R kennedy hfes 2012 visual aids

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  • 1. The Influence of Visual Aids onDetecting Early and Late Decelerationsin Maternal Fetal Heart Rate PatternsRebecca A. Kennedy, Brittany L. Anderson-Montoya,Mark W. Scerbo, Erik Prytz, Lee A. Belfore, IIOld Dominion UniversityAlfred Z. Abuhamad, Stephen S. Davis, Suneet P. ChauhanEastern Virginia Medical SchoolOctober 23, 2012HFES 56th Annual Meeting
  • 2. Introduction Maternal-fetal heart rate (MFHR) Presented on either a computer screen or a paper strip Clinicians assess for different critical patterns NICHD proposed a three-tiered system (Category I, Category II,Category III) (Macones et al., 2008)
  • 3. Introduction Clinicians must identify decelerations (decels) in theFHR and discriminate between those that are earlyand late in nature Late decels are considered abnormal Early decels look similar, but are considered reassuring
  • 4. IntroductionEarlydecelsLatedecelscontractionscontractionsfetal heartratefetal heartrate
  • 5. Introduction Several studies have found disagreement in theinterpretation of FHR signals Between individuals, and within the same individual at twodifferent points in time (Blackwall et al., 2011; Chauhan et al., 2008; Freeman,2002)
  • 6. Introduction Anderson and colleagues have assessed how wellindividuals could differentiate between early and latedecels… …under different levels of beat-to-beat FHR variability As signal-to-noise (S/N) ratio decreased, fewer correct detectionswere made (Anderson et al., 2008) …with late decels occurring at different time frames In the first study: Undergraduate students had trouble differentiating types of decels,especially at shorter onset delays (Anderson et al., 2010) In a second study: Trained clinicians produced the same pattern of results (Anderson et al., 2011)
  • 7. Introduction Results from previous studies suggest that theinspection of FHR tracings might be improved with avisual aid Visual cues can help direct attention, increaseaccuracy, and decrease response time (Wickens & Hollands,2000; Chaney & Teel, 1967)
  • 8. Present Study Purpose: examine how well individuals can differentiatebetween early and late decels using Four different signal-to-noise ratios (absent, minimal,moderate, marked) Five different onset times (0, 4, 8, 12, and 16 sec) With and without the visual aids Hypothesis: visual aid would act as a cue and wouldimprove detection performance Primarily at lower S/N ratios and shorter late decel onset times
  • 9. Method Participants were 21 undergraduate students (14male; 7 female) from ODU Ranged in age from 18 to 24 (M = 19.33) All had normal or corrected-to-normal vision
  • 10. Method Static images were created using a MFHR simulator Each image contained one contraction and either a latedecel or early decel
  • 11. Method Four S/N ratios for FHR were generated Conformed to the four categories designated by theNICHDAbsentS/N Ratio =10:1ModerateS/N Ratio = 2:1MinimalS/N Ratio = 5:1MarkedS/N Ratio =1:1
  • 12. Method For the visual aid condition, a semitransparentturquoise crosshair cursor was overlaid on the image Horizontal bar placed at mean of beat-to-beat FHRvariability Vertical bar placed at the peak of the contraction
  • 13. Method Prior to the experimental session, participants viewedexamples of early and late decels Responded verbally to 8 practice images In the experimental session, participants twice viewedthe same 80 images Image presented for 3 sec, after which a response screenappeared Session performed in two blocks – with/without visual aids
  • 14. Results 2 (aid presence) x 2 (block order) x 4 (variability) x 5(signal delay) mixed factorial ANOVA Order of aid-absent and aid-present blocks was a betweensubjects factor DV was proportion of correct identifications (early orlate)
  • 15. Results Significant main effect of visual aid presence, F(1, 19) =25.23, p < .05, partial ƞ2 = .570Aid present Aid absent.74 (.02) .66 (.02)Mean (and standard error) proportion of correctdetections for each aid condition
  • 16. Results Significant Delay x Variability interaction, F(12, 228) =13.25, p < .05, partial ƞ2 = .411Mean proportion of correct detections for eachS/N ratio and signal onset delayProportion ofcorrect detections
  • 17. Results For late decels, correct responses increased asdelayed onset increased Sidak Bonferroni test indicated that all means were significantlydifferent except between 0- and 12- sec, 0- and 16-sec, and 8- and12-sec delaysMean SE0 sec 0.83 0.034 sec 0.40 0.048 sec 0.69 0.0312 sec 0.74 0.0216 sec 0.84 0.02Mean proportions of correct responses for each signal onset delayNote: A delay of 0 indicates an early deceleration
  • 18. Results As S/N ratio decreased (i.e., variability increased),correct response rate decreased Sidak Bonferroni test indicated that all means differed significantly,except for between the absent and minimal categoriesMean SEAbsent 0.81 0.02Minimal 0.80 0.02Moderate 0.69 0.02Marked 0.50 0.02Mean proportions of correct responses for each level of variability
  • 19. Discussion Hypothesis: visual aids would improve detectionperformance especially for lower S/N ratios and shorteronset times Partially supported Presence of visual aids was associated with higher overall levels ofcorrect responses Delay x Variability interaction revealed that the benefit of the visualaid was seen primarily in the minimal variability category However, under lower S/N ratios (moderate and markedvariability), the aid did not make a statistically significantdifference Presence of decels may be masked to such a degree that aids donot help
  • 20. Conclusion The results provide initial evidence that a visual aidwas useful However, the visual aid is not a complete solution Decels occurring at moderate and marked levels of FHRvariability, especially with short onsets, are stillproblematic A next step is to evaluate the potential benefit of thevisual aid with clinical providers manipulating thevisual aid in real time
  • 21. Thank you!Questions?Rebecca A. Kennedy, M.S.rkenn014@odu.edu