Heart Wall - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 303

Visfatin associates with the insulin receptor to induce hypoglycemia. Visfatin
level is elevated in patients with coronary artery disease [ 584 ]. Other adipokines
comprise vaspin, omentin, and chemerin, but they do not have identified function in
healthy or diseased heart.

6.2.4 Heart Valves

The cardiac valves are sheets of connective tissue that begin at the annulus fibrosus .
The valve cusps are passive soft tissues attached to the wall at the insertion line.
The ventriculoarterial — aortic and pulmonary — valves have smooth ventricular
and wavy arterial faces. The free edge is indented. The middle part of the free edge is
thicker with the Arantius nodule , characterized by a high concentration of collagen
fibers.
These geometric features influence both valve motion during the cardiac cycle, 51
as well as flow in the aortic sinus when it is open, and thus the transvalvular pressure.
Effective boundary conditions or wall laws for laminar pattern can be introduced.
Roughness elements are supposed to be periodic with a length scale greater than the
flowing cell size [ 585 ].
The cardiac valves, covered by an endothelium and containing smooth myocytes,
are reinforced by many internal bundles of collagen and elastic fibers (Table 6.5 ).
Sparsely distributed valvular interstitial cells have extensive contact with proteogly-
cans of the extracellular matrix, as well as with elastin and collagen fibers.
Collagen-1 forms a dense content beneath the endothelium. Collagen fibers of
the outer layer of the cusp are mainly oriented in the azimuthal direction. Collagen
fibers are more randomly oriented in the cusp central part. Elastin fibers are more
abundant near the fibrous ring. In the fibrous ring, collagen fibers form massive wavy
twisted bundles and elastin fibers have different directions. Also in the commissures,
collagen fibers form massive twisted bundles.
Chordae tendinae mingle with valvular connective tissue. The myocardium
penetrates into the valve leaflets. The valve components and their estimated elastic
moduli are given in Vol. 7 - Chap. 5. Rheology. Whatever the transvalvular pressure
at which the porcine aortic valves are fixed (

12 kPa), the fibers mainly run along
the circumferential direction [ 586 ]. Moreover, strong collagen fiber bundles that
travel through the valve cusps and attach to the arterial walls behave like suspension
cables for force transmission.
The cusp is a multilayer structure. The 3 layers are the fibrosa ,the spongiosa
(which is absent in the coaptation region), and the ventricularis (Fig. 6.3 ). The fi-
brosa, located toward the arterial wall, contains a large number of circumferential 52

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51 In addition to the valve cross curvature of the open leaflet, the Arantian nodule induces axial
curvature due to stiffer medial thickening.
52 Collagen bundles run from commissure to commissure, spreading out near the cusp belly and
combining again toward the opposite commissure.