Valvular
Disease of the Heart
Inflammation of a valve can cause the edges of the valve cusps
to stick together. Later, fibrous thickening occurs, followed by loss of
flexibility and shrinkage. Narrowing (stenosis) and valvular incompetence
(regurgitation) result, and the heart ceases to function as an efficient pump.
In rheumatic disease of the mitral valve, for example, not only do the cusps undergo
fibrosis and shrink, but also the chordae tendineae shorten, preventing closure
of the cusps during ventricular systole.
Valvular
Heart Murmurs
Apart from the sounds of the valves closing, lu¯ b-du˘ p,
the blood passes through the normal heart silently. Should the valve orifices
become narrowed or the valve cusps distorted and shrunken by disease, however,
a rippling effect would be set up, leading to turbulence and vibrations that
are heard as heart murmurs.
The
Anatomy of Cardiopulmonary Resuscitation
Cardiopulmonary resuscitation (CPR), achieved by compression
of the chest, was originally believed to succeed because of the compression of
the heart between the sternum and the vertebral column. Now it is recognized
that the blood flows in CPR because the whole thoracic cage is the pump; the
heart functions merely as a conduit for blood. An extrathoracic pressure
gradient is created by external chest compressions. The pressure in all chambers
and locations within the chest cavity is the same. With compression, blood is
forced out of the thoracic cage. The blood preferentially flows out the
arterial side of the circulation and back down the venous side because the
venous valves in the internal jugular system prevent a useless oscillatory
movement. With the release of compression, blood enters the thoracic cage, preferentially
down the venous side of the systemic circulation.
