How is nail clubbing related to lung disease?

Because breathing affects all of our organs, clues to lung disease are often evident in faraway places, like your fingertips. When the fingertips of corresponding digits of opposite hands are directly opposed, fingernail to fingernail, a small diamond-shaped "window" is apparent between the nailbeds. If this window is obliterated, then you have clubbing of your fingers and need to check out possible causes, especially in the lungs, heart, and intestines. These diseases cause dilation of the small arteries in the fingertips, which leads to hypertrophy of the tissue of the nail beds and clubbing of the fingernails.