Noninvasive determination of skin perfusion pressure using a laser Doppler

Laser Doppler (LD) measures blood flow in approximately one cubic millimeter of tissue. The LD instrument is well suited to the determination of the initiation of flow in the microcirculation after a period of arrest due to externally applied counterpressure. Radioisotope clearance and photoplethysmography have been used to measure skin perfusion pressure (SPP) in an effort to predict healing of ischemic ulcerations and amputation wounds. By placing the LD probe beneath a blood pressure cuff, SPP was measured at the forearm, thigh, calf, foot, dorsal and plantar great toe. The SPP was measured in 32 normal limbs and 26 limbs with rest pain, ulceration or gangrene. Skin of normal extremities and forearm and thigh skin of patients with ischemic lower extremities had a mean SPP of 47 mmHg (+/- 5 SEM). The SPP in ischemic extremities was significantly lower at the calf 22 +/- 4 (p less than .001), the foot 10 +/- 2 (p less than .0001), and the toe 16 +/- 4 (p less than .0001). SPP was greater at the plantar toe (73 +/- 5) than in all other locations. Skin of the plantar toe was unique among the sites measured because it is rich in arteriovenous anastomoses, which have a thermoregulatory function. The higher pressure probably reflects the fact that the larger arterioles have a higher intraluminal pressure than the capillaries and, therefore, a more proximal level of the microcirculation is measured by the LD instrument in thermoregulatory areas of the skin.(ABSTRACT TRUNCATED AT 250 WORDS)