title: The effect of aorta unfolding and remodelling on oesophageal Doppler readings as probe depth is varied.
abstract: BACKGROUND
  The thoracic aorta elongates and unfolds with advancing age. Lateral displacement and tortuosity of the descending part may affect oesophageal Doppler monitoring (ODM) readings because probe alignment becomes slanted. This investigation aimed to relate aortic displacement as it appears on the chest radiograph with variations in ODM readings as the probe is inserted to different depths.
  
  
  METHODS
  In anaesthetized patients a series of three to five ODM stroke volume (SV) readings were obtained at insertion depths of 35-45 cm during stable haemodynamics. The coefficient of variation (CV=standard deviation/mean %) was calculated. The degree of descending aorta unfolding was measured by (i) lateral displacement (LD), that is, the difference in the maximum and minimum distances between the midline and para-aortic line; and (ii) curvature angle (CA), the angle formed by a tangential line from the intersection of the para-aortic line and the diaphragm to its curve with the vertical line.
  
  
  RESULTS
  Data from 70 patients were analysed. The median CV of SV readings was 14% (range 4-48). Variation between ODM readings, shown by the CV of SV readings, increased linearly with aortic unfolding: R2=0.44 for LD and R2=0.60 for CA. Patients with a CA ≤15° were younger and had significantly lower CVs of ODM readings than those with a CA >15° (P=0.001). Age and hypertension was associated with increased CA.
  
  
  CONCLUSIONS
  Increased lateral displacement and tortuosity of the descending aorta reduces the reliability of ODM measurements as probe depth is varied, especially with aging.
authors.affiliation: Department of Anesthesiology, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, China.
authors.forename: J
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Department of Anaesthesia and Intensive Care, Prince of Wales Hospital, Chinese University of Hong Kong, Shatin, New Territories, Hong Kong SAR hcritchley@cuhk.edu.hk.
authors.forename: L A H
authors.initials: LA
authors.lastname: Critchley
authors.affiliation: Department of Anesthesia and Surgical Intensive Care, Peking University First Hospital, Beijing, China.
authors.forename: L
authors.initials: L
authors.lastname: Huang
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000473:pathology; D000768:Anesthesia, General; D001013:Aorta, Thoracic / Q000000981:diagnostic imaging / Q000473:pathology*; D015150:Echocardiography, Doppler / Q000295:instrumentation / Q000379:methods*; D017548:Echocardiography, Transesophageal / Q000295:instrumentation / Q000379:methods*; D005260:Female; D006439:Hemodynamics; D006801:Humans; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000295:instrumentation / Q000379:methods*; D012372:ROC Curve; D013318:Stroke Volume; D014057:Tomography, X-Ray Computed
keywords: aortic unfolding; oesophageal Doppler; stroke volume