The regulation of subcutaneous adipose tissue blood flow in the ischaemic forefoot during 24 hours. Studies using the 133-xenon wash-out technique continuously over 24 hours

Abstract

A method for continuous measurement of subcutaneous adipose tissue blood flow in the forefoot during 24 hours (SBF) is described. The method is based on the radioisotope wash-out principle using 133-Xenon. A portable semiconductor detector is placed just above a local depot of 1-2 microCi 133-Xenon in 0.1 ml isotonic saline injected into the subcutaneous adipose tissue in the forefoot. The detector is connected to a memory unit allowing for storage of data. Due to the short distance, the recorded elimination rate constant must be corrected for combined convection and diffusion of the radioactive indicator. Characteristic 24-hour blood flow patterns were unveiled in patients with normal peripheral circulation and in patients having ischaemic nocturnal rest pain. In normals SBF doubled from day to night. This is ascribed to the local veno-arteriolar sympathetic axon reflex, which induces arteriolar vasoconstriction when the transmural pressure of the veins exceeds approximately 25 mmHg. In patients having ischaemic rest pains SBF was reduced by 37% on the average from day to night. This was caused by nocturnal hypotension, which is reflected proportionally in the foot. As the resistance vessels most probably are fully dilatated in feet with rest pain, the blood pressure drop during sleep causes the perfusion pressure and thus blood flow to come below a certain critical limit. There was a pronounced correlation between the reduction of systemic mean arterial blood pressure and SBF. The patients complaining of intermittent claudication, but no rest pains showed a variety of changes in SBF compatible with the continuous spectrum of the peripheral arteriosclerotic disease. After reconstructive vascular surgery, the 24-hour blood flow pattern normalized although the ankle/arm systolic blood pressure index did not come within normal range. SBF during day-time activities decreased by up to 50% postoperatively. This is caused by the reappearance of the local, sympathetic, veno-arteriolar vasoconstrictor response. During sleep SBF increased by 71%. The term postreconstructive hyperaemia seems improper, at least in a long-term context, normalization of preoperative ischaemia is a more correct notation. The coefficient of variation of nocturnal SBF was calculated to 10%. The method thus seems apt as a monitor in medical therapy for occlusive arterial disease. Changes of lambda has, however, to be considered in each study.