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Dyspnea
Another common symptom associated with angina pectoris is dyspnea.
In this text, Schwartzstein and Harver (Chapter
23: Clinical Research on Dyspnea) discuss multiple mechanisms
by which cardiac ischemia can lead to dyspnea.
Dyspnea probably
occurs as a result of a mismatch between the heart's demand for
oxygen versus the delivery of oxygen. Inadequate blood flow to
the heart leads to cardiac ischemia and angina pectoris. In addition,
inadequate blood flow leads to an inadequate cardiac output with
consequent reduced oxygen delivery to the tissues. As a result
of inadequate emptying of the heart, left ventricular pressure
increases.
This increased
pressure "backs up" into the lungs, which causes increased
fluid retention in the lungs and decreased lung compliance, which
are detected by afferents in the lungs. Lowered PO2 causes ischemia
to respiratory and other muscles.
Hypoxia and
hypercarbia stimulate chemoreceptors which will attempt to increase
breathing but may exacerbate the problem. Anxiety about the chest
pain activates limbic areas that receive respiratory input. The
individual attempts to breathe harder to deliver more oxygen to
the blood, but this is ineffective due to the low cardiac output.
As a result the person feels short of breath.
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