An intravascular cuff was devised with a short plastic cylinder and a latex membrane wrapping it, in order to examine the responsiveness of the canine inferior vena cava in vivo. The cuff was inflated by injecting saline through a catheter to make the membrane contact the vascular wall closely, and the change in the cuff pressure was recorded. An in vitro experiment with an isolated segment of the vein proved that the cuff detected quantitatively the active response of the vascular smooth muscle to norepinephrine (NE). The sensitivity to NE under this experimental condition was equal to that obtained previously with the isolated strip preparation. In the in vivo experiments, the cuff inserted into the segment between the liver and the renal veins of the inferior vena cava exhibited spontaneous rhythmic changes in pressure. In response to NE injected intravenously, dose-dependent increases in cuff pressure were observed. The responses recorded with the intravascular cuff were considered to be predominantly the active tension of the vascular smooth muscle, since influences of intestinal motion and changes in venous pressure on the cuff pressure were ruled out. The cuff picked up the response of the supradiaphragmatic segment of the inferior vena cava as well. The method seems to be useful for measuring the tone of larger veins.
