The ornamental design for a sphygmomanometer, as shown and described.
FIG. 1 is an isometric projection from an upper right perspective of a sphygmomanometer according to the invention;
FIG. 2 is an isometric projection from a lower right perspective of the sphygmomanometer according to the invention;
FIG. 3 is a front view of the sphygmomanometer according to the invention;
FIG. 4 is a right side view of the sphygmomanometer according to the invention;
FIG. 5 is a left side view of the sphygmomanometer according to the invention;
FIG. 6 is a top view of the sphygmomanometer according to the invention; and,
FIG. 7 is a bottom view of the sphygmomanometer according to the invention.
The broken lines immediately adjacent the shaded areas represent the bounds of the claim, while all other broken lines are directed to environment and are for illustrative purposes only; the broken lines form no part of the claimed design.