Measurement of the suspension stability of blood in vivo in large blood vessels of the upper limb and in varicose veins

Abstract

A method of measuring the suspension stability of blood in vivo in large blood vessels of the limbs is described. The method is based on observation of the rate of increase of haematocrit resulting from settling of red cells under gravitational field in the vessels during temporary occlusion. The direction of settling may be centripetal from the microcirculation or centrifugal towards it, depending on the orientation of the limb. When centripetal, the rate of increase of haematocrit in an occluded large vessel of a limb provides a measure of the suspension stability of blood in that part of the microcirculation in continuity with the vessel. The method was applied to measurement of centripetal settling from the microcirculation under differing flow velocities in it. The low settling velocity into a normal superficial vein of the forearm when the circulation in the limb was unrestricted was consistent with high suspension stability of blood in the microcirculation during normal flow. The high settling velocity into the vein and into the brachial artery during temporary arrest of the limb circulation was consistent with low suspension stability of blood in the microcirculation in stasis. When the method was applied to measurement of centripetal settling -into the varicose great saphenous vein in the thigh from the microcirculation in continuity with it, the circulation of the limb being unrestricted, a high settling velocity was observed. This finding was consistent with reduced suspension stability of blood in the microcirculation drained by varicose veins. Centrifugal settling in the unoccluded great saphenous vein in the leg and thigh during standing resulted in a small but statistically significant increase of haematocrit in it.