The ornamental design for a sphygmomanometer, as shown and described.
FIG. 1 is a front view of the sphygmomanometer;
FIG. 2 is a rear view of the sphygmomanometer;
FIG. 3 is an end view of the sphygmomanometer;
FIG. 4 is an opposite end view of the sphygmomanometer;
FIG. 5 is a right side view of the sphygmomanometer;
FIG. 6 is a left side view of the sphygmomanometer; and,
FIG. 7 is a perspective view of the sphygmomanometer.
In FIGS. 1, 3, 5, 6, and 7, the dash-dot line indicates a boundary of the claimed subject matter and the dashed lines within the dash-dot lines indicate environmental subject matter that forms no part of the claimed subject matter.