title: A new and simple Doppler method for measurement of fetal cardiac isovolumetric contraction time.
abstract: OBJECTIVE
  The fetal cardiac isovolumetric contraction time is defined as the interval between mitral valve closure and aortic valve opening. The objective of this study was to develop a simple and reliable Doppler method for measuring fetal isovolumetric contraction time using a digital filtering and processing system.
  
  
  METHODS
  Cardiac Doppler signals were recorded from 40 fetuses at 18-40 weeks' gestation using a continuous-wave ultrasound transducer. The raw signal was digitized, filtered and divided into five different frequency ranges: 250-375, 375-500, 500-750, 750-1000 and 1000-1500 Hz. To determine the most suitable filter setting for detecting mitral valve closure and aortic valve opening signals, we examined whether they were detected clearly in each filter range.
  
  
  RESULTS
  Both mitral valve closure and aortic valve opening signals were detected clearly in the 500-1000 Hz range. The atrioventricular flow and outflow noises in the 250-500 and 1000-1500 Hz ranges helped us to identify the signals. It was found that dividing the raw signals into three ranges of 250-500, 500-1000 and 1000-1500 Hz was the most suitable digital-filter setting for measuring isovolumetric contraction time.
  
  
  CONCLUSIONS
  We have developed a simple Doppler method for measuring fetal isovolumetric contraction time. The advent of digital processing has simplified the equipment and the simultaneous multidisplay of three different filtered signals enables easy and accurate measurement.
authors.affiliation: Department of Obstetrics and Gynaecology, University of Sydney, Westmead Hospital, Westmead, NSW, Australia. fwl@westgate.wh.usyd.edu.au
authors.forename: T
authors.initials: T
authors.lastname: Koga
authors.forename: N
authors.initials: N
authors.lastname: Athayde
authors.forename: B
authors.initials: B
authors.lastname: Trudinger
authors.forename: H
authors.initials: H
authors.lastname: Nakano
mesh_terms: D001021:Aortic Valve / Q000000981:diagnostic imaging / Q000502:physiology; D002306:Cardiac Volume; D015150:Echocardiography, Doppler / Q000379:methods*; D005260:Female; D005318:Fetal Heart / Q000000981:diagnostic imaging*; D006801:Humans; D008943:Mitral Valve / Q000000981:diagnostic imaging / Q000502:physiology; D009200:Myocardial Contraction; D011247:Pregnancy; D016216:Ultrasonography, Prenatal