title: Measuring venous oxygenation using the photoplethysmograph waveform.
abstract: OBJECTIVE
  We investigate the hypothesis that the photoplethysmograph (PPG) waveform can be analyzed to infer regional venous oxygen saturation.
  
  
  METHODS
  Fundamental to the successful isolation of the venous saturation is the identification of PPG characteristics that are unique to the peripheral venous system. Two such characteristics have been identified. First, the peripheral venous waveform tends to reflect atrial contraction. Second, ventilation tends to move venous blood preferentially due to the low pressure and high compliance of the venous system. Red (660 nm) and IR (940 nm) PPG waveforms were collected from 10 cardiac surgery patients using an esophageal PPG probe. These waveforms were analyzed using algorithms written in Mathematica. Four time-domain saturation algorithms (ArtSat, VenSat, ArtInstSat, VenInstSat) and four frequency-domain saturation algorithms (RespDC, RespAC, Cardiac, and Harmonic) were applied to the data set.
  
  
  RESULTS
  Three of the algorithms for calculating venous saturation (VenSat, VenInstSat, and RespDC) demonstrate significant difference from ArtSat (the conventional time-domain algorithm for measuring arterial saturation) using the Wilcoxon signed-rank test with Bonferroni correction (p < 0.0071).
  
  
  CONCLUSIONS
  This work introduces new algorithms for PPG analysis. Three algorithms (VenSat, VenInstSat, and RespDC) succeed in detecting lower saturation blood. The next step is to confirm the accuracy of the measurement by comparing them to a gold standard (i.e., venous blood gas).
authors.affiliation: Department of Anesthesiology, Yale University School of Medicine, 333 Cedar Street, P.O. Box 208051, New Haven, CT 06520-8051, USA.
authors.forename: Zachary D
authors.initials: ZD
authors.lastname: Walton
authors.forename: Panayiotis A
authors.initials: PA
authors.lastname: Kyriacou
authors.forename: David G
authors.initials: DG
authors.lastname: Silverman
authors.forename: Kirk H
authors.initials: KH
authors.lastname: Shelley
mesh_terms: D000465:Algorithms; D003627:Data Interpretation, Statistical; D004947:Esophagus / Q000378:metabolism*; D006801:Humans; D010100:Oxygen / Q000097:blood*; D017156:Photoplethysmography / Q000295:instrumentation* / Q000379:methods*; D011673:Pulsatile Flow; D014680:Veins
chemical_list: D010100:Oxygen