The ornamental design for a sphygmomanometer, as shown and described.
FIG. 1 is a front, top and right side perspective view of an embodiment of a sphygmomanometer showing our new design;
FIG. 2 is a rear, bottom and left side perspective view thereof;
FIG. 3 is a front elevational view thereof;
FIG. 4 is a rear elevational view thereof;
FIG. 5 is a top plan view thereof;
FIG. 6 is a bottom plan view thereof;
FIG. 7 is a right side elevational view thereof; and,
FIG. 8 is a left side elevational view thereof.
The broken lines shown in the drawings are for illustrative purposes only and form no part of the claimed design. The dotted chain lines shown in the drawings define the bounds of the claimed design and form no part of the claimed design.