title: The development and testing of new instruments for operative vaginal delivery.
abstract: OBJECTIVE
  Little innovation has occurred in recent years in the instruments available for operative vaginal delivery. The purpose of this study is to develop a technique to test the utility of an investigational device, the obstetric bonnet, and measure the forces it places on the fetal head.
  
  
  METHODS
  We constructed a model of the fetal head capable of measuring both compression and vacuum created by an applied device. A total of 18 devices were tested to a maximum traction of 60 pounds.
  
  
  RESULTS
  A significant linear relationship exists between the traction applied and the compression (R2 = 0.42, p = 0.0004) and vacuum (R2 = 0.85, p = 0.0001) created. Compression and vacuum recorded at maximum recommended traction were 1.1 lb/sq in and 31 cm Hg, respectively.
  
  
  CONCLUSIONS
  These findings explain the mechanics of this interesting device, and demonstrate forces that compare favorably with those known to occur with forceps or vacuum extraction.
authors.affiliation: Department of Obstetrics and Gynecology, University of Texas Health Science Center, San Antonio 78284-7836.
authors.forename: B D
authors.initials: BD
authors.lastname: Elliott
authors.forename: L E
authors.initials: LE
authors.lastname: Ridgway
authors.forename: M D
authors.initials: MD
authors.lastname: Berkus
authors.forename: E R
authors.initials: ER
authors.lastname: Newton
authors.forename: W
authors.initials: W
authors.lastname: Peairs
mesh_terms: D005260:Female; D005333:Fetus; D006257:Head; D006801:Humans; D011247:Pregnancy; D014143:Traction; D014620:Vacuum Extraction, Obstetrical / Q000295:instrumentation*