Hemorheological changes during venous stasis as result of tourniquet application.

We read with interest the paper of Rosenson and Tangney [1] on the effect of tourniquet application on plasma viscosity measurements. Hemorheological changes have been detected in various conditions in which there are variations in blood velocity and pressure. They have been demonstrated, for instance, in vascular diseases with the reduction of the blood supply to the tissue due to an obstruction or a stenosis in the arterial tree and the consequent increase in the viscosity of the blood coming from the ischemic area [2,3]. The important increase in venous blood viscosity that we have seen in these conditions was, in our opinion, dependent on relevant hemodynamic and metabolic changes in the capillary bed, with consequent variations in the rheological behavior of circulating blood cells [4]. As these hemorheological variations probably happened in microcirculation as the result of hemodynamic changes in the arterial tree, it seemed important to study if hemodynamic changes in the venous tree, capable of modifying the microcirculatory blood flow and velocity, could determine similar effects. In order to study this problem we prepared an experimental model of venous stasis in man. The results that are here presented have been already published in 1987 [5] and 1990 [6]. Venous stasis was performed in an arm we placed at heart level on a table with the subject in sitting position. We examined 10 volunteers (6 males, 4 females, mean age 56± 8). Venous stasis was obtained with a pneumatic cuff, inflated at a pressure 10 mm Hg lower than the diastolic pressure, around the arm. This model was prepared with the purpose of stopping venous blood flow only for a limited amount of time, as we saw that pressure in the veins, measured by means of a Quartz Transducer, is 5–10 mm Hg ahead of that in the cuff after no more than 30 seconds. So, after this first period, in the venous bed under stasis the blood continues to flow, even if at a higher pressure and at a lower velocity, and we collect the venous blood distally to the cuff when it leaves the microcirculatory bed. Blood samples were withdrawn from the antecubital vein, before and after 1, 2, 3, 4, 5, 10 minutes of venous stasis and 1 minute after the release of the cuff pressure. Hematocrit (Wintrobe), Blood Viscosity (Haake Rotovisco), Whole Blood Filterability [7], pH, pO2, pCO2 (I.L. 1302 Gas Analyzer) were measured in the samples. Transcutaneous pO2 and pCO2 were measured simultaneously by means of a Kontron Tc Microgas 7640, placing the transducer on the forearm. Statistical analysis was made using Student’s t-test for paired data.