Oxygen lack as a possible cause of reactive hyperemia

Abstract

The relationship of blood flow through the hind leg of a dog to the gaseous content of the blood has been studied in 20 dogs by two different methods. In 15 dogs the oxygen saturation of the blood flowing through the leg was gradually changed by adding various amounts of venous blood to arterial blood. As the oxygen saturation decreased the blood flow increased—slowly at first, then progressively more rapidly as the oxygen levels fell lower and lower. Even though the oxygen saturation in most experiments was decreased to 30%, the total oxygen transported to the tissues each minute (O₂ saturation times blood flow) decreased only to 75% of the control value. This showed that a definite compensatory mechanism exists, with an efficiency of about 65% for preventing tissue hypoxemia. In five animals the oxygen saturation of the blood was maintained constant while the dogs were allowed to breathe 20% carbon dioxide for an hour. By checking the blood flow every 10 minutes it was found that there was no increase in blood flow but rather in three of the animals a decrease to the extent of 35% of the control blood flow and in the remaining two no change. These studies indicate that oxygen deficiency might well be one of the causes of reactive hyperemia but that excess carbon dioxide probably is not involved.