English

Heat-washout: A New Method for Measuring Blood Flow Rate in Areas with and without Arteriovenous Anastomoses.

The thesis is based on seven articles made at the Panum Institute and Skejby Hospital.

The heat-washout method is a new atraumatic method for measuring blood flow rate (BFR) in skin. A tc-PO2 -probe made by Radiometer and specially constructed with a thermostatcally controlled cap that minimizes loss of heat to the surroundings was used. The probe is placed on the skin and fixed by adhesive tape, baseline temperature is registered, and subsequently the probe is heated electrically to a few degrees above normal skin temperature. After a few minutes the heating is turned off, and the local temperature under the probe is registered every 10 s until baseline temperature has been reached. Using the formula of Kety, f = k × λ × 100 ml(100g × min)-1, BFR under the probe can be calculated. When BFR was measured by heat in the capillaries of the skin of the underarm and compared to BFR in same areas measured by the 133xenon washout method, a correlation coefficient of 0.986 was obtained. BFR in the arteriovenous anastomoses (AVA´s) can be calculated by subtracting the BFR measured in the capillaries of the skin by the 133Xe-washout method from the total skin BFR measured by heat-washout in the same area.

Physiological and pathophysiological examinations were made of the AVA´s in the skin of the thumb and toe pulp. The measurements have shown that autoregulation of blood flow rate was not present in the AVA´s , nor was a veno-arteriolar reflex contrary to in the arterioles supplying the capillaries of the areas examined. Reactive hyperaemia was not registered in the AVA´s. At the onset of exercise with a moderate load, BFR in the AVA´s of the thumb decreased. After about 4 min of exercise, BFR increased to normal values again. In contrast, BFR in the skin fold between the thumb and the forefinger remained constant during the entire period of exercise. BFR in the thumb and toe pulp decreased with increasing age. No difference between men and women was registered, but BFR was significantly higher in the pulp of the thumb than in the toe pulp, and higher in the toe pulp in children than in adults.

BFR in the toe pulp of healthy subjects was compared to patients with claudication and critical ischaemia. The results showed that the AVA´s exhibited a distinct characteristic reaction as response to orthostatic changes. BFR in the AVA´s increased with a factor of 1.6 when the foot was placed 50 cm below heart level. Vascular surgical intervention normalised skin perfusion and responses to orthostatic changes.

BFR was measured in the subcutaneous capillaries of the forefoot and in the AVA´s of patients previously operated for a non-specific abdominal aneurysm and compared to normals. The measurements showed that capillary BFR in the patients increased with a factor four, indicating a reduced amount of elastic fibres in the wall of the capillaries even though the reaction to orthostatic changes was normal. The AVA´s reacted normally in all groups.

The heat-washout method has been found useful for measuring BFR in skin as well in a laboratory as in patients, and the method is considered useful within several specialities (clinical physiology, vascular surgery, dermatology, etc.)