Introductory Chapter: Fascinating Blood

1. Introduction

“The blood jet is poetry and there is no stopping it.”

Sylvia Plath, ‘Ariel’.

Ancient people were aware of blood’s importance and fascinated by its mystery. According to the belief, Medusa had two kinds of blood circulating through her vessels: lethal blood on her left side, and life-giving blood on her right side. Later the humoral pathology theory of Hippocrates proposed the human body as a vessel for four liquids: yellow bile, black bile, white phlegm, and red blood. Each corresponds to one of the four classical elements – fire, earth, water, and air and one of the traditional four temperaments – sanguine, choleric, phlegmatic, and melancholic. Later, Galen proposed that blood was made in the liver from food and drink carried from the digestive tract. An ideal balance among the four humors was the key to good health [1]. Inspecting blood samples from patients and determining the relative amounts of each humor was the method for the diagnosis of an imbalance. Bloodletting treatments were common practice, and described in detail by Avicenna in his “Canon of Medicine”. This theory shaped the practice in Greek, Roman, and Islamic philosophy and medicine for many centuries until the nineteenth century [2].

In today’s view, blood is a type of connective tissue in fluid form. Formed elements suspended in the plasma fluid circulate throughout the body within the cardiovascular system. While the primary function is to transport oxygen, nutrients, and other substances; its specific functions also include defense, distribution of heat, and maintenance of homeostasis throughout the body.

2. Hemodynamics

Hemodynamics is the study of the mechanical and physiologic properties controlling blood pressure and flow through the body, “the physical study of flowing blood and of all the solid structures (such as arteries) through which it flows” [3]. This classical area of physiology emphasizes the fluid and solid mechanics of the cardiovascular system, concerning the distribution of pressures and flows in the circulatory system. Control of the circulatory system is through the homeostatic mechanisms of autoregulation. Many biological processes, physical factors influence blood flow (and vice versa). In addition to systemic hemodynamic alterations, microvascular alterations are frequently observed in critically ill patients. The hemodynamic response continuously monitors and adjusts to conditions in the body and its environment. Some parameters have been defined to quantify blood flow and its relationship with systemic circulatory changes. There is a constant development of the instrumentation and the techniques together with increasing capabilities for numerical computation. Complex and extensive factors influence hemodynamics. Understanding the interactions between different blood flow variables help to better interpret their implications in variable physiopathological conditions. Also, the help of improved imaging techniques is undeniable. Future research is expected to focus mainly on the interactions between hemodynamics and biological processes involving active cellular responses [4].

3. Hemorheology

The study of blood flow is called hemodynamics, and the study of the properties of the blood flow is called hemorheology. Blood is a non-Newtonian shear-thinning fluid and therefore is most efficiently studied using rheology rather than hydrodynamics [5]. The blood flow properties include blood viscosity which depends on plasma viscosity, hematocrit, red blood cell (RBC) aggregation, and RBC deformability [6]. The RBCs have a unique ability to deform and pass through small capillaries before rapidly recovering their initial shape. Under most flow conditions RBCs behave like fluid drops [7]. Due to the liquid-like behavior of RBCs under shear stress, blood can also be considered as a liquid-liquid emulsion. White blood cells and platelets can also affect blood rheology but, under normal conditions, RBCs represent most of the cellular components and make the biggest contribution to blood viscosity [8].

Hemorheological alterations occur in a wide range of physiological and pathophysiological conditions. In many diseases, the deformability of RBCs is impaired as a result of defects in cell membrane skeletal architecture, RBC aging, and mechanical damage [9, 10, 11]. Adverse hemorheological alterations may decrease tissue perfusion. Since control of blood flow is directly related to the metabolic conditions of the tissue, the perfusion change can be compensated by controlling the vascular geometry (i.e., diameter) component of flow resistance.

4. Thalassemia

RBCs show rheological abnormalities, also when thalassemia is present. Currently seen most frequently in the tropical belt, thalassemias remain a serious global health problem. Thalassemias are a group of inherited microcytic, hemolytic anemias characterized by defective hemoglobin synthesis. Alteration of the cell membrane may result from the interaction between the defective hemoglobin chain and the membrane cytoskeleton [12]. However, other changes are caused by hemoglobin denaturation [13]. Previous works suggest that the decreased RBC deformability is probably due to microcytosis that is present even in thalassemia carriers [14]. Recent work also suggests the presence of additional but yet unknown causes [15]. Thalassemia results from unbalanced hemoglobin synthesis caused by decreased production of at least one globin polypeptide chain. Symptoms and signs result from anemia, hemolysis, splenomegaly, bone marrow hyperplasia, and if there have been multiple transfusions, iron overload. Endothelial injury, splenomegaly, and transfusion-related hemodynamic alterations play an important role in the altered hemodynamics of thalassemia [16, 17, 18].

5. Conclusion

For future research, the concepts of hemodynamics and hemorheology will retain their importance with their basis in the understanding of fluid and solid mechanics. A better understanding of the biological processes involving active cellular responses provided by advanced techniques is the key.

To serve this purpose, the first section of the present book is dedicated to present novel developments and updates on various topics in the frame of hemodynamics:

• Four-dimensional flow magnetic resonance imaging (4D flow MRI) is a relatively new imaging technique. It offers the ability to measure and visualize the temporal evolution of complex blood flow patterns within an acquired 3D volume, allowing for the computation of multiple hemodynamic metrics.

• Robot-assisted laparoscopic pelvic surgery seems safe and efficacious. A thorough understanding of the underlying pathophysiology together with meticulous monitoring would help to better cope with the possible cardiovascular complications.

• Autoimmune diseases is another factor affecting hemodynamic homeostasis. Multiple sclerosis may present with altered cervical and cerebral perfusion that is important for the pathophysiology and the clinical implications of the disease.

• Recent work designates oxidative stress as a critical determinant of blood flow dynamics. Hemodynamic laminar shear stress in oxidative homeostasis regulation by the induced shear stress/Krupple-like factor2/Nrf2/ARE pathway appears significant.

• Anemia patients under critical conditions require hemodynamic guidance for accurate assessment of the volume and the transfusion threshold and deciding the best algorithm for the resuscitation of these patients.

The second section of this book is a thalassemia update. Concisely, this section gives an update and novel developments in thalassemia. Four chapters present an outline of B-thalassemia, the early diagnostic tools, and strategies in thalassemia, together with the approaches for the obstacles of pulmonary hypertension and Hepatitis C virus infection.

The chapters of this book may not seem to be in complete harmony. However, in the present era of fast communications, we aimed to provide some novelties in the field. This work serves an audience from different backgrounds providing a review on a variety of selected topics with the purpose of an update.

Acknowledgments

I would like to thank Prof Talip Asil for his kind effort in reviewing one of the chapters. I would also like to appreciate Author Service Manager Ms. Marica Novakovic and Commissioning Editor Ms. Ana Simcic for their constant help.