Regional hypoxic pulmonary vasoconstriction in prone pigs

Departments of 1 Medicine, and 2 Physiology and Biophysics, University of Washington, Seattle; and 3 Mountain Whisper Light Statistical Consulting, Seattle, Washington Submitted 2 August 2004 ; accepted in final form 15 March 2005 Hypoxic pulmonary vasoconstriction (HPV) is known to affect regional pulmonary blood flow distribution. It is unknown whether lungs with well-matched ventilation ( )/perfusion ( ) have regional differences in the HPV response. Five prone pigs were anesthetized and mechanically ventilated (positive end-expiratory pressure = 2 cmH 2 O). Two hypoxic preconditions [inspired oxygen fraction (F I O 2 ) = 0.13] were completed to stabilize the animal's hypoxic response. Regional pulmonary blood and distribution was determined at various F I O 2 (0.21, 0.15, 0.13, 0.11, 0.09) using the fluorescent microsphere technique. and in the lungs were quantified within 2-cm 3 lung pieces. Pieces were grouped, or clustered, based on the changes in blood flow when subjected to increasing hypoxia. Unique patterns of response to hypoxia were seen within and across animals. The three main patterns (clusters) showed little initial difference in / matching at room air where the mean / range was 0.92–1.06. The clusters were spatially located in cranial, central, and caudal portions of the lung. With decreasing F I O 2 , blood flow shifted from the cranial to caudal regions. We determined that pulmonary blood flow changes, caused by HPV, produced distinct response patterns that were seen in similar regions across our prone porcine model. hypoxia; altitude; pulmonary vascular resistance Address for reprint requests and other correspondence: M. P. Hlastala, Division of Pulmonary and Critical Care Medicine, Box 356522, Univ. of Washington, Seattle, WA 98195-6522 (E-mail: hlastala{at}u.washington.edu )