Distribution of Pulmonary Perfusion in Healthy and Injured Lungs

Abstract

The classical concept for understanding the heterogeneity of regional pulmonary blood flow distribution is West’s concept of lung zones; Zones have been defined by the relationship of blood pressure in pulmonary arteries and veins to the pressure of air within the alveolar space [1]. Three such zones have been described: Areas of no flow where alveolar pressure exceeds arterial pressure; areas of ‘waterfall’ flow where alveolar pressure exceeds venous, but not arterial blood pressure; and a zone of continuous flow through arteries and veins where alveolar pressure is lower than both blood pressures. In this article, current data are reviewed that may challenge this model for the in-vivo situation. Since West’s classical description, much has been learned about the design principle nature uses to create complex trees such as the pulmonary vasculature and bronchial tree. New imaging techniques provide the clinician with overwhelming amounts of data, and progress in this field will continue to enhance resolution of pulmonary structures. We will outline a new concept of distribution of pulmonary blood flow which at the same time gives due credit to the complex structure of the pulmonary vessel tree and can reduce any amount of data on pulmonary perfusion to a single parameter describing heterogeneity.