Blood circulation in rat lungs under conditions of reduced oxygen level in inhaled air.

According to some authors, reduction in oxygen level in the lung alveoli results in constriction of afferent vessels, while others observed no vessel constriction. The issue is of principle importance in relation to the lung involvement in body adaptation to hypoxia. Conventional methods are inefficient to solve it, therefore we used a contact microscope allowing observation of lung circulatory system structure and condition of the lung circulatory system in whole, virtually intact animal, on whole undamaged lungs in situ, at normal physiological lung position in the thorax. We found that large vessels carrying blood to the alveoli do not constrict or dilate at reduced Po(2)in lung alveoli. These vessels with a diameter of 15 to 40 μ and more are the only blood source for alveoli.