the disclosure of my above - mentioned u . s . pat . no . 5 , 301 , 680 , issued apr . 12 , 1994 , entitled &# 34 ; apparatus and method for the diagnosis of labor &# 34 ;, is incorporated by reference herein in its entirety . as employed herein , the term &# 34 ; pregnant mammal &# 34 ; is not intended to be limited to only a pregnant human female , in that the methods and apparatus of this invention may be utilized by both medical and veterinary practitioners . also , as employed herein , the term &# 34 ; diagnostic information &# 34 ; is intended to refer to data and / or signals ( audible and / or visible ) emanating from the apparatus of the invention , the data and / or signals being the result of the processing by the apparatus , in accordance with the methods of the invention , of the voltages detected by suitable transducers , such as but not limited to electrodes , that are attached to a pregnant mammal . these voltages may be detected and then processed in close proximity to the pregnant mammal , or may be transmitted over a suitable telemetry or communications link and processed remotely from the pregnant mammal . furthermore , the data and / or signals are presented to a practitioner in such a manner so as to aid the practitioner in at least distinguishing true from false labor . the data and / or signals are additionally presented to a practitioner in such a manner so as to aid the practitioner in determining and predicting the onset of true labor . fig1 a and 1b illustrate the labor onset monitor ( lom ) 33 that is constructed and operated in accordance with the invention . the lom 33 includes a set of electrodes 1 . the electrodes 1 may be ekg or equivalent electrodes , or may be capacitively coupled electrodes of type described by w . h . ko and j . hynecek in &# 34 ; dry electrodes and electrode amplifiers &# 34 ;, biomedical electrode technology - theory and practice , pgs . 169 - 181 , ed . miller , h . a . and harrison , d . c ., academic press , new york ( 1974 ). in general , any suitable transducer for detecting electrical energy can be employed . the set of electrodes 1 are positioned on the abdomen of the pregnant mammal , midway between the fundus and the symphysis pubis , at an inter - electrode spacing of from approximately 1 to 7 cm . a ground electrode is positioned on a part of the body remote from the abdomen ; e . g ., the thigh . the electrodes 1 are connected to a differential amplifier 2 , with the following typical characteristics : the amplified electrode signal is converted to digital form with an analog to digital ( a / d ) converter 3 , at an a / d sampling rate in a range of 8 to 256 conversions per second . the digitized signal is digitally filtered by a filter 5 in a selected frequency range ; e . g . 0 . 1 to 5 . 0 hz , and may be displayed on an appropriate display device 6 , ( display1 , fig2 ), such as a conventional crt , and also stored in a storage device 7 , such as semiconductor memory and / or a conventional fixed or removable disk . the presence of electrical activity from the uterus is detected by an envelope detector 4 , which determines and stores the time ( t1 ) of the start of the electrical activity , and which also determines and stores the end of the electrical activity ( t2 ). the envelop detector 4 activates a control loop 27 , which causes the storage device 7 to initiate an incremental transfer of the currently acquired data to a fourier transform ( ft ) or power spectral density ( psd ) module 8 . this incremental transfer continues until the envelop detector 4 senses the end of the contraction at t2 , at which time the envelop detector 4 deactivates the control loop 27 . a fourier transform or a power spectral density 8 is then incrementally calculated for the filtered signal , and the incremental calculations are summed in a summation device 9 . a suitable embodiment for the ft / psd block 8 is discussed below . the ft or psd is integrated , by an integration module 25 , in a plurality of selected frequency ranges ; e . g ., α , β , γ and ε , selected from the range of filtering , to give the energy in the ranges h . sub . α , h . sub . β , h . sub . γ , and h . sub . ε , respectively . suitable , but not limiting , frequency ranges are as follows : α = 0 . 1 - 1 . 25 hz ; β = 1 . 25 - 2 . 5 hz ; γ = 2 . 5 - 3 . 75 hz ; and ε = 3 . 75 - 5 hz . the duration , λ = t2 - t1 , of the electrical activity is obtained from the envelope detector 4 . next , a discriminant δ for the electrical activity is determined , in a calculation module 26 , from a combination of the energies , as for example : where constants ρ , σ , τ and φ are selected so that δ has a negative value for false labor contractions , and a positive value for true labor contractions . this is preferably accomplished by taking measurements from a representative sample of pregnant mammals , and thus establishing the values of the constants accordingly . in a further technique in accordance with this invention the discriminant is obtained by first determining the average frequency ( f avg ) of the electrical activity within a burst , and then employing constants as follows : where the constants κ and λ are selected , as above , so that δ has a negative value for false labor contractions , and a positive value for true labor contractions . as before , this can be accomplished by taking measurements from a representative sample of pregnant mammals , and thus establishing the values of the constants accordingly . the average frequency can be determined by , for example , performing a discrete fourier transform ( dft ) of the measured signal to obtain the frequency in accordance with : where n i is the value of the fourier transform at f i , and n t is the total number of points ( see fig7 ). the average frequency may also be obtained by measuring a number of crossings of the signal through the x - axis per unit time , or by any suitable technique . however determined , the discriminant δ may , for example , range in value from - 10 to + 10 . the value of δ is stored , along with the time t1 of the termination of the electrical activity , as an ordered pair ( t1 , δ 1 ) in a storage device 11 , and may also be displayed on a suitable display device 12 ( display2 , fig3 a ). at the end of the next contraction , the slope σ of the two discriminants δ ( i . e ., the discriminant obtained for the contraction just ended ( t2 , δ 2 ) and the discriminant from the preceding contraction ( t1 , δ 1 ) is calculated as : that is , the change in the discriminant δ is determined between two successive contractions . alternatively , a plurality of the ordered pairs ( tn , δ n ) can be accumulated for a plurality of successive contractions , and the slope determined over the plurality of ordered pairs . if the value of the slope σ exceeds a critical ( c ) value σ c , and if δ exceeds a critical ( c ) value δ c , as determined by a comparator 13 , an audible and / or visual warning signal is given using the display device 14 ( display3 , fig3 b ) to indicate the onset of true labor . otherwise , the output of the comparator 13 is employed to display a &# 34 ; normal &# 34 ; signal on the display device 14 , indicating that true labor has not begun . by example , and referring to fig3 a , the critical values may be established such that the onset of true labor is indicated when the discriminant line passes , with a predetermined positive slope , through a range of discriminant values located on or near the x - axis . it is also within the scope of the teaching of this invention to employ a combination ( e . g ., a linear combination ) of σ and δ to obtain a value of a critical determinant . when the value of the critical determinant is determined to exceed a threshold value , the onset of true labor is indicated . a further embodiment of the lom ( designated 34 ) is shown in fig4 a and 4b . the operation of this embodiment is similar to that as described for the embodiment as shown in fig1 except for the absence of the display devices 6 and 12 . this embodiment is intended to be carried on , by , or in close proximity to the pregnant mammal within a suitable battery - powered electronics enclosure 15 . in this embodiment of the invention , when the comparator 13 senses the onset of true labor an audible and / or visual signal is given . a pictorial representation of the embodiment described in fig4 b is shown in fig4 a . this representation depicts the electronics enclosure 15 , electrodes 1 and associated wiring and connectors , an on / off indicator 16 , a low battery indicator 17 , and the labor warning signal 18 . that is , in this embodiment the display3 is embodied in the labor indicator 18 . a further embodiment of the lom , designated as 34 &# 39 ;, is shown in fig5 . this embodiment is intended to enable the remote monitoring of a pregnant mammal via a communications link . in this embodiment of the invention , the output of the a / d converter 3 is stored in a storage device 20 . when the comparator 13 senses the start of true labor , a signal is sent via a control link 13a to a transmitter 21 . the transmitter 21 accesses the storage device 20 and transmits the data contained therein via a telemetry link 22 to a practitioner &# 39 ; s console 30 . the telemetry link 22 can be any suitable data transmission means , such as an rf link , a telecommunications link , and a data link . fig6 is a block circuit diagram of the practitioner &# 39 ; s console 30 . a receiver 23 receives the data from the telemetry link 22 and stores the received data in a storage device 24 . the data is then replayed , at high speed , into the envelope detector 4 , and is subsequently processed as described with regard to fig1 b . alternatively , and referring again to fig5 in the lom 34 &# 39 ;, the input to the transmitter is coupled instead to the storage device 7 , or to the storage device 11 , thereby simplifying the construction of the practitioners console 30 . that is , in these other embodiments the practitioner &# 39 ; s console 30 relies on the processing of the contraction - related signals that is performed by the lom 34 &# 39 ;. in these other embodiments it may still be desirable to provide the storage device 20 , and to also transmit the &# 34 ; raw &# 34 ; a / d converter data from the storage device 20 to the practitioner &# 39 ; s console 30 . in this manner the practitioner &# 39 ; s console 30 , is enabled to check the accuracy of the calculations performed by the lom 34 &# 39 ;, and / or to employ other and / or more sophisticated calculations on the raw a / d converter data . the practitioners console 30 is modified , in accordance with the instant invention , so as to determine the discriminant values by using the average frequency of the electrical activity , as described above . as was also described above , it is preferred to calculate some form of the fourier transform ( e . g ., a fast fourier transform , a discrete fourier transform , a power spectral density ( psd )) in the block 8 of fig1 b , 4b , and 5 . in a presently preferred , but not limiting , embodiment of this invention the lom employs a discrete fourier transform ( dft ) when processing the filtered spectral data obtained from the electrodes 1 . by example , one suitable software package for performing a discrete fourier transform is available from national instruments , and is described in a publication entitled &# 34 ; fast fourier transforms and power spectra in lab windows ®&# 34 ;, application note 020 , j . pasquarette , national instruments corporation ( 8 / 91 ). furthermore , and as is described at page 10 of this publication , the software package includes a function named spectrum that enables the power spectrum of a signal to be determined . thus , the psd blocks 8 of fig1 b , 4b , 5 and 6 can also be implemented with this particular software package . in more detail , the power spectrum , s xx , of a time domain signal is defined by : s xx ( k )=| x ( k )| 2 / n 2 , where s xx ( k ) is the discrete power spectrum of a discrete time domain signal x ( i ), x ( k ) is the discrete fourier transform of x ( i ), and n is the number of data points . although described above in the context of discrete circuit elements such as envelope detectors , digital filters , etc ., it should be appreciated that all or most of the illustrated blocks could be implemented with a suitably programmed data processor , such as a digital signal processor ( dsp ). in like manner the various separate memories could all be contained within a single memory device or medium . thus , while the invention has been particularly shown and described with respect to presently preferred embodiments thereof , it will be understood by those skilled in the art that changes in form and details may be made therein without departing from the scope and spirit of the invention .
disclosed are systems and methods for detecting an onset of true labor in a pregnant mammal . in accordance with a method of this invention the following steps are executed : detected electrical signals from a succession of muscular contractions associated with labor ; determining an average frequency of the electrical signals for each contraction ; determining a discriminant from the determined average frequency for each contraction so as to provide a set of discriminants , individual ones of the set of discriminants being associated with an individual one of the contractions ; and indicating a beginning of true labor when a slope of at least two discriminants of the set of discriminants exceeds a first threshold value and when a magnitude of a last determined discriminant exceeds a second threshold value . the onset of true labor can also be indicated when a value of a critical determinant exceeds a threshold value , the value of the critical determinant being obtained from a combination of the slope of at least two discriminants of the set of discriminants and a magnitude of a last determined discriminant .