Influence of peripheral arterial disease on capillary pressure in the foot

Background: Capillary perfusion and transmural pressure are delicately regulated by microvascular constriction mechanisms, which are activated upon a change in posture. Capillary flow is known to be disturbed in patients with severe peripheral arterial disease. To date, however, the influence of this disease on capillary pressure is unknown. Methods: Capillary pressure in the nail fold of the hallux, ankle, and toe blood pressures were measured in the sitting and supine positions in 8 patients with intermittent claudication (F2), in 7 patients with rest pain and/or ischemic ulcers (F3-4), and in 12 age-matched healthy controls (F0). Red blood cell velocity, laser Doppler flux, and continuous blood pressure of the second toe were measured simultaneously. Toe, ankle, and brachial pressure were measured after the experiment in both positions. Results: Capillary pressure did not increase significantly with increasing disease severity (F0, F2, and F3-4) in supine (P =.37; medians, 17, 21, and 14 mm Hg, respectively) and sitting (P =.96; medians, 59, 60, and 60 mg Hg, respectively) positions, whereas toe systolic pressure did, both in supine (P <.001; medians, 91, 49, and 14 mm Hg, respectively) and sitting (140, 104, and 64 mm Hg, respectively) positions. Nutritive skin perfusion (red blood cell velocity) decreased with increasing disease severity (F0, F2, and F3-4) while supine (P =.005; medians,. 19,.20, and .04 mm/s, respectively) and while sitting (P =.06; medians,.22,.15, and .04 mm/s, respectively). Conclusions: An increase in orthostatic pressure increases both toe and capillary pressures. Arterial insufficiency of the leg seems to leave the capillary pressure unscathed. Apparently, arteriolar vasodilation compensates for the lower arterial pressure in both positions, even in patients with rest pain and low nutritive perfusion.