Cardiopulmonary interactions occur because both systems occupy space in the confined thoracic cage, because the heart pumps
blood through and sucks blood from the lungs, and because the lungs hinder the flow of blood from right ventricle to left
ventricle. Diseases of both systems share many signs/symptoms (e.g., cough, cyanosis, cardiomegaly, exercise intolerance)
but fortunately disease of each system possesses a unique set of signs/symptoms.
Lung disease may be of the large airways (tracheal compression, compression of left mainstem bronchus, bronchitis) and/or
small airways (bronchitis, edema, asthma), but all vesicular breaths sounds are made by air tumbling through the large airways,
while adventitious breath sounds (crackles, wheezes) are made by airways scrunching close and popping open. Remember you
and your patients have only 1 trachea, but as large as it may be, it is minute compared to the total cross-sectional area
of all of the small airways put together. So through what region do you believe air tumbles most vigorously?
Lung disease is classified as: restrictive (e.g., fibrosis), obstructive (e.g., bronchitis), abnormal perfusion (less important),
abnormal diffusion (less important); all may lead to ventilation-perfusion abnormalities (very important) that ultimately
"do the patient in" by producing asphyxia. Most animals that die from either heart failure or lung failure, die from asphyxia
due to fatigue of muscles of ventilation.
How might you determine if symptoms come from the heart or lungs, if diseases of both may be present? It may be very difficult,
but below are the pieces of the puzzle that, when put together, may help in the differentiation!