title: Lung ventilation and perfusion in prone and supine postures with reference to anesthetized and mechanically ventilated healthy volunteers.
abstract: BACKGROUND
  The literature on ventilation (V) and lung perfusion (Q) distributions during general anesthesia and controlled mechanical ventilation in supine and prone position is contradictory. The authors aimed to investigate whether V, Q, and ventilation to perfusion ratio (V/Q ratio) matching in anesthetized and mechanically ventilated volunteers are gravity dependent irrespective of posture.
  
  
  METHODS
  Seven healthy volunteers were studied at two different occasions during general anesthesia and controlled mechanical ventilation. One occasion studied ventral to dorsal V and Q distributions in the supine posture and the other in the prone posture. Imaging was performed in supine posture at both occasions. A dual radiotracer technique and single photon emission computed tomography were used. V and Q were simultaneously tagged with Tc-Technegas (Tetley Manufacturing Ltd., Sydney, Australia) and In-labeled macroaggregates of human albumin (TechneScan LyoMAA, Mallinckrodt Medica, Petten, The Netherlands), respectively.
  
  
  RESULTS
  No differences in V between postures were observed. Q differed between postures, being more uniform over different lung regions in prone posture and dependent in supine posture. The contribution of the vertical direction to the total V/Q ratio heterogeneity was larger in supine (31.4%) than in prone (16.4%) (P = 0.0639, two-tailed, paired t test) posture.
  
  
  CONCLUSIONS
  During mechanical ventilation, prone posture favors a more evenly distributed Q between lung regions. V distribution is independent of posture. This results in a tendency toward lower V/Q gradients in the ventral to dorsal direction in prone compared with supine posture.
authors.affiliation: Department of Molecular Medicine and Surgery, Karolinska Institute, Solna, SE 171 76 Stockholm, Sweden. sven.nyren@karolinska.se
authors.forename: Sven
authors.initials: S
authors.lastname: Nyrén
authors.forename: Peter
authors.initials: P
authors.lastname: Radell
authors.forename: Sten G E
authors.initials: SG
authors.lastname: Lindahl
authors.forename: Margareta
authors.initials: M
authors.lastname: Mure
authors.forename: Johan
authors.initials: J
authors.lastname: Petersson
authors.forename: Stig A
authors.initials: SA
authors.lastname: Larsson
authors.forename: Hans
authors.initials: H
authors.lastname: Jacobsson
authors.forename: Alejandro
authors.initials: A
authors.lastname: Sánchez-Crespo
mesh_terms: D000328:Adult; D000768:Anesthesia, General; D005260:Female; D006801:Humans; D007205:Indium Radioisotopes; D008168:Lung / Q000000981:diagnostic imaging / Q000502:physiology*; D008297:Male; D010092:Oximetry; D010100:Oxygen / Q000097:blood; D016684:Prone Position / Q000502:physiology*; D011652:Pulmonary Circulation / Q000502:physiology*; D019275:Radiopharmaceuticals; D012121:Respiration, Artificial; D015656:Respiratory Mechanics / Q000502:physiology*; D013670:Sodium Pertechnetate Tc 99m; D016683:Supine Position / Q000502:physiology*; D015899:Tomography, Emission-Computed, Single-Photon
chemical_list: D007205:Indium Radioisotopes; D019275:Radiopharmaceuticals; C056708:Technegas; D013670:Sodium Pertechnetate Tc 99m; D010100:Oxygen