Rheological Therapy
Gordon D. O. Lowe in Clinical Blood Rheology, 2019
The chapter presents a general overview of rheological approaches to therapy. With linear increase in hematocrit, systemic oxygen transport capacity increases linearly, whereas blood viscosity increases logarithmically. Increase in total and local blood volume flow rates is the major mechanism by which systemic oxygen transport capacity is maintained during acute hemodilution. Donor human albumin may be provided as a solution or as a freeze-dried powder for reconstitution with sterile water immediately before transfusion. Hydrodynamic and rheological factors are important in the filter design, to minimize pore plugging and flow decay. Ancrod and batroxobin are thrombin-like enzymes which are purified from pit viper venom, and are commercially available in Europe for their anticoagulant and rheological therapeutic effects. Intramuscular injection of lignocaine to normal subjects caused transient, small but significant decreases in plasma and blood viscosity, without change in hematocrit or red cell filtration.
Rheology of Cerebrovascular Disease
Gordon D. O. Lowe in Clinical Blood Rheology, 2019
The relationship between cerebral blood flow and viscosity is a closer one than that between cerebral blood flow and hematocrit, both on baseline measurement before any treatment and also in individuals who have been venesected or hemodiluted. Vasodilatation can compensate for the increase in peripheral resistance produced by a rise in viscosity. Changing blood viscosity by the means described is likely to be much more effective than surgical attempts to improve cerebral perfusion. Factors raising blood viscosity, notably the hematocrit, have been demonstrated to have an important effect on reducing cerebral blood flow. More experimental work needs to be done on plasma factors that influence viscosity and also on red cell flexibility, before their effects on the cerebral circulation can be satisfactorily assessed. The potential dangers of rheological treatment should be appreciated, particularly the reduction in oxygen carrying capacity of blood after hemodilution.
Rheology of Normal and Abnormal Pregnancy
Gordon D. O. Lowe in Clinical Blood Rheology, 2019
Pregnancy presents a dynamic challenge to maternal cardiovascular physiology and the alterations that take place during pregnancy are among the most wide-ranging occurring in pathological states. Before considering the changes in materal hemorheology found in pathological pregnancy, it is important to have a good understanding of the hemorheological profile throughout normal healthy pregnancy. Maternal cigarette smoking in pregnancy has been clearly associated with low birth weight of the fetus, preterm delivery, increased fetal loss, and long-term impairment of mental and physical growth in the child. Abnormal hemorheology has been extensively reported in diabetic patients, the main components of their diabetic hyperviscosity being a reduction in red cell deformability and an elevation in plasma fibrinogen level. Artificial elevation of the hematocrit by unnecessary administration of iron in pregnancy could be disadvantageous, and factors which are known to produce hyperviscosity states in the nonpregnant subject, such as cigarette smoking and hypertension are associated with impaired fetal nutrition.
Neural Network Predicts Fetal Hematocrit in Fetal Isoimmunization
Published in Journal of Maternal-Fetal Medicine, 1993
Andrzej Lysikiewicz, Steven Inglis, Luis A. Bracero, Frank Chervenak, Nergesh Tejani
A neural network was used for prediction of fetal hematocrit in the fetal isoimmunization syndrome. In cases of isoimmunization, fetal hematocrit was predicted by artificial intelligence. Using parametric variables of last measured fetal hematocrit, gestational age, estimated fetal weight, interval since the last transfusion, antibody titer, and the nonparametric criteria of type of isoimmunization and sequence of transfusion, a neural network was programmed. The fetal hematocrit predicted by a formula based on an expected hematocrit decrease of 1% per day was compared with fetal hematocrit predicted by the neural network for accuracy of prediction of fetal anemia. Correlation coefficients, sensitivity, specificity, and positive and negative predictive values were compared for accuracy of the prediction. Fetal hematocrit predicted by the neural network correlated more closely with actual fetal hematocrit than hematocrit predicted by the formula. Both predictors showed only a modest correlation with actual values (R = 0.36 and 0.08, respectively). The neural network had significantly better sensitivity to predict fetal anemia than the formula of hematocrit decrease of 1% per day (P < 0.05). A neural network can identify more anemic fetuses with a hematocrit less than 20% than the formula of hematocrit decrease of 1 % per day.
Studies of the Bodyhematocrit Phenomenon: Dynamic Hematocrit of a Large Vessel and Initial Distribution Space of Albumin and Fibrinogen in the Whole Body
Published in Scandinavian Journal of Clinical and Laboratory Investigation, 1968
Larsen, O. A. Studies of the Bodyhematocrit Phenomenon: Dynamic Hematocrit of a Large Vessel and Initial Distribution Space of Albumin and Fibrinogen in the Whole Body. Scand. J. clin. Lab. Invest. 22, 189-195, 1968. By measuring the mean circulation times of 125I-labelled albumin and 51Cr-labelled red cells from the femoral vein to the pulmonary artery it has been shown that the dynamic hematocrit of this vascular area is 99 per cent of the hematocrit determined by centrifugation of a venous blood sample. It is therefore possible for all practical purposes to regard the centrifuge hematocrit as equal to the dynamic hematocrit in a large vessel. The distribution volume of T-1824 and 131I-labelled fibrinogen has been determined simultaneously in 10 patients. T-1824 space exceeded fibrinogen space by 6.4 per cent. The explanation for the difference between the bod yhematocrit and the large vessel hematocrit appear to a major degree to be due to a low intravascular hematocrit caused by a more rapid passage of the red cells than of the plasma through the microvasculature and to a lesser degree to the fact that the normally used plasma indicators overestimate the plasma volume.
Influence of Hypotension on Cochlear Blood Flow in Polycythemic Condition
Published in Acta Oto-Laryngologica, 1996
Yoshimitsu Ohinata, Kazuo Makimoto, Hiroaki Takahashi
We examined the influence of hypotension by infusion of acebutolol hydrochloride (AH), a cardioselective β-receptor antagonist, on cochlear blood flow in guinea pigs with various hematocrit values. AH infusion lowered the mean blood pressure to almost the same degree in all animals, regardless of the hematocrit level. the degree of the concomitant decrease of CBF varied with the hematocrit, being greater in animals with a higher hematocrit. in those with the highest hematocrit CBF did not return to the initial level. From these values we calculated the 02 transport capacity after AH infusion and found it to be lower than in animals without AH infusion. the difference was greater at higher hematocrits. These findings suggest that the microcirculation of the inner ear is responsive to transient decreases of perfusion pressure at high hematocrits.