Regulation of Blood Flow to Respiratory Muscles during Hypoxia and Hypercapnia 1

Abstract

The effect of systemic hypoxia or hypercapnia on regional blood flow was measured in respiratory muscles, limb muscles, and kidneys of rabbits by using radioactive microspheres. Blood flow to both the diaphragm and the intercostal muscles was increased in a direct relationship with the severity of the hypoxia or hypercapnia in spontaneously breathing animals. Blood flow to the kidneys decreased while blood flow to limb muscle remained unchanged. During mechanical ventilation, following paralysis with Flaxedil, blood flow to the respiratory muscles was about 10% of that seen during quiet breathing and was unchanged by hypoxia or hypercapnia. Renal flow decreased as in the nonparalyzed animals while flow to limb muscle remained unchanged during the hypoxic and hypercapnic episodes. It is concluded that the major factor involved in regulating blood flow to the respiratory muscles is their level of activity.