W. F. Walker

The preparation and stability of radioiodinated antipyrine for use in local blood flow determinations

The accurate assessment of local blood flow by recording the washout of a deposit of radiolabelled 4-iodoantipyrine (4-IAP) requires the use of a stable radiopharmaceutical. This communication shows that it is possible to produce a 125I and 131I-4-IAP compound which fulfills this requirement under simulated conditions of use.

The effect of the transcutaneous electrode on the variability of dermal oxygen tension changes

Transcutaneous oxygen measurements (TCPO2) are being used increasingly for the assessment of tissue viability in the ischaemic limb. The major objective with such a technique is to determine the critical level of TCPO2 which defines the boundary between skin viability and non-viability. To be able to do this, an assumption is made that measurements from different centres using various TCPO2 sensors are comparable. This study shows that static and dynamic changes of TCPO2 (air to oxygen breathing) made with two commercially available instruments are not directly comparable. We suggest that the physical characteristics of present TCPO2 electrodes are not optimal for measurements on adult skin. TCPO2 measurements made in conditions of skin ischaemia should be interpreted with caution because the ratio of local oxygen demand to blood flow is such that the measurement may be underestimated by TCPO2 electrodes with a high oxygen consumption.

A rationale for skew flaps in below-knee amputation surgery

The use of thermography in the assessment of amputation levels has demonstrated a medial to lateral thermal gradient in many cases. In order to see whether this reflected a true medial to lateral skin blood flow gradient, a prospective study was set up to measure blood flow medially and laterally below the knee. Twenty-one patients, presenting for amputation assessment with end-stage peripheral vascular disease, were studied. Skin blood flows were measured using an intradermal radioisotope clearance technique. Results showed a highly significant difference between medial and lateral skin blood flows (t = 4.79; p < 0.001). In view of the significantly higher blood flow in the medial skin of the lower leg, it is suggested that a more medially based posterior below-knee amputation skin flap may be of more value in some patients.

Assessment of tissue viability in relation to the selection of amputation level

Assessment of the optimum level of amputation of an ischaemic limb can be exceptionally difficult. For this reason there has been an intensive effort, particularly in the past 20 years, to find suitable non-invasive ancillary methods to aid in the amputation level selection. This paper reviews three separate research and development areas which have evolved simultaneously in our laboratory: skin partial oxygen pressure, skin blood flow, and infrared thermography. The physiological basis for each of these measurements is discussed along with the merits and demerits of each.

The relationship between temperature isotherms and skin blood flow in the ischemic limb

This study was conducted in order to establish a relationship between thermographically defined levels of viability in the ischemic limb and a measurement of skin blood flow. Color thermograms (10 colors, 0.6 degree C apart) defined the temperature gradient and skin blood flow was measured, using the radioactive clearance method in three discrete isotherms set 1.8 degrees C apart. The differences in skin blood flow measured in the three separate isotherms were significant (P less than 0.001). The results of this study support previously unqualified assertions that thermographic temperature gradients along an ischemic limb are indicative of local microcirculatory status. The potential of the thermographic method for demarcating viable and nonviable skin flaps at the chosen site of amputation is confirmed.

Arterial Systolic Pressures in Critical Ischemia

Segmental systolic pressures were measured in a group of patients with clinically irreversible ischemia. There was a good relationship between the level of pressure in a limb and the eventual outcome, but a particular level of pressure was found to be a poor indicator of a specific level of viability. These results support previous concern about the limitations of systolic pressure measurements in determining the level of limb viability. We suggest that local intrinsic regulation of the microcirculation plays a major role in the ultimate survival of tissues in an ischemic limb.

Further Experience in the Healing Rate of Lower Limb Amputations

Results of lower limb amputation in the Tayside Region in the years 1981-1985 have been analysed. Three-hundred and twenty-four amputations were performed on three-hundred and eight patients. Two-hundred and thirty-six amputations were attempted at the below-knee level. Only 19 required proximal revision. Prior to amputation, all patients should have a detailed vascular assessment, and the operation should be performed by experienced amputation surgeons using meticulous technique.

QUANTITATIVE MEASUREMENT OF CUTANEOUS BLOOD FLOW USING RADIOACTIVE TRACERS

A great deal of effort has focussed on the research and development of non-invasive techniques for evaluating cutaneous blood flow. Significant methodological improvements have been made but the structure, function and architectural arrangement of blood vessels in the skin has meant that the “ideal” technique has yet to be found. Indeed, the concept of an average or mean skin blood flow is itself erroneous because of the complexity of the microvascular arrangements in a solid tissue matrix. Yet, in a clinical context, there is a demand for a simple average measurement of skin perfusion. Clearly, a compromise has to be reached between what in reality is “impossible” to measure and that which is a crude but clinically useful index of nutritional status. Clinically, a method should preferably be noninvasive, inexpensive, easy to use, reproducible and have diagnostic reliability and credibility such that the measurements provided are easily understood by all who use them. Of the techniques so far developed none would appear to fulfil all of these criteria.