Can anyone more familiar with this field elaborate on exactly what "chronic circulating inflammation throughout the blood stream" is? Inflammation I understand,

Can anyone more familiar with this field elaborate on exactly what "chronic circulating inflammation throughout the blood stream" is? Inflammation I understand, but how does it circulate throughout the bloodstream? Does this refer to inflammation of the blood vessels, the heart, or somehow your blood itself? And is there a reason to suspect causality goes in the direction implied in the article (i.e. bad sleep -> plaque) and not (i.e. X -> plaque and X-> bad sleep, where X could be stress or emotional state, etc.)?