit is connected with a supply circuit including a primary adapted to be connected to an electric mains and a secondary connected in the supply circuit, a full wave rectifier and a means for controlling the voltage of the current supplied to the oscillator circuit.
3. An endoscope as claimed in claim 1 wherein the oscillator circuit is connected with a supply circuit energized by an electric battery, the said circuit including a switch connected in series with the battery and a capacitor and a pilot light, connected across the circuit 4. An endoscope as claimed in claim 1 wherein the oscillator circuit includes a pair of low power silicon transistors.
5. An endoscope as claimed in claim 4 having means for switching off the oscillator when there is a short circuit in the endoscope.