Although general clinical conceptions of the mechanism of cyanosis are vague, it has long been recognized that it may be due to four main causes: (1) deficient oxygenation of the blood; (2) obstruction to normal flow in the capillaries; (3) combinations of 1 and 2, and (4) chemical transformation of the hemoglobin.
Demonstration of the mechanism of the form arising in the capillaries, has, so far as we have been able to determine, not been made and it is conceivable that it might prove important from the standpoint of diagnosis in obscure cases. The first question to decide in such a case would be whether the cyanosis could be due to insufficient oxygenation of the blood. In this connection it is well to emphasize, as Hoover1 has recently done, that cyanosis arising in the thorax is always due to the passage of venous blood to the left heart. In pneumonia
LANGSTROTH L. CHRONIC CAPILLARY CYANOSIS. Arch Intern Med (Chic). 1919;23(1):56–60. doi:10.1001/archinte.1919.00090180061004
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