Extracellular Matrix Organization

The cardiac extracellular matrix consists primarily of the fibrillar collagens, type I (85 ) and III (11 ), synthesized by the cardiac fibroblasts, the most abundant cell type in the heart. Collagen is the major structural protein in connective tissues but only comprises 2 to 5 of the myocardium by weight, compared with the myocytes, which make up 90 Weber, 1989 . The collagen matrix has a hierarchical organization (Fig. 11.3), and has been classified according to conventions established for...

Illustrative Clinical Case

As indicated above, the information available for clinical gait interpretation may include static physical examination measures, stride and temporal data, segment and joint kinematics, joint kinetics, elec-tromyograms, and a video record. With this information the clinical team can assess the patient's gait deviations, attempt to identify the etiology of the abnormalities, and recommend treatment alternatives. In this way, clinicians are able to isolate the biomechanical insufficiency that may...

Preface

MECHANICS IS THE ENGINEERING SCIENCE that deals with studying, defining, and mathematically quantifying interactions that take place among things in our universe. Our ability to perceive the physical manifestation of such interactions is embedded in the concept of a force, and the things that transmit forces among themselves are classified for purposes of analysis as being solid, fluid, or some combination of the two. The distinction between solid behavior and fluid behavior has to do with...

References

Anversa P, Puntillo E, Nikitin P et al. 1989. Effects of age on mechanical and structural properties of myocardium of Fischer 344 rats. Am J Physiol 256 H1440. Arts T, Reneman RS, Veenstra PC. 1979. A model of the mechanics of the left ventricle. Ann Biomed Eng 7 299. Arts T, Veenstra PC, Reneman RS. 1982. Epicardial deformation and left ventricular wall mechanics during ejection in the dog. Am J Physiol 243 H379. Backx PH, Gao WD, Azan-Backx MD et al. 1995. The relationship between contractile...

Resting Myocardial Properties

Since, by the Frank-Starling mechanism, end-diastolic volume directly affects systolic ventricular work, the mechanics of resting myocardium also have fundamental physiological significance. Most biome-chanical studies of passive myocardial properties have been conducted in isolated, arrested whole heart or tissue preparations. Passive cardiac muscle exhibits most of the mechanical properties characteristic of soft tissues in general Fung, 1993 . In cyclic uniaxial loading and unloading, the...

Ventricular Hemodynamics

The most basic mechanical parameters of the cardiac pump are blood pressure and volume flowrate, especially in the major pumping chambers, the ventricles. From the point of view of wall mechanics, the ventricular pressure is the most important boundary condition. Schematic representations of the time-courses of pressure and volume in the left ventricle are shown in Fig. 11.4. Ventricular filling immediately following mitral valve opening (MVO) is initially rapid because the ventricle produces a...

Ergogenic Aids Anabolic Steroids

Anabolic steroids are drugs that function similar to the male sex hormone testosterone. Upon binding with specific receptor sites, these drugs contribute greatly to male secondary sex characteristics. These drugs have been used frequently by a large number of competitive athletes, particularly those involved FIGURE 10.7 Blood viscosity related to blood hematocrit. FIGURE 10.7 Blood viscosity related to blood hematocrit. in strength and power sports. Increases in muscular strength, total body...

Transport of Oxygen and Carbon Dioxide

One of the most important functions of the microcirculation is the delivery of O2 to tissue and the removal of waste products, particularly of CO2, from tissue. O2 is required for aerobic intracellular respiration for the production of adenosine triphosphate (ATP). CO2 is produced as a by-product of these biochemical reactions. Tissue metabolic rate can change drastically, e.g., in aerobic muscle in the transition from rest to exercise, which necessitates commensurate changes in blood flow and...

Ventricular Pressure Volume Relations and Energetics

Pressure Volume

A useful alternative to Fig. 11.4 for displaying ventricular pressure and volume changes is the pressure-volume loop shown in Fig. 11.5a. During the last 20 years, the ventricular pressure-volume relationship has been explored extensively, particularly by Sagawa 1988 , who wrote a comprehensive book on the approach. The isovolumic phases of the cardiac cycle can be recognized as the vertical segments of the loop, the lower limb represents ventricular filling, and the upper segment is the...

Lubrication

Elastohydrodynamic Lubrication

Lubrication is a process of reducing friction and or wear or other forms of surface damage between relatively moving surfaces by the application of a solid, liquid, or gaseous substance i.e., a lubricant . Since friction and wear do not necessarily correlate with each other, the use of the word and in place of and or in the above definition is a common mistake to be avoided. The primary function of a lubricant is to reduce friction or wear or both between moving surfaces in contact with each...

Viscoelastic Properties

Cartilage Viscoelastic

As stated earlier, bone along with all other biologic tissues is a viscoelastic material. Clearly, for such materials, Hooke's law for linear elastic materials must be replaced by a constitutive equation which includes the time dependency of the material properties. The behavior of an anisotropic linear viscoelastic material may be described by using the Boltzmann superposition integral as a constitutive equation FIGURE 1.5 Comparison of predictions of Katz two-level composite model with the...