SPHYGMOGRAPH, an instrument by which we ascertain, and permanently record, the form, force, and frequency of the pulse-beat, and the changes which that beat undergoes in certain morbid states. This instrument consists of two essential parts: (1) Of two levers, one of which is so delicately adjusted on the vessel the pulsation of which it is desired to examine, that on each expansion of the vessel the lever undergoes a correspond ing slight elevation: this lever communicates by a perpendicular arm with a second, to which it transmits the impulse received from the vessel; the extremity of this second lever is armed with a pen-point, which records the movements thus iudicated on a mova ble plate, controlled by the second part of the instrument. (2) The second portion con sists of a plate, moved by watch-work, and bearing a strip of paper on which the sphyg mographic tracery is formed.
Mode in which the Tracery is the pulse transmits through the levers a ver tical movement to the pen-point, and the plate, on which the tracery is formed, is moved steadily across the pen-point, an undulating line is the result: the height of the elevations indicating the strength of the pulse; and the number of the elevations delineated in the time the pen takes to travel its frequency. The tracings produced by the pulse at the
wrist in forms of cardiac disease exhibit the manner in which the tracing is modified in diseased states of the circulatory system. In the case of a patient suffering from an incompetent state of the valves guarding the orifice of the aorta, the great vessel con veying blood from the heart, the blood, when propelled into the aorta, distends it, and communicates a pulse throughout the arterial system. When the vessel again contracts, regurgitation takes place into the cavity of the heart, as the valves, which should prevent this regurgitation, andmaintain the arterial tension, are unable to perform their function. The pulse-beat is accordingly abrupt, and of short duration, and the sphygmographic tracing presents a series of abrupt elevations and depressions. In a different form of cardiac disease, in which the valves are so affected as to obstruct the passage of the blood into the circulation, the effect on the pulse is to render its beats weakly marked and irregular; and in the sphygmographic tracing, the elevations are dimin ished in height and regularity. The pulse, in extreme forms of this lesion, is represented in sphygmographic tracing by a slightly waving line.