Regional ventilation-perfusion distribution is more uniform in the prone position

Abstract

The arterial blood PO(2) is increased in the prone position in animals and humans because of an improvement in ventilation (VA) and perfusion (Q) matching. However, the mechanism of improved VA/Q is unknown. This experiment measured regional VA/Q heterogeneity and the correlation between VA and Q in supine and prone positions in pigs. Eight ketamine-diazepam-anesthetized, mechanically ventilated pigs were studied in supine and prone positions in random order. Regional VA and Q were measured using fluorescent-labeled aerosols and radioactive-labeled microspheres, respectively. The lungs were dried at total lung capacity and cubed into 603-967 small ( approximately 1.7-cm(3)) pieces. In the prone position the homogeneity of the ventilation distribution increased (P = 0.030) and the correlation between VA and Q increased (correlation coefficient = 0.72 +/- 0.08 and 0.82 +/- 0.06 in supine and prone positions, respectively, P = 0.03). The homogeneity of the VA/Q distribution increased in the prone position (P = 0.028). We conclude that the improvement in VA/Q matching in the prone position is secondary to increased homogeneity of the VA distribution and increased correlation of regional VA and Q.

Quantification of pulmonary blood flow (PBF): Validation of perfusion MRI and nonlinear contrast agent (CA) dose correction with HO positron emission tomography (PET)

“…Therefore, the combination of Eqs. [3] and [A1] can be simplified to S͑c͒ ϭ S 0 .f͑T 1,0 ,T* 2,0 ,c͒, [4] where f is a sole function of T 1,0 , T * 2,0 , and c for a certain set of pulse sequence parameters. Dividing this SI by an arbitrarily chosen normalization SI S norm at concentration c norm eliminates the constant S 0 and yields…”

“…Hence, it is desirable to quantitatively measure hemodynamic parameters like regional pulmonary blood flow (PBF) for evaluation of regional variations (2,3). Different approaches for quantification of pulmonary perfusion have been made using microspheres (4), positron emission tomography (PET) (5), and magnetic resonance imaging (MRI) (6,7).…”

Advances in magnetic resonance imaging of lung physiology

“…Functional differences between prone and supine postures need to be considered; for example, blood flow and V A/Q heterogeneity are more uniform in the prone posture (68). Gravity has an influence on the distribution of pulmonary perfusion, lung density, and alveolar size (11,12,29) that is dependent on posture (51), and the prone and supine postures differ both from one another and also from the upright posture (51).…”

Pressure-controlled versus volume-controlled ventilation during one-lung ventilation in the prone position for robot-assisted esophagectomy

“…When assuring free abdominal and chest movements, the prone position does not significantly affect the respiratory system compliance and hemodynamics and improves oxygenation during general anesthesia [6,15,16]. The suggested mechanisms of improving oxygenation during the prone position are alveolar recruitment, improved V/Q matching, and reduced parenchymal lung stress and lung strain through the elimination of compression of the lungs by the heart and redistribution of perfusion and ventilation, which provide the rationale for ventilating patients with acute respiratory distress disease (ARDS) in the prone position [16][17][18][19][20]. However, the development of hypoxemia during OLV depends mainly on the magnitude of the Qs/Qt of the nonventilated lung and the matching of the V/Q in the ventilated lung, in which gravity plays a pivotal role [4,5].…”