title: Can the descending aortic stroke volume be estimated by transesophageal descending aortic photoplethysmography?
abstract: OBJECTIVE
  The aim of this study was to investigate the ability of transesophageal photoplethysmography detected from the descending aorta (dPPG) for predicting low descending aortic stroke volume (dSV) level in cardiac surgical patients.
  
  
  METHODS
  Fifteen patients scheduled for elective cardiac surgery were enrolled in our study. A transesophageal echocardiography (TEE) probe with an attached oximetry sensor was placed into the esophagus for paired dPPG signal and descending aortic Doppler blood flow signal acquisition. Metrics, including alternating current (AC), direct current (DC), area under the curve (AUC) and width (W), were extracted from the dPPG signals. The TEE-measured dSV, which was defined as the blood flow through the descending aorta during a cardiac cycle, was chosen as the standard reference. A receiver operating characteristic (ROC) curve was built to evaluate the performance of dPPG metrics in predicting low dSV level, and dSV measuring agreement between TEE and dPPG was analyzed by the Bland-Altman method.
  
  
  RESULTS
  A total of 644 paired dPPG and Doppler signals of the descending aorta were acquired. Significant correlations were found between the dPPG metrics and TEE-measured dSV, and the correlation coefficients between TEE-measured dSV and AUC or AC were 0.64 and 0.66, respectively. AUC and AC values obviously decreased with the reduction of dSV level among the three groups (<20 mL, from 20-40 mL, and >40 mL). The areas under the ROC curve for AUC and AC in predicting low dSV level (<20 mL) were 0.85 and 0.88, respectively. Bland-Altman plot showed a small bias (0.02 mL) but a wide limit of agreement (-18.62 to 18.66 mL) in dSV measurement between dPPG and Doppler technology.
  
  
  CONCLUSIONS
  The AC and AUC extracted from the dPPG signal provided a sensitive and qualitative prediction for dSV level. The dSV value could not be accurately measured by dPPG metrics.
  
  
  BACKGROUND
  Chinese Clinical Trials Register Identifier: ChiCTR-OCS-12002789.
authors.affiliation: Department of Anesthesiology, West China Hospital, Sichuan University, No. 37 Guo Xue Xiang, Chengdu, 610041, Sichuan, People's Republic of China.
authors.forename: Peng
authors.initials: P
authors.lastname: Ling
authors.affiliation: Department of Orthopedics, West China Hospital, Sichuan University, Chengdu, 610041, Sichuan, People's Republic of China.
authors.forename: Gong
authors.initials: G
authors.lastname: Quan
authors.affiliation: Department of Anesthesiology, Children's Hospital, Chongqing Medical University, Chongqing, People's Republic of China.
authors.forename: Yu
authors.initials: Y
authors.lastname: Siyuan
authors.affiliation: Department of Physics, Sichuan University, Chengdu, 610041, Sichuan, People's Republic of China.
authors.forename: Gao
authors.initials: G
authors.lastname: Bo
authors.affiliation: Department of Anesthesiology, West China Hospital, Sichuan University, No. 37 Guo Xue Xiang, Chengdu, 610041, Sichuan, People's Republic of China. 111weiwei@sohu.com.
authors.forename: Wei
authors.initials: W
authors.lastname: Wei
mesh_terms: D000328:Adult; D000368:Aged; D001013:Aorta, Thoracic / Q000503:physiopathology*; D006348:Cardiac Surgical Procedures / Q000379:methods*; D015150:Echocardiography, Doppler / Q000379:methods; D017548:Echocardiography, Transesophageal / Q000379:methods; D017558:Elective Surgical Procedures / Q000379:methods; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010092:Oximetry; D017156:Photoplethysmography / Q000379:methods*; D012372:ROC Curve; D013318:Stroke Volume
keywords: Descending aorta; Doppler flow pattern; Photoplethysmography; Transesophageal echocardiography