CA1177894A - Process and device for regulating the stimulation frequency of heart pacemakers - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A process and a device for regulating the stimula-tion frequency of heart pacemakers are disclosed. The process comprises generating with the aid of light emitted by a light-emitting element, reflected by the blood of a patient, and received by a light-receiving element, a current flow which causes, in a measuring probe, an increasing of the current flow at a constant probe voltage or a damping of the probe voltage at constant current flow. Thereafter, one of the possible changing values is measured and the change, with time, is evaluated as a measured quantity proportional to the charge, with time, of the blood oxygen saturation, and, as a function of the measured quantity, the stimu-lation frequency of the heart pacemaker is regulated in such a manner that the greatest possible blood oxygen saturation is always achieved with the lowest stimulation frequency. The device for practicing the invention comprises a measuring probe containing at least one combination of only two active optoelectronic elements, one light-emitting element and one light-receiving element; a control circuit electrically con-nected to the measuring probe; a stimulation catheter in which the measuring probe is incorporated, and at least two electric lines leading through the stimulation catheter and electrically connecting the measuring probe to the control circuit of the measuring probe.

Description

13l778~3~

"Process and device for regulating the stimu-lation frequency of heart pacemakers"
This invention relates to a process and a de~lce for regulating the stimulation fre~uency of heart pace-- makers. The devlce can thus be used in all patients requiring a heart pacemaker.
The invention has the aim, in heart pacemaker , patients, of optimally covering the oxygen demand of the body via the blood circulation, so that the pulse fre-~; quency of the heart, 2S in the natural case, adapts itself to the particular load conditions, the optimum hemodynamic situation being found by the pacemaker itself.
In spite of the extended pacemaker function, the ; invention has, at the same time, the aim of virtually not changing the hitherto well-proved embodiment of the heart pacemakers and the associated pacemaker catheters, so that the known implantation techniques remain the same and, also, the high requirements with xespect to ` the long-term use can be fulfilled.
', In the case of heart pacemakers, controlling the ~r~ 20 pacemaker frequency via a measurement of the central venous oxygen saturation and thus adaptlng the frequency to the particular load conditions has already been described in German Published Patent Application No. 27 17 659. In this known process, ~he measurement 25 of the blood oxygen saturation is carrled out with the aid of a light-guide probe which is incorporated in 78~L
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., `' !~,` the stimulation catheter. The measurement principle of reflectLon ox1metry, which ls used ln the proces~, i5 based on the determination of the reflection intensi-ties of light of the measured wavelength of 660 nm (R660) ~ 5 and of the reference wavelength of approximately 800 nm `~; (R800~ ln the blood. A characteristic of the applied frequency adaptation is a firm association of the pace-maker frequency f wlth each determined measured value of the oxygen saturation S02 f = k S02, wherein fmin~ f < fmax-values for k~ fmin and fmax must be fixed ~ before the implantation.
`~ Furthermore, it is known from German Published Patent Application No. 21 13 247 that the ratio of the ;; 15 two measured values R800/~660 is directly proportional r.,' ~
to the blood oxygen saturation So2 expre sed by the rat~o ObO2 Hb (wherein ~b represents hemoglobin and HbO2 represents oxyhemoglobln).
The heart pacemakers constructed accordlng to the principle indicated in German Published Patent Applica-; tion No. 27 17 659 exhibit a number of problems whlch :., have hitherto hindered a clinical use of pacemakers of this kind:
The measurement method does not tolerate any changes in the optical transmission path ~light guide, _ 2 _ , :

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reflection space and coupling polnts), whlch cause a wavelength-dependent effect on the slgnal.
This can occur through defect~ve coupllng points;
material changes in the llght guide; deposlt~ on the S light opening in the catheter, and forelgn object~ in the reflection region (heart wall, trabeculae).
Furthermore, the control of the pacemaker frequency in dependence on the oxygen saturation, according to a fixed prescr~bed characteristic curve, can have dls-advantageous consaquences ~f, on advancement of the ; basic cardiac illnes~, a change in the relationshlp of power of the heart to pulse Prequency occurs. A deterlo-ration in the hemodynamics can even occur through too . great an increase in the frequency.
The measurement principle and control princlple ~ require a calibrat1on before the implantatlon and : correspondingly increase the service requirement5.
In addition, the catheter has only a llmited ~er-viceability, since the end supports of the llght guides become unstabl~ over long periods because they have to accept the greatest part of the tensile ~train actlng on the catheter.
~n addition, the fatigue strength of the light guides for long-term use is not given with the materials available at present, and ~he necesslty of arranging the light aperture laterally ln the comblnation ; 3 ~L7~8~
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catheter allows no margin technically for the further lntroduction of a mandri~ (3teel wire which ls pushed lnto the highly elastic catheter during the :. implantation, ~n order more easily to introduce the .. ` 5 catheter ~nto the ventricle) beyond thi~ point. In - addltion, the coupling system between the combination . catheter and the pacemaker is much more complicated in . .
c the production, sensitive in use and volumlnous than ln the case of conventional pacemaker technology.
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.. ; 10 Since the energy losses while using the light-~: guide technique and the measuring prlnciple mentloned can only be kept small by means of high optical precision, ~'~ the costs for the total system compared wlth convent~onal ~':. technology increase several-fold.
~;~ 15 It i~ an object of the present inventlon to avoid ;~, tha disadvantages described above and to provide a ",,.
measuring process and a device for the determlnation of .` the blood oxygen saturation.
- Another object of the present invent~on 18 to i 20 provide a process and a devlce for xegulating the :, stimulation fre~uency of heart pacemaerks so that a long-: term, undisturbed data acquisition and the best possible hemodynamic situation in the blood circulation are . ensured, and at the same time the operational sa~ety is not decreased but increased as much a3 possible, it being intended to employ non-critical servicing and ~L77~3~

production practices which have been proved technlcally over long periods of time.
To attaln these objects the present invent~on pro-vides a proces~ for regulating the stlmulatlon freguency of heart pacemakers which comprises the ~teps of generating with the aid of light emitted by a llght-.~ emittin~ element and reflected by the blood of a ` patient, in a light-recel~lng element, a current flow which causes, in a measuring probe, an lncreasing o~ the current flow at a constant probe voltage or a damplng ; of the probe voltage at constant current flow;
measu~ing one of the possible changlng values; evaluatlng the change, with time, as a measured quantity propor~
.` tional to the change, with time, of the ~lood oxygen saturation, and regulating, as a function of the measured quantlty, the stimulation frequency of the heaxt pacemaker in such a manner that the greatest possible blood oxygen saturation is always achieved : with the lowest stimulation frequency.
'~ 20 For carrying out this process, the present lnventlon provides a device for the frequency requlation of heart pacemakers havlng a stimulation frequency which adapts itself to the load condltions o a patient, tha central venous blood oxygen saturation being opto-electronically measured as a reference or control quantity for the adaptation, this measurement being carried out wlth ~7t~
.:', the aid of an intracardiac measuring probe, and the acqulsitlon and evaluatlon of the mea3ured value occurrlng by means of a circuit additionally arranged in the heart pacema~er, ~ald device comprislng a S measuring pro~e ~ontalnlng at least one comblnatlon '~ of a single active light-emitting element and a slngle active light~recaivlng element; a control circuit electrically connected to the mea~uring probe;
a stimulation catheter tn which the measuring probe t~
~: 10 incorporated, and at least two electric llnes leadi~g throuqh the stimulation catheter and electrically con-necting the measuring probe to the selectlon circuit of the measuring probe.
~he advantages which are achieved with the invention are as follows:
-. The cathetex with the measurlng probe i6 vlrtually identical in its mechantcal construction with the bi-polar catheters which have long been in use, and , accordlngly enta~ls no additional problems with re~pect to the long-term mechanical strength and the implanta-tion technique and has the best propertles wi~h respect to a long-term optical measurement of the blood oxygen saturation.
The data acquisltion makes it po~slble to manage with only two electric lines in the form of wire windings ~n the catheter, and thus to use the well-proved catheter ~78''39L

techniques, The data processin~ makes it posslble to measure, with uniform accuracy, normal variations with tlme in the body load of the patient, independently of very ;~ 5 short or long-term changes along the measuring dlstance.
~; The regulating process for adapting the stlmulation .~, frequency to the load~ of the patient makes posslble a ~, dixect re-adjustment ln the case of varlations lnthe ': load as well as an autonomous optimum regulatlon ln the context of a best possible oxygen Rupply wlth as small a heart load as possible, thu~ a~low a stimula--~ tion frequency as possible.
r ~ The detection of exrors makes poRslble the recog-nition of failures ln the data acquisition and evaluatlon ., 15 and due to break~ in the electric linefi in the catheter, ; and makes possible the known use of two llnes for the vital stimulation.
~ Two embodiments of the in~ention will now ~e - descrlbed by way of example and with reference to the accompanying drawings in which:
Fig. 1 is a diagrammat~c view show~ng a heart pace-` maker with a stimulation catheter and measuring probe for stimulatlon of a heart muscle;

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~`~; Fig. 2 is a longl~ud~nal section, on an enlarged scale, through the measuring probe provlded by concentrically arranged elect~lc llne~
in ~he form of wire wlndlng~;
~' 5 ~lg. 3 is a longitudinal section through a f urthex embodiment oP a measurlng probe wlth electrlc lines ~ n the form of wire windlngs arranged ;' ln parallel;
Fig. 4 is a section along line IV-IV of Fig. 3;
Flg. 5 is a section along llne V-V of Fig. 3;
Plgr 6 1~ a ~chematlc diagram of a control circult o the measuring probe~
` Fi~. 7 is a circuit of the measurlng probe;
`~ Flg. 8 is a diagrammatic view showin~ th~ current-voltage Gharacteristics of the measurlng . probe;
Fig. 9 i~ a schematic dlagram of a ~lgnal converter ci~cuit;
Fig.10 is a block dlagram of a heart pacemaker, and Fig. 11 1 s a schematic dlagram of the variativn of the stlmulatlon frequency w~th time, a~ a function of the central venou~ blood oxygen saturation.
Fig. 1 shows a heart pacema~er H5 contalnlng a power supply component Ba, an electronlc clrcult compo-nent Sch and a blpolar electrical connector EK~ A blpolar 3~7t7~3~3~

electrlcal plug ES of a stlmulation catheter K ls flrmly screwed lnto the electrical connector EK. The stlmula-tion cathe~er K leads via the superlor vena cava HV
lnto the right auricle RV and then into the right ven-~ 5 trlcle RH~ of a patlent, so that, at this point, the ;' blood oxygen saturation iæ measuxed by a measuring probe M and the heart muscle H is stimulated by a . stimulatlon electrode E.
Two embodiments of a measuring probe ar shown in more deta$1 ln Fig, 2 and in Figs. 3 to 5, respectlvely.
There are essent1ally two forms of construction of the bipolar stimulation catheters in use at the pre~ent tlme.
: In both forms of construction, the two electric lines are ~ wire windings 30 and 36. The wire winding~ 30 and 36 are :~ 15 arranged concentrically with one another ln the embodi-~. ment shown in Fig. 2, whereas in the embodiment shown ln : Figs. 3, 4 and 5 wire winding~ 301 and 361 are u~ed which extend parallel to each other.
In the embodiment as a combined measuring catheter and stimulation catheterr both wire winding3 30 or 301 and 36 or 361 serve as a supply line to the st~mulation elec-; trode E and al~o as the current supply to the mea~uring pro~e M. The electrical contact with the measurlnq probe M occurs via a first metallic annular element 31 tn ; 25 Fig. 2 and a flrst metallic annular element 311 in Fig. 3.
This first annular element has an inner thread which g `:
~ 1~7 51~3~
~: `
.~ en~ures a permanent pre~sure contact, and simultaneou~ly :. serve~ as a carrier for at least one llght-transmitting elemant 32 which is a red-light-emittlng diode ln each .
; case and which ls in contact, e.g. in adhe~ive contact, ....
; 5 at the cathode side, with the first metalllc annular ~ Y,.
; element. Furthermore, the first metalllc annular element is electrically connected via threaded and/or pressure contact, w~th a wire winding 33 in Fig. 2 and 331 in Fig. 3 each of which also lead~ to the ~timulation electrode E and is provided as a spare component, as a safety deYice for the ~tlmulatlon~ An annular insula-tion 35 in Fig. 2 and 351 in Fig. 3 which is firmly ` adhesively ~onded is mounted between the plug-side par~
of the first metallic annular element and a second annular metallic element 34 in Fig. 2 and 34 in Fig. 3.
The second annulax metalllc elemen~ ha~ threaded and~or pressure contact with the probe line, i.e. with the wire winding 36 in Fig. 2 and 36 in Fig. 3, and serve~ as a carrier for one or more light-recelvlng element~ 37 which may be a phototransistor in each ca~e. If a bridging diode Do, not shown in Flgs. 2 and 3, l~ not integrated ir. the light~receiving elem~nt or the light-emitting element it must be additionally attached, a~
an individual element, to one of the two annular ele-ments 31 or 34 in Fig. 2 or 311 or 341 in Fig. 3. The ; second ~upply line to the light-emittlng and l iqht-;1 :
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.., receiving elements 32 and 37 (or to the ~ridglng diode) ls, in each case, a bond wlre 38 fxom the opposite ., annular element.
As a protection for the light-emittlng and light-receiving elements, a transparent protectlve jacket 39, pr~ferably a glas8 ring, s~rround~ the body of the measuring probe composed of the two annular metallic elements, the glass ring 39 being firmly welded at its edges to the metallic annular ~lements which are mutually lnsulated.
An electrically insulating tube 40 serves a~ an insulation between the ~upply lines, l.e. the wire windings, and, on the other hand, an outer transparent insulating tube 41 serves as an insulation, from the ex-terior.
Fig. 7 shows the cixcuit of the measur~ng probe M
consisting of the light-emltting element 32 tn th~
form of a light diode~ the light-recelvlng element 37 ln the form of a npn-photo transistor, and the bridgin~
diode Do, In Fig. 8, the functional principle of the measuring probe M can be recognlzed with reference to ~ts current-voltage characterlstics 42 and 43. If a re-flecting object 44 is lack~ng in the mea~uring arrange-z5 ment of Fig. 7, the I~U characteristic 42 ~esults, However, if light from a reflecting object 44 (in the 1177E~
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.
: present case, blood) stxikes the li~ht-recelvlng ele-. .j ment 37, the I-V characterlstlc 43 results.
At constant current IK, the lntenslty of th~ re-flected llght is thus proportional to the change ln the voltage ~ Us, and corre~pondingly,at constant : voltage Ux, proportional to the current ehange ~ IS.
The above-mentloned comblnation of ~ight-emittlng element and light-rece$vlng element retains the principle of its mode of unction, even when connected in parallel wlth one or two further combinatlons.
Fig. 6 ~hows by way of example an embodlment of a -~ control circult of the measurlng probe, which clrcuit produces a pulse with a constant voltage characterl~tlc at the supply lines, i.e. at the wire windings, to the measuring probe~ o that the characterlstic (response) curve of the current IS through the mea~urlng probe i~
; dependent on the reflected light acc0pted by th~ measuring : probe and thus al~o the voltage characteristic ~t load resl~tance ~v~ Thu~, tf the probe voltag~ Us , ~ 20 reache~ a flxed value UK, the measured voltage UM at .i: thi~ moment i8:
UM = IS-Rv and thus proportional to ~he intenslty of the llght raflected by the blood and accepted by the mea~urlng : ~, : 25 probe, the reflection factor of the blood, according to the wavelength, being a function o~ the blood .' .

:`

~L7713~14 oxygen saturation.
Fig. 9 shows the functional principle for an analog cixcuitry of the signal converter ~. The measured signal UM, consi~tlng o~ a positive measured pulse UMM
arriving in th~ pulse phase T1 and a negative error-detection pulse -UMF arriving in the pul~a pha~e ~2 i8 thu~ recelved by two sample and hold circuits S+~l and S+H2 80 that the ~torage S+H1 store~ the amplitude of the mea~ured pu1se UMM via a switch S1 closed in the pulse phase T1 a~d the other storage S+~2 stores the , amplitude of the error-detection pul~e -U~ via a switch S2 closed in the pulse phase T2. In the following -~ ~ummation circuitry ~he signal values UM and U~F are ~ evaluated in such a manner that the measuring error `` 15 included inthe measured pulse and caused by changes in the resistance of the wire windings 30, 301 and 36, 361 .~ and a temperature drift of the optical measuring probe M
is elimi~ated.
The most important functions of the heart pacemaker -: 20 accordlng to the inventlon are represented in Fi~. 10.
In this figure, the areas enclosed by broken llnes lndicate the major functional units and denote, in particular:
I Catheter;
II Catheter control;
III Evaluation of measured values;

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IV Frequency regulatlon~
V Proyram control, According to ~lg. 10, a fixed-fr~quency pulse gene~
: rator 1 gives the time base for a program control 2 S which controls all the measuring and xegulating processe~
of the pacemaker circult.
Depending on a tlme code prescrl~ed by a stimulatlon frequency generator 3, the program control 2 ~tarts the transmlsslon of the stimulation pulse by a stlmula-tion pulse generator 4 via a stimulatlon electrode 5, and dlrectly subsequently the measurement of the blood oxygen saturation via the measuring prob~ M w~th a ~; measuring probe control circuit 7. The measured signal is evaluated and ampl~fied in a signal converter & and, ~ 15 in the case o using digital data proces~ng, is con-:.~ verted into digital form. ~n integrator 9 forms the .~
,h average value of the measured signal~ over a pre~cribed perlod of time. Storages 10 to 15 acGept the integrated signal value, the storages 10 and 11 alternately in tlme ~o period ~ t1 and the ~torages 12 and 13 alternately in time period ~t4. The highest measured 6lgnal value occurring in a prescribed time range ~ to ls stored in the maximum value storage 14, and the lowest value ln each case is stored in the minimum value storage 15.
In a difference-former 16, the dif~erence ~ S02 in the measured value hetween the naw and each of the ;:
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previous measured slgnals in storage 10 or storage 11 i~
determined and in a difference-former 17 the difference in the measured value between the contents of storage 12 or 13 i5 determined. In a difference-former 18, the S maxlmum measured value variation range is S02maX-SO2min~
~ S02max, ~o that the ratio, determined in dividers 19 and 20, of short-term measured value varlation to .~ maximum variation range yields a normallzed measured : quantity BS in each case:
aSO2- ~to 02max- at1 1~) ~ In the frequency regulation IV, a comparator 21 `. determines whether the change in the normalized measured quantity ~ BSl with time is larger or smaller than a predetermined value + A1 or - A1.
In a stimulating frequency control 23 which follows, a change is effected in the ~timulation fre-quency by a positive value + ~ f in the case in whlch ~ BS1 C -A1 and by a negative value - ~ in the case ln which ~ BS1 > ~A1, and the slgn of the change i8 stored in a storage 24. In the case in which -A~< ~ BS1 ~ + A1, a change in the stimulation frequency ls automatically initiated in the frequency control 23, after a fixed pre-determined time interval a t5, the sign of the change being opposite to that which is retained ln the storage 24, as long as the tendency control 25 does not effect a ;' ; -15 -,. .

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repetition of the sign. After the prescribed time lnter-val ~ t4, a comparator 22 assesses whether the change in the measured quantity ~ Bs4 is larger than a flxed value A2 or smaller than -A2, whereupon the preceding frequency change is either reversed or rema~n~.
An error detection 26 compares the ~ignal received by the data evaluation with allowed limltlng values and sets the stimulation frequency genexator 3 to a fixed frequency fO if these limiting values are exc~eded, and short-circuits, via a switch 27, the two catheter connections, whe~eby the measurement and regulation are put out of action.
In an electrocardiogram amplifier 28, the lntrinsic activity of the heart is monitored between the stimula-tions, and, in the case of a self-excitation of the heart, the stimulation by the pulse generator is hindered via a comparator 29.
~ig. 11 shows the regulation, according to the invention, of the heart pacemaker stimulation frequency as a function of the load of the patient, represented by the relationship in the variation, with time, of the measured value of the blood oxygen saturation So2, the ; changes thexein per time unit ~ t1 and ~t~, and the change in the frequency f e~fected thereby.
At the be~inning of a load phase BP, the central venous oxygen saturation So2 decreases, that is to ;~ - 16 -~77~

say, the change per time unlt ~ tl, relatlve to a maxlmum variatlon rAnge a S02max/ ~ to between the llmiting values 02max and S02min, gives a negative value for B
If this is smaller than -A1, a frequency change by + ~ f1 S follows automatically durlng the course of the time lntex-val ~ t2. If, in contrast, the oxygen saturation S02 reaches, in the load phase BP, a certain equlllbrium state, so that the value of BS1 oscillates between -A1 ~ .
and +A1 7 the optimum regulatlon begins, in particular . 10 always with a positive fxequency change ~ a f2 after ~ t5, at first, to provide a ~etter supply of oxygen. If this t ~ f2 causes an ~ncrease in the So2 value during the course of the time unit ~ t4, and if this value, agaln 02max~ ~ t~,is greater than a fixed value + A2, the frequency change is retained and inltiated at the same time, owing to the positive result, a further increase of the frequency by a f~ after further a t5. If ; this does not yield a positive S02 change, thus, if the Bs4value, after ~ t4, ls smaller than ~A2, the frequency change is reversed, If the rest phase RP then b~gins~
and the ~S1 value increases above the fixed value +A1, a ne~ative frequency change follows automatically until BS1 is again smaller than ~A1. The optimum ragulation then begins ayain with a positive frequency change + ~ f2 after a t5, and repeats this until, after ~ t4, th~ B~4 value is greater than +A~, that is to ~ay, an improve-ment in the oxygen saturation So2 is effected.

~ 17 -' ~77i3~3~

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The embodiments are therefore to be considered in all respects as illustrative and not restrlctive.

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Claims (18)

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:

1. A process for regulating the stimulation frequency of heart pacemakers as a function of the measured change of a physiological parameter of the blood circulation, preferably the central venous oxygen saturation, com-prising the steps of (a) forming the quotient from the change of the measured value of the physiological parameter .DELTA.SO2 within relatively short time ranges .DELTA.t1(4) divided by the maximum change of the measured value .DELTA. SO2max within relatively long time ranges .DELTA.to in order to determine the control value BS1(4), thus (b) regulating the stimulation frequency (f) of the heart pacemaker, with a utilization of the central venous oxygen saturation as physiological parameter depending on the control value BS1(4), in such a manner that always the greatest possible blood oxygen saturation is achieved with the lowest possible stimulation frequency, and (c) measuring the central venous oxygen saturation by means of an optical measuring probe (M) in such a manner that the light emitted by a light-emitting element (32) and reflected by the blood (44) causes an electrical current flow in a light-receiving element (37) which effects, at a constant voltage (UK) of the measuring probe, an increase (.DELTA.Is) of the flow of current (Is) through the measuring probe, or at a constant flow of current IK, a damping (.DELTA.Us) of the probe voltage (Us).

2. A process as claimed in claim 1, wherein a follow-up control (17) regulates the stimulation frequency (f) of the heart pacemaker in such a manner that, for changes in the oxygen saturation .DELTA.SO2 per time unit .DELTA.t1, the stimulation frequency (f) is changed by the amount .DELTA.f1 after a further time interval .DELTA.t2, thus a results in each case, as long as the absolute value of the measured change in the oxygen saturation is greater than A1 wherein:

and wherein:

after + BS1 or after - BS1 are only effected until a prescribed limiting value fmin or fmax is reached.

3. A process as claimed in claim 1, wherein a second, optimizing regulation regulates the stimulation frequency (f) in such a manner that it independently causes a change, with time, in the stimulation frequency at time intervals .DELTA.t5 in which the amount of the measured quantity BS1 is smaller than the value A1, thus , and, after a further time interval .DELTA.t4, evaluates the measured quantity (?) BS4 to the effect that a positive frequency change is only retained if it has caused a posi-tive change in the oxygen saturation, if, therefore:

and a negative frequency change is always retained if it does not cause a negative change in the blood oxygen saturation, if, therefore:

4. A process as claimed in claim 1, wherein the optimizing regulation of the stimulation frequency has a tendency to a fixed frequency fO which is achieved by the independent frequency change more frequently being negative if the stimulation frequency is greater than a prescribed fixed value fO, and by more frequently being positive if the stimulation frequency is smaller than fO.

5. A process as claimed in claim 3, wherein, in the case in which , a check is provided which determines whether an independent frequency change .DELTA.f2 has previously taken place in the period .DELTA.t5 and which sign the frequency change had, and which reverses this change if it is opposed to the answer, provided by the follow-up control, to , a check, therefore, which ensures the dominance of the follow-up control over the optimum regulation.

6. A process as claimed in claim 1, wherein a program control starts the data acquisition and evaluation direct-ly before or after the emission of the stimulation pulse, or after receiving the detection signal in the case of a self-excitation of the heart.

7. A process as claimed in claim 1, wherein the value of the measured pulse of the constant voltage (UK) or the constant current (IK) for a long time depends on the value SO2max stored in the maximum value storage (14) in such a manner that a value for SO2max sufficient for the required measuring accuracy is achieved with a minimum current consumption of the measuring probe.

8. A process as claimed in claim 1, wherein a check is provided, which detects, by a comparison with limiting values, an error during the data acquisition, the data evaluation and the frequency regulation, and, in each case of error, switches the stimulation frequency to a fixed value, and galvanically switches two electric supply lines (30, 36) to the measuring probe for the stimulation.

9. A device for the frequency regulation of heart pacemakers having a stimulation frequency which adapts itself to the load conditions of a patient, the central venous blood oxygen saturation being opto-electronically measured as a reference or control quantity for the adaptation, this measurement being carried out with the aid of an intracardiac measuring probe, and the acquisi-tion and evaluation of the measured value occurring by means of a circuit additionally arranged in the heart pacemaker, said device comprising (a) an optical measuring probe (M) containing at least one combination of only two active optoelectronic elements, namely a light-emitting element (32) and a light-receiving element (37), as well as additional-ly at least one semiconductor element (Do);
(b) a control circuit (7) electrically connected to the measuring probe (M), said control circuit generating with the aid of the measuring probe (M) a measuring signal (UM);
(c) a stimulation catheter (K) in which the measuring probe (M) is incorporated;
(d) at least two electric lines (30, 36; 301, 361) leading through the stimulation catheter and elec-trically connecting the optical measuring probe (M) to the control circuit (7), and (e) a signal evaluating and converting circuit (8) including means to separate the measured signals (UM) attained with the optical measuring probe (M) and the control circuit (7) from interfering signals, amplify said measured signals and convert said measured signals into a signal form suitable for a digital frequency regulation;
(f) said measuring probe (M) comprising a body of two mutually insulated metallic annular elements (31, 34;
311, 341), each of which serves as a carrier of at least one light-emitting element (32) or light-receiving element (37) and which, at the same time, are electrical connectors to the electric lines (30, 36; 301, 361) serving as probe supply lines.

10. A device as claimed in claim 9, wherein the light-emitting element (32) is a light-emitting diode and the light-receiving element (37) is a phototransistor, said diode (32) and said phototransistor (37) being con-nected with one another in parallel, in the measuring probe (M), in such a manner that, when an npn or pnp phototransistor is used, the cathode of the diode (32) is connected with one of the emitter and collector of the phototransistor (37) and the anode of the diode (32) is connected with the other of the emitter and collector of the phototransistor (37).

11. A device as claimed in claim 9, wherein several light-emitting elements (32) and light-receiving elements (37) are arranged on the metallic annular elements, cir-cularly around the axis of the catheter, in such a manner that the measuring angle in the cross-sectional plane of the catheter can be up to 360°.

12. A device as claimed in claim 9, wherein both electric supply lines (30, 301; 36, 361) to the measuring probe (M) are used as supply lines to the stimulation electrode (E).

13. A device as claimed in claim 10, wherein a semiconductor diode Do is integrated into the measuring probe (M) in such a manner that the cathode of the diode Do is connected with the anode of the light-emitting diode (32) and the anode of the diode Do is connected with the cathode of the light-emitting diode (32).

14. A device as claimed in claim 9, wherein a transparent protective jacket (39) is mounted around the body of the measuring probe (M) to prevent the pene-tration of blood constituents.

15. A device as claimed in claim 9, wherein the electric line (30, 301) is constructed as a wire winding and the measuring probe (M) is arranged between said wire winding and an outer transparent insulation tube (41) in such a manner that the latter is neither interrupted nor substantially deformed.

16. A device as claimed in claim 12, wherein the measuring probe (M) is integrated into the stimulation cathether (K) in such a manner that the measuring probe can be positioned in the region of the atrioventricular valves during implantation about 4 to 8 cm behind the stimulation electrode (E).

17. A device as claimed in claim 9, wherein the control circuit (7) of the measuring probe (M) is an electrical pulse generator arranged to produce a positive and a negative pulse of controlled voltage (UK) or current (IK) which are then passed on, via at least one load resistance (Rv) to the probe supply lines (30, 301;
36, 361) and to the measuring probe (M) in such a manner that the voltage (UM) at the load resistance (Rv) can be used as a measured value.

18. A device as claimed in claim 9, wherein the signal converter circuit (8) includes means for eva-luating the positive and negative pulses (+UMM; -UMF) sequentially applied at the load resistance (Rv) in such a manner that the measuring errors included in the proper measured pulse (UMM) caused by changes in the resistances of the electric lines (30, 301; 36, 361) and a temperature drift of the measuring probe (M) are eliminated.