title: Dual-channel photoplethysmography to monitor local changes in vascular stiffness.
abstract: OBJECTIVE
  Monitoring arterial distensibility changes is important to understand the cardiovascular status of patient. Pulse transit time (PTT), which is an inverse equivalent of pulse wave velocity (PWV), has shown its potential in such studies. However, its methodological approach in using an electrocardiogram and a peripheral photoplethysmography (PPG) is limited due to the inclusion of pre-ejection period (PEP) in its computation. Previous studies have suggested the using the transit time difference between two peripheral measuring sites (PTT-D) instead. However, it requires two medical instruments and may not be efficient in terms of equipment utility, especially in prolonged clinical studies.
  
  
  METHODS
  Postural changes are known to cause complex haemodynamics adaptation and thereby affecting transit time measurements. A customised dual-channel PPG system based on discrete electronic devices was constructed to evaluate against conventional peripheral-based PTT. 10 healthy adults (7 male; mean age 27.0 yr) were recruited to assess the differences observed in PTT and PTT-D during two postural change test activities.
  
  
  RESULTS
  PTT-D derived from the customised PPG system registered 43.3+/- 5.6 ms and - 31.1+/- 3.8 ms relative changes for the two regulated activities while conventional PTT recorded 43.6+/- 10.3 ms and -31.0+/-m 6.5 ms respectively. The former may have similar results but have significantly lower variance (< 0.05).
  
  
  CONCLUSIONS
  Findings herein suggest that PTT-D derived from the customised PPG system shows potential. It can be used as an alternative to conventional peripheral-based PTT and possibly as a direct assessment of arterial distensibility or PWV variations as it does not include PEP in its time-related computations.
authors.affiliation: Biomedical Engineering Research Centre, Nanyang Technological University, 6th Storey, XFrontiers Block, 50 Nanyang Drive, Research Techno Plaza, Singapore, 637553, Singapore. jong@ntu.edu.sg
authors.forename: Jong Yong Abdiel
authors.initials: JY
authors.lastname: Foo
authors.forename: Chu Sing
authors.initials: CS
authors.lastname: Lim
mesh_terms: D000328:Adult; D000465:Algorithms; D001158:Arteries / Q000502:physiology*; D003936:Diagnosis, Computer-Assisted / Q000379:methods*; D004548:Elasticity; D005260:Female; D006801:Humans; D008297:Male; D017156:Photoplethysmography / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D018924:Vascular Capacitance / Q000502:physiology*; D014655:Vascular Resistance / Q000502:physiology*