Large venous compliance in carboxyhemoglobinemia and hemodilutional anemia

Anesthetized dogs were prepared for the measurement of compliance of the inferior vena cava by placement of a catheter for pressure measurement and a pair of ultrasonic dimension transducers for the measurement of transverse diameter. Measurements of compliance were made in a control state, after the induction of carboxyhemoglobinemia or hemodilutional anemia, by measuring pressure changes and diameter changes during brief occlusions of the inferior vena cava downstream from the transducers. Carboxyhemoglobinemia caused an upward shift of the averaged pressure-diameter curve while there was a negligible shift in the hemodiluted group. These results indicate that in carboxyhemoglobinemia a change in the compliance of the vena cava occurs, which favours augmented venous return by improved conductance rather than by a dislocation of blood by constriction of the large venous reservoir. In hemodilutional anemia the change in compliance is insignificant, but venous return is favoured by the reduced viscosity.