Viscoelasticity combines the elastic properties of substances and the viscous properties of fluids, and in the human body it is mainly present in soft tissues in addition to blood. In the blood, the viscosity of the substance increases as part of the hyperviscosity syndrome. In soft tissues, disorders of viscoelasticity may occur in the context of neuromuscular diseases.
What is viscoelasticity?
Viscoelasticity combines the elastic properties of materials and the viscous properties of fluids, and in the human body is found primarily in soft tissues in addition to blood. Material can behave in different ways. One possible material behavior is elasticity, which allows substances to return to their original position after force is applied. Viscosity describes the viscosity of a fluid and thus corresponds to a measure of the fluidity of a liquid. Viscoelasticity is a mixture of the material behavior of elasticity and the flowability behavior of viscosity. Accordingly, viscoelastic materials exhibit both viscous and elastic material behavior. Thus, they combine certain material properties of solids with material properties of fluids. Viscoelastic effects depend on factors such as temperature, time and frequency. In biophysics, viscoelastic properties of substances play an important role. For example, blood has viscoelasticity. The same applies to soft tissue and other cell assemblies. In this context, blood, for example, is considered a non-Newtonian fluid and does not carry its viscosity (blood viscosity) as a substance constant, but changes it with shear effects. Newtonian fluids, on the other hand, exhibit linear viscous flow behavior and thus have viscosity independent of load, whereas viscoelastic fluids such as blood respond to certain loads with elasticity.
Function and task
Soft tissues are soft tissues such as adipose tissue, muscle tissue, and connective tissue. They are composed of collagen, portions of elastin, and ground substance. This structure is called the extracellular matrix of soft tissue. The ground substance is largely composed of water, with fibroblasts and chondroblasts producing the fibers and ground substance of soft tissue. The mechanical properties of soft tissue include viscoelasticity. When relatively little strain is applied in the form of low elongation, the elastin in the tissue provides stiffness. Distortion energy is stored in the elastin. The collagen fibers contained in the tissue carry wavy shape at rest and are relatively stretchable. The more the tissue deforms, the more they stretch in the direction of the deformation. After stretching, the fibers in turn increase the fabric stiffness. The fabric behavior is similar to a nylon stocking. The elastin takes over the role of the nylon rubber band and the collagen fulfills the function of the nylon fibers. In this respect, collagen limits the stretching of the tissue and thus protects against injury. Accordingly, soft tissues of the human body can deform considerably and still return to their original shape. Physical viscoelasticity can also be observed in relation to blood. In chemical terms, blood is a suspension of the Newtonian fluid water and cellular, i.e. material, components. Blood is a non-Newtonian fluid and thus exhibits different flow properties than water. Because of the erythrocytes it contains, the viscoelasticity of blood is increased compared to plasma. The viscosity increases with the hematocrit value and the flow velocity. Because of the deformability of red blood cells ( erythrocytes), the flow behavior of blood at increasing flow velocity does not resemble that of a cell suspension, but changes to the flow behavior of an emulsion.
Diseases and ailments
Neuromuscular diseases increase viscoelasticity in muscle and fascial tissue. This viscoelasticity increase in fascia exerts pressure on the myofascial tissue. The increase in viscoelasticity in myofascial tissue itself has not been conclusively studied, but appears to be related to dysfunction or faulty regulation by the sympathetic nervous system. Neuromuscular diseases form an inhomogeneous group consisting of diseases of muscle cells, neuromuscular transmission, or peripheral nerves. Neuromuscular diseases include, in particular, myopathies and neuropathies.Myopathies are non-neurogenic diseases with structural changes or functional limitations of the affected muscles, which in most cases affect the striated skeletal muscles. Muscular dystrophy is an example of a myopathy. Neuropathies are diseases of peripheral nerves without traumatic origin. A neuropathy may affect single or multiple nerves. Common manifestations are pain or loss of sensation in the affected area. As a late consequence, sometimes flaccid paralysis of the affected muscles occurs. Myopathies are characterized by weakening or degeneration of the muscle tissue, which may be due to correlations such as genetic mutation or mitochondrial insufficiency. It is not only in the soft tissues of the body that disorders of viscoelasticity can occur. For example, a symptom complex of the blood caused by an increased concentration of paraproteins in the blood plasma is known as hyperviscosity syndrome. Because of the increased viscosity, the flowability of the blood is reduced. Hyperviscosity syndrome occurs particularly in the context of malignant diseases, such as multiple myeloma or Waldenström’s disease. Benign diseases such as Felty’s syndrome, lupus erythematosus or rheumatoid arthritis can also be associated with the increase in viscosity. Patients usually suffer from fatigue, feelings of weakness and shortness of breath. Anemia (anemia) is caused by mucosal and nasal bleeding. It is favored by impaired platelet function. Platelet dysfunction results from obstruction of the clotting receptors. The platelets are covered by paraproteins and no longer bind to the receptors, but interact with fibrin formation. The resulting symptomatology resembles that of microangiopathy. The risk of thrombosis and thromboembolism increases markedly.
