METHOD AND DEVICE FOR MEASURING THE PULSE BEAT FREQUENCY

Abstract: A method and a device for measuring the pulse beat frequency on the basis of the formation of the mean value of the time intervals between a number of consecutive pulse beats. According to the invention measurement of a sequence of four consecutive pulse intervals between the pulse beats is carried out, the second time being compared with the first, the third with the second and the fourth with the third. If in no case the difference DELTA T between a time and the preceding one exceeds a certain absolute amount, for instance +/-10%, the mean value of the four times is formed, is inverted and is indicated with a factor 60 as the number of pulse beats per minute. If, on the contrary, a time is found to deviate from the preceding one with more than DELTA T, for instance owing to a passed-over or an extra pulse beat, the measuring and comparing cycle is restarted until each time interval of the sequence is maintained within the permitted limits, after which the mean value is formed and indication takes place as in the former case. A device for carrying out the method can consist of a sensor (S) applied in the region of an artery, which sensor is connected to a signal processor (SB) in the form of a semicustom-chip for amplification, filtration and detection for emitting spike pulses to a pulse beat frequency calculating unit (PFB) in the form of a microprocessor programmed to perform the above-mentioned comparison repetition of the measuring cycle, if any, formation of mean value and inversion, and factor output of the result to an LCD-indicator (I). The whole pulse frequency meter can be made in a wristwatch model.

Description: Method and device for measuring the pulse beat frequency This invention relates to a method for measuring the pulse beat frequency, the time between consecutive pulse beats being measured and a mean value being formed in order to be converted thereafter into an indication of the number of pulse beats per minute. In sports, exercise, and other physical exertions it is often of interest for the practiser - or an observer - to be able to follow, during the very activity, how the pulse is varying. For this purpose different types of pulse meters have been developed which, as a rule, are to be carried around the wrist like wrist watches to make possible a simple and comfortable reading of the pulse. A sound and pressure sensitive sensor bears on the artery and converts the pulse beats into the corresponding electric signals. which are treated in a calculating unit to indicate direct¬ ly on a digital indicator the number of pulse beats per minute. The calculation is either based on measurement of the number of pulse beats for a certain time or measurement of the time intervals between a certain number of pulses ._ At the latter method 10-15 pulse beats are normally measured * (see US patent 4 058 118), and the mean value of the times between the pulse beats is formed to give a measure of the pulse beat frequency. In respect of the fact that a pulse beat may be passed over, also at an otherwise regular pulse, or else that an extra pulse beat is added it is obvious that the measurement in such a case will be much distorted and gives quite a misleading indication. Of course an extension of the measurement to include a far larger number of pulses should improve the result in a correspond¬ ing degree, but this should again give a misleading in¬ dication at sudden or short efforts of perhaps shorter duration than the total measuring time. To this must be added that the mean value of the error will still be systematically included in the calculation. Another dis¬ advantage of the known pulse meters is their complicated signal analysis and indication and, consequently, high costs associated with this. j -ϊE OMPI A , IPO The above-mentioned drawbacks are eliminated by the method of the invention in which in a sequence of a pre¬ determined small number of time periods between consecutive pulse beats the times are compared to each other, the mean value is formed merely of the times, the mutual difference of which does not exceed a certain minor relative amount, such as _+ 10%, which mean value is inverted and is directly indicated as the number of pulse beats per minute using the factor 60, after which the whole cycle is repeated. The invention is described more in detail below with reference to the enclosed drawing, wherein Fig. 1a, b shows schematical examples of pulse beat sequences, Fig. 2 shows a block diagram of the arrangement according to the in- vention, Fig. 3 shows an example of a flow chart, Fig. 4 shows an example of a block diagram of a calculating unit included in the arrangement and Fig. 5 shows a sensor in section useful for the invention. In Fig. 1 a pulse beat sequence is shown at a, where one pulse was absent (marked with a dash line) so that four times between the remaining pulses are measured, viz. T-,., T-, T, and T., of which T 2 is markedly longer than the other times. - At b another pulse beat frequency is shown, where an extra pulse beat has appeared so that the two times T, and- T. of the four measured times T. , T- , T, and T. become markedly shorther than the other ones. - The normal time of a regular pulse with five beats is indicated by ' a dash and dot line at Tt.ot, . It is the object of the invention, using a fixed sequence of a few number of times, four times in the case shown, to eliminate the disturbing influence of unduly presence or absence of pulse beats Cor another temporary strong irregularity) on the mean value on which the in¬ dication of the pulse beat frequency is to be based. This principle can be realized by the aid of the device shown in the block diagram in Fig. 2, which consists of a sensor S, a signal processor SB, a pulse beat frequency calculating unit PFB and an indicator ("display") I. The sensor S can be of a sound or pressure sensitive, type for such an application to an individual that it by OMPI his pulse is activated to emit a corresponding varying electric signal, as indicated in the Figure, to the input of the signal processor SB. The function of the latter is to amplify, to filter in a band pass filter and to detect the input signal in order to emit at its output a corresponding sequence of spike pulses, also indicated in the Figure, to the calculating unit PFB. In the latter unit the time intervals between the spike pulses are measured, for instance as the quotient between the number of high-frequency clock pulses during a pulse interval and the clock frequency. Evaluation of the times between the pulses in the sequence is then made by comparison, dis¬ crimination, correction, formation of mean value and in¬ version, after which the result is presented on the indicator I. - All this can be performed using discrete components in known manner, but to reduce the dimensions and - in series production - also the costs, a chip of semi-custom type, a microprocessor as calculating unit, e.g. of the type SAA 6000, and an LCD-display as indicator can preferably be used. Assuming that the calculating unit is a microprocessor and the time sequence of the pulse beats comprises four times the way of action of the invention is described be¬ low in connection with the flow chart in Fig. 3 and the two typical cases in Fig. 1a, b. If a sequence according to Fig. 1a appears at the moment of the start of measurement (start with extinguished indicator) the time T.. is first measured as first reference. The time T~ then measured is compared with T-, , it being found (in this case) that T~ strongly exceeds T. , i.e. the time difference is greater than the allowed maximum deviationΔT, which can be selected e.g. to 10% (absolute value) . According to the flow chart ("YES") the time sequence is then restarted. If this is regular within the allowed limits, i.e. the time difference between the second time and the first, between the third and the second and between the fourth and third time does not exceed JΔTJ (throughout "NO"), formation of the mean value τ m = ( τ ι + T 9 + T, + T /1 )/4 and inversion of T with multiplication by 60 take place in the next step. OMPI The pulse beat frequency thus obtained is presented on the indicator, after which the whole cycle is immediately repeated so that constantly current pulse beat frequencies can be read. The way of action at a sequence according to Fig. 1b is analogous. Thus, the first two times T, and T 2 are accepted, while the difference between T, and T 2 exceeds JΔτ| and, consequently, releases a restart of the time sequence, after which the process is the same as in the previous case. It can be said that the system of the invention provides an "intelligent" judgement of a reasonable pulse and that the inversion gives an accurate measure of the pulse. - As the sequence comprises so few pulses Cfour in the case described) an optimally rapid follow-up of the pulse is obtained, and a repetition of the sequence that may be required only means a delay of the indication for some second. It has been mentioned previously that the signal processing and calculation can also be performed by means of discrete components. An example of such an arrangement is shown in Fig. 4. According to this Figure the digitally presented spike pulses co ing from the sensor S via en amplifier F, a band pass filter BP, a detector D and an analogue-digital- converter A/D pass a time measuring means TM, which emits, in digital form, the time intervals T , T~ , T, and T^ to a four-step shift register SKR for temporary storage of four consecutive values. The respective differences be- tween the four time values are calculated in three differential circuits D1/2, D2/3 and D3/4 connected to the steps of the shift register and are fed to three threshold circuits T1/2, T2/3 and T3/4, respectively. Each of these decides whether the input difference value is within or outside the allowed margin (e.g. 10%). In the first- - entioned case the associated threshold circuit emits a logical 1. Only when a pulse sequence is such that all the three threshold circuits emit 1's, an AND-gate 0 connected to the circuits is opened and emits a signal to a digital OMPI indicator l, whicn is t us act vate . The value then presented is decided by a summer SU which sums up the four values T 2 - T. in each pulse sequence and emits the sum to an inverter INV. The in- verted sum signal is fed to a multiplier M for multi¬ plication of the signal by 15 and consequently indication of the pulse beat frequency on the activated indicator I. It is seen that the multiplication factor 60 used in the description of the flow chart in Fig. 3 also occurs in- directly in the embodiment according to Fig. 4, where the four summed up time values are multiplied by 15 instead of first being divided by 4 and then multiplied by 60. In this way a separate mean value forming means is not necessary. The invention is not restricted to the example given above. Instead of the consecutive comparison of the times between the pulse beats one might thus be able to store and compare the times in a sequence with each other at the same time and to accept the times of the formation of a mean value as soon as the differences between for example 3 times in a sequence of 5 are kept within the permitted limits. Fig. 5, finally, shows an example of a suitable sensor. A body of a flexible material, such as foam rubber, is shown there, which is partly encompassed by a. piezoelectric band foil 2, which, in its turn, is enclosed in a box 3 of a relatively stiff material. The flexibility of the body 1 keeps the foil 2 in intimate contact with the inner walls of the box .so that the pulsating pressure of an artery, when the box is applied to the skin in the region of the artery, can be derived in the form of electrical signals across the free ends 2a and 2b of the band foil and fed on to the signal processor. As the sensor can be made with very small dimensions it can be constructed as a compact unit together with the miniaturized units for signal processing and pulse beat frequency calculation, which can be strapped onto a person's wrist like a wristwatch. OMPI

Claims: atent Claims 1. A method of measuring the pulse beat frequency, the time between consecutive pulse beats being measured and a mean value being formed in order to be converted there¬ after into an indication of the number of pulse beats per minute, c h a r a c t e r i z e d in that the times (T.,,T 2 ...) in a sequence of a predetermined number of times between consecutive pulse beats , are compared to each other, the mean value (T ) is formed only of the times, the mutual difference of which does not exceed a certain minor relative amount (ΔT) , such as + 10%, which mean value is inverted and is directly indicated, using the factor 60, as a number of pulse beats CP) per minute, after which the whole procedure is repeated. 2. The method as claimed in claim 1, c h a r a c t e r¬ i z e d in that in the sequence, which can e.g. comprise four times (T- j ,T 2 ,T,,T.) , the second time (T 2 ) is compared with the first CT.,), the third time (T,) with the second (T 2 ) etc. , the comparison being interrupted and restarted for a new sequence if and when the comparison results in a time difference exceeding said minor relative amount (ΔT) , but at a completed sequence with all the differences lying within the relative amount, the mean value (Tm) of the times in the sequence is formed, inverted and indicated. 3. The method of claim 1, c h a r a c t e r i z e d in that the times ' are measured in known manner by emission of clock pulses having a high frequency, calculation of these between two consecutive pulse beats and formation of the quotient between the calculated pulses and the clock frequency. 4. A device for carrying out the method of claim 2, a pressure-sensitive sensor (5) being contactable with the region of an individual's artery to emit an electric signal varying with the pulse beats to a signal processing unit (SB) for pulse formation and thereafter to a calculating unit (PFB) for evaluation of the times (T^,T 2 ...) between the pulses and formation of the mean value and representation of the mean value (T ) on a digital indicator (I) per minute, c h a r c t e r i z e d in that the signal processing unit (SB) comprises an amplifier, a band pass filter and a detector to form spike pulses with the time T . , T ? . . . defined by the relative number of high frequency clock pulses between the spike pulses, and the calculating unit (PFB) comprises a time interval measuring unit (TM) , memories (SKR) for temporary storage of the times in a sequence of a predetermined small amount of times, e.g. four (T- ,T 2 ,T,,T.) , differential circuits (D) for consecutive comparison of each time (e.g. T 2 ) in a sequence with the immediately preceding time (T. ) , threshold circuits (T) to restart, at a comparative difference exceeding a certain permitted relative amount (ΔT) , such as _+ 10%, the comparison of a new sequence re¬ placing the times of the memories with the times of the. new sequence, a summer (SU) for adding the times (T., - T,) of the memory at a completed sequence having differences maximally up to said relative amount, and an inverter (INV) in combination with a multiplier (M) to display the pulse beat frequency on the indicator (1) with a corresponding factor. 5. The device of claim 4, c h a r a c t e r i z e d in that the signal processing unit (SB) consists of a chip and the calculating unit (PFB) of a microprocessor. ' 6. The device of any one of claims 4 or 5 , the sensor comprising a piezoelectric member which can be brought into, flexible contact with the region of the artery by means of a band around the wrist, c h a r a c t e r i z e d in that the sensor consists of a piezoelectric band foil (2) partly enclosing a body (1) of a flexible insulating material which is contained in a box (3) carried by the wrist band, the free ends (2a,2b) of the foil forming connection for conductors to the signal processing unit (SB) . ___OM?I -> vr-Pc

Inventors: SINHA BRAJNANDAN, SINHA, BRAJNANDAN
Applicants: BRAJNANDAN SINHA, SINHA, BRAJNANDAN
Application year: 1984
Main classification: A61B5
IPC codes: A61B5