Traumatic Shock. Xii. Hemodynamic Effects of Alterations of Blood Viscosity in Normal Dogs and in Dogs in Shock 1

Abstract

Striking differences have been noted between dogs in hemorrhagic and in tourniquet shock (1). In both types, there is a reduction in blood volume, but the hematocrit and blood viscosity, which remain substantially unchanged in hemorrhagic shock, increase in tourniquet shock. At a blood pressure level of 80 to 100 mm. Hg, the dog in hemorrhagic shock is only mildly depressed and is still responsive to ordinary stimuli; whereas, in tourniquet shock he is already severely depressed, unresponsive to strong stimulation, much more sensitive to further slight blood loss, and is in a state of rapid deterioration. When the pressure falls below 70 to 80 mm. Hg in tourniquet shock, the collapse is precipitous; whereas, the unanesthetized dog in hemorrhagic shock can tolerate a blood pressure of 50 mm. Hg for many hours. These differences have been explained on the basis of a toxin from devitalized tissue (2, 3) or bacteria (4) in the tourniqueted extremity. The successful treatment of tourniquet shock in the unanesthetized dog by plasma infusion alone (1) constitutes evidence against the "toxin" hypothesis.Since the increase in blood viscosity in tourniquet shock is one of the outspoken differences between tourniquet and hemorrhagic shock, the effect of increased blood viscosity on blood flow in the intact and shocked animal was investigated to see how far it might explain the sharp disparity between these two types of shock. METHODAccording to Poiseuille's equation (5) that the formula can be used to relate viscosity to blood flow through the perfused isolated hind limb of the dog.In the intact animal, therefore, blood flow (or cardiac output) may be considered to be determined by the mean arterial pressure, a constant, and the total peripheral resistance (TPR). The TPR is the product of blood viscosity (v) and the peripheral resistance (R) which is dependent upon the number, length, and diameter of the blood vessels. The data obtained in the following experiments represent an effort to quantitate all the factors in Poiseuille's equation. The cardiac output, the mean arterial pressure and the blood viscosity (X) were measured, while the constant and peripheral resistance (R) were determined indirectly. With such data the effect of blood viscosity on total blood flow can be evaluated.(a) Determination of peripheral resistance (R)Total peripheral resistance (TP R) in the animal as a whole is ordinarily calculated from the formula TP R = Pressure

The Determination of Blood Viscosity in Man by a Method Based on Poiseuille's Law

“…Absolute viscosity of a fluid can be determined by passing the fluid through a tube of known length and radius while measuring the rate of flow and the difference in pressure between the ends of the tube. This relationship is expressed by the following formula: fTr q81' (1) where vi = absolute viscosity in grams sec. per cm.3; q = volumetric rate of flow as cm.'…”

“…diameter, blood behaves as a homogeneous mixture (10), and at physiological pressures its flow is laminar (8). According to formula (1), viscosity is independent of the character of the vessel wall and a tube may be substituted for a blood vessel to allow an accurate determination of length and radius. The insertion of such a branching system does not invalidate Poiseuille's law.…”

“…The viscosity of the blood is an important factor in any consideration of blood flow or peripheral resistance (1). In addition, a change in blood viscosity has been implicated in many clinical conditions (2)(3)(4)(5)(6).…”

The Circulating Red Cell and Plasma Volume and the Distribution of Blood in Large and Minute Vessels in Experimental Shock in Dogs, Measured by Radioactive Isotopes of Iron and Iodine 1

“…Hg in mean arterial pressure. It has been pointed out (38) that the blood pressure may be a misleading guide to the state of the animal when the blood viscosity is abnormally high due to a high hematocrit. In such event, the blood flow, as indicated by cardiac output, is very poor in spite of nearly normal blood pressure.…”

Myocardial Blood Flow and Oxygen Uptake During Acute Red Cell Volume Increments

“…In a hemodynamic evaluation of shock, Seligman 1 indicated that enhanced blood viscosity promoted the onset of irreversibility, presumably through an effect on flow. More recently Richardson 2 assigned a major role to viscosity in the development of a diminished cardiac output during acute normovolemic polycythemia.…”