An elderly woman who resides in a nursing home has a pressure sore on her left heel a few days. She has hypertension and coronary arterial disease. Vital signs are normal. Both feet feel cool and are of equal temperature. She has weak but palpable distal pulses on the good foot, but her distal pulses on the left side are not palpable. There are unilateral petechiae on the dorsum of the left foot.