US3409737A - Foetal monitor - Google Patents

Description

NOV 5, 1968 M. sETTLr-:R ETAL 3,409,737

FOETAL MONITOR Filed June 24, 1965 zoK 2 1? 2 2 44 MONITOR 23 45 L2oj l L2o lzo I 47 F 1S. 6 FIS. 5 /nf/xwfulr.'

10M-r .Cfmfz www United States Patent 3,409,737 FOETAL MONITOR Morris Settler, 590 vNiagara St., and Bert Settler, 723 Queenston St., both of Winnipeg 9, Manitoba, Canada Filed .lune 24, 1965, Ser. No. 466,634 1 Claim. (C l. 179-1) ABSTRACT OF THE DISCLOSURE Foetal heartbeat is monitored by a plurality of transducers mounted on an elastic belt. A switch selects which transducer is fed to the amplifier which has a filter for discriminating between the foetal heartbeat and the mothers heartbeat.

This invention relates to new and useful improvements in foetal monitors. Y

Occasionally a foetus dies in the womb during labor without sufficient warning. This may occur in an otherwise normal labor but is more likely to occur in more specific obstetrical situations.

The alteration of the normal foetal heart rate is an important sign in the diagnosis of intrauterine foetal distress.

The object of the present invention is to enable the detection of very weak foetaly sounds against the background of the maternal sounds and maternal muscular movement during labor.

A further problem of detecting foetal heart sound is the constant change of position of the foetus in the womb.v

By providing a plurality of transducers, independently connectable to the amplier, the attendant is provided with a continuous audible or visible monitoring of the foetal heartbeat during labor.

Our invention also includes a novel belt to hold the transducers in constant contact with the patient and a resilient link is provided to accommodate the expansion and contraction of the abdomen during labor.

This is important inasmuch as it is essential to maintain the continuity of the foetal heart sound during a contraction and it also prevents the early or premature col-l lapsing of the microphones or transducers if excessive pressure is encountered. i

Also provided in the amplifier is an output jack to record the foetal heart sounds graphically. It is therefore possible-to provide phonocardiography of the foetal heart sounds. A tape recording may be made of the sounds from the output jack and a pen lrecording may also be made at the same time which will permit the operator to study visually what has been heard aurally and to analyze more intensively and in greater depth, the significance of these foetal heart sounds.

The device uses rechargeable batteries and desirably 3,409,737 Patented Nov. l5, 1968 ice foetal heartbeat contrasted to the relativelydslow rise and decay and relatively wide width of the maternal heartbeat.

I The device is useful in diagnosing anticipated caesarian delivery, to observe the effects of drugs administered to the mother, `on the foetus, to determine the effects of the birth process on the linfant and to monitor the heartbeat contains two separate batteries. One is required to energize the two coupled amplifiers and the other is used to energize the output stage.

Because of the high gain required, separate power sources are desirable to overcome feed back and interference between the two components.

Another feature of the present device is that it is completely transistorized and is therefore light, portable and relatively inexpensive, safe and free from any electric or explosive hazards and simple and easy to use.

A significant feature of the present invention is the detection and amplifying of the foetal heart sounds to the total exclusion of maternal heart sounds, a fault prevalent in all other foetal heart monitors at present in use.

We obtain this result by the selection of a capacitor coupling the two amplifiers together which is only triggered by the relatively sharp rise and narrow width of a of a foetus being transfused by intrauterine, intraabdominal method.

` In this particular type of operation, due to continuous monitoring, it is possible to monitor the condition of the foetus during the insertion of the needle, plastic tube, and eventually the transfusion of the blood.

A graphic recording of the heart sounds can also be obtained during an operation of this type which permits subsequent analysis to be made.

With the foregoing in view, and all those objects, purposes or advantages which may become apparent from consideration of this disclosure and specification, the present invention consists essentially of the inventive concept embodied in the method, process, construction, arrangement of parts, or new use of the same, as herein particularly exemplified, in one or more specific embodiments of such concept, reference being had to the accompanying figures in which:

FIGURE 1 is a schematic wiring diagram of the electronic portion of the device.

FIGURE 2 is a front elevation of the belt carrying the transducers.

FIGURE 3 is a schematic view of' the belt showing the three position switch and the connections to the electronic portion.

FIGURE 4 is a schematic representation of a graphical recording of a foetal heartbeat.

FIGURE 5 is a view similar to FIGURE 4 but showing a maternalheartbeat.

FIGURE 6 is an enlarged longitudinal cross sectional view showing the mounting of the transducers within the belt.

In the drawings like characters of reference indicate corresponding parts in the different figures.

Proceeding therefore to describe the invention in detail reference should first be made to FIGURE 2 which shows the belt collectively designated 10,

This consists of an elongated length of flexible, nonextensible surgical belting or the like 11, having a plurality of eyelets 12' secured to one end 13 thereof. 1

-A flexible rubber link 14 is secured to the other end lan an eye hook 15 is secured to the end 16 of this rubber This hook is adapted to be engaged in any one of the eyelets 12 depending upon the girth of the patient so that the belt may be snugged secured around the patients abdomen and yet can extend and contract therewith.

Intermediate the ends of the belt 11 is secured a further length of belting 17 by stitching 18, forming a rein,- forcement and having eyelets 19 formed therethrough to hold the transducers or microphones 20 in spaced apart relationship as clearly seen. 1'

In this connection, studs 20' are connected to the rear of the transducers and engage through the eyelets 19. Electrical conduits 21 extend Ifrom these microphones to a common cable 22 and thence to a multiposition switch 23 which is adapted to select and connect any one of the electrical conduits 21 to the input 24 of the amplifier section.

The switch is shown schematically in FIGURE l and as this switching is conventional, it is not believed necessary to describe same further.

FIGURE 1 shows the electronic circuit relative to the amplifier and includes two rechargeable batteries 25 and 26.

l 3 The charger input 28, or, alternatively, to power the amplifiers, the positive of the battery 25 being connected to the Bplus-29-andthe negative .of the batteryto the negaive side 30. A o

The battery 26 is specifically for powering the output amplifier collectively designated 31 which inturn is connected toa speaker 32, the volume of which maybe adjusted by means of variable resistor 33.l

The amplifier comprises two multistage amplifiers, co1- lectively designated 34 and 35, coupled together by means of a capacitor 36. The input 24 is connected to the transistor 37 of the first amplifier 34 and the signal is then fed to .the second stage transistor 38 and thence to the third stagetransistor 39.

.ln this connection We use an NPN transistor at stage 37 and connectthe input to the emitter of this transistor. By ensuring that the polarity atthe input signal is positive, we have found that the sensitivity of the device is increased approximately threefold, compared to the sensitivityif the polarity is negative. l

. The output from transistor 39 is then passed through variable resistor 40 to one side of the capacitor 36 and thence to the input of the first transistor 37 of the second amplifier 35. y

The signal then passes to the second stage transistor 38 of amplifier 35 and then to transistor 39 of this amplifier.

From'there the signal passes through transformer 41 to the output amplifier 31 which is conventional in construction. l -It is sometimes desirable that the signal be visual rather than aural in order that the foetal heartbeat is not heard by the expectant mother. This visual recording enables the operator to count visually by the swing of milliammeter 41 in circuit between the primary side of transformer 41 and the B plus voltage.

A recording output 42 also extends from the outputof the transistorr39' through smoothing condenser 43 and this recording output may be connected either, to a pen recorder (not illustrated) or a tape recorder (also not illustrated).

Also provided is an additional speaker outputjack 32 which can be connected to a remote speaker or station or multiple of speakers or stations which relieves the nurse of the necessity of remaining at the patients bed- ,side inasmuch as one nursel can monitor a plurality of patients at one location.

` The first amplifier 34 triggers the second amplifier 35 through the coupling capacitor 36 and the value of this coupling capacitor is .such that the maternal heartbeat pulses have no effect n the triggering action.

FIGURES 4 and 5 show schematically the difference between a 'foetalheartbeat pulse and a maternal heartbeat pulse.

The foetal heartbeat pulse is characterized by a relatively steep rise 44 and a relatively narrow width 45 whereas the maternal heartbeat is characterized by a relatively slow rise 46 and a relatively wide width 47.

Y, Thesecharacteristics decide value of the capacitor 36 so that only the steep, sharprise of the foetal impulse will trigger the second amplifier 3S.v

eliminated entirely from thewdevice so that only the foetal heartbeats are monitored.

The adjustable resistor 40 between the first amplifier 34 and the capacitor 36 also assists in the selection of the signal strength at this .point-in order to eliminate the undesirable maternal heartbeat impulse from the yinstru'- ment. v

In operation, the `belt'is secured around the abdomen of the mother and the switch 23 is utilized to locate the position of the foetus, by detecting the point of maximal signal.

Since various modifications can be made tov=the invention herein described within .the scope of the inventive concept disclosed, it is not intended that protection of the said invention should be interpreted as restrictedv to the modification or modifications or known parts of such concept as have been particularly described, defined, or exemplified, since this disclosure is intended to explain the construction and operation of 'such concept, and not for the purpose of limiting protection to any specific embodiment or details thereof.

Whatwe claim as our invention is:

1. Means for detecting foetal heartbeat comprising in combination an elongated belt, a plurality of transducers mounted upon -said belt in spaced apart relationship, a resilient link secured to one end ofl said belt, fastening means on yboth ends of said belt cooperating together to secure said belt around the abdomen of the patient, said resilient link permitting expansion andcontraction of the belt within limits responsive to expansion and contraction of the abdomen thereby maintaining said belt at a relatively constant tension, electrical conduit extending from each of said transducers, a multistage switch connected to said conduits, a further electrical conduit extending from said switch, said switch connecting any one of said first mentioned conduits to said last mentioned conduit, a pair of multistage amplifiers coupled together by means of a resistance-capacitance filter, said single electrical conduit from said switch being connected to the input of one of saidampliers, an output amplifier connected to the output :of the other of said amplifiers, and speaker means connected to said output amplifier, said resistance-capacitance coupling ybetween said amplifiers having values whereby said second amplifier responds only to pulses having'a steep attack characteristic and a narrow pulse width as characterized by the heartbeat of the foetus.

References Cited UNITED STATES PATENTS OTHER REFERENCES IBM Tech. Disclosure, Respiration Transducer, G.. R. Willis, Novemberl963.. v

KATHLEEN H. CLAFFY, Primary Examiner. R.v P. TAYLOR, Assistant Examiner.

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