A MESA COPD study suggested that the number of microparticles that reflect apoptosis of CD31+ endothelial cells was significantly increased and negatively correlated with PMBF in mild patients with COPD,[53] suggesting that microvascular endothelial injury presented in early-stage of COPD might lead to abnormal PMBF. This evidence concerns the gene PECAM1 and chronic obstructive pulmonary disease.