any conditions u can name that can cause hypoxia......(of corse there are always some exceptions in medicine)....clubning occurs when there is less blood flow or less oxgenated blood to the tissue under the nail...this causes release of hypoxia derieved Growth factors leading to tissue growth under the nail...forming a clubbed nail........causes ..cyanotic heart disease ,cystic fibrosis, lung cancer lung abscess , ulcerative colitis , bronchiectasis , benign mesothelioma , infective ensocarditis , neurogemic tumors , GI distress..(pmuemonics are the first letters of every cause itself CLUBBING)...also refer schamroths window , lovibond angle , kurths angle