Spatial distribution of hypoxic pulmonary vasoconstriction in the supine pig

• Published in: Journal of applied physiology (1985) 2004-05, Vol.96 (5), p.1589-1599
• Main Authors: Hlastala, Michael P, Lamm, Wayne J. E, Karp, Adam, Polissar, Nayak L, Starr, Ian R, Glenny, Robb W
• Format: Article
• Language: English
• Subjects: Airway Resistance; Animals; Biological and medical sciences; Female; Fundamental and applied biological sciences. Psychology; Hogs; Hypoxia - physiopathology; Inhalation; Lungs; Male; Microspheres; Oxygen; Pulmonary arteries; Pulmonary Circulation; Respiratory system; Supine Position; Swine; Vasoconstriction; Ventilation-Perfusion Ratio
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.00211.2003

Departments of 1 Physiology and Biophysics and 2 Medicine, University of Washington, Seattle 98195-6522; and 3 The Mountain-Whisper-Light Statistical Consulting, Seattle, Washington 98112-2913 Submitted 28 February 2003 ; accepted in final form 18 November 2003 Hypoxic pulmonary vasoconstriction (HPV) serves to maintain optimal gas exchange by decreasing perfusion to hypoxic regions. However, global hypoxia and nonuniform HPV may result in overperfusion of poorly constricted regions leading to local edema seen in high-altitude pulmonary edema. To quantify the spatial distribution of HPV and its response to regional P O 2 (Pr O 2 ) among small lung regions, five pigs were anesthetized and mechanically ventilated in the supine posture. The animals were ventilated with an inspired O 2 fraction (F I O 2 ) of 0.50 and 0.21 and then (in random order) 0.15, 0.12, and 0.09. Regional blood flow ( ) and alveolar ventilation ( A ) were measured by using intravenous infusion of 15 µm and inhalation of 1-µm fluorescent microspheres, respectively. Pr O 2 was calculated for each piece at each F I O 2 . Lung pieces differed in their response to hypoxia in a manner related to their initial A / with F I O 2 = 0.21. Reducing F I O 2 < 0.15 decreased to the initially high A / (higher Pr O 2 ) regions and forced into the low A / (dorsal-caudal) regions. Resistance increased in most lung pieces as Pr O 2 decreased, reaching a maximum resistance when Pr O 2 is between 40 and 50 Torr. Local resistance decreased at Pr O 2 < 40 Torr. Pieces were statistically clustered with respect to their relative response pattern to each F I O 2 . Some clusters were shown to be spatially organized. We conclude that HPV is spatially heterogeneous. The heterogeneity of response may be related, in part, to the heterogeneity of baseline A / . hypoxia; pulmonary circulation; high-altitude pulmonary edema; heterogeneity; ventilation-perfusion; fluorescent microspheres 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 ).