Reflex control of the veins in cardiovascular function

The veins are more than conduits for the return of blood. In this presentation, I plan to give perspective, some of what is known, and place major emphasis on pitfalls of understanding and inter-preting venous physiology. First of a!, what do we know for sure? The veins are compliant, such that an increase in internal pressure causes an increase in volume. They have smooth muscle, for, when stimulated, they contract and thereby reduce the contained volume at the same pressure. But, they are innervated sparsely. We also know much about the elastic nature of the large veins (>2 mm in diameter) and quite a bit about the pharmacology of the veins that can be easily visualized. What we do not know for sure is the importance of the veins in the reflex control of cardiovascular function. How much do they influence arterial pressure and /or cardiac output and under what conditions? Many of us think they are important, but many others disagree. The effect is clearl