Is abdominal fetal electrocardiography an alternative to doppler ultrasound for FHR variability evaluation?

ORIGINAL RESEARCH published: 16 May 2017 doi: 10.3389/ phys.2017.00305 F on ie s in Physiology | www. on ie sin.o g 1May 2017 | Volume 8 | A icle 305 Edi ed by: Ahsan H. Khandoke , Khali a Uni e si y, UAE Re iewed by: Hai ham Alanga i, Khali a Uni e si y, UAE Faezeh Ma zban ad, Monash Uni e si y, Aus alia Yoshi aka Kimu a, Tohoku Uni e si y, Japan *Co espondence: Janusz W obel [email p o ec ed] Special y sec ion: This a icle was submi ed o Compu a ional Physiology and Medicine, a sec ion o he jou nal F on ie s in Physiology Recei ed: 20 Ma ch 2017 Accep ed: 27 Ap il 2017 Published: 16 May 2017 Ci a ion: Jezewski J, W obel J, Ma onia A, Ho oba K, Ma inek R, Kupka T and Jezewski M (2017) Is Abdominal Fe al Elec oca diog aphy an Al e na i e o Dopple Ul asound o FHR Va iabili y E alua ion? F on . Physiol. 8:305. doi: 10.3389/ phys.2017.00305 Is Abdominal Fe al Elec oca diog aphy an Al e na i e o Dopple Ul asound o FHR Va iabili y E alua ion? Janusz Jezewski1, Janusz W obel1*, Adam Ma onia1, K zysz o Ho oba1, Radek Ma inek2, Tomasz Kupka1and Michal Jezewski3 1Ins i u e o Medical Technology and Equipmen ITAM, Zab ze, Poland, 2Depa men o Cybe ne ics and Biomedical Enginee ing, VSB-Technical Uni e si y o Os a a, Os a a, Czechia, 3Ins i u e o Elec onics, Silesian Uni e si y o Technology, Gliwice, Poland G ea expec a ions a e connec ed wi h applica ion o indi ec e al elec oca diog aphy (FECG), especially o home elemoni o ing o p egnancy. E alua ion o e al hea a e (FHR) a iabili y, when de e mined om FECG, uses he same c i e ia as o FHR signal acqui ed classically— h ough ul asound Dopple me hod (US). The e o e, he equi alence o hose wo me hods has o be con i med, bo h in e ms o ecognizing classical FHR pa e ns: baseline, accele a ions/decele a ions (A/D), long- e m a iabili y (LTV), as well as e alua ing he FHR a iabili y wi h bea - o-bea accu acy—sho - e m a iabili y (STV). The esea ch ma e ial consis ed o eco dings collec ed om 60 pa ien s in physiological and complica ed p egnancy. The FHR signals o a leas 30 min du a ion we e acqui ed dually, using wo sys ems o e al and ma e nal moni o ing, based on US and FECG me hods. Reco dings we e e ospec i ely di ided in o no mal (41) and abno mal (19) e al ou come. The complex p ocess o da a synch oniza ion and alida ion was pe o med. Ob ained low le el o he signal loss (4.5% o US and 1.8% o FECG me hod) enabled o pe o m bo h di ec compa ison o FHR signals, as well as indi ec one—by using clinically ele an pa ame e s. Di ec compa ison showed ha he e is no measu emen bias be ween he acquisi ion me hods, whe eas he mean absolu e di e ence, impo an o bo h isual and compu e -aided signal analysis, was equal o 1.2 bpm. Such low di e ences do no a ec he isual assessmen o he FHR signal. Howe e , in he indi ec compa ison he inconsis encies o se e al pe cen we e no ed. This mainly a ec s he accele a ion (7.8%) and pa icula ly decele a ion (54%) pa e ns. In he signals acqui ed using he elec oca diog aphy he ob ained STV and LTV indices ha e shown signi ican o e es ima ion by 10 and 50% espec i ely. I also u ned ou , ha abili y o clinical pa ame e s o dis inguish be ween no mal and abno mal g oups do no depend on he acquisi ion me hod. The ob ained esul s p o e ha he abdominal FECG, conside ed as an al e na i e o he ul asound app oach, does no change he in e p e a ion o he FHR signal, which was con i med du ing bo h isual assessmen and au oma ed analysis. Keywo ds: Dopple ul asound, e al elec oca diog am, e al hea a e analysis, e al s a e assessmen , e al ou come Jezewski e al. FHR om: aFECG s. US INTRODUCTION Fe al hea ac i i y is a p ima y sou ce o in o ma ion which enables assessmen o he e al s a e du ing p egnancy and a labo . This in o ma ion is ob ained mainly h ough analysis o he e al hea a e (FHR) signal being o med om he ins an aneous alues calcula ed acco ding o he o mula: FHR [bpm] =60000/T [ms]. The FHR alues a e exp essed in bea s pe minu e, and T is he ime in e al be ween wo consecu i e e al hea bea s ha comp ises one comple e ca diac cycle. Toge he wi h addi ional signals desc ibing he u e ine con ac ile ac i i y and e al mo emen p o ile, he FHR signal cons i u es he ca dio ocog aphic eco d. Acquisi ion o hese addi ional signals is qui e simple, bu measu emen o he e al hea a e has been always a challenge. Al eady in 1960s he e al elec oca diog am was eco ded o he i s ime by means o elec ode a ached o e al head. The quali y o such eco ded di ec e al elec oca diog am (FECG) is usually e y good, and hus i enables, using a qui e simple p ocessing me hod, de e mina ion o he bea - o-bea in e als wi h e y high accu acy. Howe e , he in asi e app oach and applica ion limi ed o he labo only caused ha di ec me hod did no ound wide applica ion in clinical p ac ice. As a esul o u he esea ch and de elopmen he nonin asi e ul asound (US) me hod has become a s anda d app oach since ea ly 1970s, as i can be used bo h du ing p egnancy and labo . A p esen , all bedside e al moni o s in ended o use in clinical condi ions a e based on he pulsed Dopple ul asound echnique, wi h measu emen ansduce a ached o ma e nal abdomen. P inciple o ope a ion elies on in e nal p ocessing o he en elope o he US beam e lec ed om mo ing pa s o e al hea s— al es o walls, o ind he episodes co esponding o consecu i e hea bea s. Howe e , a complex s uc u e and a ying con en o he US signal, usually caused by eloca ion o he e al hea in ela ion o a ansduce du ing moni o ing session, make a de e mina ion o he bea - o-bea in e al e y di icul (Khandoke e al., 2009; Ma zban ad e al., 2014). The e o e, a co ela ion echniques, conside ing ull shape o he analyzed signal, ha e been applied. The c oss-co ela ion echnique wi h changeable empla e appea ed o be oo sensi i e o US signal changes, which esul ed in conside able signals loss. Thus, an au oco ela ion unc ion wi h adap i e window selec ion has been applied in nex gene a ion e al moni o s. Howe e , he au oco ela ion unc ion does no de ec he consecu i e hea bea s bu only de e mines he ins an aneous pe iodici y o he US signal en elope which co esponds o ca diac cycle being measu ed. This leads o e ec o a e aging o neighbo ing ca diac cycles and hus dec easing o FHR de e mina ion accu acy in ela ion o e al elec oca diog aphy (Lee e al., 2009; Voicu e al., 2010). The ob ained FHR signal is p o ided by he bedside moni o as he ace in a p in ou wi h es ablished ime scale o 1, 2, o 3 cm/min. As long as he FHR ace has been analyzed isually, he lowe accu acy did no a ec signi ican ly he e al s a e assessmen . Mo e impo an was o ensu e he ace con inui y which allowed clinicians o obse e a gene al endency o he e al hea a e changes, and o ecognize he ea u es ep esen ing longi udinal FHR pa e ns ela ing o he e al s a e, like accele a ion o decele a ion. I was ound ha he e alua ion o e al s a e, when based on isual in e p e a ion, has been mainly a ec ed by low in e - and in a- obse e ag eemen (Jezewski e al., 2002; Romano e al., 2016a). Tha was a esul o bo h complexi y o he FHR signal and he ac ha impo an pa o in o ma ion ela ing o ins an aneous changes o FHR alues has been hidden om a naked eye. These changes a e conside ed o be e y impo an FHR cha ac e is ics, e lec ing app op ia e neu ological modula ion o he FHR. Thus, u he de elopmen s age o e al moni o ing was aimed a au oma ed analysis o he FHR signal and i s implemen a ion as buil -in p ocedu e o bedside moni o s as well as in compu e -aided e al moni o ing sys em. Some o he equi emen s impo an o moni o ing he p egnan women in hospi al, like su eillance o many pa ien s, de ec ing and ale ing o symp oms o e al dis ess, o elec onic a chi e wi h he signals and pe ina al da a, ha e made he compu e -aided sys em wi h online au oma ed analysis he s anda d in mode n obs e ics (W obel e al., 2013, 2015a). Au oma ed analysis comp ises de ec ion and desc ip ion o he abo e men ioned FHR ea u es, like accele a ion and o he s, as well as de e mina ion o he ins an aneous FHR changes by p o iding a se o indices o e alua e he long- e m and sho - e m (bea - o-bea le el) a iabili y o he e al hea a e. Au oma ed online analysis p o ides a quan i a i e desc ip ion o he FHR, bu he inal in e p e a ion o he eco d is s ill done by a clinician. The e a e a numbe o pape s ela ing o au oma ed classi ica ion o he FHR eco dings by using di e en me hods o compu a ional in elligence like neu al ne wo k, suppo ec o machines o epsilon-insensi i e lea ning (Czabanski e al., 2008, 2013). Howe e , aking in o accoun ha he inpu da a se comp ised he au oma ically de e mined ea u es o he FHR signals, collec ed om he clinical da abases (Chudacek e al., 2014), he ob ained classi ica ion esul s should be aced o he limi a ions o he ul asound app oach as i is discussed below (Voicu e al., 2014; W obel e al., 2015c). The a iabili y indices we e o iginally de ined using he bea - o-bea in e als de e mined om he di ec elec oca diog am. Thei s aigh applica ion o he FHR signals being p o ided by e al moni o s aised a ques ion how a limi ed accu acy o he ul asound app oach a ec s de e mina ion o he ca diac in e als, and hus he a iabili y indices alues. Se e al esea ch s udies we e aimed a e alua ion o he eliabili y o he ul asound me hod in e e ence o he di ec elec oca diog aphy (Ib ahimy e al., 2003; Reinha d e al., 2010, 2012; Cohen e al., 2012; Kimu a e al., 2012; Desai e al., 2013; Ko ding e al., 2015). Howe e , hey we e aimed a compa ing he signal loss episodes o di ec ly he FHR alues. In ou s udy we showed ha he e o o ca diac cycle de e mina ion (ins an aneous FHR alue) has no been co ela ed wi h he FHR a iabili y indices e o . I means ha he measu emen accu acy esul ing om he e al moni o speci ica ion canno be di ec ly ela ed o he esul s o he compu e -aided analysis o he FHR a iabili y. In gene al, we concluded ha mode n e al moni o s using he Dopple US echnique a e no able o p o ide he signal wi h he accu acy equi ed o eliable quan i a i e e alua ion o ins an aneous FHR a iabili y, pa icula ly he sho - e m F on ie s in Physiology | www. on ie sin.o g 2May 2017 | Volume 8 | A icle 305 Jezewski e al. FHR om: aFECG s. US a iabili y, based on he indices calcula ed au oma ically (Voicu e al., 2014). Fo una ely, he alues o indices de e mined in ha way a e unde es ima ed, which p e en s he e al dis ess signs om being unde ec ed. Se e al a emp s we e ca ied ou o imp o e he eliabili y o he ul asound me hod by using ad anced signal p ocessing o he Dopple en elope (Jezewski e al., 2011), bu none o hem ha e been applied in he bedside moni o s ye . In W obel e al. (2008) he me hod has been p oposed o imp o e he eliabili y o he FHR a iabili y indices, which elies on he e o s ecognized in he ul asound measu emen channel. The ac , ha he FHR signal ob ained om he ul asound app oach has been ecognized as no good enough o ully exploi he po en ial o au oma ed analysis o e ed by compu e - aided e al moni o ing sys em, b ough back an in e es o he e al elec oca diog aphy (Fuchs, 2014). Howe e , aking in o accoun he need o moni o a whole p egnancy pe iod, only a nonin asi e app oach could be conside ed, which elies on indi ec eco ding he FECG om elec odes loca ed on ma e nal abdominal wall (Ungu eanu e al., 2009; Vullings e al., 2010; Kimu a e al., 2012; Khala e al., 2013; Beha e al., 2014; Agos inelli e al., 2015b). Ano he impo an issue o de elopmen o e ec i e abdominal elec oca diog aphy e e s o a g owing in e es in high- isk p egnancy elemoni o ing a home (W obel e al., 2015b). When using he ul asound-based e al moni o he ansduce has o be ca e ully placed o ensu e he ul asound beam is ocused on he e al hea . Wha ’s mo e, du ing moni o ing session he ansduce may equi e eposi ioning due o a change o e us posi ion. O he wise, he signal loss occu s which may cause, in case when a woman pe o ms he moni o ing session alone, he un ounded ea and unp edic able eac ion. When he abdominal elec odes a e ixed on he abdomen, he pa ien can easily e i y he signal loss, which in ha case occu s only when one o he elec odes peels o (Ka ounis e al., 2007; Kolomeye s and Roshche skaya, 2013; Agos inelli e al., 2015b). Imp o emen o he measu emen ins umen a ion, elec ode echnology and he signal p ocessing me hods ha ha e been no iced du ing ecen yea s, enabled o cope wi h he p oblems connec ed wi h de elopmen o he abdominal e al elec oca diog aphy (Ko as, 2008; Vullings e al., 2010). The signal acqui ed om e us head is in ac “pu e” e al elec oca diog am, whe eas he abdominal signal includes also he ma e nal elec oca diog am (MECG) and some noise coming mainly om muscle ac i i y (Ta alunga e al., 2009, 2014; Ma inek e al., 2016). Thus, he c ucial s ep in ex ac ion o he FECG om he abdominal signal is a supp ession o ma e nal elec oca diog am while p ese ing he e al QRS complexes (Melillo e al., 2014; Agos inelli e al., 2015a). The ene gy o MECG is many imes highe han he ene gy o FECG, and wha ’s mo e he equency band o bo h hese componen s pa ly o e laps which makes simple il e ing useless (Ka ounis e al., 2007). A numbe o di e en app oaches o MECG supp ession and de ec ion o e al QRS complexes we e p esen ed in li e a u e (Ungu eanu e al., 2007; Liu and Luan, 2015; Poian Da e al., 2016). The sys em o acquisi ion o abdominal signals and o iginal me hod o FECG ex ac ion we e p oposed by he au ho s, and he indi ec e al elec oca diog aphy was e alua ed in ela ion o he gold s anda d—di ec FECG app oach (Jezewski e al., 2012). Re e ing o he esul s ob ained in ou p e ious s udy, conce ning a compa ison o ul asound app oach wi h he di ec FECG (Jezewski e al., 2006), we concluded ha he abdominal e al elec oca diog aphy p o ides accu acy no wo se han he ul asound me hod does. Howe e , in all s udies whe e he US me hod o abdominal FECG was compa ed wi h di ec FECG, he esul s we e ob ained only o he signals being acqui ed du ing labo . Conside ing ha e al de elopmen , aking place du ing a whole p egnancy pe iod, a ec s he cha ac e is ics o he FHR signals, we decided o ca y ou he compa ison o he abdominal FECG and ul asound me hod based on he signals collec ed du ing p egnancy. I is ob ious ha such app oach excludes he di ec elec oca diog aphy om he s udy, and causes some p oblems o compa ison me hodology due o a lack o e e ence da a (Sa o e al., 2011; Cohen e al., 2012; Kimu a e al., 2012). Since bo h ypes o he signals we e acqui ed by means o wo se s o ins umen a ion, ano he impo an p oblem has been ecognized— he FHR signals synch oniza ion, i.e., inding he co esponding ca diac cycles. I should be no iced ha in case o ul asound-based moni o , he FHR signal is p o ided h ough i s ou pu only as he measu emen alues o ins an aneous hea a e e enly spaced wi h 250 ms. On he o he hand, he sys em o nonin asi e FECG is able o p o ide, along wi h he e enly spaced signal, he ime e en se ies wi h du a ions o consecu i e ca diac cycles. In his wo k he me hodology is p oposed o compa e wo di e en me hods o e al hea a e moni o ing. I s o iginali y ela es o he ac ha compa ison has been ca ied ou no only in ela ion o he co esponding ca diac cycle alues, bu also o he clinically impo an indices desc ibing he ins an aneous FHR a iabili y. METHODS The esea ch ma e ial comp ised he FHR signals acqui ed simul aneously using he Dopple ul asound as well as he elec oca diog aphic me hods in a g oup o 70 p egnan women. F om a numbe o moni o ing sessions pe o med o each pa ien , we selec ed only one eco ding acqui ed a ound 1 week be o e deli e y, wi h a leng h o a leas 30 min (Geo gie a e al., 2014). All he eco dings a e accompanied by in o ma ion on e al ou come: ges a ional age a bi h, blood gas pa ame e s pH and BE, pe cen ile o e al bi h weigh , Apga sco e, in o ma ion abou a possible s ay in he NICU. The pa ien s we e moni o ed by simul aneously using wo popula in ma e ni y wa ds, sys ems o e al and ma e nal moni o ing: MONAKO and KOMPOREL. Un o una ely, hese sys ems we e unable o synch onize eco ded signals du ing he moni o ing session. The ime shi be ween signals beginnings in each session could each up o a ew minu es, whe eas in case o compa a i e s udies he p ecise synch oniza ion is equi ed (e en on he le el o indi idual hea bea s). Hence, he p oblem o signals synch oniza ion has been conside ed as a signi ican challenge. F on ie s in Physiology | www. on ie sin.o g 3May 2017 | Volume 8 | A icle 305 Jezewski e al. FHR om: aFECG s. US As he esul o each simul aneous moni o ing session, wo iles we e ob ained o he na i e o ma , whe e he FHR signal is ep esen ed by he alues measu ed e enly wi h 250 ms pe iod. Files om he MONAKO Sys em comp ise he FHR_U signal cap u ed om he ou pu o e al moni o equipped wi h he ul asound ansduce (Hewle -Packa d M1351). The iles om he KOMPOREL Sys em p o ide he FHR_E signal being de e mined on a basis o e al elec oca diog am eco ded om he abdominal wall o he mo he . The e al elec oca diog am is eco ded by using ou elec odes placed on he ma e nal abdomen. The c ucial s ep in ex ac ion o he FECG om he abdominal signal is a supp ession o ma e nal elec oca diog am while p ese ing he e al QRS complexes (Cas illoa e al., 2013; Ma inek e al., 2015). The p oposed me hod o he MECG supp ession is based on sub ac ing he pa e n o ma e nal P-QRS-T complexes and spa ial il e ing. I ensu es co ec de e mina ion o he iducial poin s as well as he ac o s scaling he pa e n. The algo i hm o de ec ion o he e al QRS complexes is based on a ma ched il e ing app oach in o de o educe he sensi i i y o in e e ences. Addi ionally, he de ec ion is ca ied ou wi h a se o decision ules o p edic he du a ion o he nex bea - o-bea ca diac cycle (Ma onia e al., 2006). As a esul o he FECG analysis, he ime e en se ies is ob ained— as he ime ma ke s when he successi e e al hea bea s we e de ec ed— he QRS complexes, which is hen used o de e mine he FHR_E signal as he alues wi h 250 ms pe iod (Gue e o Ma inez e al., 2006; Almeida e al., 2013, 2014). Signals Synch oniza ion The p ocedu e o synch oniza ion o each pai o he FHR_U and FHR_E signals consis ed o wo s ages. In he i s s age an ini ial isual adjus men was suppo ed by a dedica ed p og am o isualiza ion o he signals. This p og am as well as all he o he s, c ea ed o he pu pose o his wo k, was de eloped in LabView en i onmen (Na ionaI Ins umen s) (Desai e al., 2013). A e coa se synch oniza ion o he signals he common pa o FHR_U and FHR_E signals was sepa a ed. I elied on mo ing he beginning and end o one signal, o indica e he agmen o in e es acco ding o he o he signal. A his s age he signals quali y had o be good enough o allow ecognizing he cha ac e is ic ea u es common o bo h signals, and cons i u ing he so called cen e ing poin s, and he common pa o he signals had o ha e non-ze o leng h. These condi ions we e no me in case o h ee eco dings, hence in u he p ocessing only he se o 67 pa ien s we e included. In he second s age he signal alida ion was conduc ed, as well as p ecise synch oniza ion o bo h signals, a he le el o indi idual FHR alues p o ided e e y 250 ms. The de eloped so wa e enabled semi-au oma ed synch oniza ion. The p og am au oma ically ound he ime shi be ween he signals o ensu e he minimum di e ences be ween he co esponding alues, which mos ly led o p ope synch oniza ion. A e ha , he isual e i ica ion was ca ied ou wi h a possibili y o addi ional ime shi co ec ion, ollowed by he inal accep ance (Figu e 1). The so wa e o de e mina ion o he op imal ime shi be ween he analyzed signals was using he synch oniza ion unc ion based on he mean absolu e di e ences (MAD), de e mined o he co esponding (applying he ime shi ) FHR_U and FHR_E alues. To imp o e he pe o mance o synch oniza ion unc ion i was necessa y o u he educe he in luence o andom in e e ences appea ing in he FHR signals, as well as sudden alue changes esul ing om he measu emen e o s o po en ial accele a ion and decele a ion episodes. Hence, he segmen s wi h sudden changes in he FHR signal we e excluded om he unc ion de e mina ion, i he absolu e di e ence be ween a gi en alue and he p eceding one was highe han 10 bpm (Spilka e al., 2012). I a gi en FHR alue was ejec ed, he nex one was compa ed o he mean calcula ed om he p e ious alues (including he ejec ed) in he 240 alues window. The FHR alues we e also ejec ed om he signal, which we e suspec ed o ep esen he ma e nal hea a e— he de ails o he algo i hm a e p esen ed in W obel e al. (2015b). This ype o e oneous measu emen s occu s in he FHR_U signal, as i is ypical o he ul asound me hod and qui e equen in he US-based e al moni o s. The abo e-men ioned p ep ocessing is only in ended o synch onize he signals and do no change hei in o ma ion con en . The op imum ime shi , co esponding o he ully synch onized signals, was ob ained o he unc ion minimum, when applying addi ional shi in he ange om −25 o +25 FHR alues (measu ed e e y 250 ms), in espec o he signals synch onized a e he i s s age. I a he beginning o end o a gi en signal any in e e ence associa ed wi h he s a o end o he moni o ing session occu ed, hey we e also emo ed in he imming p ocess. T imming o he ull minu es in u n, esul s om he ac ha he analysis o he ins an aneous FHR a iabili y is always ca ied ou wi hin a 1-min signal segmen s. Finally, as a esul o he synch oniza ion p ocedu e some signal pai s could be sho ened by as much as 4 min. A e he second s age o synch oniza ion he common pa o he analyzed signals is immed o he la ges whole numbe o he minu es ( he numbe o FHR alues was a mul iple o 240). We assumed ha he minimum leng h o synch onized signals (cons i u ing he pai ) subjec ed o u he analysis should be 10 min. Acco ding o ha c i e ion only one eco ding was ejec ed, and 66 eco dings we e le . Signal Loss Analysis The nex p ocessing s ep consis ed o e i ying he signal pai s in e ms o hei quali y, measu ed bo h by a size and na u e o he signal loss episodes. Episodes o signal loss a e p elimina ily de ec ed by he moni o ing sys ems used, and ep esen ed by ze o alues in he FHR signal. Fo he pu pose o his wo k also he po en ial e oneous FHR alues, as no mee ing he adop ed c i e ia, we e ma ked as signal loss episodes, using he dedica ed de eloped p og am. Signal segmen s we e conside ed o be signal loss i hey did no mee he an Geijn modi ied c i e ion ( an Geijn, 1980), p oposed in Jezewski e al. (2012). Tha was applied o hese FHR alues, which we e conside ed as e o s by a p ocedu e o sudden changes emo al used in he second s age o synch oniza ion. In his case, he es ablished h esholds a e: he absolu e di e ence be ween a gi en FHR alue and he p eceding one g ea e han 20 bpm, and window wid h equals o 100 alues. The segmen s, suspec ed o con ain F on ie s in Physiology | www. on ie sin.o g 4May 2017 | Volume 8 | A icle 305 Jezewski e al. FHR om: aFECG s. US FIGURE 1 | The sc een illus a ing he ope a ion o he p ocedu e o synch onizing he wo signals, de e mined ia he ul asound ( ed FHR_U) and elec oca diog aphic (blue FHR_E) me hods. (A) P esen s he concep o au oma ed synch oniza ion ia minimizing he mean e o . The cu en alue o he mean absolu e di e ence MAD pa ame e is displayed on he gauge. Au o mode had au oma ically se up he alue o he shi pa ame e o 9 samples o wa d. Howe e , basing on a isual analysis o he signals, ha shi was manually co ec ed using a slide — he FHR_U signal was shi ed by 2 samples backwa d in ela ion o he FHR_E signal. (B) Shows he enla ged signal agmen om pa A, bu a e a p ocedu e o emo ing he sudden FHR changes. I allows o addi ional manual synch oniza ion and inal alida ion o he eco ding o u he in es iga ions. he ma e nal hea a e signal, we e indica ed as he signal loss episodes—simila ly as in he second s age o synch oniza ion. Finally, as a esul o he signal loss analysis, he FHR_U and FHR_E signals we e ob ained wi h addi ional in o ma ion abou de ec ed gaps (FHR alues equal o ze o). The signal loss le el is de ined as a pe cen age o he du a ion o signal loss episodes ( he numbe o FHR alues equal o ze o) in ela ion o he o al du a ion o he signal (all FHR alues). Taking in o accoun he maximum le el o signal loss o 30% in ei he FHR_U o FHR_E signal, i e eco dings we e emo ed. Addi ionally, in e ms o uni o mi y o signal loss dis ibu ion in ime, ou ques ionable eco dings wi h signal loss be ween 20 and 30% we e isually assessed. Only one eco ding was excluded due o he accumula ion o he signal loss (equal o 23%) in he middle pa o he FHR_U signal. The inal esea ch ma e ial consis ed o signal pai s om 60 moni o ing session. The o al leng h o eco dings was equal o 1995 min. The leng h o indi idual eco dings a ied om 11 o 64 min, wi h an a e age o 33.3 min. Di ec Signals Compa ison Fo he inal se o eco dings, consis ing o he FHR_U and FHR_E signal pai s, some desc ip i e s a is ics o signal compa ison we e calcula ed, bo h on a global basis as well as a he le el o pa icula FHR alues. These s a is ics include (calcula ed o indi idual eco dings): he eco ding du a ion, signal loss le el, mean alue o he di e ences be ween he co esponding ins an aneous FHR alues (MD), s anda d de ia ion (SD), mean absolu e di e ence (MAD), as well as he summa y s a is ics o he en i e esea ch ma e ial. The di e ence be ween he pai s o co esponding ins an aneous alues o FHR_U and FHR_E was exp essed dually: as he hea bea s pe minu e (bpm) as well as in milliseconds. The second ep esen a ion is ob ained by con e sion o he FHR alues in o in e als be ween successi e hea bea s, acco ding o he hype bolic ans o ma ion wi h he 60,000 ac o . As equally impo an i is assumed he compa ison o he signals in a o ma commonly used in au oma ed analysis o he low a iabili y FHR signal componen s (Jezewski e al., 2002). In his o ma he successi e alues o he signal a e de e mined by a e aging 10 consecu i e o iginal FHR alues ( ime se ies measu ed e e y 250 ms). Impo an pa in he a e aging p ocess is he emo al o he signal loss episodes, ma ked as ze o alues. I , while a e aging 10 o iginal FHR alues, mo e han ou alues a e ma ked as signal loss, he esul ing alue o 2.5 s pe iod is also conside ed as signal loss and is assigned wi h ze o alue. Indi ec Signal Compa ison ia Clinical Pa ame e s As shown in he li e a u e (Jezewski e al., 2016), he di e ences om he di ec compa ison o signals a e o en no co ela ed F on ie s in Physiology | www. on ie sin.o g 5May 2017 | Volume 8 | A icle 305 Jezewski e al. FHR om: aFECG s. US wi h di e ences in alues o clinically impo an pa ame e s o quan i a i e desc ip ion o FHR signal, de e mined by he e al moni o ing sys ems (Geo gie a e al., 2012). These pa ame e s a e used by clinicians, in e p e ing he FHR signals in o de o assess he e al s a e. The e o e, i was conside ed as impo an o iden i y he impac o he FHR signal acquisi ion me hod on he clinically signi ican pa ame e s. Fo ha pu pose, he synch onized FHR_U and FHR_E signals we e sa ed in o he na i e o ma iles (measu ed wi h 250 ms) and eloaded o he a chi e o MONAKO Sys em. Thanks o an op ion o eanalysis o he a chi al eco ds, o each o 60 eco dings (120 FHR signals), he quan i a i e pa ame e s desc ibing he a iabili y pa e ns de ec ed in he FHR signal we e de e mined au oma ically. As he esul , he lis s o pa ame e s we e ob ained o he FHR_U and FHR_E signals. They included he pa ame e s desc ibing some pa e ns o FHR a iabili y in he ime domain: mean alue o FHR (M_FHR), mean alue o he FHR baseline (M_BL), numbe o de ec ed accele a ion (ACC) and decele a ion (DEC) episodes (Geo gie a e al., 2012; W obel e al., 2013). Addi ionally, an assessmen o he ins an aneous FHR a iabili y was p o ided as: du a ion and alue o he high (HE_D and HE_V) and low (LE_D and LE_V) a iabili y episodes, a e age alue o he long- e m a iabili y (LTV) and sho - e m a iabili y (STV) indices, as well as he FHR oscilla ions (OSC) oge he wi h he pe cen age o di e en oscilla ion ypes (OSC_I÷OSC_IV) (Jezewski e al., 2016). Inconsis encies o he abo e pa ame e s calcula ed o he co esponding FHR_U and FHR_E signals we e es ima ed using he symme ic mean pe cen age di e ence SMPD, whe e he di e ences be ween alues a e ela ed o hei mean. Since he no mali y assump ion was e i ied using he Shapi o-Wilk es , he s a is ical signi icance (using pai ed S uden ’s - es ) o he di e ences be ween he co esponding pa ame e s ob ained in he FHR_U and FHR_E signals was examined. Indi ec Signals Compa ison ia Bea - o-Bea Va iabili y I is gene ally belie ed ha a e y high p edic i e alue in ela ion o he ea ly de ec ion o he e al dis ess is p o ided by he ins an aneous FHR a iabili y pa ame e s (Cesa elli e al., 2009). They a e de e mined om he FHR signal in a o m o he ime e en se ies—a sequence o e en s une enly loca ed in ime, p o iding he successi e ca diac cycles du a ion exp essed in milliseconds. This o ma signi ican ly di e s om ha a ailable a he ou pu o a e al moni o — he FHR alues e enly spaced a e e y 250 ms. This measu emen pe iod has been es ablished o be no longe han he sho es physiologically allowed hea cycle, howe e wi h cha ac e is ic in o ma ion edundancy o low FHR alues (e.g., he FHR alue equal o 50 bpm is ep esen ed by ou duplica ed subsequen alues; Lee e al., 2009; Goncal es e al., 2013). The e o e, he FHR_U and FHR_E signals we e subjec ed o econs uc ion o he abo e men ioned ime e en se ies ep esen a ion. This p ocedu e elied on aking om he e enly dis ibu ed ime se ies, he alues acco ding o he iming signal being cons i u ed by he e al QRS complexes addi ionally ob ained om he KOMPOREL Sys em. The esul ing signal is a sequence o ime-o de ed e en s co esponding o subsequen occu ences o he e al QRS complexes (o mo e p ecisely he R-wa es). C ea ed acco ding o he desc ibed p ocedu e he FHR_U and FHR_E signals in he o m o ime e en se ies, p o ided he basis alues o de e mina ion o he ins an aneous a iabili y indices. These indices, widely acclaimed in he li e a u e (Romano e al., 2016b), quan i a i ely desc ibe he long- and sho - e m FHR a iabili y. In his s udy he ollowing indices we e analyzed: Haan_LTI, Haan_STI, Yeh_II, Yeh_STI, O gan_LTV, O gan_STV, Dal on_LTV, Dal on_STV, Zugaib_LTV, Zugaib_STV. In o de o s anda dize he esul s he indices we e de e mined wi hin 1-min segmen s (Kubo e al., 1987; Jezewski e al., 2006). Each consecu i e segmen comp ised only hose ins an aneous FHR alues which we e de e mined using he hea bea s con ained in he gi en segmen (Cesa elli e al., 2009). While p ocessing a gi en segmen , i pe cen age o alid alues, ele an o a gi en index (acco ding o i s de ini ion), was less han 20%, i was assumed ha he index alue was unde e mined o ha minu e. Such cases a e he esul o he signal loss episodes in he analyzed signals. In a se ies o minu e alues calcula ed o a gi en signal, hey a e de ined as a 1-min loss o he gi en index alue and ma ked wi h he alue o −1. The index a e age alue o a gi en signal is calcula ed om all 1-min alues, excluding hose ma ked as unde e mined. Addi ionally, a non-linea pa ame e o ins an aneous FHR a iabili y was p oposed, in a o m o he egula i y measu e— he sample en opy index (SampEn) (Signo ini and Magenes, 2014). I was de e mined in he windows co e ing 300 hea e en s (FHR alues), and exp essed in milliseconds as a measu e o pe iod. The pa ame e s o SampEn unc ion we e se a : dim =1 and =0.1. Fo he gi en signal, he SampEn index ep esen s he mean alue o sample en opy de e mined in successi e windows. Inconsis encies o indices desc ibing he ins an aneous FHR a iabili y, de e mined o co esponding FHR_U and FHR_E signals we e e alua ed wi h he SMPD, whe e he di e ence be ween alues a e ela ed o hei mean. The s a is ical signi icance (using pai ed S uden ’s - es ) o he di e ences be ween he alues o he indices ob ained o each signal pai was also examined. Indi ec Signals Compa ison ia Fe al Ou come P edic ion Analysis o he FHR signal leads o i s classi ica ion as co esponding o no mal o abno mal e al s a e. Since a he ime o e al moni o ing, he e is no o he diagnos ic me hod which could be able o con i m a co ec ness o he signal classi ica ion, he FHR signals, being acqui ed du ing p egnancy, a e e ospec i ely assigned o ue e al ou come (newbo n s a e) (Chudacek e al., 2014; Romano e al., 2016a). I is jus i ied, as in obs e ics i is assumed ha he no mal e al ou come has o be esul o p ope e al de elopmen du ing he p egnancy pe iod. Excluding he cases when he labo p ocess i sel caused nega i e e ec s o he e al s a e, he same assump ion can be applied F on ie s in Physiology | www. on ie sin.o g 6May 2017 | Volume 8 | A icle 305 Jezewski e al. FHR om: aFECG s. US o abno mal e al ou come. I is gene ally belie ed ha his ela ionship is main ained in case o deli e ies by cesa ean sec ion due o he ma e nal easons. In he collec ed da abase he as majo i y o cases we e o his ype. The 60 pa ien s ( eco dings) we e classi ied as belonging o a no mal o abno mal g oup using he in o ma ion on e al ou come. The abno mal s a e was se i a leas one o he ollowing condi ions was me : Apga sco e (a 5 min) <7, pH <7.2, BE >12, NICU s ay >24 h, o bi h weigh pe cen ile <5%. Finally, he esea ch ma e ial included 19 eco dings wi h abno mal s a e and 41 wi h no mal s a e assigned e ospec i ely. I is impo an ha o he majo i y o pa ien s wi h abno mal e al ou come, he p egnancy was ended by cesa ean sec ion due o he ma e nal indica ions (16 cases). I sugges s ha cou se o deli e y imposed no nega i e e ec on he newbo n. The da abase con ains six eco dings o which he abno mal s a e was se due o h ee o mo e condi ions me . The analysis o abili y o p edic ion o he e al ou come was pe o med sepa a ely o he ul asound and he e al elec oca diog aphy app oaches. Each FHR_U (FHR_E) signal was ep esen ed by he ea u e se comp ising: 15 pa ame e s de e mined by he MONAKO Sys em, 10 indices desc ibing he ins an aneous FHR a iabili y and SampEn en opy measu e. The di e ences be ween he alues o hese ea u es ob ained in wo g oups (no mal and abno mal e al ou come) we e exp essed by he mean pe cen age di e ence (MPD) o bo h g oups— whe e he no mal ou come g oup was aken as e e ence. The s a is ical signi icance o he di e ence be ween he mean alues o each ea u e ob ained o wo g oups was assessed using S uden ’s - es . The indi ec compa ison o FHR_U and FHR_E signals, as o p edic ing he e al ou come, was based on he capabili y o classi y he FHR signals om a gi en acquisi ion me hods in o no mal and abno mal analyzing he de e mined clinical FHR pa ame e s. RESULTS Compa ison analysis conside ing wo di e en me hods o FHR signal acquisi ion has been ca ied ou using 60 pai s o FHR_E and FHR_U signals, which we e ob ained du ing he moni o ing sessions o 60 pa ien s. A e a ull signals synch oniza ion and imming, he o al leng h o eco dings was equal o 1995 min, wi h an a e age leng h o 33.3 min (SD =10.9 min). The eco dings we e cha ac e ized by low signal loss (de ails in Table 1). Fo he US me hod he mean signal loss was equal o 4.5%, whe eas o he FHR signals ob ained ia FECG, he loss le el was mo e han wo imes lowe , which is exp essed by he mean signal loss o only 1.8%. High signal loss was obse ed in ew eco dings, especially o FHR_U. I could be no ed ha o mo e han hal o he eco dings, he signal loss o bo h me hods did no exceed 1%. Such low le el o he signal loss and he su icien leng h o indi idual eco dings enabled u he es ima ion o he inconsis ency be ween bo h acquisi ion me hods, using he mean alues o clinical quan i a i e pa ame e s, de e mined du ing he FHR signal analysis. A di ec compa ison o he FHR_E and FHR_U signals has been based on es ima ion o he di e ences be ween he co esponding ins an aneous FHR alues (p o ided e e y 250 ms). I enabled he me ological assessmen o he inconsis ency be ween he wo acquisi ion me hods. Compa ison a ha s age was pe o med o each indi idual eco ding and he summa y o desc ip i e s a is ics o en i e esea ch ma e ial is p esen ed in Table 1. The mean di e ence alue (MD) ob ained o all eco dings was −0.23 bpm, which in ela ion o an a e age alue o FHR (abou 140 bpm) gi es a ela i e e o o 0.2%. I means ha he measu emen bias be ween he wo me hods does no occu . When analyzing he MD alues calcula ed o pa icula eco dings we no ed ha i did no depend on he measu ed FHR signal alue. I is shown by he Bland-Al man plo o MD alues agains he a e age FHR alues ( om FHR measu ed a 250 ms) ob ained o pa icula eco dings (Figu e 2). F om he poin o iew o bo h isual and au oma ed assessmen o he FHR signal a iabili y, he mo e impo an seems o be he MAD, which was equal o 1.24 bpm o all he conside ed signals. Such alue does no a ec a isual e alua ion o he signal, since i is lowe han he p in ing esolu ion o he FHR wa e o ms, as well as he esolu ion o a human eye. In he compu e -aided sys em, he au oma ed analysis aimed a de e mina ion o clinically impo an FHR pa e ns is ca ied ou using he FHR alues a e aged o e 2.5 s. I makes he compa ison be ween FHR_E and FHR_U signals ep esen ed by such a e aged alues especially impo an . A e aging p ocesses caused a sligh dec ease o he signal loss in bo h ypes o TABLE 1 | Desc ip i e s a is ics o he signal loss and alues o di e ences MD, MAD, de e mined o he inal se o eco dings om he elec oca diog aphy (FECG) and he ul asound me hod (US), whe e he FHR signals we e exp essed as he o iginal 250 ms measu es, and as he alues a e aged o e 2.5 s pe iods. FHR 250 ms FHR 2.5 s Signal loss (%) FECG-US (bpm) FECG-US (ms) Signal loss (%) FECG-US (bpm) FECG US MD MAD MD MAD FECG US MD MAD Mean 1.80 4.53 −0.23 1.24 0.71 3.83 1.35 4.29 −0.09 0.71 SD 3.01 6.52 0.38 0.46 1.25 1.62 2.59 6.42 0.40 0.43 Median 0.60 0.95 −0.19 1.12 0.59 3.36 0.35 0.75 −0.05 0.58 Min 0.00 0.10 −1.29 0.50 −4.52 1.39 0.00 0.00 −1.50 0.23 Max 14.70 26.80 1.54 2.86 5.33 9.91 12.50 26.40 1.49 2.50 F on ie s in Physiology | www. on ie sin.o g 7May 2017 | Volume 8 | A icle 305 Jezewski e al. FHR om: aFECG s. US FIGURE 2 | Bland Al man plo showing he dependence o he mean alue o he di e ences MD (Y axis) be ween co esponding ins an aneous alues o FHR_U and FHR_E, in ela ion o he a e age e al hea a e in he eco ding (X axis), o each o he 60 pai s o signals. The alues a e exp essed in bea s pe minu e—bpm. signals, o he alues: 4.3% in US, and 1.4% in FECG (Table 1). Compa ison a his s age was pe o med o pa icula eco dings and he summa y o desc ip i e s a is ics o en i e esea ch ma e ial is p esen ed in Table 1. In gene al, inconsis ency be ween FHR signals a e a e aging dec eased. In his case, he bias be ween he wo me hods also does no occu . The MAD alue has dec eased signi ican ly, o only 0.7 bpm, which is below he 1 bpm le el— he minimum accu acy o he FHR measu emen . In ela ion o he a e age alue o he FHR signal (140 bpm), he ela i e inconsis ency was equal o 0.5%. Conside ing hese esul s we could assume ha such small inconsis ency should lead o he simila alues o clinical pa ame e s p o ided by bo h me hods. Howe e , we ha e o keep in mind ha some o hese pa ame e s a e pa icula ly sensi i e o he FHR changes, being a esul no only o he mean FHR di e ence, bu a he o he dis ibu ion o FHR di e ences in ime. In con as , some o he pa ame e s o he FHR signal a e sensi i e o empo a y high di e ences in he FHR signals. So, in case o hese pa ame e s he di e ences be ween bo h me hods may occu . Such o mula ed assump ions ha e been e i ied in he nex s age o he inconsis ency analysis— he indi ec compa ison o bo h signals. I was based on he in e p e a ion o he di e ences be ween he pa icula FHR signal pa ame e s, which a e p o ided by an au oma ed analysis in he e al moni o ing sys em. Desc ip i e s a is ics (mean alues and SD) o indi idual pa ame e s desc ibing quan i a i ely he FHR signal, which ha e been de e mined o signals om bo h me hods, a e p esen ed in Table 2. Fo each pa ame e he di e ences be ween he FHR_E and FHR_U signals, we e assessed using he SMPD. I was jus i ied because o any o hose pa ame e s no signi ican di e ence be ween hem was no ed. As i could be expec ed, he low SMPD alue o 0.1% ob ained o M_FHR and M_BL pa ame e s (being signi ican ly dependen on an a e aging p ocess o he FHR measu emen s), was simila o he ela i e inconsis ency epo ed in he di ec signals compa ison. In u n, he SMPD alues calcula ed o he ollowing pa ame e s: HE_D, LE_D, STV, ACC, DEC, OSC_IV, di e signi ican ly om he alues epo ed o o he pa ame e s, and e en mo e TABLE 2 | Values o clinically impo an pa ame e s o quan i a i e desc ip ion o FHR-E and FHR-U signals, om FECG and US, ob ained in a compu e -aided e al moni o ing sys em, oge he wi h he symme ic mean pe cen age di e ence SMPD es ima ing he inconsis encies be ween bo h he me hods. Pa ame e s FHR_E FHR_U SMPD (%) Mean SD Mean SD M_FHR (bpm) 143.19 9.35 143.32 9.49 −0.1 M_BL (bpm) 141.70 9.55 141.79 9.60 −0.1 ACC (numbe ) 6.62 5.31 6.12 5.29 7.8 DEC (numbe ) 0.40 0.87 0.23 0.56 54.0 LTV (ms) 39.54 11.90 37.91 11.40 4.2 STV* (ms) 6.35 2.41 5.68 2.02 11.1 HE_D (min) 12.72 12.15 10.60 11.49 18.2 LE_D (min) 7.85 8.01 8.72 7.91 −10.5 HE_V (ms) 53.59 9.67 54.99 7.81 −2.6 LE_V (ms) 18.67 3.22 18.78 3.39 −0.6 OSC (ms) 13.40 3.80 12.91 3.70 3.7 OSC_I (%) 10.51 14.39 11.05 15.30 −5.0 OSC_II (%) 27.77 15.59 29.29 15.39 −5.3 OSC_III (%) 45.31 18.19 45.48 19.11 −0.4 OSC_IV (%) 8.96 9.25 7.81 9.06 13.7 *p<0.05 (pai ed - es ). om he esul s o he di ec compa ison. I con i ms he abo e men ioned assump ion ha some pa ame e s (e.g., STV) a e sensi i e o dis ibu ion o he FHR di e ences in ime, whe eas ano he ones (e.g., DEC) o a empo a y high di e ence alue. Pa icula ly, high SMPD =54% no ed o he numbe o ecognized decele a ions, is a esul s o wo ac o s: he di ec di e ences be ween he signal alues and he di e ences in he signal loss episodes. The signal loss o FHR_U is on a e age wice highe han o FHR_E. In addi ion, he au oco ela ion echnique, commonly used in he US me hod o de e mine he signal pe iodici y, is o en no able o ollow he apid dec ease o FHR signal ela ed o decele a ion, which esul s in signal loss episodes (Figu e 3). This, in u n, causes ha he decele a ion is F on ie s in Physiology | www. on ie sin.o g 8May 2017 | Volume 8 | A icle 305 Jezewski e al. FHR om: aFECG s. US no ecognized, because i does no mee he es ablished c i e ia o ampli ude and du a ion. Indi ec compa ison o he FHR_U and FHR_E signals was pe o med on he basis o he a iabili y indices de ined o signal ep esen ed as ime e en se ies— he hea bea s. Summa y o he esul s (mean alues, SD, and SMPD) o he selec ed 11 pa ame e s desc ibing he FHR signal a iabili y is p esen ed in Table 3. The esul s clea ly show ha he FHR_E signal is cha ac e ized by highe a iabili y hen he FHR_U. Inconsis encies o he long- e m a iabili y indices we e a abou 10%, whe eas o he sho - e m indices hey we e i e imes highe , eaching abou 50%. Fo he sho - e m a iabili y we no iced signi ican di e ence o bo h me hods. TABLE 3 | Resul s o he FHR_E and FHR_U signal analysis, conce ning he long- and sho - e m a iabili y, calcula ed using signal in a o m o ime e en se ies—a sequence o e en s une enly localized in ime, oge he wi h he SMPD alues es ima ing he inconsis encies be ween bo h he me hods. Index FHR_E FHR_U SMPD (%) Mean SD Mean SD Haan_LTI 21.89 14.69 20.62 14.59 6 Yeh_II 1022.89 1.60 2.57 1.53 12 O gan_LTV 8.18 4.46 7.35 4.35 11 Dal on_LTV 12.18 6.68 10.78 6.36 12 Zugaib_LTV 1022.22 1.25 2.01 1.21 10 Haan_STI 103# 6.29 1.94 3.10 1.02 68 Yeh_DI 103# 6.08 2.33 3.62 1.30 51 Geijn_STV* 15.27 23.70 8.98 13.51 52 Dal on_STV#1.80 0.65 1.01 0.32 56 Zugaib_STV 103# 2.77 1.02 1.76 0.58 45 SampEn+1.57 0.57 1.27 0.48 21 *p<0.03; +p<0.001; #p<0.0001 (pai ed - es ). Wi h ega d o such la ge inconsis encies i has o be decided which o he wo me hods may be conside ed as p o iding he FHR a iabili y desc ip ion being close o he ue one. The answe is no ob ious, because in his wo k no e e ence signal was acqui ed simul aneously wi h wo analyzed me hods. Such gold s anda d can be p o ided by p e iously men ioned he di ec e al elec oca diog aphy, whe e he pu e FECG is acqui ed om he e al head. In he p e ious s udies whe e he FHR signal om ul asound me hod was compa ed wi h he e e ence one, i has been shown ha ul asound me hod unde es ima es he sho - e m a iabili y on a le el be ween 20 and 40% in e e ence o di ec e al elec oca diog aphy. A simila end can be seen in Table 3, whe e he FHR_U is compa ed wi h FHR_E ob ained om he abdominal e al elec oca diog am. The signal da abase has been di ided in o wo g oups: no mal and abno mal, acco ding o he es ablished e al ou come c i e ia. The desc ip ion o wo signal g oups is shown in Table 4. Summa y o he FHR signal analysis esul s, comp ising 15 clinical pa ame e s de e mined o bo h g oups o e al ou come, a e shown sepa a ely o he ul asound me hod (Table 5) and abdominal elec oca diog aphy (Table 5). In addi ion o he mean alue and s anda d de ia ion, he mean pe cen age di e ence MPD was calcula ed, assuming he alues ob ained in no mal e al ou come g oup as he e e ence. Apa om assessing he s a is ical signi icance o he di e ence be ween he no mal and abno mal g oups, also he endency o changes was s udied o he pa icula pa ame e s be ween hese g oups. I was ca ied ou o check whe he he obse ed endency would be consis en wi h he clinical in e p e a ion o hose pa ame e s. Conside ing he numbe o ACC pa e ns, a signi ican di e ence be ween he abno mal and no mal g oups was no ed, and he endency was consis en . Bu o he numbe o DEC pa e ns no signi ican di e ence was obse ed. The MPD ook he opposi e alues: nega i e alue o ul asound (−48%) and posi i e o elec oca diog aphy (38%). Thus, a clinical in e p e a ion o decele a ions as a sign o e al dis ess has been con i med FIGURE 3 | An example o a 12-min agmen o signal pai — esul o an indi ec compa ison o e alua e he impac o he FHR signal acquisi ion me hod on clinically ele an pa ame e s, de e mined by a compu e -aided e al moni o ing sys em. The au oco ela ion echnique, commonly used in he US me hod o de e mine he signal pe iodici y, is o en no able o ollow he apid dec ease o FHR_U signal ela ed o decele a ion, which esul s in signal loss episodes. This, in u n, causes ha he decele a ion is no ecognized, because i does no mee he es ablished c i e ia o ampli ude and du a ion. G aphic ma ke s o he analysis esul s illus a e he signal loss (abo e he cu e), he es ima ed FHR baseline (line i ed on FHR cu e) and de ec ed decele a ion episodes (ho izon al ba s unde he cu e). F on ie s in Physiology | www. on ie sin.o g 9May 2017 | Volume 8 | A icle 305