Foot vascular resistance index: a noninvasive method to assess foot vasomotor tone

A new objective hemodynamic technique has been evaluated to assess foot vasomotor tone pre- and postoperatively in patients undergoing lumbar sympathectomy alone or as an adjunct to vascular reconstructive surgery. A foot vascular resistance index at rest (FVRIR) and after reactive hyperemia (FVRIHT) was determined with a noninvasive plethysmographic method. The ankle-to-toe systolic pressure gradient and foot blood flow were measured with strain gauge plethysmorgraphy and were combined in a ratio to provide an index of vascular resistance. The indices were measured in patients without vascular disease who were used as controls and in patients undergoing lumbar sympathectomy alone or in conjunction with aortic reconstructions. Patients who underwent reconstructive procedures alone had a mean FVRIR which approximated the control value. In contrast, those patients who, in addition, had a lumbar sympathectomy had a significant reduction in the mean postoperative FVRIR which equalled the mean preoperative FVRIHT. Three of five patients undergoing lumbar sympathectomy alone had excellent preoperative hyperemic responses and benefited from the operation, whereas two patients with poor hyperemia had no benefit and had subsequent amputations. Our studies suggest that this technique is of value in the pre- and postoperative assessment of foot vasomotor tone and also may be useful in the preoperative prediction of response to lumbar sympathectomy.