Biophysics in Cardiovascular Dynamics
SINCE the first employment of the U-tube mercury manometer by Poiseuille, to measure blood pressure, nearly a century ago, almost all study of hemodyna-mics has been by observation of blood pressure alone. In the last few decades it has been possible to measure also mean cardiac output in momentary fragments by the indirect methods of oxygen consumption and dye dilution. We have been primarily concerned with continuous and instantaneous direct measurement of flow into the arterial system, and its relations to blood pressure and peripheral resistance. A second concern is that measurements in experimental animals should be made under natural conditions, or without surgical trauma and the disturbance of anesthesia.
To this end, special electronic and surgical technics were developed. Figure 1 shows the position of an implanted electromagnetic flow transducer around a dog’s ascending aorta, and a catheter for sensing blood pressure. Connections to the outside are made through skin buttons; the flowmeter plugs into one, and a strain gauge pressure transducer is connected to another. A third button communicates with a small intravenous catheter, used for infusion and injection of vasoactive substances. At operation, performed at least one week before experiments and measurements, pressed polyvinyl sponge is placed between the edges of the flow transducer and the aorta, to prevent rapid erosion of the blood vessel wall. The junction of the artery and pressure-sensing tube is reinforced with Dacron arterial graft material sutured to the vessel and tied around the catheter.
Several electromagnetic flowmeters were investigated for this . . .