Sphygmovolumetry

SPHYGMOVOLUMETRY, a method for measuring the dynamic work of the heart, based on determining the pulse wave volume and intravascular pressure; proposed and developed by Sahli. Sahli regards the pulse wave as a systolic increase in filling occurring almost throughout the entire arterial system. By measuring this systolic increment, respectively the stroke volume, we obtain one of the multipliers in the formula A (work) = V (volume) × P (pressure within the system). To measure the pulse wave volume during sphygmovolumetry, a trough-shaped pad 5 cm long and 2 cm wide made of hard rubber is placed over the radial artery. The edges of the pad are connected to each other by soft and elastic rubber. Inside the pad, an air space is formed that receives and transmits the vibrations of the pad to the recording system (see figure). The latter consists of a graduated capillary containing 0.2–0.5 cm³ of alcohol colored with fuchsin. This liquid index oscillates inside the capillary depending on the vibrations of the pad. The pad is pressed against the radial artery by a cuff equipped with a screw that regulates the degree of pressure. This entire system—the graduated capillary and the pad—is connected to a mercury manometer, which indicates the height of the pressure in the system, and to a bulb that makes it possible to change this pressure by adjusting the screw. The amplitude of the index oscillations changes depending on the height of the pressure in the system, becoming greatest at the so-called optimal pressure, when the external pressure on the vessel wall is in such a relation to the intravascular pressure that the resistance of the vascular wall to the transmission of the systolic increment of blood volume is eliminated, i.e., the extravascular and intravascular pressures are balanced. The optimal blood pressure is the second desired factor in the above formula—the extensibility factor P. By multiplying volume and pressure, we obtain the expression for heart work (at a constant coefficient—the specific gravity of mercury being 13.6); by multiplying the obtained value by the heart rate, we obtain the expression for the minute work of the heart. The average volume values in a healthy person are 0.1, and the optimal pressure is 90; consequently, the pulse work is equal to 9.0, and the minute work at a pulse rate of 70 is equal to 630.0. A series of clinical studies shows that sphygmovolumetry in combination with other research methods can provide certain indications of the functional state of the cardiovascular system. Thus, in states of sub- and decompensation of the heart, the values of volume and pulse work are reduced. In mitral insufficiency in a state of compensation, the values are unchanged; in stenosis, they are at the lower limits of the norm; in sub- and decompensation, a significant decrease in volume and pulse work is markedly noted. Aortic valve insufficiency is accompanied by a large pulse volume at a low optimal pressure. Arteriosclerosis with a satisfactory condition of the heart muscle yields average values; with cardiosclerosis, a significant decrease thereof. Essential hypertension yields high values of volume and pressure until heart failure develops. The method of sphygmovolumetry caused a major discussion and underwent serious criticism, in particular from Straub. Recently, the close relation of optimal pressure to the mean arterial pressure has become clear (Gelfand). Very close to sphygmovolumetry is the energometry proposed by Christen, which has essentially the same prerequisites.