"In high grade thickening of the arterial walls, however, especially where calcification had occurred, Fischer found that the sounds were distinctly less loud than normal, the more so in the arm, which showed the greater degree of hardening. According to Ettinger's experience, the rapidity of the flow distinctly increases the auscultatory phenomenon." (Gittings.)
The sounds depend upon the resonating character of the cuff, upon the size and accessibility of the vessel, upon the force of the heart beat, and upon the velocity of the blood.
The Maximum and Minimum Pressures
The maximum (systolic) pressure is read at the point where the first audible click is heard after the cuff is blown up and the pressure gradually reduced by means of the needle valve in the hand bulb or on the upright of the glass containing the mercury. All are agreed upon this point. There has been some dispute as to the place where the diastolic pressure should be read. Korotkov considered that the diastolic pressure should be read at the fourth phase when the loud tone suddenly becomes dulled. Others held that the diastolic pressure should be read at the fifth phase, the absence of all sound. Experiments carried out to determine this point were made by me with the assistance of Prof. Eyster and Dr. Meek at the Physiological Laboratory of the University of Wisconsin. We arranged apparatus making it possible to hold the pressure in the carotid artery of dogs at maximum or minimum. A femoral artery was then dissected and an instrument devised to compress the artery with a water jacket. The whole was connected up with a kymograph. A time marker was put in so as to record the place where changes in sound were heard while listening below the cuff around the femoral artery. Two sets of records were taken. One with pressure greater than minimum pressure and a falling pressure over the femoral artery (Fig. 29), the other with pressure at zero and gradually raised to minimum pressure (Fig. 30). Both sets of records showed the same result; viz., that at a point corresponding to the sudden change of tone the pressure on the artery corresponded to the minimum pressure. It was therefore concluded that experimentally in dogs the point where diastolic pressure should be read is at the tone change from clear to dull, not at the point where all sound disappears.
Fig. 29.—Tracing of auscultatory phenomena. (See explanation in legend of Fig. 30.)
